"Other" Lake Superior Agates

Transcription

The “Other” Lake Superior Agates
The “Other”
LAKE SUPERIOR AGATES
BY
JOHN D. MARSHALL
All Photographs by the Author except where noted
1
Copyright June, 2009 by John D. Marshall
Third Edition-revised
All rights reserved. No portion of this book may be reproduced in any form
including text or images without the permission of the author.
ISBN 0-9722568-2-2
Manufactured in the United States of America
Llao Rock Publications
Beaverton, Oregon
2
TABLE OF CONTENTS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
Foreword
Introduction
What Are the “Other” Lake Superior Agates?
Agate Formation Theory and Common Sense
Banded Agate Formation
Why Aren’t All Agates Banded?
Band Distortion by Fluid Pressure
What Is a Sagenite Agate?
A Gallery of Lake Superior Radial Sagenite Agates
Lake Superior Sagenite Agate Summary
What Is a Moss Agate?
Lake Superior Moss Agate Summary
What is a Tube Agate?
How Do Tube Agates Form?
Lake Superior Tube Agate Summary
What Is An Eye Agate?
Lake Superior Eye Agate Summary
What Is a Water Level Agate?
A Gallery of Lake Superior Water Level Agates
Lake Superior Water Level Agate Summary
The Other “Other” Lake Superior Agates
What Is a Ruin Agate?
What is a Breccia Agate?
What is a Geode Agate?
Gallery of Lake Superior Agate Geodes
What Are Agates With Mineral Inclusions
And Crystal Replacements?
Gallery of Inclusions In Lake Superior Agates
What Are Crystal Impressions in Agate?
Are There “Real” Plumes in Lake Superior Agates?
What Are Paint Agates?
Combinations and Unique Lake Superior Agates
Unanswered Questions Certainly Remain!
Ice Ages, Continental Glaciation, Lake Superior Agates, and Time
That’s Why I Collect the “Other” Lake Superior Agates
Dedication
About the Author
Postscript
Appendix: Polishing Lake Superior Agates
3
4
5
6
8
8
14
14
21
22
46
52
53
67
68
68
83
84
90
92
106
114
121
121
125
129
129
131
134
139
145
148
152
166
176
181
181
182
183
184
Foreword
By
Scott F. Wolter
It’s about time! Someone has finally taken the time to write at length about those “other” varieties of Lake
Superior agates. Anyone who has ever marveled at the beauty of our beloved Lakers knows what these
interesting, yet puzzling features are. Since I first began collecting over 20 years ago, I’ve looked closely at
these odd formations and wondered; how did they form?
Early on I could imagine the crystal impressions on the surface of many agates were minerals that have
since weathered away, or “healed” cracks that cut through some agates were caused by faulting while still in
the host lava. These features were relatively easy to figure out, but there were many more things in the
agates I found that defied explanation. To complicate matters, there is still not a consensus among the
“experts” as to how the common banded agates are formed. As hard as it was to admit, many of these
unusual agates had me stumped.
In the quest to try and understand these oddballs, I would often seek out the opinion of other collectors.
Most offered little interest or input because they were focused on the pretty banded ones. In the summer of
1990, I met somebody who cared enough to investigate the detailed intricacies involved in these stones. His
name was John Marshall. Ironically, we disagreed on some of the basic fundamentals of agate formation
but this did not impede our friendship or the lengthy “agate talks.” In fact, our differences inspired us both
to more carefully consider our ideas before we bounced them off each other. When the debate is calm,
reasoned and conducted with mutual respect, I firmly believe that you learn more from people who disagree
with you. I have learned a lot from John and look forward many more years of agate debates.
In my past agate books I have only scratched the surface in attempting to explain what we think is going on
with these various features. Finally, somebody has picked up the ball and scored a touchdown in presenting
well thought-out ideas about how these features came to be. John went about his work quietly and has
produced a book that is visually stunning and intellectually challenging. When a full-color draft
unexpectedly arrived for me to review, I smiled and laughed realizing how silly I was not to have figured
out the clues he had given about the “surprise” he was working on. During our many agate conversations
John was compiling the information that has become this book.
John’s work is presented in an easy reading style with excellent images that clearly illustrate his ideas. For
anyone who has ever wondered about those strange and unique Lakers, this book will be a very satisfying
experience. I’m sure John would agree that all the mysteries behind these curious agates are not yet solved.
However, The “Other” Lake Superior Agates has taken us all one giant step closer toward a better
understanding.
4
1
Introduction
You could have found me almost any lazy summer afternoon in the mid-1950’s through the mid-1960’s
sorting through the products of the day’s Lake Superior Agate hunting expeditions. As a boy I liked to go
out collecting in the mid-morning. By mid afternoon it was time to head home for a late lunch and the
examination of my finds.
My passion for collecting Lake Superior Agates had begun in 1956 when, as a boy of six, I was “helping”
my father rake our front yard in preparation for a new lawn. I happened to find a small Lake Superior Agate
and asked him if he could identify this unusual stone. Having just moved to Mendota Heights, Minnesota
from Tulsa, Oklahoma I had never seen such an interesting pebble.
Dad knew it was an agate but was surprised to learn that they could be found in the sand and gravel of our
new front yard. He said that the sand was “glacial drift” from the ice age and that the agate must have come
from a long way off. He was correct on both counts. I still have that little Lake Superior Agate.
This single incident set me on a lifetime course of great interest in not only agates but also glaciology,
vulcanology, plate tectonics, and biological evolution. I became particularly interested in agate formation.
At the time this was a very unsettled subject with few definitive answers. Most experts agreed on the way
banded agates formed but had little, if anything, to say about the many non-banded varieties.
From that moment onward I spent countless hours roaming the fields and gullies of my neighborhood
searching for the elusive Lake Superior Agate. My interest led to family vacations on the North Shore of
Lake Superior where we collected agates and thomsonites. I soon discovered that Ray Lulling, a wellknown local rockhound and discoverer of silkstone, lived about a half block away. It was from him that I
received my first instruction in lapidary. Later I was fortunate to meet and know Bill Bingham as well.
From almost the beginning of my days as a Lake Superior Agate collector I began to notice and value the
more unusual agates. I would sort my agates into piles that shared common characteristics. I soon noticed
that the largest pile was always composed of common banded agates. From my collecting experience I now
know that this variety of Lake Superior Agate accounts for approximately ninety percent of all the agates
the collector will find. Most, but by no means all, Lake Superior Agates are banded.
The common variety of banded agate can be very attractive. The range of color in Lake Superior Agates is
wide though reds predominate. The fantastic wavy patterns of banded Lake Superior Agates can be very
eye catching and pleasing. Fundamentally, though, the biggest pile of agates always seemed a bit
monotonous to me no matter how fantastic the banded shapes and colors.
It was always the smaller piles of agates that attracted my special attention. Some seemed to be composed
of “mossy” growths of interwoven designs. Others had tube like formations while the ones I treasured most
were those with straight needle like inclusions. I also developed a special liking for agates having
horizontal bands or that included combinations of these “other” varieties with banded agate.
5
I soon realized that while many agates were a “pure” variety composed, for example, of all tube formations
or all mossy formations, many other agates were combinations of several types. This fact can cause
considerable confusion when it comes to creation of a catalog of varieties of Lake Superior Agate. If the
collector defines each potential combination as a separate variety then the number of varieties will become
quite large.
I prefer to keep the list of varieties of Lake Superior Agate short by defining only the major “pure” varieties.
In some cases the dividing line between varieties is blurry. In fact, the difference between what the
collector calls a tube agate and a moss agate may be no more than the size of the inclusions.
If the tube like formations within the agate are larger it may earn the title of “tube agate”. In they are so
small that they almost require a hand lens to be seen clearly they will be called “moss agate”. The important
thing for the collector to remember is that these two types may, in fact, simply be different versions of the
same variety of agate. They lie on a continuum of agates having inclusions.
2
What Are the “Other” Lake Superior Agates?
Several excellent books about Lake Superior Agates have been written in recent years. These books explore
the personalities and history of Lake Superior Agate collecting. There is a wealth of knowledge available
for the interested reader. You can even learn the names of some of the largest and most valuable Banded
Lake Superior Agates ever found. I strongly recommend all editions.
However, for the most part, the focus of these books is on collecting the banded variety of Lake Superior
Agate and documenting with photographs the “trophy” status of the largest and finest. The non-banded
varieties are mentioned but not covered in great detail or with many photographs.
This book is the first to describe in great detail the “other” Lake Superior Agates that have fascinated
many past collectors and which today, sadly, are hardly given a second glance by many. I think it is
about time. Banded Lake Superior Agates are wonderful but only part of the story.
In this book the “other” Lake Superior Agates are defined as all varieties except those having predominantly
concentric banded patterns (also called fortification patterns). Included in my “other” group will be some
combinations of types, which may, at times, include concentrically banded agate. The term “banded agate”
as used in this book will always refer to concentrically banded agate. Using that as a guide the following is
my list of the “other” varieties of Lake Superior Agate with my favorite listed first:
1/
2/
3/
4/
5/
Sagenite
Moss
Tube
Eye
Water Level
Agates having needle-like inclusions
Agates having small filamentous moss-like inclusions
Agates having inclusions that resemble tubes
Agates with eye-like formations near the exterior
Agates with horizontal layers
6
In addition to these five “pure” varieties of non-banded Lake Superior Agate there are a number of odd and
unusual variations that attract interest and attention by their sheer strangeness. These include but are not
limited to the following:
1/
2/
3/
4/
5/
6/
7/
8/
Ruin
Breccia
Geode
Mineral Inclusions and Crystal Replacements
Crystal Impressions
Plume
Paint Coloration
Combinations and Unique Agates
This photograph will give you an idea of the many potential
combinations possible in a single Lake Superior Agate. All
these types of agate will be explained and illustrated later.
This agate has tube structures; normal banding, mineral crystal
inclusions, and crystals replaced with agate. Not visible in the
photo are several large crystal impressions as well. What
should we call this agate?
It is, in just about equal parts, a banded agate, tube agate,
crystal inclusion agate, crystal replacement agate, and crystal
impression agate. This is an accurate description. For short I
call agates such as this combination pattern agates.
Below are two close-up photographs of this agate showing details of the tube and crystal patterns.
Crystal Patterns
Tube Patterns
7
Most non-banded varieties of Lake Superior Agate are much better appreciated with a polished surface
rather than in their natural condition. This is especially true of moss agates and sagenite agates which, in
their natural state, are frequently rather drab. Also, many of the most interesting and beautiful structures
within non-banded agates are very minute in size. Tiny details are generally difficult to view clearly in
rough agates. A light coating of mineral oil will assist in viewing small details in rough agates.
For this reason most of the agates chosen to illustrate this book about “The Other” Lake Superior Agates are
polished. It is my belief that of all high quality banded Lake Superior Agates perhaps twenty-five percent
are better appreciated polished. However, my opinion is more than reversed in the case of non-banded Lake
Superior Agates of which I believe that at least eighty percent are better appreciated polished.
3
Agate Formation Theories and Common Sense
I have been very interested in how agates form since I was seven years old. This interest includes not only
Lake Superior Agates but also all of the many types that are known from around the world. I guess that I
am no different than most agate collectors in wondering how the fantastic patterns and colors came to be.
Some types of agates such as the Laguna Agate from Mexico occur primarily in the banded variety. Others
like Oregon Thundereggs can be found in banded, water level, moss, and tube but almost never sagenite.
Lake Superior Agates are special in that they are found in ALL varieties known to exist at other locales.
I have always believed that to fully explain agate formation it is necessary to explain all varieties and not
simply banded. Many agate formation theorists have chosen to virtually ignore most of the non-banded
varieties since they may not fit the theory chosen to explain banded agates.
Those sections of the book devoted to specific non-banded varieties of Lake Superior Agate will include
discussion of how I believe that particular variety was formed.
4
Banded Agate Formation
If you just called a “time out” I don’t blame you. I just told you that this would be a book about the nonbanded varieties of Lake Superior Agate.
Please let me explain. A short discussion of banded agate
formation is important at the beginning for several reasons. First, the non-banded agate varieties share
most of the initial formation history of concentrically banded agates. Second, many non-banded agates
include banded areas in their patterns. It would be impossible to fully understand how such combination
pattern agates formed without some understanding of banded agate formation. Lastly, no comprehensive
theory of agate formation is complete without consideration of banded agates.
Almost all of the world’s agates form in volcanic rock. In popular terminology this rock could be called
“lava rock”. It could at some point have been erupted onto the surface of the earth forming vast flood-like
layers of lava dozens of feet thick and covering many hundreds of square miles. The lava rock could also
have been injected into shallow zones near the surface.
8
In either case the rock (in liquid form it would be termed “magma”) came close enough to the surface so
that gas would come out of solution in the melted rock material. This gas then formed bubbles of various
sizes which, when the magma hardened into rock, became the cavities in which nodular agate forms.
Agates are primarily composed of the common element silicon, which, in combination with oxygen forms
quartz (silicon dioxide). Quartz can take numerous forms. In fact, a fully banded agate nodule and one that
has only a thin outer layer of bands with a center completely composed of clear quartz have an almost
identical chemical composition. Agates are mostly silica. If this is so then why are they so different? The
answer lies in certain trace amounts of non-silica materials present within the forming agate.
The secondary materials of which agates are constructed are generally present in only trace amounts.
However, these trace “impurities” are what determine whether the cavity will be filled with virtually all
clear quartz or banded agate. Further, it is the proportions and quantities of these trace materials that
determine whether the eventual agate will be banded, non-banded, or a combination. I will refer to the trace
material that is necessary for the formation of bands as band mediating material. In excessive quantities
this material will prevent the formation of bands. The proportional concentration is critical to the outcome.
With only two exceptions, water level and hydrothermal vein, all agates form from an original single mass
of silica rich gel material. This original “single gel” also contains trace amounts of other non-silica
materials that may include elements such as copper or minerals such as hematite, rutile, or barite. In any
undisturbed agate deposit (Lake Superior Agates have all been transported many hundreds of miles from
their place of formation.) different varieties of agate may be found immediately adjacent to one another.
This fact supports the idea that it is the unique proportions of materials within each forming agate that will
determine the variety that will result and not fluctuations in the external environment outside the cavity.
If external condition were in total control of agate formation then each agate in any particular location
would be of the same variety and perhaps even have similar or identical coloration. However, this is not
what is found in nature. The reason for this is that each agate, early in its formation, contains a unique
combination of silica and other materials. Certainly, commonalities existed in the early stages of formation
of Lake Superior Agates. However, each was unique and therefore developed in a unique manner.
For example, the common reddish color of many, but not all, Lake Superior Agates is due to high
concentrations of iron minerals. A mostly banded agate from Africa, Botswana Agate, forms pressure
release patterns very similar to those in Banded Lake Superior Agate. However, lack of iron minerals
means that these agates generally do not have the beautiful reds of Lake Superior Agates.
The pattern and coloration of all Lake Superior Agates, except some of the water level variety, is
determined the moment the silica filled cavity becomes sealed off from the external environment.
The silica may come from dissolution of crystals of quartz in the rock itself or from other sources. It exists
as part of a molecule that is small enough to move through tiny pores and fissures in the rock. It “passes
through solid rock”. The silica moves between areas of differing concentration until a uniform
concentration of silica is reached in the entire system. It is probably, by our standards, a slow process.
In the case of banded agates it seems that there is a critical silica concentration level at which chalcedony
fibers will begin to form on the walls of the cavity. This may be due to the presence there of “nucleation
points” that give the tiny crystals a point from which to grow. Once the process of chalcedony growth
begins band formation will continue until all available silica in the original gel is depleted provided that
crucial trace materials that regulate band formation are present in proper quantities.
9
If there are VERY low levels of these band-mediating materials present in the original gel then what may
form is what collectors often refer to as a “quartz ball”. This will consist of a few bands of agate on the
“Quartz Ball”
outside followed by an interior that is almost totally clear crystalline quartz. Sometimes a few bands may
form in the interior of the nodule. Without sufficient band mediating materials present and dispersed in the
original gel the chalcedony fibers will continue to grow unhindered becoming large intergrown
“macrocrystals” sometimes called “sugar quartz”.
What is needed is something to repeatedly stop the
chalcedony fiber growth and thereby form what we call a “band”. Something is needed to mediate band
growth.
This “something” is micro impurities present in the original silica gel. These impurities cannot be
incorporated into the forming chalcedony fibers and are excluded from their structure. As they accumulate
a point is reached at which no more silica from immediately adjacent areas of the gel can migrate to become
part of the forming band of chalcedony fibers. This will stop further growth of the chalcedony fiber band.
The “band” as we commonly define it will then consist of this usually white or clear band and the
accumulated layer of materials that could not become part of the crystal structure of the band.
10
The coloration of the bands will depend on the nature of the trace materials that are present. Also, bandform
patterns may repeat themselves in a rhythmic manner as the nearly uniformly constituted gel is gradually
converted to chalcedony bands and intervening layers of excluded materials. This property of banded agates
was first recognized by Scott Wolter who coined the term “similar banding sequences”. Changes in the
width of the bands reflects lower levels of excluded materials (if wider) and higher levels (if lower). Agates
having very low levels of non-silica band mediating materials may form widely spaced crystalline quartz
layers between agate bands. Also, a “floating center” may result when impurities do not build up to
sufficient levels to stop the formation of macro quartz until near the center of the forming agate nodule.
Agates may also form that have significant banded areas on the outside of the nodule with a center of quartz.
These quartz-centered nodules are almost as despised by collectors as quartz balls. In fact, not all banded
agates consist of agate to the center of the nodule. This is because in these banded agates a point is reached
when all trace materials that mediate band formation are depleted. When this point is reached a central area
of large crystal (macrocrystalline) quartz will result. It will grow unhindered by accumulation of excluded
material until all silica is incorporated into large, generally intergrown, crystals.
A banded agate with no quartz at all in the center suggests that the original starting condition of the silica
gel had a perfect balance of silica and non-silica trace materials to result in a total banded pattern. Such a
banded agate is shown in the photograph below: (see another example on page thirteen-center bottom)
11
Typical banded Lake Superior Agate. The
center of the agates is toward the wide white
bands. Band formation proceeded from the
bottom of the photo to the top as layers of
chalcedony fibers formed until limited by the
accumulation of non-silica trace impurities I call
band mediation materials.
Microscopic view of a single white band of
chalcedony fibers. Visible is the orientation of
fibers perpendicular to the banding plane. Also
visible is the red layer of accumulated non-silica
trace impurities (iron oxide) which “shut down”
the further growth of the band. Another band
then began to form as silica concentrations once
again built to a sufficient level to initiate growth
of another chalcedony fiber band.
The accumulated red particles of iron oxide lay
flat and parallel to the banding plane. They
sometimes take the form of round plates and
also dendritic growths.
A banded Lake Superior Agate that shows wide
bands of macrocrystalline quartz alternating
with agate bands. Note that agate bands consist
of microcrystalline fibers of chalcedony arranged
perpendicular to the band while the interlayers of
quartz are composed of large interlocking quartz
crystals that are also oriented perpendicular to
the bands.
The “floater” is a banded agate that has a center of agate that is surrounded to a greater or lesser degree by
macro quartz. These agates had adequate levels of trace materials to mediate the development of agate
bands up to a point at which they became almost totally depleted and band formation gave way to growth of
large quartz crystals which generally form perpendicular to the existing bands. If no more trace materials
had been present a quartz-centered agate would have resulted.
However, if the central area of the forming agate gel contained additional trace materials then a band
forming rhythm could reassert itself producing an agate center “floating” in quartz as the examples on the
following page. Some collectors class the “floater” as a variety of Lake Superior Agates. In fact, they are a
variety of banded agates.
12
Banded to the center-a perfect balance!
13
5
Why Aren’t All Agates Banded?
If the silica gel reaches a silica concentration at which the initiation of band formation is inevitable why do
non-banded varieties form? The answer lies in the proportions of trace impurities that are present in the
original silica gel. These other non-silica materials may have been present within the gas bubble prior to the
introduction of the silica solutions or may have come in solution along with the silica.
