xid-2839758_1

Chapter 23
Sulfates, phosphates and related
minerals
Apatite as a biogenic mineral
Introduction

Fundamental building block:


Several phosphate structures identical to silicate
structures






PO43- (phosphates) or SO42- (sulfates) tetrahedron
Berlinite (AlPO4) – quartz (SiO2)
Triphyline (LiFePO4) – olivine (Mg2SiO4)
Xenotime (YPO4) – zircon (ZrSiO4)
Mostly isolated polyhedra unlike most silicates were
tetrahedrons are polimerized into sheets, chains, frameworks
Phosphates are related to arsenates (AsO43-), vanadates
(VO43-) and tungstates (WO42-)
Economic interest: apatite, gypsum, scheelite
Classification





Class VIII: Phosphates, arsenates and vanadates
Class IX: Sulfates
Class X: Tungstates and Molybdates
Class XI: Chromates
Class XII: Nitrates
Class VIII: Phosphate, arsenates and
vanadates (Table 23.1)



250 minerals; very small amount of earth’s crust
Apatite very important
Be-Al-Mg association



Fe-Mn-Na association



Pharmacosiderite Group
Triphyline Group
Na-Ca-REE association



Variscite-Strengite Group
Lazulite Group
Apatite Group
Monazite Group
Zn-Cu-Pb association





Tarbuttite-Adamite Group
Pyromorphite Group
Descloizite Group
Tobernite-Zeunerite Group
Carnotite Group
Na-Ca-REE association
Apatite
Ca5(PO4)3(F,Cl,OH)







Single phosphate
Hexagonal
Fluorapatite (F), chlorapatite (Cl), hydroxylapatite (OH),
carbonylapatite (CO3)
Can contain Sr or Ce
Well-developed crystals: prismatic, ending with pinacoidal faces
Occurrence: widespread; usually as small grains – largest grains in
granite, pegmatites and marbles; can make up 80 wt% of alkaline
rocks
Used as fertilizer and for phosphoric acid
Na-Ca-REE association
Monazite
CePO4




Contains other REE, as well as Th and U
Found in granite pegmatites: resembles garnet,
but have cleavage and lower hardness
As minute inclusions in gneisses: usually in
cordierite producing pleochroic halos
Mined from river and coastal sands as REE, Th
and U source
Zn-Cu-Pb-(U) Association
Uranium micas



Torbernite (Cu2(UO2)2(PO4)2.10H2O
Autunite (Ca(UO2)2(PO4)2.10H2O
Carnotite (K2(UO2)2(VO4)2.3H2O
Occur as powdery aggregates or platy crystals
 High radioactivity
 Carnotite: ore for vanadium and uranium

Turquoise
CuAl6(PO4)4(OH)8.4H2O




Cryptocrystalline
Blue – blue-green aggregates
Secondary mineral in veins of altered volcanic
rocks
Rare gemstone
Class IX: Sulfates
(Table 23.2)


Salt of sulfuric acid: H2SO4
Important associations:

Na(K)-Ca-Ba association
Anhydrite
 Gypsum
 Celestite
 Barite


Cu-Pb-Zn association
Chalcanthite
 Anglesite

Anhydrite
CaSO4





Evaporite mineral
Hydrothermal sulfide ore deposits
Some metamorphic rocks
Does not react with HCl
Raw material for cement production
Gypsum
CaSO4.2H2O

Evaporite mineral





Forms alternating layers with anhydrite
and halite precipitating from solutions
Hydrothermal mineral from meteoric
water
On surface of clay or sand – flowerlike morphology (desert rose)
Mostly flattened and prismatic crystals;
distinctive swallowtail twins very
common
Use: cement and plaster in
construction industry
Celestite and Barite
(SrSO4 and BaSO4)



Limited solid solution
Found in druses and granular aggregates
Forms in



Barite: Hydrothermal deposits
Celestite: Secretions in sedimentary rocks
Uses


Barite: paint, in chemical, rubber, paper industries, drilling
additive
Celestite: sugar manufacturing, pyrotechnology,
pharmaceuticals
Anglesite
PbSO4




Massive granular and colloform aggregates
Prismatic-tabular crystals
Product of galena oxidation
High S.G.

So does barite and cerussite
Anglesite and cerussite often associated with galena, barite
not
 Cerussite, PbCO3, effervesce with HCl

Alunite
KAl3(SO4)2(OH)6

Hydrothermal alteration of felsic rocks
Felsic volcanic rocks interact with sulfuric
hydrothermal solutions
 3KAlSi3O8 + 2SO42- + 10H+ 

K-feldspar
KAl3(SO4)2(OH)6 + 9SiO2 + 2K+ + 4H2O
Alunite
 Aluminum
ore and source of K
Class X: Tungstates

Closely related to sulfates


WO42- tetrahedra instead of SO42-
Wolframite



Isomorphic series: FeWO4-MnWO4
Monoclinic
Often mistaken for sphalerite:




Sphalerite has several cleavages, isometric crystals, lower density
Forms in quartz veins and placers
Tungsten ore
Scheelite



CaWO4
Forms in quartz veins and in skarns
Can be mistaken for quartz or calcite


Blue and white fluorescence diagnostic;
much softer than quartz; heavier than calcite
Major tungsten ore
Biogenic processes

Biogenic minerals forms in surface
environments by:



Originate from living organisms or with their assistance







Transformations of primary organic aggregates or
Biochemical processes
Not strictly minerals, but is the same substance as produced inorganically in rocks
Crystallize within organism and are surrounded with organic material
 Bones & teeth: platy crystals closely related to carbonate-hydroxylapatite
suspended in protein – comprise up to 70% of dried bones
 Various minerals in: mollusk shells, corals, trilobites, algae, egg shells
 Aragonite in mother-of-pearl
 Kidney stones, gall stones
80 different minerals in fossil and recent animals and plants
Calcite in eye-lenses in extinct trilobites and on body of eyeless
brittlestar (starfish)
Magnetite: biomineralogical navigation system for pigeons, bacteria
Bacteria NB in formation of some ore deposits and weathering
processes
Table 23.3