If the proportion of trace materials to silica is “just right” a banded agate will form. It will have varying
amounts of crystalline quartz present ranging from almost all quartz (quartz ball) to a banded agate nodule
with no quartz present at its center. It depends on the proportions of the constituents. Collecting experience
indicates that larger agates more often have macro quartz than smaller.
I believe that band formation in agates is mediated by the presence of trace amounts of non-silica materials.
If no such materials are present no bands will form. On the other side of the spectrum is a dense moss or
sagenite agate, which is totally choked with tiny mossy forms or needle-like crystals with no banding to be
seen. In other words if sufficiently high levels of non-silica impurities are present in the original gel they
will disrupt or prevent the band formation. Low levels promote bands and excessive levels prevent them.
Frequently in combination pattern agates you will see small areas of bands that have attempted to selforganize. This can be seen in moss, tube, and sagenite agates. The natural propensity to form bands of the
silica gel is still present and it will assert itself anytime the level of non-silica materials is high enough to
mediate band growth but not so high as to prevent it. It must be neither too low or too high.
Before we leave the subject of banded agate formation it is important to note that all agates of any variety,
except certain water levels agates, begin as a single mass of silica gel of unique constituents. This gel will
develop independent of external conditions based solely upon the proportions of constituents present silica
vs. non-silica. Agates, except for some water levels, develop as “closed self-organizing systems”.
All banded agates and most non-banded agates go through a phase in which they are semi-plastic in
consistency. This condition is key to understanding how the many delicate structures of non-banded agates
are produced and preserved. In the case of banded agates this semi-plastic phase is subject to forces that
frequently distort the banded pattern giving us the amazing crazy patterns that we value as collectors.
6
Band Distortion by Fluid Pressure
As the microcrystalline chalcedony fiber bands of a banded agate form from the outside to the center of the
gel mass silica is taken from solution and incorporated into tiny fibers of chalcedony arranged perpendicular
to the bands. This crystal forming process has water as a by-product. The original silica gel mass when
fully converted into either chalcedony fiber bands (agate) or macro crystalline quartz (large crystals visible
to the unaided eye) will occupy MORE volume than the original silica gel.
This is because the regular crystal form produces tiny spaces between the crystals and the orderly
arrangement of atoms in crystals requires more space than when in unorganized form. What results is that
as the crystallization process proceeds water is liberated and fluid pressure builds toward the center of the
still semi-plastic gel mass as the volume of material increases. At some point the increasing pressure
overcomes the resistance of the newly formed agate and is released via “pressure escape channels”.
14
As pressure is equalized these channels move material from the central areas of the gel mass to the outer
areas of lower pressure causing distortion of the newly formed bands. Later, all this material will become
converted into a hard crystalline mass and forever freeze the results of the processes of band formation.
It is important to note that there are no forms of non-banded Lake Superior Agate which exhibit these
pressure relief features except when concentric banded agate forms in combination with waterlevel agate.
You will never find a moss, sagenite, tube, or purely water level agate that has pressure escape channels.
The photograph below and those on the next page show a typical banded Lake Superior Agate with pressure
escape features. Notice how reddish material from the very center of the agate has been pushed to the
exterior of the agate to produce an equalization of pressure. Sometimes a number of these “relief” valves
are present in the same agate. You may also notice banded agates in which pressure escape structures do
not reach the exterior of the agate. In these cases the pressure was insufficient to overcome the resistance of
the newly formed banded agate or was equalized prior to reaching the exterior of the agate. An example of
this in two consecutive slabs of Brazilian Banded Agate can be seen on pages seventeen and eighteen.
In light of current understanding of agate formation the concept that these pressure escape channels are
really “entrance channels” for silica bearing solutions is no longer plausible. These theories required
sometimes-fanciful explanations to attempt to explain observed phenomenon. The fact is plain, internal
pressure builds as banded agates form and then distorts the newly formed banded pattern outward.
15
Close-up views of the pressure escape channel shown in the agate on the preceding page. Notice how the bands are
deformed away from the central region of the agate. Also notice that reddish agate from the center of the once semisolid agate has been transported to the “surface” of the nodule. Internal pressure accounts for the wild patterns in
Banded Lake Superior Agates. Sometimes a small lump of this material can be detected on the surface of the agate
where it was deposited by fluid pressure from the interior of the agate.
The water by-product of crystallization eventually migrates through the spaces between the chalcedony fibers of the
hardened agate. That this is possible is proven by the ease with which agate can be dyed using chemical solutions.
A half-pound example of a banded Lake Superior Agate showing multiple pressure escape channels.
16
A major difficulty in the study of agate formation using Lake Superior Agate is the physical condition of the
agates. Collectors frequently have only fragments of larger agates. Complete nodules are very scarce when
compared to agate types such as Laguna, which is mined from the source rock. Therefore, it is sometimes
advisable to consult other types of agate for additional observations.
In the case of the entrance channel/escape channel controversy regarding banded agate formation Lake
Superior Agates fail, in my opinion, to provide material with which to answer one clear criticism of the
escape channel theory. This is in the identification of a specimen that shows with absolute clarity a
“channel” that begins in the central area of the nodule but fails to reach the exterior of the agate.
Proponents of the entrance channel theory argue that all channels reach from the exterior to the very center
of the banded agate. This would be necessary if formative silica in solution was deposited from the outside
to the inside of the forming agate. They readily agree that we find many specimens in which channels seem
to fail to reach the exterior. However, they argue that these specimens have been modified by nature or
cutting and polishing in such a manner that the full evidence has been destroyed.
Therefore, identification of agate specimens in which channels originate in the central area of an agate but
clearly fail to reach the exterior would support the escape channel theory and seriously discredit the entrance
channel theory.
For assistance I have turned to a type of agate that is available in complete nodules, is usually banded,
generally has prominent “channel” features, and is widely available. This is Brazilian Agate.
The two specimens below and close-ups on the next page are back to back slabs of a Brazilian banded agate.
The prominent channel feature was accidentally cut into almost equal parts. There is no evidence elsewhere
on the slab that the channel “could have” reached the surface at some other unseen location in the agate
nodule. Like the channels in the upper left and right of the slabs these are completely contained within the
slabs. There is absolutely no explanation other than that these features are pressure release features that
reached only approximately half the distance from the central area to the exterior of the agate prior to being
“frozen” in position by the increasingly resistant banded agate.
17
Brazilian Agate showing pressure escape channel that failed to reach the exterior of the agate nodule. Note
the compression and distortion present in the banding immediately in the path of the once moving material.
18
19
20
7
It is certainly undeniable that banded Lake Superior Agates are among some of the most beautiful banded
agates in existence. While red colors predominate virtually every imaginable color can be found in Lake
Superior Banded Agates. In addition to world class color Lake Superior Banded Agates exhibit
extraordinarily beautiful patterns, distorted as we have seen, by internal pressure during their formation.
This is not the end of the story, though, when comparing Lake Superior Agates with the best agates the rest
of the world has to offer! Lake Superior Agates produce some of the most outstanding sagenite, moss, tube,
and eye agates to be found anywhere. I have chosen to discuss first my favorite non-banded form of Lake
Superior Agate, Sagenite. The one below is one of my favorites and weighs about a half-pound.
21
8
What Is a Sagenite Agate?
In popular rockhound terminology a sagenite agate is one in which are present a myriad of usually tiny
needle-like crystals. The mineral that forms the needles is usually rutile (TiO2). “Sagenite” is a descriptive
term and not a scientific term. Therefore, if you exhibit your sagenites at some competitively judged events
you may not be allowed to use the term “sagenite” agate.
Lake Superior Sagenite Agates are found in two basic types and generally the two types are not found mixed
together. The large agate on page thirty is what I have called the “needle” type. This type is characterized
by randomly oriented crystals or small groups of crystals. However, in this type you will see no general
organization of the entire stone as in the second type, which I call “radial” sagenite.
In a radial sagenite the crystals have all grown from a common point in a 360-degree radial “burst”. The
resulting pattern depends upon how you view the agate. Seen in cross section as the agate below you see a
fan-like radial display in one plane. From the bottom or top you will see what appears to be a circular
pattern. This agate below weighs two pounds and the radial structure in cross section is easy to discern.
Sometimes, as in the radial sagenite on the preceding page the radial structure is not immediately apparent
due to changes in shape of the agate due to erosion or polishing. At first glance the agate on page twentyone might seem to be a needle sagenite. However, it actually has several radial sagenite bursts.
22
The radial sagenite on the preceding page is very typical of all Lake Superior Agates of this variety. The
radial “burst” of sagenite needles all appear to originate at a common point on the bottom center of the
nodule. This single pincushion-like burst of mineral crystals has invaded virtually the entire available space
within the original silica gel filled cavity. A close up of this specimen can be seen on page twenty-seven.
I believe that such sagenites are formed when very high concentrations of sagenite forming minerals are
present and well dispersed throughout the original silica gel. In this specimen the sagenite formation began
prior to the initiation of concentric band formation. As it progressed the needles became surfaces on which
chalcedony was deposited thus removing it from possible formation into banded patterns.
Some specimens of Lake Superior Radial Sagenite have both banded and sagenite patterns. I interpret these
as cases in which band formation and sagenite crystal formation started at nearly the same point in time.
Occasionally a specimen is seen in which the banded pattern can actually be seen being disrupted by the
advancing sagenite crystals as they intrude into it. It all depends on the original composition of the silica gel
and, apparently to a degree, which type of formation got the head start!
The specimens below are both examples of combined sagenite and banded pattern. Generally such
combinations are with radial sagenite. Banded pattern combined with “needle” sagenite is not common.
23
The disruptive effect of sagenite needles growing into bands in the process of forming can be seen on the
previous page in the close up of the photograph on the left. I believe that this shows that the banded pattern
and sagenite pattern were forming simultaneously and, in essence, competing for both silica and trace
materials present in the gel medium. As the sagenite crystals intruded into the banded pattern the orderly
rhythmic process necessary to produce bands was disrupted and ultimately stopped.
Some very knowledgeable theorists believe that the rutile crystals that we call sagenite formed first and are
then preserved by the influx of silica gel. My observations lead me to believe that the sagenite forms in the
gel concurrently with banded agate. However, it seems reasonable to admit that both modes of formation
may have taken place. However, specimens such as the one below clearly demonstrate to me simultaneous
formation of sagenite and agate.
Lake Superior Radial Sagenite Agate are found in just about equal numbers as pure forms comprised only of
sagenite and as combinations with banded pattern. I do not recall ever seeing a radial sagenite in
combination with water level or moss though I never say never when speaking about Lake Superior Agates.
The combinations and variations on the central themes sometimes seem endless!
The photograph below shows a Lake Superior Radial Sagenite that was “trying” to become a banded agate
at the same time. You can clearly see and follow the banded pattern across discontinuous areas disrupted by
the growth of sagenite needles. High levels of non-silica materials inhibit or prevent band formation.
24
The coloration in needle versus
radial Lake Superior Agate Sagenite
is very distinct. Notice how the
colors in the agate on page thirty
seem to be randomly dispersed.
Now look at the radial sagenite in
the photograph to the right. Notice
how there are bands or “zones” of
color. Also note how colors in the
radial sagenite on page twenty-two
are arranged in bands equidistant
from the origin point of the sagenite
crystal burst.
I believe that this is due to a sorting
of colorative materials based upon
their size or perhaps their mobility
in the silica gel medium.
This is just more evidence of the
organized nature of radial sagenite
versus the needle sagenite.
Another example of color “zoning” in radial sagenites. This agate is a double radial.
25
In addition to the key defining characteristic of “zoning” in radial sagenites there are two others that are
almost always observed. The first of these are the “arrow” features such as those present in the upper agate
on the preceding page. These always appear at the apex of long shafts of a dark mineral material that has
apparently grown rapidly and “broken through” a membrane that is usually a portion of forming bands.
The shape may be the result of a combination of speed of movement and a small initial area of penetration
of the membrane barrier followed by expansion. Two close-up examples are provided below:
The other common characteristic of almost all Lake Superior Radial Sagenites are minute spherical
formations that seem to float amidst the radial needles and color zones. Sometimes the sagenite needles
pierce these spheres. Did the sphere grow around the needle or did the growing needle pierce the sphere?
Many of these radial sagenite spheres can be seen in the agate on page twenty-two. A detailed close-up
photograph of this radial sagenite appears on the following page. It is amazingly intricate.
I believe that the spheres present in radial sagenites form from free silica that has become relatively more
concentrated due to the growth of crystals of non-silica materials that comprise the sagenite needles. This
silica seldom self-organizes into bands. Instead, I believe that fibers of chalcedony begin to form on small
particles of material suspended in the silica gel. These particles, or nucleation points, provide a place of
origin for the new chalcedony fibers in the same way that irregularities on the inner wall of the cavity serve
to initiate band formation by providing places for chalcedony fibers to begin their growth there.
The fibers arrange themselves in an almost perfectly spherical shape supported as they are by the semi-solid
silica gel. I have never observed a radial sagenite in which these spheres have “settled” gravitationally. I
believe that this is because they form relatively late in the self-organization of the radial sagenite at a time
when the silica gel is rapidly becoming altered from a gel to a solid. In fact, some radial sagenites have
spheres that appear to have risen in the silica gel medium! This may be due to a lowering of their relative
density as crystallization and exclusion of water from their structure proceeds.
26
Detail of agate on page twenty-two showing numerous tiny spheres.
This Lake Superior Radial Sagenite is polished from the “top”
of the sagenite burst. It has very dense red agate packed with a
myriad of tiny 1.0mm to 1.25mm spheres seen in cross section
under 100x magnification above. The spheres appear to have
risen to the upper region of the agate away from the origin
point of the sagenite burst.
27
I have also found possible evidence that some spheres served to collect water, which was released as the
silica gel was being converted into a crystalline structure. The radial sagenite below has numerous small
spheres as most other similar agates. However, this agate also has a group of larger spherical voids
positioned roughly equidistant from the origin of the radial spray. Upon microscopic examination several of
these can be seen to be covered on the inner surface with quartz crystals. Were these water “droplets” rising
through a denser medium until they reached an equilibrium point? Whatever they are they were frozen in
this position well over one billion years ago!
Viewed from the underside a radial sagenite will present a spherical shape and betray its true construction.
The huge complete Lake Superior Radial Sagenite Agate below weighs over three pounds.
28
The radial sagenite below is composed of very dense black sagenite needles that virtually choke the silica
gel medium. At the bottom (assumed) of the agate you can see spheres being created that are very dark in
color and apparently composed of a spherical membrane of white chalcedony enclosing the dark mineral
material of the sagenite.
As these spheres rose in the gel medium they aggregated for some reason into two distinct bands. This may
have been an equilibrium point given their density versus that of the surrounding medium. Some spheres,
however, can be seen to have passed through this double layer of spheres and risen further in the agate.
Those uppermost in the specimen are very clear and whitish compared to those farther down in the gel.
These “clean” spheres can be seen “budding off” the double layer. I believe that it is possible that a
fractionation process was operating that caused silica concentrations within the spheres to increase while
that of other materials decreased. This caused them to rise in the gel medium due to lower relative density.
29
Coloration in needle sagenite agates may be due simply to uneven distribution of colorative minerals in the
original gel material. Color zoning is generally not present. Below is a superb example of a Lake Superior
Needle Sagenite Agate. This Lake Superior Needle Sagenite Agate weighs approximately three and onehalf pounds and is the largest known example of this type.
30
The agate below is one of the finest examples in my collection of a Lake Superior Sagenite Agate in which
the sagenite needles completely fill the interior of the agate. This agate formed a thin border of normally
banded agate followed by the development of the single sagenite burst. The outer layers of enclosing
banded agate suggest that the sagenite formed simultaneously with the banded agate from materials in the
original silica gel. This agate also shows very well that the size of a Lake Superior Agate does not matter in
the least when speaking of quality, interest, and beauty, as you will see on the following page.
31
32
This exceptional Lake Superior Sagenite Agate
shows classic color zones and spherical
formations.
It weighs almost exactly one-half pound and
was polished with a broad curved face.
The photograph below illustrates how the
curved face wraps around the agates showing
off the interior of the stone in a three
dimensional manner.
Notice how the light pink area to the left of the
stone seems to have “flames”. You can view a
close up of this area on the following page.
The range of color from the origin point of the
single radial sagenite spray on the right (dark)
to the pink on the left is among the most
pronounced ever seen. A photograph of this
area can be seen on page thirty-five.
The colors include black, red, green, amethyst,
white, and numerous shades of pink. At times
like these the paucity of words that describe
color in the English language is acutely
evident.
The fist sized 11.5 ounce
Lake Superior Sagenite
Agate on the left shows
what happens when sagenite forming minerals are
present in unusually high
concentrations.
When this agate was polished the coolant water
became dark black.
Similar Sagenite Agates
from other locales freqently will not polish due
to the presence of the
softer minerals.
This agate, however, did
take a high luster due to
the presence of sufficient
silica.
33
34
35
A chunk of rough, as found, Lake
Superior Sagenite Agate.
This specimen is unusual in that the
arrow formations originate directly
from the exterior margin of the
agate nodule.
Polishing this agate would almost
certainly destroy these fragile
arrows. For this reason it has been
left in the natural condition.
A common practice is to lightly coat
such natural specimens with light
mineral oil. This better permits light
transmission and viewing of the
surface.
36
This 14.5 ounce Lake Superior Agate exhibits multiple small radial sprays
of sagenite needles and fine tube structures in the central area. The face was
polished in a curved style and two slabs were taken and polished on both sides.
Prior to cutting and polishing this agate weighed well over one pound.
37
A rare golden needle Lake Superior Sagenite Agate
38
This one-third pound Lake Superior Sagenite Agate defies classification as
either needle or radial in structure. Notice the “arrow” feature as well as
highly unusual golden filaments surrounding inclusions in the red agate.
These fine structures can be studied in more detail in the photographs on the
following page.
39
40
Filamentous radial sagenite forms a net like pattern in these halves of Lake Superior Agate both
polished with curved faces. The total weight of the agate is one pound twelve ounces. (white line = 1” )
Photographed against
a pink background to
bring out the natural
colors this filagree
patterned Lake
Superior Sagenite
measures approximately one inch wide.
41
A Lake Superior Radial Sagenite polished on the bottom of the radial spray to
highlight the prominent ruin fracture. This fracture has been recemented and
can be seen to break through tube formations present in addition to the
sagenite display.
42
The two pound Lake Superior Sagenite Agate above gave no hint of interior color and pattern as the complete
wind polished nodule pictured on the right. ( photo by Scott Wolter )
Cutting and polishing revealed an enormous range of color and pattern and includes both radial sagenite
sprays and needle sagenite formations. Lapidary treatment is generally required for most Lake Superior
Sagenite Agates though some specimens are best left in their natural condition.
The ten ounce Lake Superior Agate below has a central banded pattern with small radial sprays that grew
inward. A close up of the quadruplet sagenite sprays is provided on the right. This stone was polished in an
unusual style having three flat ‘faceted’ faces rather than a curved polished face.
43
Above a one-third pound Lake Superior
Sagenite Agate with multicolor radial bursts
that originate from different points throughout the agate.
Since this agate resembles a fireworks show
I call it “Fireworks over English Bay”.
The agate on the left is a very highly silicified
single burst radial sagenite. The individual
sagenite needles, encased in agate, have been
eroded out to produce a detailed relief effect.
44
A highly unusual Lake Superior Radial Sagenite Agate with two sprays of
radial sagenite seen from the bottom on this very finely eroded specimen.
Softer material between the two sprays eroded away leaving the sagenite in
high relief. Judging from the remaining agate in the “base” this was
originally a large agate with included sagenite sprays with origin points on
the walls of the formative cavity.
45
A Gallery of Lake Superior Radial Sagenite Agates
46
An unusual radial sagenite with rare golden color, radial zoning, floating spheres,
and a central origin point of clear agate. This specimen has been polished in cross
section through the center of the single radial sagenite spray.
47
A one half pound complete nodule of Lake Superior Radial
Sagenite Agate. Visible are the characteristic radial
sagenite “sprays” and color zones discussed in the text.
48
Glacial erosion has revealed intricate sagenite patterns across a broad face on this large
one and one-third pound agate. Elsewhere on the surface are signs of tubes and more
sagenite. While most Lake Superior Sagenite Agates require polishing the decision was
made to keep this extraordinary specimen in natural as found condition.
49
50
Golden Eyes
12.5 ounces
51
10
Lake Superior Sagenite Agate Summary
It is my opinion that Lake Superior Sagenite Agates are the finest of this variety found on Earth. I base this
upon their extreme level of detail complexity, fantastic range of color, and wide variety of shapes. I enjoy
these agates both at arm’s length and with magnification in the form of a hand lens all the way up to a
binocular microscope. No matter at what level the collector views a Lake Superior Sagenite Agate it will
offer astounding detail, color, pattern, and interest to the collector.
Amazing detail in a Lake Superior Sagenite Agate
52
11
What Is a Moss Agate?
Like sagenites the Lake Superior Moss Agate is, in my opinion, one of the finest varieties of moss agate
found anywhere in the world. Occasionally a sagenite agate is found that is better displayed in its natural
rough condition. However, in the case of Lake Superior Moss Agates such stones are seldom found.
As a matter of fact I have always suspected that there is actually a great deal more Lake Superior Moss
Agate than is found by collectors. I feel the same about sagenite and tube agate varieties as well.
Everybody these days is walking around looking for perfect banded agates of, say, an average weight of five
or six pounds. They will stoop to pick up smaller but only if they are banded. Moss may stay unnoticed and
undisturbed.
I think that the main reason for this is that all three of these non-banded varieties generally require lapidary
work to bring out their beauty. Many banded agates as well require polishing. However, a high percentage
of high quality banded agates are actually better in their natural state than polished. Unfortunately, lapidary
as a hobby and artform has been declining steadily since its heyday in the fifties and sixties.
Back then a great deal of really fine banded Lake Superior Agates was “slabbed and cabbed”. It was a great
loss. However, also at that time the interest and skill existed to turn otherwise very drab and sometimes
unattractive moss, tube, and sagenite agates into very attractive specimens. Today with very few practicing
or even understanding lapidary treatment of Lake Superior Agates the emphasis by most collectors is put
squarely on banded agates since most of the best of these can be displayed without being polished.
I began cutting and polishing Lake Superior Agates at the age of seven soon after having found one in our
new front yard. Therefore, for me at least, these “need to be polished” varieties of Lake Superior Agate
have always been highly desirable. Most collectors of that era polished their own agates. Some of my finest
Lake Superior Moss Agates, in fact, were given to me by collectors who saw them only as a nuisance to be
sorted out of the real agates-the banded ones that might need to be cleaned and oiled but nothing more.
So make no mistake about it if you find these polished specimens of Lake Superior Moss Agate attractive
and want to collect them yourself, you will either have to invest and learn lapidary or take your agates to
someone who can polish them. Rough Lake Superior Moss Agates are generally unattractive. I just cannot
get around it.
Some of the finest Oregon Priday Plume Thundereggs look like nothing more than hardened mud balls.
Sometimes nature hides her most beautiful objects under a drab exterior.
Having made the statement that most Lake Superior Moss Agates are unattractive in their natural condition I
would like you to examine the 30mmx40mm cabochon on next page. This is high grade Lake Superior Moss
Agate. Do you feel that this ranks with the best moss agates of the world?
53
54
Lake Superior Moss Agates, like sagenites, are “inclusion” type agates. That is, they owe their name and
nature to various types of crystal growths that are “included” within the agate. We can speak of “trace”
non-silica materials or call them “impurities” when referring to banded agates. However, in the case of
most inclusion agates like the moss agate on the preceding page, we must be aware that the “trace
impurities” might actually be present in higher proportions than the silica in which they are preserved.
Neither moss, tube, or sagenite Lake Superior Agates ever show any evidence of pressure deformation if
they are primarily that variety alone. If they constitute a minor sideshow for a regular banded agate then the
banded agate portion of the agate may show evidence of pressure relief deformation.
I believe that only concentrically banded agates have these pressure effects because of containment. As
soon as bands begin to form from the outside inward the cavity is essentially sealed. As water is released as
a by-product of the crystallization process the volume of material required to be contained within the cavity
increases. This will causes pressure to develop in the interior of the forming agate in excess of the ambient
pressure of the surrounding rock formation. This pressure then seeks equalization with external conditions.
In the case of moss, tube, and sagenite agates a continuous layer of growing chalcedony fibers forms no
such seal. The formation of chalcedony fibers begins throughout the silica gel with the included crystals of
non-silica materials as nucleation surfaces. The process liberates water, which can slowly escape.
Additionally, the very nature of these types of agates is that a high proportion of their substance are minerals
which may liberate little if any water as a product of their crystallization.
Lake Superior Moss Agates, like sagenites, form as crystals of non-silica minerals grow within the medium
of the silica gel cavity filling. While the minerals responsible for the production of sagenite produce
crystals that are linear those that form what we call moss agate usually do not. Moss agate inclusions twist
in all directions and seem to have no overall organizing force guiding their formation as in radial sagenites.
There is, however, a clear commonality between “needle” sagenites and moss agates. The materials that
form the inclusions are, of course, usually different. However, the process is the same. In both types the
apparently random growth of mineral crystals within the original silica gel medium eliminates most
production of banded agate.
Like sagenites that are combined with banded pattern to produce, as you choose, banded sagenites or
sagenites with banding, it is possible for bands to form in a portion of the cavity providing the disruption by
the growing sagenite or moss crystals is not too severe. Such combinations with banded pattern are
frequently found for both sagenites and moss agates. In fact, the result of the interaction of pattern type
produces some interesting hybrids.
Lake Superior Moss Agates are also similar to needle sagenites in their coloration. It is as if all the colors
that can be found in banded agates were thrown into a mixing pot and swirled randomly. However, the
process was stopped while each color still retained its individuality and the stone was not reduced to a single
blended color. Instead the colors are dispersed in “clouds” within the silica gel.
I believe that the relatively “thin” silica gel medium from which banded agates form permits colorative
materials to disperse more or less evenly throughout resulting in uniform bands. However, the denser gel
of a future moss agate or needle sagenite agate does not permit this mixing. Therefore, we see splotchy
areas of different colors in each of these types of agates.
55
A curious property of Lake Superior Moss Agate is their resistance to damage in glacial transport when
compared to all other varieties. The random interlocking filaments of the moss itself apparently impart an
extra resistance to the ravages of glacial and water transport. Many nodules of Lake Superior Moss Agate
will be found to be completely rounded by water action. Close inspection discloses that the surface of many
of these agates shows an extreme level of impact damage yet the interior may be virtually free of fractures.
The usual lapidary treatment of larger moss agate specimens is to cut them into slabs for use in making
cabochons. Alternatively, several slabs can be taken and then the remaining portion of the agate face
polished. The amazing thing about Lake Superior Moss Agates is that the serious external damage in
evidence on many nodules does not carry into the interior of the agate.
I believe that the effect is similar to “rip-stop” filaments in tent fabrics. The force of fractures does not
penetrate into the interior as it would in banded agate. The random interlocking filaments of moss-like
mineral growths prevents this from happening. The practical effect of this is that those wishing to fashion
cabochons from Lake Superior Moss Agate have very few of the troubles present due to fractures associated
with other varieties of Lake Superior Agate.
This Lake Superior Moss Agate has been photographed to show its
rough side. This is a typical appearance for this variety. It requires a
sharp eye to spot these among the many other pebbles found in glacial
outwash deposits.
This agate is an example of lapidary treatment of moss agate that goes
beyond simple “face polishing”. This stone was hand ground and
polished on its entire surface except for the portion left to act as a base.
The grinding process preserved the original contours of the rough agate.
This sort of polishing lends itself well to display on small motorized
turntables, which allow the viewer to see all sides of the specimen.
This is one of the polished surfaces of this green moss agate.
The grinding and polishing process that produces this result
is very time consuming. It is more similar to a carving than
any usual form of face polishing of agate specimens.
There is almost no red in this agate most of the colors being
shades of green or black. It is also obviously only a portion
of what might have been a much larger agate.
Lake Superior Moss Agates like this one are, in my opinion,
about as close as agate can come to being a precious gem.
Many collectors don’t even pick these up.
56
Collectors who specialize in banded Lake Superior Agates treasure the natural shape of the specimens. All
types of agate are inherently one of the most three-dimensional objects produced by nature. The natural
erosion and weathering that Lake Superior Agates undergo during glacial transport opens up the pattern and
permits the stones to be appreciated in a way unique among the world’s agates.
Consider the justly famed Laguna Agates of Mexico or the large agates of Brazil. These are almost always
prepared as display specimens by cutting slabs or flat surfaced specimens, which are then polished. This
provides a very attractive, even stunning, two-dimensional display of the interior of the agate. However, the
result is an attempt to appreciate a three dimensional object by viewing it in only two dimensions.
A few Lake Superior Moss Agates are very attractive in their natural condition. The photograph below is
one such agate. This exceptional stone has a smooth, almost polished, surface and what may at first glance
seem to be quartz actually is fine milky agate. This one weighs two and one-half pounds.
57
The agate on the preceding page illustrates an important point regarding the dividing line between tube
agates and moss agates. Each collector draws his or her own line! As a moss agate this specimen has rather
large intergrown tube like structures (large for moss agate that is). As a tube agate this specimen would be
described as having very small, almost tiny, tube structures.
So call this agate moss or call it tube the point to be made is that sometimes the dividing line between these
two varieties of Lake Superior Agate is purely subjective. If you like the agate and add it to your collection
then you get to call it what you wish! I call this one a moss agate. Below is an enlarged portion of the agate
shown on the previous page.
Another rather arbitrary dividing line in classification of non-banded Lake Superior Agates lies between
moss and plume. Many collectors will tell you that Lake Superior Agate does not produce plumes. This is a
true statement if the standard of comparison is materials such as Graveyard Point Plume or other various
plume agates from the Pacific Northwest or other plume agate producing locales.
Such specimens can have plume like formations that are sometimes measured in inches. However, if you
look closely you can locate small plume-like formations in Lake Superior Agates that have usually been
classified as moss. The specimen on the following page is one such agate. An enlarged area is shown
below the top photograph.
Like the green agate on page fifty-six I polished this agate on its entire surface except for the base upon
which it rests.
58
59
Due to the relative freedom from internal fractures in Lake Superior Moss Agate it is a prime material for
marbles and spheres. The sphere below measures two inches in diameter and weighs 12.5 ounces. It is the
largest known sphere of Lake Superior Moss Agate.
Lake Superior Moss Agate
60
One of the most attractive things about all but the most dense moss agate is the fact that it can be viewed in
direct light (on the surface) or transmitted light (shown through the material). A slab of red Lake Superior
Moss Agate is show below in both manners:
61
Lake Superior Moss Agates, like sagenites, can be appreciated as shelf specimens or studied under
magnification. Even an inexpensive hand lens of perhaps five or ten power opens a new world of detail in
sagenite and moss agates. For example the specimen below is a polished slice of moss agate combined with
banded agate. The photograph to the right shows the view with only ten-power magnification of an
interesting area of mineralization within the agate. Further magnification would provide even more detail.
Of course, backlighting a slab of translucent Lake Superior Moss Agate provides yet another view.
62
This is another example of a “carving” made from
Lake Superior Moss Agate similar to the one shown
on page fifty-six. The entire stone, except for an area
left natural to serve as a base, has been contour
polished by following the original shape of the agate.
This specimen reminds me of seaweed and the sea
froth of the Pacific Coast. I view this lapidary
technique as an artform in which the objective is to
retain the character of the original stone in the
finished product.
In this way the effects of millennia of patient erosive
forces that sculpt Lake Superior Agates is maintained
while being enhanced by the polishing.
The polished surface permits the viewer to gaze into
a material that, at over one billion years of age, is the
oldest known agate on Earth.
Working and possessing these agates is in some ways
equivalent to experiencing the time of their history.
Many Lake Superior Moss Agates exhibit an
exquisite blending of colors such as the reds, blues,
whites, browns and other colors present in this
specimen.
Along with this coloration comes very high levels of
detail. Is this a moss agate or is this a plume agate?
Under twenty-power magnification shown on the
following page it is difficult to decide.
63
An example of the
tremendous range of
colors that can be found
in Lake Superior Moss
Agates.
This specimen has a
small area of banded
pattern in addition to
the multi colored mossy
growths.
64
65
A magnificent two and one quarter pound
Lake Superior Moss Agate. The exterior of
this agate is very smooth and free from
defects. This fine exterior must have been
due to erosion in a very low energy
environment such as a gentle beach or
stream.
The entire surface of the agate is busy with
multiple colors and fanciful patterns such
as the one enlarged to the right. In fact, if
you look closely you can see sagenite in this
small feature which measures only about
5mm across.
66
12
Lake Superior Moss Agate Summary
Lake Superior Moss Agates have provided me with some outstanding opportunities to create threedimensional freeform agate carvings. This variety has exquisite colors, fantastic detail, and is much easier
to work from a lapidary’s point of view than any other variety of Lake Superior Agates.
The truth is, though, that to really appreciate Lake Superior Moss Agate it must be polished. Very few
specimens are very attractive in their natural condition. The good news is that not many collectors of Lake
Superior Agates today practice the art of lapidary. The supply of Lake Superior Moss Agate is therefore
plentiful and very inexpensive. The multicolored specimen below weighs about a pound.
Extraordinary color, pattern, and complexity in a Lake Superior Moss Agate
67
13
What Is a Tube Agate?
The reader should keep in mind that to a scientist, or an official judging a gem and mineral competition,
there may be virtually NO difference between any of the many fascinating and THOROUGHLY UNIQUE
varieties of Lake Superior Agate that we have been discussing.
All are basically quartz in slightly different forms with slightly different mixtures of ingredients. Even
agate is not agate in some of these lofty realms that attempt to apply scientific terminology to their hobby.
Of course, that is why I long ago let my last rock club membership expire and NEVER compete or show in
organized gem and mineral events. Do we really have to call agate quartz? Why be so serious?
Collecting should be, above all else, fun for the collector. Worrying about someone else’s rules regarding
how to name my specimens is a waste of my time. Heck, some of these people won’t even let you call an
agate an agate! I stay away from these potentates of the picky.
For me, though, tube agate is a separate variety of Lake Superior Agate. In fact there are two basic types of
Lake Superior Tube Agates based upon their mode of formation (And, for the daring, there is a very rare
third type of Lake Superior Tube Agate which some collectors might term plume....more on that one later!)
Tube Agate, like sagenite and moss agate, is named on the basis of appearance though the method of
formation of the tube structures may be quite different. Tube agates, like banded, moss, sagenite, and many
but not all water level agates form from a single mass of silica rich gel that also includes variable levels of
other materials that are crucial to the variety of agate that will form, generally, in a gas bubble cavity in
volcanic rock.
Like all varieties except banded agate, tube agates show no evidence of pressure escape structures except in
rare cases when they are combined with banded agates. This occurs as well with combination water level
and concentric banded agates but it is always the banded agate portion of the pattern that shows pressure
effects. I have never seen such effects in the tube or water level portion of a combination agate.
14
How Do Tube Agates Form?
The most common formation style of Lake Superior Tube Agates is virtually identical in principle to how
moss agate forms. A tiny filament of crystalline mineral material grows into the original silica gel that will
eventually become an agate. The difference between moss and tube agate is, as previously stated, often just
a matter of subjective classification. This type of tube agate, based on method of formation, I call filament
tube agate.
In the case of moss agates the mineral filament grows into the silica gel medium and is supported. This is
one of the basic reasons for believing that a single original quantity of silica gel is involved rather than some
kind of successive deposition of silica in an open cavity. The difference between tube agates and moss
agates has to do with what happens after the mineral filament forms.
In tube agates of this type concentric bands of agate form around the mineral filament drawing silica for
their construction from the surrounding gel medium. As with banded agates (Remember I promised to tell
you why we had to consider banded agate formation in a book about non-banded agates?) the growth of
these concentric bands is mediated (controlled) by the presence and accumulation of trace amounts of nonsilica materials that exist in the original gel but cannot become incorporated into the chalcedony fibers.
68
As in the case of banded agates we find that most or all of the tubes in a particular tube agate will have the
same coloration and arrangement of bands. This is logical since they were all formed from constituents
present and evenly dispersed, as in banded agates, in the original silica gel.
Generally, tube agates are not as dense as moss agates. It is probably accurate to say that most tube agates
had a lower proportional amount of non-silica material present in the original silica gel than the average
moss agate. This also helps to explain why there are areas of color concentration in many moss agates and
needle sagenites but not in tube agates. In a silica gel much “thicker” with non-silica materials it would be
much more difficult for colorative minerals to evenly disperse throughout the medium.
In most tube agates, though, colorative materials seemed to disperse much more evenly resulting in the
formation of almost identical bandforms in each tube. Some tube agates, however, can be quite dense and
still exhibit very uniform dispersal of coloration.
The photograph below shows a typical Lake Superior Tube agate of the filament type. Such tube agates are
very frequently found in association with macrocrystalline quartz. I believe that this is the quartz that would
have been in the center of this agate had it formed as a banded agate instead of a tube agate. The growth of
the tubes depleted the silica gel of non-silica materials, which resulted in, as in banded agates, the
unmediated growth of macrocrystalline quartz around the tubes rather than in the center as in banded agate.
Lake Superior Filament Type Tube Agate ( hand polished on the entire surface )
69
As in the case of sagenite agates I believe that the growth of tubes, as in the agate on page sixty-nine,
prevents the banded pattern that would otherwise almost certainly have formed. The growth of the
filaments provides a large “nucleation surface area” for the growth of the chalcedony fibers we call agate.
This reduces free silica available to accumulate on “nucleation” points on the outer walls of the cavity thus
preventing the formation of banded agate, though combinations do occur.
As with sagenite agates combination banded and tube Lake Superior Agates are quite common. In these
agates the chalcedony fibers began to form simultaneously on both portions of the cavity wall and on the
filaments. Pressure relief effects are seldom seen in these cases as the cavity as a whole is not sealed from
the external environment.
Below is a closeup of the specimen on the preceding page. Note that the tubes are virtually identical.
Enlarged area
approximately
.5” X .75”
Though very uncommon smoky
quartz is sometimes found in Lake
Superior Agates. This tube agate
is identical in form and structure
to the one pictured on the previous
page and above in close-up except
for the coloration of the quartz.
70
Lake Superior Tube Agates are also found in combination with water level agates. Generally the tube
formations are found on the outer portions of the water level pattern and not penetrating them. I believe that
the tubes formed first in such combination agates followed by the formation of the horizontal water level
bands.
Below are two Lake Superior Agates that combine both tube and water level bandforms together with close
up photographs of each at ten-power magnification.
Note that the agate directly above includes not only tube and water level formations but also
an area of banded agate superimposed on the water level pattern. Combinations of water
level and banded agate taking this form are extremely common in Lake Superior Agates and
will be discussed in detail in the section covering water level agates.
71
This is another example of a filament type Lake Superior Tube Agate with surrounding quartz. It is likely
that the mineral filaments that form the nucleation points for the banded tube structures grew “upward”.
This is a conjecture based on the observation that there is no other apparent force or influence, other than
gravity, which would cause the alignment present in this striking one-third pound specimen.
Sometimes, however, tubes are found in Lake Superior Agates that have formed in an apparently chaotic
manner with little or no external organizing influence. The rough specimen below exhibits this
characteristic. This specimen has what collectors term a “waterwashed” surface. This is thought to be the
result of the smoothing action of what geologists would term a “low energy environment”. This stone likely
received this smooth shaping on a gentle wave lapped beach rather than in a torrential glacial melt-water
river or stream.
Why is this specimen considered a tube
agate and not a sagenite?
The
“inclusions” appear to be linear in form.
Isn’t this the defining characteristic of
sagenite agates?
No, the definition of a sagenite agate is
one that includes straight mineral crystals
included within the agate.
Close examination of this agate shows
that each “tube” is a small reproduction
of the larger filament tubes seen on
previous pages. (19.5 ounces )
72
Before moving on to the second type of Lake Superior Tube Agate here is an unusual example of a filament
tube agate. This agate very well illustrates the fun a collector can have searching for unusual combinations
or features in Lake Superior Agates. This is one of the main reasons that I find collecting non-banded Lake
Superior Agates so rewarding. This agate has been photographed looking directly down at the tube
formations.
The central filaments around which the tubes have grown are plainly visible. Unlike the previous examples
the tubes in this filament type tube agate grew into a silica gel that was rich enough in silica AND non-silica
materials to result in the formation of banded agate surrounding the tubes.
However, the brick colored banded agate in this specimen has been mostly converted to what collectors
term “paint” agate. This makes reference to the fact that the original colors and patterns of the banded agate
have been blended into a homogenous state. Some paint agates lose much or all of their original patterning
and their coloration is blended. Some banding is still present on this specimen to the left.
There is no conclusive answer to how paint agates form. Any of the varieties of Lake Superior Agate can be
found as so-called “paint stones”. Collectors theorize that this effect may be caused by surface weathering
or perhaps heating or chemical alteration of the agate while it is still encased in the rock in which it was
formed
It is generally thought that paint agates have significantly higher concentrations of iron oxide as pigment.
Some believe, in fact, that this may be the sole explanation for paint agate formation. Many collectors
consider agates with this “paint” coloration to be a separate variety.
Another interesting feature of this agate is the presence of native copper. The native element copper is
present in the rock formations in which Lake Superior Agates formed. Sometimes glittering and perfect
crystals of copper can be found in Lake Superior Agates. In this specimen the copper crystal is just below
the surface and reflecting the light. The point of copper is in almost the exact center of the close up
photograph on the right. (See arrow)
A closer view of native copper in Lake Superior Agate can be seen on page one hundred thirty-five.
73
Another interesting feature found in a few Lake Superior
Agates is called “ruin”. More examples will be shown
later. A ruin feature is a fracture in the agate that was
formed well after the agate was completely hardened.
The fracture then rehealed when additional silica
migrated into the opening.
In a way this is a fossil remnant of an earth movement
that took place unknown millions or hundreds of
millions of years ago. This ruin is in a filament Lake
Superior Tube Agate. Many collectors consider ruin
agates to be a separate variety.
Other runes have been found in Minnesota. Their
historical veracity has been documented by some of the
best and most creative researchers of our time.
The second type of Lake Superior Tube Agate does not depend on fine mineral filaments for the origin of
tube structures. This second type I call “diapiric tube agates”. The word diapiric refers to the rising of less
dense material through material of higher density. This term is most often applied in geology as, for
example, the rising of salt domes through the surrounding rock strata. In the case of Lake Superior Agates
the hypothesis regarding the presence of two viscous fluids having different densities is conjectural and
based on observation of agates and inferences taken from those observations.
The basic idea is that the original silica gel in some agates was composed of two regions having
significantly different densities. We have already seen a hint of density differences in the spheres that seem
to rise in some Lake Superior Radial Sagenite Agates while they appear to remain stationary in others
hinting at variation in density of the gel and its constituents.
This is a combination pattern diapiric tube and
banded Lake Superior Agate. The “tube”
structure appears to have distorted the banded
pattern as it moved upward through more
dense material.
The entire lower portion of the agate seems to
be composed of this lower density material as
evidence of additional movement can be seen
at other places.
Why this dissimilarity in fluid densities should
be present in the original silica gel is
unknown.
74
This is a twenty-power magnification close
up photograph of the diapiric tube shown in
the agate on the previous page. It appears
that the “agate diapir” is moving upward
and distorting the already formed bands as
it does. Note the tiny spheres!
It is also possible, as suggested by respected
theorists, that the tube structure formed
prior to the banding and thus the apparent
distortion of the banding did not occur. In
this case the band would have simply been
conforming to the preexisting tube.
Whatever, the timing of events I believe
that this could only have occurred in a
single silica gel.
Diapiric Tubes in
quartz. Note origin
of structures in
cloudy mass at the
bottom of the agate
and identical parallel orientation.
This agate measures
about four inches in
width.
75
This series of three Lake Superior Agate
Slices are a combination of banded and
diapiric tube.
It is evident that almost the entire lower half
of the agate is unique and separate from the
upper area of banded agate.
Numerous “tube” structures can be seen
rising through what is inferred to be fluid
material of higher density.
Lake Superior Diapiric Tube Agate
76
“Waterwashed Surface” diapiric tube Lake Superior Agate
This unusual specimen of Lake Superior Diapiric Tube Agate exhibits an amethyst lined geode cavity in which
diapiric tube structures have grown. Subsequent erosion has removed the less resistant amethyst leaving the
tubes in relief and appearing similar to stalagmites in a cave. Could these, in fact, have somehow grown “free” ?
77
The third and last type of Lake Superior Tube agate (by method of formation) is quite rare. This form is
common at familiar locations in the Pacific Northwest such as Graveyard Point Plume Agate. Like
Graveyard Point I believe that this very scarce type of Lake Superior Tube Agate formed in fissures or
cracks instead of rounded gas cavities in volcanic rock.
It is also possible, but not proven, that this type of Lake Superior Tube Agate differs fundamentally from all
other varieties of Lake Superior Agate. I believe that it is possible this type forms from hydrothermal fluids
circulating in the fissure systems. Such fissures, by their physical nature, would be incapable of containing
a silica gel and keeping it separate from external forces once the crystallization process had begun.
Therefore, this could constitute an exemption to the single silica gel model of formation for all Lake
Superior Agate except certain water levels.
Such “vein” agates form on the Columbia River Plateau in parallel sided fissures. Generally the agate
contained within appears to originate from both walls of the fissure simultaneously and meet in the middle.
Frequently there are open spaces in the center portion of the fissures in these agates. Importantly for our
discussion of Lake Superior Agates this type of agate almost always contains a high level of metallic
inclusions.
The presence of metallic inclusions at high levels supports the proposition of deposition by hydrothermal
fluids that are hot enough to carry high levels of dissolved metal compounds.
Below are two specimens of what I call Lake Superior Hydrothermal Tube Agate. The bottom photograph
shows the underside of the specimen on the right. This clearly did not form in a rounded gas bubble.
78
79
A Lake Superior Tube Agate polished with the tube formations in cross section. As
with many tube agates this specimen includes banded pattern. There is even a bit of
shadow and some tiny waterlevel lines. A busy and attractive agate.
80
81
A very finely rounded large specimen of Lake Superior Tube Agate in Smoky Quartz
82
15
Lake Superior Tube Agate Summary
Lake Superior Tube Agates are very attractive. Unlike most moss and sagenite varieties many of them are
worthy of display in their natural condition. They are frequently combined with other varieties of Lake
Superior Agate giving the collector added enjoyment and interest.
Lake Superior Tube Agates have things to tell us about how they form that bear directly upon the formation
of other varieties of agate. It is nearly impossible to view a Lake Superior Tube Agate and, with the
possible exception of the very rare hydrothermal tube agate, fail to see a single silica gel as the only possible
explanation.
Has this variety of Lake Superior Agate given up all its secrets regarding agate formation? I do not believe
so. We do not have a clear understanding of how two distinct regimes of fluid density could develop within
a forming Lake Superior Diapiric Tube Agate. The issue of hydrothermal tube agates is an open one. I
personally believe that these may, in fact, originate elsewhere than all other Lake Superior Agate. The Iron
Range area is one possible source of these agates.
However, this type of agate is so rare that deduction is impossible especially since we do not know the
locale in which existing specimens were found.
I enjoy having “open” questions about agate formation. Fewer of them are “open” now than in my past.
However, we may never know the whole story. The “final” book on agate formation may never be written.
This specimen of what I have named Lake Superior Hydrothermal Tube Agate speaks for itself regarding
whether it was formed in a rounded gas bubble or in a fissure or crack in the host rock.
83
16
What Is An Eye Agate?
An eye agate includes formations that resemble eyes. In fact some writers have called “eye” agates “hemi”
agates instead. This is because by its nature the “eye” of an eye agate is named solely on the appearance of
the structure in two dimensions. In fact, eye agates are hemispherical in shape-hence the contraction to
hemi-agate. They are not spherical.
Lake Superior Eye Agates are almost certainly the finest eye agates found anywhere. The only close
contender is the Botswana Agate from Africa, which produces some exceptional eyes. They are, however,
much scarcer than Lake Superior Eye Agates and usually do not have the range of colors.
Speaking of scarcity the Lake Superior Eye Agate is also almost certainly the rarest and most valuable of all
the varieties. You just don’t find many.
Generally Lake Superior Eye Agates are found in combination with banded and some water level agates.
The eyes themselves always occur on the exterior of the agate, that is, they formed closest to the walls of the
cavity, which enclosed the forming agate. While eye agates form on the surfaces of banded agates I have
never seen any pressure related effects indicated in the eye structures themselves.
I believe that this may be due to the timing of their formation. If we assume that they are the first structures
to crystallize from the original silica gel it is possible that they had hardened sufficiently to preclude any
distortion at a later time when pressure relieving events took place in the banded agate.
I believe that eye formation requires the same approximate proportions of silica vs. non-silica materials in
the original silica gel as that required to produce a banded or water level agate. If true, this would explain
the absence of eyes on most moss, sagenite, and tube agates. This further seems reasonable when you
consider that an eye agate is really just banded agate that has adopted a radial form with chalcedony fibers
radiating outward from a common point of nucleation.
It is unknown why eye agates form on some banded and water level agates but not all. I believe that the
answer may lie in the degree of dispersal of silica and non-silica band mediating material in the original gel.
If the materials necessary to form bands were initially distributed unevenly in the silica gel then chalcedony
fiber formation could have been limited to specific zones. This might result in growth of eyes instead of
bands since not all areas could support chalcedony fiber creation or growth.
Alternatively, there may be some aspect of the nucleation points (origins of chalcedony fibers) that could be
different in eye producing cavities. Perhaps a scarcity of` nucleation points on the outer walls of the cavity
initially make development of concentric bands impossible. The few suitable nucleation points in the cavity
would then have an ample supply of materials and the freedom to grow radially unhindered by the more
usual continuous “band” of growing chalcedony fibers.
Eye agates share with tube and banded agates the strong tendency to appear nearly identical in terms of
colors and band patterns in a particular specimen. This would tend to contradict the idea of incomplete
dispersal of band mediation materials as the cause of eye formation and point to a nucleation cause.
Whatever the true reason it is clear that in agates having eyes some process or factor resulted in a hold being
put on the formation of “normal” banding until the eyes had formed.
84
To fully understand the hemispherical nature of eye formations in Lake Superior Agates it is necessary to
view them in cross section. Just as a radial sagenite will seem to be hemispherical in cross section so will an
eye. The photographs below demonstrate this observation.
Once an eye begins to form multiple bands will be deposited from the silica gel medium under the same
circumstances as the formation of normal banded agate. That is, chalcedony fibers will grow until excluded
non-silica materials halt the process, which then restarts past the boundary of the excluded materials. These
excluded materials mediate, or control, band formation, causing it to stop and start as in banded agates.
This can be seen in cross section in the photographs above. If the eye is viewed from a point looking
directly at its center into the hemisphere a series of concentric, and many times almost perfectly circular,
band rings will be seen as in the photograph below. This eye grew virtually free from any competition.
85
This Lake Superior Eye Agate illustrates perfectly how, like filament tube agates, the individual eyes
possess nearly identical coloration and bandforms.
86
Two more examples of Lake Superior Eye Agate having multiple eyes with identical coloration and bandforms
Both of these eye agates have only a single eye instead of multiples as the previous two examples. Both are in their
natural, as found, condition. Approximately fifty percent of eye agates are polished. This is generally done because
it is necessary to remove the outer layers of the agate to better expose the eye structure. Refer to the eye agate in the
upper left-hand corner of page eighty-five and you will see a layer approximately one millimeter thick of clear agate
upon which the eye agate rests. This common observation contradicts the proposition that nucleation points on the
cavity wall result in the initiation of eye formation.
The single eye agate above on the right is an example of “differential erosion”. This means that the more easily
eroded macro quartz has been removed at a faster rate leaving the more resistant eye in relief.
87
This striking Lake Superior Eye Agate shows off nearly identical twin eyes. Uniformity
of coloration and size of eyes strongly suggests their simultaneous formation.
88
Lapidary treatment of Lake Superior Eye Agates seldom amounts to more than simply removing the outer
layer of agate that may be obscuring clear viewing of the eye. However, sometimes a very brave person
will attempt an almost impossible feat of lapidary-the creation of a Lake Superior Eye Agate marble.
The series of three photographs below of a small marble with a single perfect eye gives further insight into
the structure of the eye formations. This diameter of this agate marble is just over one-half inch.
This is a combination water level and eye Lake Superior Agate. Notice that the main eye is surrounded by many
other smaller eyes in close association. The water level agate is unusual in having unbroken horizontal bands of
amethyst. Eyes are never included within the water level pattern strongly suggesting that they formed first.
89
17
Lake Superior Eye
Agate Summary
Lake Superior Eye Agates are the rarest
and most valuable of all varieties. Eyes
seldom occur on really large agates.
A number of theories regarding the
formation of eye agates have been
offered. I believe that the “eyes” of an
eye agate, like filament tube agate, must
be viewed as a different form of banded
agate. This will tell us “how” the bands
of an eye agate form but not “why” they
take this form.
The answer may involve nucleation
points, silica gel variances, or some
other as yet unknown explanation. It is
certain that these agates, however they
form, offer the collector the utmost in
beauty and rarity.
Twin-Eyed Lake Superior Eye Agate Marble
Diameter .84 inches
Botswana Eye Agates from Africa
90
This large eye agate has a single eye
comprised of two joined eyes that
resemble a double yolked egg.
Most notable about this specimen is
the pronounced green outer band
visible in the photograph.
Just visible in the photograph
to the right are a myriad of
sparkling flecks of copper suspended in the bands of the eye.
The combination of green,
white, red, and other colors together with the copper makes
this a most attractive agate.
91
18
What Is a Water Level Agate?
Water level agates are found in many different localities around the world. For example Brazilian, Scottish,
Australian, and Oregon, USA locales all produce high quality water level agates. Interestingly, some agate
locales produce NO water level agates. The famous Laguna deposits of Mexico produce none.
A water level agate is simply one that exhibits a series of perfectly flat bands that remind the observer of
levels of water in a container. Water level agates have always been held as prime evidence by some agate
formation theorists that agates form “open” to their local environment. They believe that each band of a
banded agate and each layer of a water level agate is deposited by a new influx of silica in solution. This is
most intuitively reasonable for water level agates and it was simply assumed that banded agates would form
in the same manner. In other words that a single mode of formation would explain all varieties of agate.
In fact, this belief was so strong that for years some theorists insisted that the pressure escape channels
present in banded agates were “entrance channels” through which the silica in solution entered to deposit
the next band. Theories were invented to explain how structures that clearly appear to have moved outward
actually had moved inward. Of course, we now believe that the bands in a banded agate are the result of
internal self-organization and not the result of individual influxes of fresh silica from outside the cavity.
A major problem with this “successive deposition” theory of agate formation is the unhandy existence of
moss, tube, and sagenite agates. All of these varieties are nearly impossible to explain using a theory that
depends upon multiple new influxes of fresh silica from outside the cavity. It just doesn’t work.
I believe that it was a mistake to conclude that the processes of formation of water level and concentrically
banded (fortification) agates were necessarily similar or identical. Not everything that seems intuitively
obvious actually is. I now believe that some water level agates alone among all the varieties of Lake
Superior Agates form from successive deposition of individual layers of agate either in whole or part.
However, other water level agates cease being water level agates and become banded agates. These
combination agates are very common. The banded agate portion of the combined agate is always on “top”
of the water level’s horizontal banding. And, while the water level portion may have formed by successive
deposition layer by layer, the top portion formed from a single silica gel as other banded agates.
The shape of the cavity in which the agate formed may determine whether it will be a water level for part or
all of its formative period. I think that vertically exaggerated cavities and those with very flat bottoms may
be prone to develop water level banding. However, this is based solely upon observation that such shapes
are frequently encountered in water level agates and is unproven at this time.
However, another possibility that I consider much stronger is that the cavity could not, for some reason,
retain silica solutions long enough for the critical concentration to be reached at which single gel agate
formation will begin. If this were the case we might expect to find some water level agates that show
evidence of having held fluid for a time but then dried out leaving a residue of the drying process.
Some water level agates are composed entirely of horizontal banding. Many others have either banded
agate or quartz above the horizontal bands. This point could represent the time at which the cavity was
finally able to retain the silica solution long enough for it to become concentrated to the critical level needed
to initiate self-organization into a banded agate or macro quartz. In these cases the water level agate would
have formed by two mechanisms, successive deposition (bottom) and single silica gel (top).
92
It is interesting to note that moss, tube, and sagenite agates are all virtually impossible to find above a partial
water level band pattern. In my experience it is always banded agate or quartz. The bandforms will be seen
to change at that point and extend from the flat “floor” and all around the inner wall of the cavity.
Many, but not all, water level agates apparently become dried out at numerous points during their formation.
When this happens a crack pattern that I named “mosaic agate” is formed either on the bottom of the cavity
or at any point in the stack of horizontal layers where the drying event took place. No such drying events
are ever found in banded, moss, tube, sagenite, or, in fact, in many water level agates.
I was visiting Scott Wolter several years ago and he showed and offered to sell me the agate of which the
underside is shown on page ninety-seven. I had been polishing and wondering about unusual patterns of the
sort that Scott pointed out on the bottom of this agate for several years but had, as yet, no possible
explanation for them. But Scott knew I collected water levels and sold me the agate. Since that time I have
resold the agate to him to commemorate the insights of that day.
I happened to pick up one of Scott’s geology textbooks and noticed a photograph of crack patterns caused
by the drying of materials that had been in solution but had insufficient time to crystallize. I showed the
photo to Scott and suggested that there could be a link with the unusual features I had been seeing on the
bottoms of water level agates. Also, at that time, I coined the term “mosaic” to describe the feature.
The connection that I made meant that the cavity in which the water level agate formed had been desiccated
early in its history. This seemed to contradict the notion that all agates form from a single original silica gel
and self-organize based upon internal dynamics with no further operation of external factors. This
observation suggested that, at least in the case of some water level agates, formation was based on multiple
successive events (fresh silica influxes) controlled by the external environment.
It must be noted that this “mosaic” pattern has NEVER been found on any other variety of Lake Superior
Agate. It is found only in some water level agates.
Further searching in my collection uncovered some water level agate specimens that showed evidence of
repeated drying events in the form of miniature “faults” running perpendicular to the plane of the horizontal
banding. Some of these cut across two or more layers suggesting multiple layers had formed and dried out.
In my opinion the discovery of mosaic pattern in water level agates does not challenge the single silica gel
theory of agate formation for any varieties except some water level agates. Also, many water level agates
become normally banded agates at some point during their formation and then begin to behave exactly as
concentrically banded agates. The evidence for this is that banded agate superimposed upon water level
banding is frequently seen to have pressure escape or distortion features and a central area of macro quartz
as commonly found in normal banded agates.
No water level agate that is composed totally of horizontal banding ever has been found to have pressure
escape features. This indicates that such agates form exclusively from successive deposition of new layers.
I believe that some water level agates become only partially dried out before the next inflow of silica
solution. Perhaps the cavity in these cases could retain the solutions longer or temperature conditions were
different. The result is that several horizontal layers may be deposited prior to drying out. In these cases we
see vertical cracks that go through more than one layer.
93
In combination pattern water level agates a level of fluid retention may eventually be reached (in the upper
portions of the cavity) that permits the concentration of silica to increase to the critical point at which the
self-organizing process of concentric band formation could begin.
This Water Level Lake Superior Agate
shows evidence of mosaic structures at
many levels in the water level pattern.
I believe that this agate formed first in
an open cavity, which periodically filled
with silica solution but could not contain
the solutions. The solutions seeped
from the cavity causing desiccation of
the already formed but as yet
unsolidified horizontal agate bands.
In some cases the crack lines that
resulted crossed many bands. The entire
assemblage then solidified.
Subsequently the cavity filled again.
However, this time the fluid was
retained and the silica concentration
could increase through osmotic flow.
When the critical agate forming level
was reached banded agate formed on the inner walls of the upper “chamber”. This “chamber” was now
essentially a separate agate behaving according to the formation mode of concentrically banded agates.
Based upon the particular proportions of silica vs. non-silica materials band formation ceased early and
macro quartz began to form. Part of this new crystal was in the form of amethyst due to traces iron.
“Faulted” appearance of mosaic fragment in a view from
the side rather than the bottom. This suggests that
drying cracks involved more than single bands.
This agate has many water level bands offset by drying
cracks that cut several bands at a time. This specimen
appears to have had a long history of drying cycles.
94
According to the proposed sequence of events leading to the formation of mosaic agate there should be very
distinct differences between the material that comprises the area of filled cracks and the interiors of the
polygonal cells themselves. In fact, proof of such differences would lend great support to the theory.
In order to test the mosaic agate formation hypothesis thin sections were prepared and photographed at both
forty and one hundred power magnification under cross-polarized light. These were prepared by American
Petrographic Testing of Saint Paul, Minnesota, and are courtesy of Scott Wolter. The Lake Superior Water
Level Mosaic Agate thin section below was photographed at forty power magnification.
It is clearly evident from the thin section that the individual polygonal cells are all somewhat dissimilar in
their structure indicating that they were effectively separated by the crack filling boundary. The photograph
on the following page is a portion of the area shown below at 100 power magnification. It can be clearly
seen that the crack was filled with chalcedony fibers that oriented themselves perpendicular to the crack
walls, the same orientation assumed by the chalcedony layers of banded agate. I believe that this
conclusively demonstrates that separate events were involved in the formation of mosaic agate.
95
This Lake Superior Water Level Mosaic Agate was prepared in a
thin section twenty-five microns in thickness and photographed in
cross polarized light at one hundred times magnification.
The diagonal line that bisects the field of view is a drying crack
that, following desiccation of the original material, filled with chalcedony fibers. The fibers are oriented perpendicular to the crack
faces and join in a center suture to which excluded non-silica
material may have been moved during the crystallization process.
Photograph and technical preparation courtesy of American Petrographic Labs, Saint Paul, Minnesota and Scott Wolter.
96
97
This rough mosaic agate on page ninety-seven is, so far at least, the finest rough example ever found. The
individual “cells” that mark polygonal areas bounded by the crack pattern are clearly visible. This agate is
now back in the collection of Scott Wolter. The large boulder of agate-bearing basalt on page one hundred
nineteen is also a part of Scott Wolter’s collection.
The photograph below is a close up of the agate on the preceding page. You can see that each individual
polygonal “cell” is surrounded by cracks. I believe that following the initial drying event a subsequent
influx of silica in solution filled the voids between the curled and cracked pieces. This created the walls of
the cells. Later, the “cell” spaces were themselves filled with silica gel and finally hardened.
In some cases adjacent cells appear to be almost identical, as if a nearly uniform material dried and cracked,
the cracks filled with more silica, and the individual cells hardened into agate. However, in other cases
there can be great dissimilarity between adjacent cells suggesting that they may have formed more like
individual single gel agates.
Lake Superior Water Level Mosaic Agate
98
But wait a minute! What if water level agates themselves formed in two distinct manners? What if some
water level agates formed, as I have just been discussing, by the successive introduction of “new” silica into
the cavity while others formed from single silica gels in the manner of all other varieties? Not just the top
portion-the entire agate. Do I have evidence that water level agates form in two ways? I believe I do.
The Lake Superior Water Level Agates below all have several common characteristics. First, all three are
free from any evidence of “mosaic” pattern suggesting that there were no drying episodes during their
formation. Second, they all have a continuous outer margin of banded agate, which totally encloses and
seals the water level pattern, and third, they all have macro quartz above the water level pattern.
Why should we find a mass of quartz ABOVE the water level bands in an agate presumably formed layer by
layer as new influxes of fresh silica entered the cavity? What external process can be proposed that would
suddenly, almost magically, switch from the formation of horizontal bands to massive quartz crystal at a
point midway through the “filling” of the cavity?
Let’s look at several of these “enclosed water level pattern” agates and see what they can tell us.
It is very important to note that these are not water
level agates with banded agates superimposed
above the water level bands. All of these agates
have superimposed quartz and none have mosaic
pattern. All have some level of exterior coating of
banded agate that may have sealed the developing
single gel agate off from the external environment.
I believe that these three agates began as normal
banded agates (the initial banding). However,
instead of continuing to form banded agate they
began to form water level. Why?
The quartz top is directly analogous to the
quartz center in a banded agate. These water
level agates formed from a single silica gel!
99
As I long suspected water level agates are the most complicated of all the varieties of Lake Superior Agate
in terms of their formation. It is clear from the evidence of mosaic pattern that some water level agates
develop during part or all of their formation as “open systems” that respond directly to fluctuations in the
external environment. This may result in the cavity in which these agates are forming to become either
partially or completely desiccated at least once and perhaps on multiple occasions due either to inability of
the cavity to retain the solution or insufficient available water levels in the external environment.
It is also clear that some water level agates with mosaic patterns can switch and begin to form normal
banded agate. I believe that this point is reached either when the cavity becomes able to contain the silica
solution long enough to produce a silica gel of sufficient concentration to form agate or when external
availability of water/silica in solution increases. When the critical silica concentration has been reached the
upper portion of the former water level agate becomes a sealed and closed system and banded agate begins
to form. At that point the formation mode of the agate changes from successive influx to single gel.
The examples of single silica gel water level agates on page ninety-nine developed in a very similar manner
to banded agates. The upper “remnant” of quartz was “left over” when all the non-silica band mediating
materials were depleted. At that point, as in quartz centered banded agates, there remained nothing to stop
the remaining silica from forming macro crystals of quartz.
The photographs below are examples of successive influx water level agates that “switched” to become
single gel banded agates during their formation.
To recap, I am proposing that Lake Superior Water Level Agates form in two distinct modes, from single
silica gels and as a result of repeated inflow of new silica from outside the cavity. Further, the water level
agates that form in the second manner sometimes switch to normal banded agate later in their formation.
I believe that the primary factor that influences the mode of water level agate formation is the ability of the
cavity to develop and maintain required the silica gel concentration. This may be due inability of the cavity
to hold solutions adequately or external conditions of temperature, pressure, and/or water availability.
The question remains, though, in water level agates that form from single silica gels why horizontal bands
form instead of concentrically banded agate. What factor causes this rather than the development of banded
agate? I believe that it is the presence of another material in the cavity that causes clumping and
gravitational settling into horizontal bands rather than formation of normal banded agate.
100
This large Lake Superior Water Level agate has been polished on the bottom to expose the
“mosaic” pattern. Many of the geometric “cells” can be seen to be unique agates that are quite
dissimilar from one another. This agate weighs about 12 ounces.
101
We know from undisturbed agate deposits that different varieties can form side by side. This suggests that
the agate variety that forms in each cavity may depend solely on the chemical contents of the silica gel in
that cavity. However, we also know that water level agates can form in groups. The photographs on page
one hundred eleven show a boulder of basalt that contains almost exclusively water level agates.
From personal conversations with Scott Wolter I have been told of shoreline in situ (undisturbed) deposits
of Lake Superior Agate that are almost all of water level variety. Higher temperatures might have prevailed
here than in other agate forming areas or perhaps there was inadequate water available to form single gel
agates. However, what factor would cause the formation of single gel water level agates instead of banded?
I believe that the answer is higher levels of trace materials in the original cavities that can act as nucleation
points in the formation of “colloidal particles”. Greater levels of these materials in the original cavity would
lead to silica gels in which “clumping” was more frequent. This would result in silica particles being unable
to remain in suspension. As particles gradually increased in size they would settle to form horizontal layers.
This gradual clumping of silica particles would result in deposition of layers as materials settled under the
influence of gravity. The apparently random distribution of color in some water level agates may result
from a process of fractionation in the gel. Similar to color zoning in radial sagenite agates this could result
in a proto layering within the gel based upon sizes of particles present. This could exert a sorting effect.
These colorative materials may be minerals whose particles are subject to growth in size in the silica gel
medium. They may actually become larger as time within the gel increased. Or the colloidal nucleation
materials may be present as ultra fine particles that are held in suspension. They could therefore be the last
materials not in solution to remain in the silica gel and could gradually become more and more concentrated
as the water level bands formed through colloidal accumulation.
If any of these materials remained in the silica gel as formation of normal banded agate began they would be
excluded as trace materials that could not be incorporated chemically into agate bands or quartz. Through
this process these materials might ultimately come to reside in spherical cells bounded by silica membranes.
These structures would become more and more distorted as agate formation proceeded and finally develop
into the wavy structures as seen in the photograph below and on the following page.
102
103
This water level agate formed from a
single silica gel. The first phase
consisted of the formation of water
level bands, which settled as
colloidal nucleation particles caused
clumping of silica material.
As most of the colloid nucleation
particles were depleted normal
banded agate was able to form. As it
did so remaining colloidal particles
were excluded from the advancing
front of chalcedony bands.
This excluded material eventually
began to operate once again as a
single silica gel colloid mediated
system. A secondary water level
band pattern was the result.
If the level of colloid enhancing materials had been high a single silica gel water level agate would have
resulted consisting of all horizontal bands or all horizontal bands with a quartz top. If the levels were lower
the result might have been horizontal bands with superimposed normal banding. Thus a waterlevel agate
with a quartz top could have formed from a single gel or in the two mode manner previously discussed.
I propose that there is a fundamental difference in these colloid nucleation supporting materials and band
mediation materials. The difference may be one of size. This would make it possible for the larger colloid
forming particles to become depleted while still leaving sufficient amounts of smaller band mediating nonsilica materials behind in the remaining silica gel to control the formation of superimposed banded agate.
I believe that the colloid nucleation materials are held in suspension in the silica gel while the band
mediation materials are present as ions in solution.
Water level agates such as those on pages one hundred two and one hundred three initially formed colloid
based horizontal banding which settled to the bottom of the cavity. There remained significant silica in the
gel as well as aggregations of colloidal material in bubbles that was prevented from settling immediately by
the rapid growth of quartz crystals. The two materials were incompatible and therefore did not combine but
were simply pushed into closer contact by the building pressure from quartz crystal growth.
The excluded aggregate of colloidal bubbles then settled to the degree possible in a confining space
resulting in the distorted “wavy” banding seen especially in the agate on page one hundred two. Such wavy
banding in water level agates may be the result of deformation of super aggregates of colloidal clumps.
104
You may recall from our discussion of Lake Superior Sagenite Agates that small floating spheres are a very
common occurrence in the radial type. I believe that there are comparable structures formed in water level
agates, possibly in the same manner. If a nucleation point (a particle in suspension in the silica gel that
serves as the starting point for chalcedony fiber formation) is present in a medium having silica in solution it
is likely that formation of chalcedony fibers will commence radially around that point.
On this page is a series of photographs of a feature that is very common in Lake Superior Water Level
Agates but that generally requires a low power hand lens to view in detail. If you look you will find
structures like these in many of your water level agates. Remember, if an excess of nucleation points were
to exist in a gel having proper concentration of silica to form agate the silica might form small spheres in
favor of bands. Many small spheres.
Once these spheres formed in the gel they would begin to fall out of suspension due to their increasing
weight. In the case of sagenites I believe that the proportion of non-silica minerals is so high that the
resulting gel is more viscous than that in a developing water level agate. Hence the spheres do not settle in a
radial sagenite.
Normal view-no magnification. Wide
white band is composed of myriad small
spheres.
Microscope photograph approx.
20x magnification
Camera close up approx. 3x mag.
Microscope photograph approx. 50x
magnification
105
Camera close up approx. 5x mag.
Microscope photograph approx.
100x magnification. Many of the
bands in your water level agates
look like this under magnification.
A Gallery of Lake Superior Water Level Agates
106
Page ninety-nine contains several photographs of Lake Superior Water Level Agates that I used as support
for the proposition that some water level agates form from single silica gels in the manner of all other
varieties of Lake Superior Agate. This proposition goes against the common sense observation that multiple
horizontal layers equals multiple “deposition events” as in a limestone formation.
My “proof” was the surrounding shell of banded agate, lack of mosaic pattern, and superimposed quartz. I
have saved until now a final point-having let you have time to consider my other ideas regarding Lake
Superior Water Level Agates. I am going to show you one of the agates pictured on page ninety-nine that
has repeating bandforms. I believe that this offers further proof of the single gel formation of this agate
when combined with the presence of the superimposed quartz.
I believe that the same band formation mediation took place in this agate as in any concentric banded agate
only the “bands” were laid down horizontally due to a high levels of colloidal clumping.
Remember this agate?
Do you agree that this agate exhibits sequences of repeating
bands formed in a single self-organizing silica gel?
107
A very interesting green Lake Superior Water Level Agate. This agate nodule was
intact and undamaged when polishing began. The specimen is unusual in that it is one
hundred percent horizontal bands without any concentric banding, quartz, or mosaic
pattern.
108
This Lake Superior Agate shows typical
mosiac structure in cross section that has
built up throughout the lower portion of
the agate.
In addition typical wavy pattern can be
seen associated with quartz in the
(assumed) upper portion of the stone.
As is frequently the case the wavy bands
are seen to diminish as they move upward
into the quartz. Sometimes these wavy
bands are intergrown with individual
crystals of quartz.
This photograph shows a never before
described relationship between wavy
water level layers associated with quartz.
This side view suggests that the wavy
layers diminish in size with distance
toward the center of the quartz region.
Each wavy layer is directly connected to
a thin concentric band within the quartz
area.
This observation offers support to the
idea that the wavy bands are composed
of material that is clumped in a manner
that prevents it from being more evenly
distributed in the bands that alternate
with quartz.
109
A highly unusual combination water level pattern with tube formations intruding into
and around the horizontal layers.
It is difficult to imagine how such delicate structures as these could form and be
preserved unless the entire mass of the agate were a gel material capable of providing support.
110
This two inch wide agate shows
classic mosaic that includes dark
amethyst and pure white agate
cells.
Above the floating crystal cavity
exhibits a smoky quartz center
and alternating agate and quartz
bands.
This two inch wide agate shows
classic “wavy” band layering that
is actually thicker than the more
normal waterlevel agate layers
below.
A very small cap of quartz can
just be seen atop the wavy area.
Lake Superior Agates can exhibit
very high levels of complexity in
relatively small physical area.
This highly complex agate measures only
about two inches from top to bottom yet
contains a significant amount of detail.
The bottom area is unusual for a waterlevel
agate and consists of uniform green moss like
agate with a perfectly flat “top”.
Above this is a mosaic layer that includes
amethyst crystal cavities and open cells
which contain tube structures. Above this
single layer of mosaic are several waterlevel
layers topped by amethyst/quartz.
111
An unusual “survivor” water level agate
that weighs just over one pound.
White wavy pattern water level is common in association with quartz and can
be found in many smaller agates.
However, agates this size are seldom
found since the fragile quartz “cap” has
been eroded away during glacial transport.
Remnant portions of larger agates of
this type are found having only the
lower water level portion intact as seen
in this agate.
This agate also has a prominent layer
of thick mosaic pattern agate.
These excellent examples of wavy pattern water level agate in quartz were able to more easily escape damage due to small size. Each of these measures only about .75 inch in greatest dimension.
Small Lake Superior Agates are frequently as complex and interesting as much larger specimens.
112
Mosaic agates are all unusual. However, this example is particularly odd. The walls
dividing the individual mosaic cells appear jumbled compared to most water level mosaic
agate. They also have unusual pigmentation compared to what is usually seen.
113
20
Lake Superior Water Level Agate Summary
Water Level agates have been of particular interest to me for many years. This has been a natural
consequence of my great and long time interest in how agates of all varieties form. From my teenage years
I was convinced that the non-banded varieties such as moss, tube, and sagenite did not form in the manner
then most widely accepted for banded agates-successive deposition of silica from outside the cavity.
Now that a new and, to me, entirely acceptable theory of banded agate formation is available, the situation
has changed much. The current theory of banded agate formation from a single silica gel as a closed selforganizing system does not conflict with the three other varieties listed in the previous paragraph. It fits
them all perfectly.
The only remaining problem is water level agate bands. How could structures so “obviously” formed
individually be the product of a single silica gel? Why would the silica gel in what will become a water
level agate differentiate into horizontal bands instead of concentric bands or some other variety entirely?
The discovery of “mosaic” agate structures only worsened my dilemma in trying to find a single over
arching theory that would explain the formation of all varieties of Lake Superior Agate. It is nearly
impossible to refute this clear evidence that water level agates having mosaic pattern dried out completely,
sometimes repeatedly, during their formation.
At this time I have a much clearer view of the divisions within water level agates-a variety that most
theorists and collectors have considered monolithic up to this point. Here is what I believe I know:
1/
Some water level agates form in the same basic manner as banded agates from a single silica gel that
self-organizes. This self-organization is controlled by the proportion and composition of constituents
present in the original cavity in which the agate forms. The formation of the agate will begin as soon as the
silica concentration reaches a critical threshold.
In exclusively single silica gel water level agates no mosaic pattern will be found. Quartz, when not
removed by erosion, will be superimposed on the horizontal banded pattern. A thin layer of concentrically
banded agate may exist around the periphery of the entire agate. Eyes will occasionally be present.
2/
Some water level agates do not form from a single silica gel. These are unlike all other varieties of
agate in this respect. They form by adding a horizontal band or perhaps several each time a new
concentrated wave of silica in solution enters the cavity. Frequently such agates dry out completely. This
results in crack patterns that can become mosaic pattern agate at any point in the horizontal “stack”.
Finding this mosaic pattern at other levels above the bottom of the agate shows that the formation/drying
cycle has been repeated and that the agate continued to be formed by successive deposition of outside silica.
This type of water level agate, formed by successive deposition of silica material, may occupy a cavity that
is incapable of holding silica-bearing solutions long enough for the silica concentration to reach single gel
agate formation levels. Solutions are held only a short time. This time may be adequate to form horizontal
agate bands. However, sometimes a precipitate forms instead and when dried out leads to formation of
mosaic agate when successive influxes of silica in solution enter the cavity.
114
This type of water level agate, in my experience, will not include eyes. Eye formation would require a stable
filled cavity with a high enough silica concentration to form agate along with sufficient dispersed quantities
of band mediation materials.
3/
Some water level agates of the second formation mode may develop the ability to retain solutions
within their cavity. This usually happens midway or later in the filling of the cavity. At this time a stable
silica gel will develop and be retained in the upper levels of the cavity. This will increase in silica
concentration through osmotic movement of silica in solution. When the critical threshold for agate
formation is reached spontaneous self-organization of the silica into banded agate or quartz will commence
in the upper area depending upon the proportion of band mediating material present.
Only concentrically banded agate will be formed and pressure escape channels may be present. The
resulting agate will have formed by two modes, successive deposition during the time the cavity could not
retain silica solutions (or lack of solutions from to the external environment), and single silica gel later on.
The single gel concentrically banded agate that forms in the upper portion of such agates is identical to one
that forms in a rounded gas cavity. The flat floor of this new single gel banded agate is only an artifact of
the prior shape of the water level bands. The upper single gel agate is simply conforming to the available
cavity. The horizontal bands in the new concentrically banded agate will be seen to increasingly deviate
from horizontal as they merge with bands following the side walls of the newly defined cavity. This may
contribute to a “lop-sided” pattern in the resulting single gel banded agate.
4/
I believe that in addition to those materials present in silica gels that mediate the growth of bands
there is another type of material that assists the development of clumps of colloidal silica that will fall out of
suspension and become unavailable for incorporation into concentric banded agate. Larger proportions of
this material in some agate forming cavities may be the reason these develop single gel water level agates in
preference to concentrically banded agates.
In summary I believe that water level agates form when there is failure to develop high enough
concentrations of silica gel to develop banded agate. This may be due to the inability of the cavity to retain
solutions long enough for high silica concentrations to develop or due to external conditions. Agates form
in this manner by successive deposition. Also, water level agates may form due to the presence of high
levels of “colloidal nucleation” materials present in the original silica gel. Such agates form as all other
varieties from single silica gels. Sometimes the first mode precedes the second but the reverse never occurs.
I expect to be dazzled and impressed by beautiful new banded Lake Superior Agates in the future but I
expect to learn very little from them regarding agate formation. I hate to say “ see one seen them all” with
regard to banded agates. However, when compared to the highly intricate and beautiful non-banded
varieties it is like night and day. Banded Lake Superior Agates are very beautiful but can be monotonous.
This concludes my discussion of what I consider to be the five major varieties of non-concentrically banded
Lake Superior Agates. Many collectors manage to arrive at far more “varieties” than just five. I
understand. Lake Superior Agates come in a bewildering number of combinations. However, considering
combinations as varieties would lead to chaos.
115
This large Brazilian Mosaic Water Level Agate has evidence of mosaic “faulting” for almost its entire eight-inch
height. It formed as successive influxes of silica solutions entered the cavity and then seeped away resulting in drying.
At the top of the agate is a final area that became a sealed single silica gel self-organizing system that produced
concentrically banded agate that conformed to a flat “floor” followed by a macro quartz center.
The flat “floor” of the newly formed single gel banded agate is simply conforming to the last water level band. As
soon as single gel formation begins you will see the band become continuous between the sides and the horizontal
bottom area, which, in a sense, is a pseudomorph after the water level bandform. (Arrow shows where continuous
concentric banded agate begins.) The flat shape is only an artifact of the previous mode of formation! Think of it as a
concentrically banded agate forced to conform to a space with sloping sides and a flat bottom. )
116
This is a “polyhedroid” agate from Brazil. Alone in the world along with “mosaic” agates this variety consists of
individual geometric “cells” occupied each by a unique agate. The proposed method of formation is that the cells
consist of spaces between interlocking crystal masses. This is not directly analogous to the proposed method of
formation of mosaic agates. In mosaic agates the cells are formed as preserved remnants of drying cracks caused by
desiccation of the cavity in which the agate is forming. Nonetheless, this is the only other known form of agate that
produces geometrically shaped agates.
In two dimensions the similarity between the polyhedroid agate and mosaic agate is exaggerated.
117
This Lake Superior Agate shows structures analogous to those thought to have resulted in the
formation of “polyhedroid” agates. The external shape of these agates results from filling three
dimensional cells formed by a jumble of preexisting crystals. This unique agate also exhibits
several pseudomorphs.
118
This twenty-four pound boulder of basalt
was found near Duluth, MN. On the
surface are visible numerous waterlevel
agates. The two visible here are very
different. One is completely filled with
macro quartz while the other is a thin shell
of agate lined with individual quartz
crystals. They are about five inches apart.
Another agate on the opposite side has a
substantial amount of agate with a
prominent quartz crystal lined cavity.
With external conditions for all three
nearly identical due to physical proximity
why are the agates so different?
The answer may be differing ability of each
cavity to retain silica solution. The two
with geodes could have formed entirely by
successive deposition while the third
formed by successive deposition and later
single gel differentiation.
Lake Superior Waterlevel agates having
such thin-walled geode cavities are unknown to this writer. It is, however,
common to find waterlevel agates that
consist of only the lower portion. The
upper macro quartz having been easily
eroded away during glacial transport.
This agate, which measures approximately 2.5
inches in diameter, is present on the opposite side
of this boulder. Waterlevel Agates such as this
are never found loose and free of the matrix that
preserved this specimen.
This agate could have formed first by successive
deposition and later as a single gel agate that
produced a geode. Alternatively, it could be the
result of a single gel with high levels of colloid
forming materials present. This would have
caused clumping of material and settling.
The remaining liquid in the cavity then, lacking
band mediation materials and with insufficient
silica to completely fill the cavity, formed a
crystal quartz lining.
119
This slab of Lake Superior Water Level Agate illustrates perfectly the concept of two modes of formation in the
“same” agate. The lower portion of the agate shows the “faulting” characteristic of mosaic agates that indicates
the cavity dried out on multiple occasions. Early in the formation of the agate the cavity filled either wholly or
partly but did not remain filled long enough for the critical silica concentration necessary to form a single gel
agate to develop. Perhaps this was because the bottom portion of the cavity allowed solutions to seep out.
Perhaps it was due to low levels of water and hence silica in solution in the formative rock formation.
Whatever the reason the first formation mode of this agate was by successive waves of silica solution that dried out
between inflow episodes. In this lower area you can see that the horizontal bands do not continue around the
periphery of the cavity either in the lower or upper areas. However, when the silica gel in the upper area of the
agate finally reached the proper silica concentration the mode of formation changed. Bands in this upper portion
of the agate can be seen to be continuous from the lower more horizontal area over the top of the pattern-a form
typical of other single gel Lake Superior Banded Agates. Even the macro quartz center typifies a Lake Superior
Banded agate formed from a single silica gel.
120
21
The Other “Other” Lake Superior Agates
In addition to the five varieties of non-concentrically banded Lake Superior Agates (also called Fortification
Agates) that we have been exploring there are also a wide variety of odd and unusual variations that attract
interest and attention among collectors. Some of these are rare and valuable. Others are practically
worthless but very interesting. Many, in addition to being interesting are very attractive. Below is my list
of the major fun “variations”.
1/
2/
3/
4/
5/
6/
7/
8/
Ruin
Breccia
Geode
Mineral inclusions and Crystal Replacements
Crystal Impressions
Plume
Paint Coloration
Combinations and Unique Agates
22
What is a Ruin Agate?
As a lapidarist I can tell you that I have personally “ruined” a number of nice and some not so nice Lake
Superior Agates. You can nick them on your grinding wheel, drop them on the garage or basement floor, or
make a fatal mistake by misjudging a fracture and where it is going. However, a ruin agate to the collector
is none of these things.
A Ruin Agate is one that at some point in its lifetime has been damaged. This damage must have occurred
following the agate’s final solidification and prior to its being released from the original formation in which
it formed. In addition, the formation must have retained the ability to supply silica in solution to the
“ruined” agate in order to heal the fracture or fractures created.
Generally, a ruin agate will be defined as one that has one or more open fractures running through the stone.
These fractures sometimes show “offset” when, across the fracture zone, the same bands no longer align. It
is like having a miniature geological fault in your agate specimen. The key attribute of a ruin agate is the
fact that the fracture or fractures have been recemented with additional silica. There are several
photographs of ruin agates on the following page.
121
This Lake Superior Water Level Agate has a jumble of mosaic pattern fragments at the bottom of the
stone. It is the only mosaic agate I have ever seen in which the mosaic pattern is broken by a ruin
fracture. The width of the fractured area is approximately two millimeters.
This “ruin” agate (remember, a ruin agate is not a
variety of Lake Superior Agate) is a small water
rounded portion of a much larger banded agate with a
quartz center.
A close look at the ruin fracture in the clearly shows
the offset between the two sides of the same white
band.
122
The Lake Superior Ruin Agate below shows what once was a continuous ring of banded agate composed of
white and dark red agate that was broken, moved, and eventually recemented by additional silica.
123
This 1.5 lb Lake Superior Ruin Agate is
very similar to the specimen on the preceding page. The offset of preexisting
sections of the banded pattern is severe.
The recemented area resembles moss agate.
This agate also shows a very attractive
wind polish on this surface.
Photographs by Scott Wolter.
124
23
What Is a Breccia Agate?
A breccia agate is also an agate that has been damaged like a ruin agate. However, instead of simply
becoming fractured the breccia agate has been literally crushed. Such agates are scarcer than ruin agates. A
banded breccia agate is shown below along with two close ups.
125
It is easy to see that the breccia agate on the previous page was pulverized and recemented. However, the
agate shown on this page goes a step further. If you had a blender strong enough to mix agate and then
poured in a bit of epoxy you might get an agate like this one. It appears to have been a banded agate.
Extreme earth movement must have been involved to produce this level of damage.
Of greatest interest is the presence of several perfectly formed color zoned amethyst crystals. These
actually appear to have grown as individual crystals perhaps in an open geode space.
126
127
This extraordinary Lake Superior Breccia Agate weighs nine ounces and appears to
have been micro-pulverized from outside pressure. The outer area of the agate resembles skip n atom agate.
It appears that this agate was an amethyst lined geode. In fact, an open area of distinct crystals still remains to the right of the specimen in this photograph.
128
24
What Is a Geode Agate?
A Geode Agate is one that has an open central cavity that is usually filled with individual crystals of quartz.
This quartz may be in the form of purple amethyst, yellow citrine, or brown smoky quartz. Geodes are rare
in Lake Superior Agates. However, the original source of Lake Superior agates may have had plentiful
geodes. Being open inside these agates are more likely to have been damaged during glacial transport.
Lake Superior Geode Agates are usually found in concentrically banded agates. I suspect that geode
cavities were formed in the upper portions of water level agates as well but that these have not survived to
be found. In fact, many water level agates that originally had quartz “caps” are found with only a thin area
of quartz present. Geode or not this quartz was very easily eroded away during the tumultuous ice age.
Gallery of Lake Superior Agate Geodes
129
This highly unusual Lake Superior Agate
Geode shows an open area of amethyst
crystals.
The unusual aspect of this specimen is the
fact that yellow citrine quartz and clear
quartz are in direct association with deep
purple amethyst.
This specimen has another unusual
surprise but that will be saved for a bit
later...
130
Geodes in Lake Superior Agates are the result of a single silica gel which contained insufficient silica to fill
the cavity completely with macro crystalline quartz. In geode agates the exhaustion of band mediation
materials caused the formation of macro quartz to begin. However, due to inadequate levels of silica
present in the remaining gel the formation of quartz stopped prior to the complete filling of the cavity.
26
What Are Agates With Mineral Inclusions and Crystal Replacements?
As shown on pages seventy-three and one hundred thirty-five pure native copper is sometimes found in
Lake Superior Agates. In addition to tiny sparkling crystals of copper some specimens contain other
crystals. The agate on page seven is an excellent example of a Lake Superior Agate having included
mineral crystals. Most of the crystals in this specimen have been replaced by agate. In the same sense that
the structure of wood can be replaced by agate to form agatized wood the substance of an included mineral
crystal can actually be replaced with agate.
This process of replacement many times, as in the case of this specimen, leaves an almost exact copy of the
original form of the replaced crystal. Such replaced crystals are called “pseudomorphs”.
If the crystals within the agate have not been replaced by agate they are referred to as included crystals or
crystal inclusions. The crystals that left the pseudomorphs in the agate on page seven and the actual crystals
in the specimen shown below and on the following page are both the mineral barite (BaS04).
131
132
Lake Superior Agates sometimes contain some very interesting groups of included quartz crystals. I have
found these in both radial sagenite and banded varieties. The crystals may have been present having grown
within the original cavity prior to the introduction of the agate forming silica gel or may have grown within
the agate.
In some specimens two forms of quartz are present. These are the crystalline variety that has grown in an
orderly manner to produce nearly water clear crystals and the macro crystalline variety seen in the centers of
banded and tops of water level agates. Several photographs of an agate of this sort are shown below.
In the upper two photographs a
circular group of pure quartz
crystals can be seen from the
underside. I believe, based upon
the absence of distortion of the
agate bands, that this crystal
group was present in the cavity
prior to beginning of formation of
the banded agate to follow. Quartz
crystal of this type is sometimes
called “rock crystal”.
The other type of quartz is
typically found in agate nodules. It
formed during the differentiation
process of the single gel cavity
filling. Individual crystals in this
area
have
grown
roughly
perpendicular to the curving white
band. Points of these crystals can
be seen in the white band that
bisects this area of “sugar” quartz.
133
Gallery of Crystal Inclusions in Lake Superior Agate
134
This banded Lake Superior Agate has a profusion of pure crystalline copper included
within the band pattern. The progression above goes from normal view to 20x
magnification to 180x magnification. The copper is present around the entire
periphery of the agate in the same bands. This agate is approximately 3” long.
Specimens like this one will sparkle when turned in direct sunlight as the individual
crystals of copper catch the light.
This specimen also shows excellent examples of pressure escape structures.
The copper was present in the original silica gel and formed crystals as the agate
band forming process excluded it. Sufficiently elongated crystals or masses of copper
crystals are always perpendicular to the bands.
This is because the individual chalcedony fibers that comprise the bands form
perpendicular to the band. This forces the copper to assume this orientation.
135
This Lake Superior Radial Sagenite Agate is 3.75”
by 2.75” and weighs 12 ounces. The two halves of
this agate together weigh 18.5 ounces. Notice the
very dense mineralization in the bands on the
bottom of the agate.
This is the point at which the redial sagenite spray
began to grow. It was only after the removal of
this high concentration of sagenite forming
minerals from the original silica gel that the
formation of chalcedony/sagenite patterns could
begin.
The included group of pure quartz crystals to the
right (about 1” across) formed soon after the
deposition of the dense sagenite was complete.
136
This extraordinary Lake Superior Agate combines sagenite with a brilliant spectrum of multicolor
quartz crystal. Just above the sagenite clear quartz can be seen which quickly becomes yellow
followed by pink/red colors and finally the purple of amethyst.
Notice the distinct layer of crystal terminations in the middle of the face. These may mark the point
which was at one time the inner surface of a crystal lined geode. Further crystal deposition filled in
more space above this until eventually a final layer of even larger amethyst crystal terminations grew
in the cavity. These in turn were capped by additional clear quartz.
Since this is just a portion of what must have been a considerably larger agate nodule we do not
know what lay “above” the top surface of this specimen or what other interesting and beautiful
patterns may have existed elsewhere in the nodule. This specimen measures approximately 2.5
inches across the face and weighs 12 ounces.
137
This Laguna Agate has a very large pseudomorph after aragonite included in the pattern along with
normal bands and sagenite. The aragonite crystal group formed inside the cavity prior to the
introduction of silica gel. It was able to retain its shape long enough for the agate to form around it.
However, being a material not compatible with the pH of silica gel it was eventually dissolved and
replaced by agate. If this had not taken place we would term this a group of “included crystals” rather
than replaced crystals or “pseudomorphs”.
The question of whether sagenite in agate precedes the introduction of silica into the formative cavity or
forms along with the agate is a matter of debate among theorists. I believe that band deformation
suggests that sagenite does form concomitantly with agate. However, as in the case of these aragonite
crystals and other types we have examined in this book, I agree that sagenite may form first in an open
cavity to be followed by influx of silica gel.
It seems probable to me from the evidence that sagenite inclusions in agate form in both manners.
138
28
What Are Crystal Impressions In Agate?
The previous discussion concerned crystals that are included within Lake Superior Agates. These crystals
may have been present in the cavity prior to the development of agate forming silica gel. It is possible that
the quartz crystal clusters could have been growing in a low concentration silica solution that began to
increase in concentration through osmotic equalization with external sources of silica.
As the concentration increased the pure quartz crystals would have continued to form, perhaps even at an
accelerated rate, as the silica gel approached the threshold at which agate production would begin. When
that point was reached the growing agate began to compete for available silica and slow the growth of the
crystals. Eventually crystal growth would have stopped as the agate neared its final form.
Sometimes crystal growth preceded development of an agate filling. In these cases the growth of the crystal
had stopped or the crystal was non-silica in composition such as calcite and therefore could not continue to
grow under conditions required for the development of the agate forming silica gel.
In these cases the developing agate assumed the form of crystals that preceded it in the cavity. Collectors
call these features crystal impressions. Many of them look as if a thick paste of very fine consistency had
been pressed against them. Striations and features of the crystals are faithfully preserved on the surface of
the agate. The crystal impression shown below is about one-half inch in length.
139
Generally nothing remains of these external crystals if they were softer materials such as calcite or barite.
They are eroded away by the processes that shape the agates themselves. The agate below shows
impressions of thin bladed barite crystals. This mineral resists erosion poorly.
These crystals undoubtedly grew in the cavity prior to the infilling of silica gel. They were strong enough to
keep their position as the gel formed casts around them. In contrast, the barite crystals in the specimen on
pages one hundred thirty-one and one hundred thirty-two probably became detached and were surrounded
by the silica gel thus preserving them from the mechanical and chemical erosion that removed the barite
crystals from the agate on this page.
The conditions required for the development of crystals of calcite, probable source of the crystal impression
on page one hundred thirty-nine, and other minerals such as barite and pyrite are not compatible with the
high pH environment of silica gel which is acidic in nature. Thus such crystals must have formed prior to
the introduction of silica gel into the cavity.
However, as we have seen in the case of sagenite agates and native copper in agate, crystals of rutile (Ti02)
and native copper (Cu), can develop within the environment of silica gel along with chalcedony fibers.
Barite Crystal Impressions in Lake Superior Agate
140
An unusual combination of excellent multiple crystal impressions
with a quartz crystal lined geode cavity.
Both crystal impressions and geode cavities are frequently found
damaged and eroded from energetic glacial and water transport.
For this reason finding both types of features in such fine condition
in the same agate nodule is unusual.
141
Imagine it were possible to “pour” agate
into a mold. I once pondered the
possibility of this when I was nine or ten
years old.
Now imagine pouring the all purpose
agate forming solution into crystal
impression voids. After waiting the
necessary time for the new agate to
solidify polish it in cross section .
The result might look something like the
agate at the left.
Relatively common in agates from some
other locales this type of feature is
exceedingly rare in Lake Superior
Agates.
A shape of a departed crystal produced in
this manner is called a “pseudomorph”.
Crater Lake: my favorite place.
Notice how the “agate”
inside the space occupied
by the former crystal
seems to be self-contained.
In a manner similar to
mosaic pattern formed at
the bases of water level
agates pseudomorphs are
unique agates themselves
just as if they had formed
in gas cavities in igneous
rock.
The formation of so-called
“polyhedroid” agates likewise occurs inside very
“nonstandard” containers.
Lake Superior Agate Crystal Pseudomorph
142
The “Airport” Agate
143
The fourteen-ounce Lake Superior Banded Agate on the previous page shows a large open angled crystal
impression, which illustrates an unusual feature sometimes seen on crystal impression surfaces. These are
tiny ridges or bubbles that appear to have formed at the contact point between the crystal and the silica gel.
Instead of creating a perfect mold impression as on page one hundred thirty-nine a space appears to have
been created between crystal and gel. In this space features such as those in the close ups below sometimes
formed. Could water have collected in this space resulting in the hemispherical voids?
144
29
Are There “Real” Plumes In Lake Superior Agate?
If a collector especially enjoys long well defined plume-like structures in agate then Lake Superior Agate is
a poor choice. Such features are very common in some materials from the Pacific Northwest and the Rio
Grande area in Texas. But every so often the sharp-eyed collector can be rewarded with a plume agate that
would make them take notice in Marfa, Texas or Prineville, Oregon.
Plume-like formations result from the growth of mineral salts in very high concentrations in the original
silica gel. Some, like the Priday Plume Agate of Oregon are highly silicified. Others, like certain plume
agates from the Rio Grande area in Texas are in a soft and earthy condition. This disparity is probably the
result of differing levels of silica in the original gel. It is an important factor if the agate is to be polished.
Agates such as these were among some of the most difficult to explain for agate formation theorists intent
on proving that all agates formed gradually, band by band, feature by feature. It is not difficult at all to
imagine a highly concentrated silica gel offering the necessary support for the growth and preservation of
feathery appearing crystal aggregates. Both of the specimens shown below have metallic plumes of the sort
common in plume agates from Texas and Oregon. They are out there; they are just very scarce!
145
Lake Superior Plume Agate not Oregon Plume Agate
146
Lake Superior Plume Agate not Texas Plume Agate
147
30
What Are Paint Agates?
Paint Agates were briefly discussed on page seventy-three during discussion of a “paint tube agate”. Many
collectors would prefer to consider “paint” agates as a separate variety. In fact, it would be a variety that
contained some of every other variety of Lake Superior Agate. Paint agates produce colors that are seldom
found in any other Lake Superior Agates such as the blue seen in the leftmost and bottom two agates.
148
Another very characteristic paint color is what collectors call “brick red”. The probable source of the
uniform reddish color in these specimens is from oxidation of iron minerals contained within the structure of
the agate. All of these are banded agates. The bottom agate combines sagenite and banded.
149
It has become common practice in recent years for collectors to name their largest and finest Lake Superior
Agates. Generally these names are chosen because of some aspect of the appearance of the agate.
Sometimes names reflect the location where the agate was found, the finder, or circumstances associated
with the event.
The agate below weighs two pounds twelve ounces. It’s name, based upon coloration, is “Peanut Butter and
Jelly”. Most Lake Superior Agate collectors develop opinions regarding agates during their collecting
careers. I am no exception. In my opinion this agate is the single finest Lake Superior Paint Agate found to
date.
Firstly, it is of the highest quality and nearly flawless. Secondly, the agate is complete and shows the full
pattern. However, it is the coloration that I find especially remarkable. Blue is generally only found in
Lake Superior Paint Agates. The shades of blue in this specimen are without peer.
There is, though, another attribute to this agate that causes me to rank it number one of this variety. This is
detail. Like the finest sagenite or moss agates this agate is as attractive when magnified as when viewed as
a whole. The photograph on the following page is only a small part of the total face of the agate-covering
an area of only approximately one-third by one-half inch. Yet within this small area is a totally outrageous
palette of color and pattern. The (very) fortunate owner of this specimen is Charlie White of Edina,
Minnesota. Photographs are by Scott Wolter.
150
151
31
Combinations and Unique Lake Superior Agates
As I said at the beginning I love beautiful Lake Superior Banded Agates. They among the finest banded
agates from any known locale. However, what keeps me going, collecting, sorting through piles of field run
agate is that first sight of a really unusual agate.
These final pages and photographs will be devoted to an area of collecting Lake Superior Agate that is the
most fun for me personally...the real oddball agates.
Remember the agate on page one hundred thirty that contained in the same geode amethyst, citrine, and
clear quartz? That is a very unique combination of types of quartz in the same agate. However, I left out
one little extra fact about that agate. Here is a hint: the base of the agate is polished. What variety of agate
would you expect to be showing under this tri color geode?
Yes, it is a twin burst of radial sagenite. Are you surprised? Lake Superior Agates will do that. It is a large
part of the fun of collecting.
152
Speaking of odd combinations how about this one. It certainly could be called a plume agate. But some
collectors might prefer moss. Whatever the unusual portion of the pattern is called it is fringed with
amethyst and shares the stone with a small area of banded agate. It appears to me that the moss-plume area
expanded and grew into the banded area. Stones like this two pounder keep me looking!
Banded, geode, crystal inclusion?
Did I leave anything out?
153
Amethyst is an intriguing material in Lake Superior Agates since it alone can transform a nearly worthless
and uninteresting agate into one that will be highly prized. The amethyst color is caused by trace amounts of
iron within the quartz crystals. Most collectors ascribe to the theory that quartz is a bad thing in a Lake
Superior Agate. Generally I agree but certainly not if it is purple!
154
The Amethyst centered Lake Superior Agate on the preceding page has a relatively thick outer area of
banded agate which served to protect the more fragile amethyst during the agate's glacial transportation
from its source. We can surmise that many attractive amethyst filled Lake Superior Agates may have not
survived the journey if they possessed a thinner outer layer of protective agate.
The Lake Superior Agate below is filled with exquisite amethyst that can be seen in the close-up photograph
on the next page to have darker and lighter zones of color. The broken face that matches this agate's is still
embedded in the basalt bedrock under about ten feet of cold Lake Superior water.
Removal of this specimen required the saw cut upon which the specimen rests and some careful prying.
This attractive specimen is surely one that would not have survived transportation during the upcoming ice
age. Where will this specimen be when the next ice age begins?
155
This is the face opposite the broken
face on the preceding page. This
was visible on the bottom of Lake
Superior embedded in basalt
bedrock.
156
While on the subject of quartz and its desirability or undesirability in a Lake Superior Agate consider one of
my favorite “unusual” types of agate. These are generally banded and consist of alternating areas of quartz
and agate bands. It’s the pattern that matters in these agates. Most collectors turn them down or throw them
back. Not me. You can’t really call these agates floaters.
For want of a better name I call them “tapestry” agates. Yes, that is NOT a new variety!
This banded agate shows a very rare
surface condition called “venification”.
The agate shows greater erosion in the
less resistant quartz area than in the
banded areas. This is called differential
erosion.
The surface “polish” of this agate, much
smoother than any waterwash or beach
washed surface, is believed to have been
created by long term exposure to the
wind. Scouring would have been by
quartz sand-natural sand blasting!
157
One of the more unusual and elusive formations to be found in Lake Superior Agates are tiny cones that
seem to float in the surrounding agate. Sometimes these cones are included in concentric bands while others
have little apparent orientation to other structures within the agate.
These tiny cones, like the eyes in eye agates, seem to originate from a single point. Unlike eyes they form
radial structures and not hemispherical. Almost always the cone remains a small simple structure without
additional bands or other material attached. Perhaps they share a family relationship with the tiny spheres
so often found in Lake Superior Sagenite Agates. Both the cones and spheres appear to be constructed of
chalcedony fibers growing from a common point in a radial shape. However, while the spheres developed a
omnidirectional structure of fibers the cones did not.
The formation of both spheres and cones may depend on presence of nucleation points in portions of the gel
in which adequate silica exists having not been depleted by the formation of bands or other structures. The
“other” varieties of Lake Superior Agates come in all sizes from small to large just as banded agates.
However, many minute structures in non-banded agates become much more fascinating and enjoyable if
you view them under even low power magnification.
This can range from very inexpensive hand lenses that provide five to twenty power magnification. Also,
relatively inexpensive binocular microscopes can now be purchased in the two hundred dollar range. Such
an instrument will literally open a new world for the collector by making available twenty to one hundred
power magnification. Adapters can be obtained that allow the attachment of cameras to many microscopes.
Such an adapter was use to produce the microscopic views in this book.
This Lake Superior Agate has tiny cones (approx. 1mm across) between bands. Perhaps the cones
formed in an area rich in silica but very poor in band mediation material. Could the presence of
multiple nucleation points have resulted in cone formation instead of macro quartz crystals?
The cones in this Lake Superior Agate
appear to float, as spheres in sagenite,
in a non-banded area.
The cone in the upper right of the agate
was cross sectioned by the polishing
process.
158
“Veil” patterns in Lake Superior Agates are found between major bands and resemble Mexican
“Flame Agate”. The patterning actually crosses numerous clear bands producing a veil-like
pattern that , as in the upper right hand portion of this agate, can be seen to originate from
opposite sides of the same major band. This pattern may be caused by staining of particular
banding zones based upon variable permeability.
In the middle left area of this agate, near the clear, white, and bluish bands can be seen bright
reflections from included copper crystals. When viewed under magnification this zone can be
seen to contain hundreds of tiny copper crystals.
The photograph on the next page shows detail of the “veil” in an area approx. 5mm x 10mm.
159
160
Shadow Agate
Shadow agate is banded agate that exhibits optical
effects when moved. The surface of the agate seems to
shimmer as a wave of motion flows across the surface.
This effect generally requires distinct bands that are
very close together and parallel. Also most shadow
agates with good “play” have band patterns that
abruptly change as in the upper right portion of this
agate. ( note correlation with shadow effect )
Illustrating the shadow effect is difficult on a static page.
This agate has been moved and photographed from the
same vantage point to capture the effect. Most shadow
agates benefit from polishing. In fact, the effect may only
be discovered when a banded agate is polished.
This effect is different from “iris” agate which is clear
agate that has bands so close together that when viewed
in a very thin slab polished on both sides cause a
rainbow like effect as a diffraction grating is produced.
Due to strong pigmentation in Lake Superior Agates the
“iris” effect has been very seldom observed.
161
Care to get really “out there” with a super unusual Lake Superior Agate? The “butterfly” cut pair below
may be one of the most unusual Lake Superior Agates I have ever found. I will tell you what I think it is
and what I call it after you’ve had a look!
My description won’t win me any awards at a stuffy gem and mineral show where every single agate is
quartz var. Agate. That is just fine with me. I would describe this specimen as a Lake Superior Banded
Moss Agate with very significant mineral inclusions.
Interpreting the formation history of a banded moss agate like this one is straightforward using the single
silica gel model. The silica gel of which this agate would form was very highly concentrated in minerals
that produced the mossy growths. Many such moss agates are entirely moss agate pattern and show no
banding at all.
In this agate, however, the heavy mineralization was eventually depleted leaving a small central area in
which only band mediation materials and silica remained. Banded agate formed as a result.
The dark inclusions in the upper portion of the slabs appears to be a very refined iron mineral such as
hematite. Two photographs of that area are shown on the following page using direct and angled lighting to
highlight the metallic character of the area.
162
I could literally keep this up for hundreds of pages, showing you odd, unusual Lake Superior Agates.
However, I am going to end with one that you might, at first glance, consider to be an ordinary, if attractive,
banded agate. You have to look a bit closer with this one! What are those spheres doing in the center of the
agate? What processes led to their development near the end of this agate’s formation? To tell you the truth
I do not know. The way I am that is a great place to leave us both. Thinking.
163
164
An outrageously mixed up one and one quarter pound Lake Superior Agate that includes:
heavy mineralized sagenite ( ruin fragments ), banded, tube, sagenite, included crystals,
crystal pseudomorphs, and “curl” formations. Notice the sharp delineation ( diagonal
reddish edge) between the left and right portions.
165
32
Unanswered Questions Certainly Remain!
In this book I have made the case that agates primarily form from masses of silica gel that behave as “closed
systems” once the differentiation process has begun. For example, banded agates form from a single silica
gel mass through a complex and repetitive process of increases and decreases in concentration of silica and
non-silica materials at the crystallizing front. Banded agates do not form as a result of successive deposition
of new bands as silica flows inward through so-called “entrance ducts” as previously, and widely, believed.
Clearly, though, some Lake Superior Agates do form as a result of successive “waves” of new silica is
brought in solution from outside the agate forming cavity. This mode of formation, as previously discussed
in chapter eighteen, is one of two modes of formation of water level or horizontally banded agate.
Inevitably it seems attempts at formulation of scientific theories, in this case the theory of banded agate
formation, encounter exceptions which seem to contradict the predictions of the theory. The theory can
never be considered completely predictive until all known exceptions are accounted for within its precepts.
Any new observations from nature must be accommodated by the existing theory or the theory must be
revised. Until these new observations are accounted for in the theory it remains a working hypothesis.
Is the book closed on agate formation theory? In my opinion it is not. In the first place I do not believe that
all agate forming locations have been discovered as yet-or all the manifestations of agate. Secondly, known
forms of agate exist which cannot comfortably be explained by the existing theory.
Do such exceptions exist in the case of Lake Superior Agates? Yes. Most long time Lake Superior Agate
collectors have encountered a very rare form of banded agate that is utterly unlike “normal” banded agate.
This form has not been described in previously published books about Lake Superior Agate and, in fact, has
no generally accepted name. I call it “Disrupted Band Agate”.
This form of Lake Superior Agate is so unusual that, though it may be a form of banded agate, I believe it
qualifies to be included with the “other” group. Many, but importantly not all, of the disrupted band agates
have extremely distinctive exteriors that resemble a compressed and contorted mass of thick fluid. Whether
this convoluted exterior form is the result of the shape of the cavity in which the agate formed is unknown,
as no such agate has ever been found still encased in the original matrix.
The photographs below show a disrupted band agate before and after it was cut and polished:
166
The photograph below is a close-up of another specimen of this type of Lake Superior Agate. As you can
see it shares the “veil like” form of the agate on the preceding page.
This disrupted band agate shows a geode
cavity. This is a feature occasionally seen in
Lake Superior Agates of this type but much
more often in such agates from other
locations.
Agates having this same general appearance
are also known in great profusion as “occo”
geode agates from Brazil. They sometimes
show the same exterior “molded” appearance
and filamentous banded patterns as seen in
Lake Superior Agates.
Several examples of this type of agate are
shown on the next page.
167
Whether the visual similarity of these Occo Geode Agates from Brazil indicates similar formation history is
unknown. However, it cannot be denied that the exterior and interior appearance is almost identical.
Did these agates form from a single original silica gel? Did “normal” banded patterns form first only to be
“disrupted” by some subsequent influence or are these the original patterns? Did it have to do with unique
chemical composition of the original silica gel? Could these unique patterns be the result of external
pressure applied to a forming agate? Could these be agates that, while still in a semi-plastic state were
severely shaken by an earthquake?
Are there any of these rare agates in your collection? Perhaps you will find one on your next collecting
outing.
168
This half pound “disrupted band” Lake Superior Agate looks appears that it was both shaken AND stirred! Did an
ancient earthquake do this while the agate was still in a semi-solid state? My view of nodular agate formation
suggests that agates form in gas cavities in solidified basalt.
However, what if an alternate hypothesis is eventually proven true that agates form from melted silica in still fluid
lava? Earth movements could then explain the sometimes contorted exteriors of disrupted band agates as having
been shaken while both the agate AND the agate bearing rock was semi-solid. The answers are elusive.
169
This disrupted band water level Lake Superior Agate raises some very important
questions even though it is only about one inch in the longest dimension.
The wavy disrupted bands on the upper portion of the agate are typical for this type
of agate. However, in a water level we would expect to see much different banded
pattern in this area.
The water level portion of the agate appears to be a blended mixture of materials and
lacks distinct horizontal bands as would be expected in such an agate. Furthermore,
the bottom region of the agate where mosaic pattern might be expected is a jumble of
apparently broken and mixed features.
Was this entire agate semisolid at one time including the area of horizontal bands?
What caused the disruption of not only the upper banded area but also the lower
portion of the agate? Could violent earth movement while the agate was still in a
semi-solid condition be responsible?
170
This Lake Superior Agate has very unique
distorted banding in the central area but
typical tight distinct banding in the outer
areas.
Could this be due to earthquake shaking
when the inner area of this agate was still
in a semisolid condition during formation?
What other potential explanations could be
offered to account for this highly unusual
Lake Superior Banded Agate?
171
The disruption in this agate is not simply on the surface as
in most disrupted band agates. The banded pattern is disrupted all the way to the quartz and floating agate center.
The forces that caused the disruption pushed a line of impurities toward the center (visible as a faint brown line
outlining the quartz). Also, the shapes of large macroscopic
quartz crystals were distorted with those in the upper right
taking on a granular appearance. Finally, these forces
pushed the central area of agate into an unusual contorted
shape.
( agate approx. 1.5 inches across )
A more typical form of disrupted band agate is shown
in this specimen. The agate is included in a matrix of
other smaller agates. This cross section shows that the
disruption effect occurs only close to the vesicle wall
while the inner banded area of the agate is undistorted.
I believe that sharp earth movements cause this effect.
That the inner portion of this agate is undistorted may
be due to it being already solidified at the time of the
earthquake or because only agate in direct contact with
the vesicle wall was mechanically coupled to the
motion. ( section approx. one inch across )
Two disrupted band agates collected at different times and locations show almost identical surface
patterns. These patterns include round formations (more eroded in the agate on the left). The left most
agate is a complete nodule and shows this patterning on the entire exterior. The other agate is cross
sectioned and shows, as the agate in matrix above, an interior that is not appreciably distorted.
Perhaps these formations are simply artifacts of the shape of the vesicles in which the agates formed.
However, the agate in matrix above does not support this. Each agate is approx. 1.25 inches across.
172
Other curious and unanswered questions surround the elusive and rare form of Lake Superior Agate known
as “Skip ‘N Atom”. The source of this name is unknown. It could have been an old-timer who thought that
the agates were just odd enough to have lost one atom of those required to be “normal”.
The Skip ‘N Atom is characterized by an unusual crenelated appearance of chalcedony fibers and quartz.
This type of formation in Lake Superior Agate is just about the most difficult to find of any of which I am
aware. If you find one by all means keep it in your collection. It is a rare and unusual specimen. Potential
explanations for this type of formation are limited at this time.
However it seems clear that some kind of chemical and/or thermal alteration is responsible which resulted in
the partial recrystalization of the agate. In fact, these agates could possibly be more accurately described as
metamorphic rocks that have been recrystalized in the manner that alters limestone into marble through heat,
pressure, and time.
Could skip ‘n atom agates, unique that they apparently are in the world among all known agates, have been
formed due to the heat and pressure of a meteoric impact? Do these agates share anything in common with
the ‘shocked quartz’ found at impact sites? A more plausible explanation is that contact metamorphism is
responsible in which hot molten rock intruded preexisting agate bearing rock to cause the alteration.
The fine group of Skip ‘N Atom Lake Superior Agates below are part of the collection of Charlie White of
Edina, Minnesota. If you look close you should be able to identify both a ruin and a breciated agate.
Lake Superior Skip ‘N Atom Agates
173
A typical Lake Superior Skip ‘N Atom Agate which exhibits altered banding in the center area.
The outer areas were once quartz or banding that has been completely modified and replaced by a
crystal pattern typical of this variety and unique among the agates of the world.
174
“Curl Agates”
Some collectors describe this rare form as
“wormy” and generally include it within
the wide definition of “moss agate”.
However, it is neither caused by worms
(which would not evolve for hundreds of
millions of years) or through the process
that forms what we refer to as moss agate.
The key to understanding curl agates is to
note that each fragment is generally curved
and almost identical in cross section to all
others. Perhaps these fragments are pieces
of a former original coating on the inner
surface of the gas vesicle.
Formed by chemical reactions taking place
in the hot volcanic rock this “coating”
would crack and fall in a jumble to the
floor of the cavity as cooling caused contraction of the rock. Later agate would
form filling in and cementing the jumble.
175
33
Ice Ages, Continental Glaciation, Lake Superior Agates, and Time
Periodically the Earth undergoes a dramatic cooling which results in the formation of gigantic ice domes
which move and spread under their own weight from areas of accumulation in Labrador and the Hudson
Bay region of Canada. This accumulation of snow and subsequent formation of miles thick ice caps occurs
more because of cooler summers than cooler winters.
During summers only several degrees cooler than at present less snow melts. When the first snow of the
next winter occurs it falls upon and preserves the growing remnants of snow from proceeding winters. The
presence of snow on larger and larger areas of the earth’s surface reflects additional solar radiation back into
space causing further cooling-an effect called surface albedo. The ice age cycle, once started, becomes a
feedback process that rapidly leads the earth into what is known as a glacial maximum.
The reasons for this periodic global cooling are now known to be changes in the earth’s orbit around the
sun, changes in the angle of the earth’s axis of rotation, and changes in the timing of summer in relation to
the Earth’s not quite circular orbit. All of these factors are periodic and repeat according to their own
independent cycles of differing durations. When the cycles overlap in just the right manner significant
global cooling or warming will occur regardless of what humans are doing at the time.
If there are landmasses in the northern latitudes during the cold periods, as there have been for millions of
years, an ice age will occur. The accumulation of snow will cause increasing amounts of solar radiation to
be reflected back into space. The snow will rapidly accumulate and change into glacial ice which, when a
critical thickness is reached, will begin to flow outward.
Other changes will include alterations in ocean currents that distribute equatorial heat northward and polar
cold southward. The sum of all these effects will plunge the earth into an ice age that will last tens of
thousands of years. It will end abruptly when the various planetary rotational and orbital cycles once again
begin to return greater solar radiation to the surface of the earth thus increasing summer temperatures.
Huge volumes of fresh water from the melting icecap will be dumped into the oceans and tens of thousands
of square miles of land formerly covered by thick moving ice will become exposed. The sheer weight of the
glacial ice will have depressed the land significantly. Even today as far south as the North Shore of Lake
Superior what is known as isostatic glacial rebound is still occurring. The deglaciation is so recent that
many of the places that we find Lake Superior Agates today are still adjusting to the retreat of the ice.
The volcanic rock in which Lake Superior Agates formed is approximately 1200 million years or 1.2
BILLION years old. It is generally assumed that the agates were formed soon after the creation of their
volcanic host rock. This makes Lake Superior Agates the oldest known agates and, in fact, among some of
the oldest unaltered rocks to be found on the surface of the earth.
The volcanic rock in which Lake Superior Agates formed came into existence as a result of a catastrophic
rift in the early North American continent, a rift similar to the great rift of Africa today. Immense volumes
of volcanic rock were erupted into this rift zone and subsequently buried under sediments from erosion of
adjacent highlands and later inland seas. The rifting stopped and the continent remained intact and very
stable to this time.
176
Lake Superior Agates were able to survive basically unaltered for this immense period of time because their
parent formations exist in what is known as a continental craton, or stable central area of a continent. Over
hundreds of millions of years the deeply buried Lake Superior Agate formations lay unchanged as mountain
ranges were crumpled up and eroded away, the margins of the continents grew by accretion of former
volcanic island arcs being carried on moving oceanic plates, and virtually all life as we know it evolved.
When the giant asteroid that caused the final extinction of all dinosaurs except birds hit the Gulf of Mexico
region sixty-five million years ago the earthquake waves that shook the entire planet were felt by the very
same Lake Superior Agate you hold in your hand today. It would have looked, except for the results of
erosion, the same then or a billion years earlier as it looks today.
These agates are ancient relics of the early earth and have ridden with it and our solar system for five
revolutions around our spiral galaxy. However, the earth processes that uncovered Lake Superior Agates
and brought them into our hands are very recent in comparison. We can still see clear evidence of the last
ice age during which the great ice age glaciers scoured out the basin of Lake Superior and carried agates
from their ancient bedrock leaving them in the sand and gravel deposits in which we find them today.
We can still see today the results of the retreat of ice age continental glaciers which covered most of
Minnesota and vast areas of other Midwestern states, not to mention virtually all of Canada, under miles
thick ice sheets. The retreat of the great ice sheets is so recent that ice may have filled the present area of
Lake Superior as recently as 12,000 years ago.
The agate rich areas of central Minnesota would have been uncovered only years or decades prior to this
time. As recently as 8000 years before present major ice caps may have remained on eastern and western
sides of the Hudson Bay. (R.F. Flint, Glacial and Quaternary Geology, Wiley, p.492, 1971) Evidence is
mounting that ice ages may both begin and end abruptly and that apparently unrelated events such as global
warming may set the process of global glaciation into motion. Today’s global warming, if real, may
actually mark the beginning of a new ice age and be unrelated to recent use of fossil fuels as some maintain.
The dual forces that created Lake Superior Agates and brought them from the depths of the Earth into our
hands were both catastrophic in nature. Continental rifts and global ice ages. Without the rift the agates
would not exist and without the ice ages they would not have been excavated and delivered into our hands.
The Lake Superior Agate that you hold in your hand bears witness to immense time equal to one-fourth the
age of the Earth. It also bears witness to the much more recent ice ages that profoundly affected the
development of our species and our civilizations. We live in an inter-glacial period. Humans like us lived
during the last inter-glacial period and were shaped by it both physically and culturally. It is only a matter
of time until the next ice age begins. Based upon very reliable ice and sea floor core data we are
probably at end of this inter-glacial period.
The photos on pages one hundred seventy-nine and one hundred eighty symbolize for me the unique duality
of time present in Lake Superior Agates. The immensely ancient Lake Superior Agate on page one hundred
seventy-seven sits atop a section of mammoth tusk from the last ice age. The tusk is about 14,000 years old
and is not a fossil. It is the actual tusk material. The great tooth on page one hundred seventy-nine was
dredged from what is now the bottom of the English Channel-dry land during the ice age.
Lake Superior Agates point us forward in time perhaps only a few decades or perhaps a few thousand years
to the onset of the next inevitable 100,000 year ice age. Some believe it has already begun.
177
Agate hunting in central Minnesota in early July 2006.
July 9, 2006 was a very hot and humid day in central Minnesota. The heat wave of this year was being
described by the media as second only to the greatest recorded heat wave that took place in the mid 1930s.
As I rode along as copilot with Scott Wolter I found myself looking skyward at the low popcorn like clouds
of the day. I know clouds like these very well having climbed through and above them many times in the
high mountains of the Pacific Northwest.
This experience allowed me to make a good estimate of the height of the bottom of the clouds that day. I
estimated it at approximately a mile with the tops extending upward another couple of thousand feet.
Whenever I travel in Minnesota I constantly see the evidence of the recently departed ice sheet. Landform
features such as eskers, moraines, kettle lakes, and kames are everywhere. The evidence of the last ice age
is omnipresent for a person with even a small knowledge of ice age landforms and deposits.
I recall asking Scott how thick he felt the continental ice sheet was in this area some hundred miles north of
the twin cities. His reply was that the ice thickness probably varied from 5000 to 7000 feet in this area. He
reminded me that this same contiguous moving ice sheet extended all the way to the Hudson Bay region of
Canada where it was at least three MILES in thickness.
The rest of the day was hot, productive of agates, and marked by my continuous awareness of the clouds
above. I could not escape the thought of that mile or more of ice above us. This ice was part of a continent
of ice that was HERE as recently as 15,000 years ago. This ocean locked in ice had resulted in the
worldwide sea level being lowered hundreds of feet for up to 100,000 years.
In the several years since I finished “The Other Lake Superior Agates” the hysterical drum beat of the
dangers of global warming have intensified. Slick media productions show us continuous replays of the
normal calving of icebergs from Greenland and Antarctica. We are warned that, though records are poor,
sea level must be rising. If the data does not support this claim then the data must be incorrect or simply
missing. We are shown remote Pacific Islands that might be inundated by a rising ocean but shown no
reliable scientific facts to support that this is actually taking place. We must trust without facts.
Understanding and appreciating Lake Superior Agates requires, for me, understanding and appreciating the
forces that delivered them into our hands and shaped our present world-the forces of the global ice age.
I urge the informed reader of this book to consult the wide range of scientific and popular writing regarding
the ice ages. I also urge the informed reader to be as wary of the science behind global warming as they
would be of the distortion, omission, and absence of fact that underlies the pseudo science of ‘creationism’.
It is my opinion that belief in either requires the denial of many pertinent facts and distortion of most of the
facts that are admitted into the theory. Ultimately, belief in what is called scientific creationism is based
upon faith not fact or science. Ultimately, in my opinion, belief in the certainty of global warming and dire
predictions of effects also rests on faith plus political partisanship, but not fact. Neither is founded upon
science. The more you learn about past ice ages the more you will doubt the threat of global warming.
Milankovitch cycles are not subject to control by any human actions and ice core data cannot be denied.
178
It was noon but the sky became purple. A hint of curve appeared on the horizon as the after-burners
shut down 10 miles above the earth. The window was warm to the touch at mach 2 as I steadied the
camera. I scolded myself for the waste of oil and air pollution this machine was causing but it would
have flown without me on board. As I looked down I mused that it could be the next ice age under the
clouds. I wondered if any machines would fly during that time in what may be the near future.
179
180
34
That’s Why I Collect Non-Banded Lake Superior Agates!
I love beautiful banded Lake Superior Agates. I like them in their natural condition as well as polished.
Some of my favorite agates are banded.
But, with all due respect to banded agates and their devotees, I prefer the non-banded varieties discussed in
this book. One clear reason for this is my love of intricate detail. With Sagenite Agates the detail
sometimes seems to never end. Like fractal patterns no matter what level of magnification I select I always
find something new and interesting to view.
Lake Superior Moss Agates impress me as some of the most exquisitely beautiful natural objects I have ever
encountered. I love the way the colors mix and swirl together amid the multiple tendrils of the mossy
mineral growths. Their lapidary and artistic potential is tremendous.
Water level agates are a special enjoyment for me since I have always loved the North Shore of Lake
Superior and ocean coastlines. In Lake Superior Water Level Agate I see beach and surf scenes that rival
some of the great ones found in Oregon Thundereggs.
But aside from detail, mixing of colors, water level bands and other reasons that I especially enjoy nonbanded Lake Superior Agates I would have to say that anticipation and surprise are really at the top of my
list.
I will go through buckets of Lake Superior Agates to find just two or three, sometimes small ones at that,
which stand out as unique. I am driven to keep looking because, in my decades of collecting, I know that
there will always be something I never expected to find just around the bend, in the next bucket, or in
someone’s rock garden.
It is my hope that these agates, and this book, will leave you as they have always left me...thinking.
DEDICATION
This book is dedicated to Scott Wolter who wrote the first “serious”
book about Lake Superior Agates. He combines great aesthetic
appreciation and scientific curiosity for these beautiful gems. He not
only wrote the first real book on the subject but has continued to issue
new editions and new titles which are each a must have for the serious
collector.
Scott is clearly the preeminent authority on Lake Superior Agates of
this generation. Knowing him now over ten years has been both
pleasant and intellectually rewarding. Thanks Scott.
This second edition has been substantially improved as a result of
Scott’s careful and thorough review. Thanks again Scott.
181
About the Author
John Marshall was born in Tulsa, Oklahoma. When he was six years of age the family moved to St. Paul,
Minnesota into a new home in Mendota Heights. He began collecting and polishing local agates at age
seven. In 1965 when John was almost sixteen the family moved again to Ft. Worth, Texas.
In 1974 John moved to Portland, Oregon in order to pursue his ambition of becoming a mountain climber
and wilderness backpacker. He joined the Mazamas Mountaineering Club in 1975 having met the
membership requirement of climbing a glaciated mountain the summit of which could be reached only on
foot. The mountain was Mt. Hood.
John has pursued a career in high technology and worked at several well-known companies including
Tektronix and Intel. He also worked at several lesser known but leading edge computer start-ups such as
Floating Point Systems. Along the way he has held positions of Customer Engineer, Regional Support
Engineer, Quality Engineer, Quality and ISO Manager, and Business Forecasting Manager.
He achieved his goals regarding climbing by scaling every major Cascade Mountain Peak and many lesserknown crags. He climbed Mt. St. Helens numerous times prior to and following the great eruption of 1980.
He has led wilderness backpacking and climbing outings for local organizations and the Mazamas and
taught wilderness survival and cross-country skiing at the local community college. In 1994 on the
occasion of the 100th anniversary of the founding of the Mazamas he received a special commendation for
his contributions to the organization.
John has studied Geology at both the University of Oregon in Eugene and Portland State University.
John and his father, John Brooks
Marshall, collect agates on the
North Shore of Lake Superior in
the summer of 1964.
Photograph by Kenneth M. Wright
182
Postscript
My intention in writing this book was to enliven the discussion regarding agate
formation with some new ideas and observations especially regarding the non-banded
varieties.
The First Edition of this book has been modified and enlarged based upon numerous
contacts with other collectors and theorists including Scott Wolter, Jack Hobart, Sean
Lincoln, Charlie White, and others. I appreciate this valuable input.
It is my wish that the reader bear in mind that I do not consider or expect that my
ideas regarding agate formation will be the final word. Rather, I wish them to be a
starting point for continued discussion among both amateur and professional
researchers regarding agate formation. I positively welcome new ideas and thoughtful
critical comment.
Of particular interest at this time is the ongoing research being conducted on land and
under the waters of Lake Superior by Scott Wolter. Scott has located some of the
original sources of Lake Superior Agates. This knowledge had eluded collectors for
several generations but now pivotal discoveries are filling in the gaps in our
understanding of where these agates formed.
Information about these discoveries can be found in Scott’s current books about Lake
Superior Agates and, I am certain, further exciting discoveries will be described in
future editions.
Crucial to furthering our understanding of agate formation is a careful scientific
gathering of a much larger database of observations of Lake Superior Agates and
other varieties. For this reason I believe that the present work of Jack Hobart in
building a gigantic searchable database of very small Lake Superior Agates for study
is important to the future of agate formation theory.
Also important is the continued sharing of photographs, information, and ideas among
worldwide collectors as unusual agates are found. It is my belief that the “rules” of
agate formation have remained the same the world over since the formation of Lake
Superior Agates, the oldest known variety. International collaboration will provide
great additional insights.
The study of all the varieties of agate provides the collector and researcher with the
excitement of discovery and the challenge to understand these beautiful and unique
natural objects.
John Marshall
Cooper Mountain, Oregon
January 2003
183
Appendix: Polishing Lake Superior Agates
Fifty years ago when I found my first Lake Superior Agate at the age of seven Lapidary was a very popular
hobby. The post war leisure boom and general prosperity of the times permitted many people to indulge
their love of agates and the craft of polishing them.
Back then very few Lake Superior Agates entered collections in their natural unpolished state. Collectors
would tumble polish the smaller agates, slab and attempt to make cabochon gems of larger agates, and hand
polish flat or curved faces on different sizes of agates. The craftsmanship evident in all this lapidary work
ranged from very poor to very good with mediocre being the standard level of attainment.
The lapidary equipment of the day used silicon carbide abrasives combined with the powerful and
sometimes massive arbors required to spin their weight at high speeds. Silicon carbide grinding wheels are
very damaging to fracture prone Lake Superior Agates since they frequently become out of round and
therefore out of balance. This results in damaging vibration that can harm or destroy many Lake Superior
Agates.
A revolution took place over the past several decades as diamond based abrasive grinding and sanding
wheels replaced silicon carbide. These new wheels work with far less damaging vibration than silicon
carbide and virtually eliminated the serious problem of grit cross contamination. The diamond abrasive
revolution in lapidary equipment made it possible to successfully polish Lake Superior Agates that would
have been destroyed by old style silicon carbide based machinery.
I do not recommend that anyone today use silicon carbide equipment to grind and polish Lake Superior
Agates. Diamond lapidary equipment is considerably more expensive than silicon carbide based equipment.
However, diamond wheels when properly used will greatly outlast silicon carbide. Longevity of diamond
abrasives together with other benefits make their greater initial expense, in fact, a bargain. I recommend
that aspiring lapidarists save a bit longer in order to afford diamond based lapidary equipment rather than
acquiring what is, in my opinion, far inferior silicon carbide ‘rock polishing’ equipment.
Unfortunately, this revolution in tools was accompanied by a great reduction in the number of hobbyists
cutting and polishing lapidary materials. Also, the tastes of Lake Superior Agate collectors changed and
moved very strongly toward all natural agates and away from lapidary work of any kind on Lake Superior
Agates. Therefore, improvements in lapidary equipment over the past thirty years have benefited only the
relatively small number of individuals who today grind and polish Lake Superior Agates.
Today the majority of high quality banded Lake Superior Agates are kept in their natural condition by
collectors. Few serious collectors polish these agates either by hand or by mechanical means in tumblers. I
feel that this is best for top grade banded agates. However, while many banded agates are very attractive in
their natural condition this is not the case for most non-banded Lake Superior Agates.
Sagenites and moss agates almost always require polishing in order to view and enjoy their intricate internal
detail. Less likely to require polishing are tube and water level agates though probably more than half of
these are more attractive polished. It has always seemed likely to me that many sagenites and moss agates
remain uncollected simply because they usually look so “unagatelike” when compared to the more common
banded agates.
184
I believe that hand polishing with a natural curved face is the best lapidary technique for Lake Superior
Agates of any variety that require polishing. Over the years there have been some lapidarists who roughly
shape agates on coarse grinding wheels and then mechanically polish them using what is called a tumbler. I
consider even this technique inferior to complete hand grinding and polishing. Tumbling causes much
greater ‘undercutting’ of soft areas of some agates and can cause damage due to impacts that is avoided
through hand polishing. Tumbling should be reserved for lower grade agates only.
I would also mention that hand polishing of Lake Superior Agates in shapes that complement the stones
themselves is an activity that I find very enjoyable and relaxing. It has merit as an experience as much as a
method which yields superior results. Hand polishing gives the lapidarist complete artistic control over the
eventual shape of the finished polished specimen as well as providing the opportunity to achieve the highest
possible quality in the polished surface.
In the days before the advent of diamond lapidary equipment the standard sequence of grinding and
polishing steps using silicon carbide were as follows:
1/
2/
3/
4/
Rough out the shape of the polished face using a coarse 80 grit silicon carbide grinding wheel.
Finish the shaping and remove all coarse scratches using a 220 grit silicon carbide grinding wheel.
Sand the surface of the agate with successively finer grit silicon carbide sanding paper held in place
over a soft foam backing. The normal grit stages were 220, 400, and 600. At all stages working
with silicon carbide it was necessary to be VERY careful that none of the prior coarser grit was
moved on to the next stage. This would result in serious scratches that were very difficult to remove.
Final polish using optical grade cerium oxide on either a hard felt or leather wheel to which the
polish was applied as a slurry.
The sequence of diamond polishing steps that I use to achieve a ‘plate glass’ finish on Lake Superior Agates
is as follows:
1/
2/
3/
4/
Rough out the shape of the polished face using a coarse 80 grit diamond grinding wheel.
Finish the shaping and remove all coarse scratches using a 220 grit diamond grinding wheel.
Sand the surface of the agate with two grit stages, 220 and 600, on expandable rubber wheels fitted
with diamond sanding belts. Grit contamination with diamond lapidary abrasives is minor compared
with silicon carbide. However, it can occur so care is required to prevent cross contamination.
No other sanding stages are required for agate or similar lapidary material including 1200 grit,
3000, or so called 14,000 grit prepolish. Moving directly from 600 grit diamond to final polish is all
that is required.
Final polish using optical grade cerium oxide on hard compressed felt wheel to which a slurry of
polishing powder has been applied.
My polishing method combines the best of both silicon carbide and diamond abrasive technique. Many
suppliers of lapidary equipment today recommend an all diamond approach to polishing with final polish of
3000, 14,000, 50,000 or even 100,000 grit diamond. I find that this produces a ‘hazy’ or ‘shiny’ polish
similar to a tin oxide polish of the past. I prefer the deep and rich plate glass like polish attainable only
when using cerium oxide as the final polish.
I use Diamond Pacific Titan and Genie lapidary arbors, Diamond Pacific grinding wheels, Rayspan
expandable sanding wheels, and Crystalite resin (with the dots) sanding belts. For years I have been
purchasing optical grade cerium oxide at Ed’s House of Gems in Portland.
185
Above a group of cleaned and lightly oiled Lake Superior Agates that include sagenite, moss,
and tube non-banded varieties. Below the same agates following rough shaping on the 80 grit
diamond grinding wheel. The next step will remove deep scratches left on the agates by the
coarse grinding wheel.
186
Following work on the 220 grit grinding wheel above all coarse 80 grit scratches have been
removed. Below is after 220 grit sanding. Though the grit is identical the sanding wheels
have a soft backing that conforms to the surface of the agate and results in a smoother
surface. All work is inspected with a 10X hand lens prior to moving to the next stage.
187
Sanding with 600 grit above has been completed prior to final polishing. Each step must
be done thoroughly or the completed surface will show visible scratches and not attain a
high polish. Below the agates have been polished with optical grade cerium oxide. When
cleaned with soap the surface of these agates feel and sound like glass. Care must be taken
to avoid generating excessive heat during final polishing using this cerium oxide.
188
These agates are from China. Can you identify the “other” varieties represented here? The types
and features include eye, amethyst, ruin, sagenite, waterlevel, tube, differential erosion, included
crystal, and crystal impression. The prominent eye above measures 15mm in diameter.
189
190

"Other" Lake Superior Agates

Transcription

Similar documents

May 2015 - Central Brevard Rock and Gem Club

Welcome to KQDS online

Fitger`s Lake View Office

2015 media kit

Captain Geech

Just Listed

Presented by: