Jade - SSEF

Transcription

Jade - SSEF

Jade
A presentation by Dr. Michael S. Krzemnicki
SSEF Swiss Gemmological Institute
September 2008
photos © mostly by Prof. H.A. Hänni, SSEF
Jade (historical)
In Asia the term jade was traditionally used for all kinds of carvings which nowadays are
distinguished into different minerals such as jadeite, nephrite, omphacite, serpentine a.s.o.
Only in the last 150 years, mineralogy established as a science and these different minerals
could be identified.
© Guillaume Soubira, 2006
© Swiss Gemmological Institute
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Jade sensu lato
Jade is a term used basically for two minerals in their
massive form, as polycrystalline quasi monomineralic rocks.
Both are chain silicates:
Jadeite is Jadeite-Jade
Tremolite-Actinolite is
Nephrite-Jade
Na Al Si2 O6
Trem Ca2 Mg5 Si8 O22 OH
Act Ca2 (Mg,Fe)5 Si8 O22 OH
Pyroxene group
Amphibole group
The CIBJO recognises Jadeite-Jade and Nephrite-Jade as “Jade”, but no other minerals.
Jadeite
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Maingkwan (amber)
Burma
Kansi
BURMA
Mawsitsit
Mt. Loimye
(5124 ft)
Lonkin
Nanyaseik (ruby)
Hpakan
Mamon
Haungpa
Kamaing
Sate Mu (Sine Naung)
Hweka
Nyaungbin
Mogaung
Makapin
Myitkyina
Lake
Indawgyi
Hopin
Mandalay-Myitkina rail line
Jade mining area
Ruby mining area
Amber mining area
Jadeite Outcrops
Mawsitsit
Burma
Lonkin
© R.W. Hughes
Hpakan
Uru boulder conglomerate
serpentinized peridotite
crystalline schists
sedimentary rocks (Tertiary)
The origin of Jade
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© Christieʼs Hong Kong
Jadeite
Jadeite-Jade: Jadeite
RI
(1.654
SG
3.34
Na Al Si2 O6
1.665 )
mean 1.66
H 6.5 - 7
Double refractive aggregate reaction under the polariscope ( optically biaxial positive )
Colours : white, green, yellow, orange, violet, black, homogeneous to spotted or mottled
Chromophores: Cr, Fe, Mn
Spectrum: Cr
438, 630, 650, 660, 690 nm
Degree of transparence: from opaque to near transparent
Structure: blocky to fibrous,
Treatments: B-Jade is impregnated with wax or epoxy resin
Absorptionspectrum of
emerald-green jadeite (Imperial Jade)
C-Jade is dyed
Sources : North Burma (Myanmar), Guatemala, Russia,
Fei Cui (Jadeite-Jade)
Definition of Fei Cui (Jadeite Jade)
after the Gemmological Association of Hong Kong
Fei Cui (jadeite jade) is a granular to fibrous polycrystalline aggregate. It is composed of
jadeite as major mineral. It may consist of other minor minerals such as opmhacite,
kosmochlore, amphibole, and feldspar.
Kosmochlor
jadeite
Omphacite
kosmochlor
omphacite
Jadeite
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Solid soution
Kosmochlor
Cr
Omphacite
Jadeite
Na
Fe
Jadeite
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Jadeite
Thin section
Jadeite
SEM picture
SEM BSE picture
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Jadeite
Jadeite is often carved
The green colour is due to chromium and iron
Jadeite
Graphite inclusions may produce greyish and black jadeite-jade
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Lavender Jadeite-Jade
Jadeite - albite assemblage (reflected light)
Jadeite of light purplish to violet colour is called
lavender jade. Some of this material
proved to be a mixture of jadeite with albite.
Nomenclature ?
The mono-mineralic composition may be quit and other minerals may form the rock.
This leads to discussions about nomenclature: is Maw Sit Sit considered a jade?
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Maw Sit Sit
A complex rock from N-Burma under
high pressure metamorphic conditions.
Maw sit sit contains minerals from the
jadeite solid solution with cosmochlore.
colour: light green to black, single colour or,
spotted, mottled, often with black spots and
white veins
density: 2.5 - 3.2 g/cm3 depending of
mineral composition
Refractive index : weak reading at 1.52
Imitation of Jadeite
Dyed marble, quartzite, or glass may be misrepresented as jadeite
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Imitation of Jadeite
dyed quartzite
Dyed marble
aventurine-quartzite
massive fuchsite
Serpentine
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Serpentine
Prehistoric stone axe, found at
Lop Nor, Taklamakhan desert
in the Xinjiang Province
(northwestern China)
Nephrite Jade
Nephrite is a term used for
fibrous Tremolite-Actinolite rock
Tremolite
Ca2 Mg5 Si8 O 22 (OH)2
Actinolite
Ca2 (Mg,Fe)5 Si8 O 22 (OH)2
Amphibole, chain silicate ( biaxial negative )
R I 1.606 - 1.632
S G 3.00
spot reading 1.62
colours: white, green, yellow, orange, brown, grey, black
(depending on iron content or actinolite proportion)
Spectrum: Fe
460, 500, ev. 690 nm
Structure: fibrous, very dense, inclusions often magnetite or chromite
Deposits in China, Russia, New Zealand, Australia, USA, Switzerland, ...
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Nephrite
Cr diffusion around
chromite inclusion
Thin section
Nephrite
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Nephrite
Art objects of historic periods
The Treatment of Jadeite
Treatments mainly affect colour
and degree of transparency
Dyed jadeite jade (C-Jade)
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Treated Jadeite
Untreated jade is referred as
A-jade.
Treatments mainly affect colour and degree of transparency. Natural Jade is
often stained by natural iron oxide. This brown colour may dramatically spoil
the otherwise good colour. Bleaching removes the brown, but leaves open
pores along the grain boundaries. They have to get filled in order to improve
the appearance. Impregnation may be performed with colourless paraffin
(wax) or epoxy (polymer, artificial resin). Such jade is called B-jade in the
trade.
Often the impregnation of bleached, porous jade is performed with fillers
which carry dye to improve the colour of the jade. After treatment with
coloured epoxy or paraffin wax, the jadeite is called C-Jade (or B+C-Jade) in
the trade.
Treated Jadeite
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Treated Jadeite
Untreated jadeite
Closed grain boundaries
400x magnification
bleached jadeite
Open grain boundaries
400x magnification
During the bleaching with acids any residual iron-hydroxide is dissolved.
The grain boundaries are open.
To enhance translucency, colour and stability, the bleached jadeite is afterwards commonly
impregnated with wax or epoxy.
Treated Jadeite
Open texture
Closed texture
Open texture
Closed texture
Iron stain
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Treated Jadeite
Green and violet dyed jadeite. The colour is concentrated in fissures and along grain boundaries.
Treated Jadeite
Dyed jadeite
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Treated Jadeite
Dyed Jadeite in different colours
Treated Jadeite
Coated with a green plastic lacquer
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Jadeite Testing
SSEF Testing procedures
Measurements
Weight
Description of colour, (colour prefix, saturation, tone)
Degree of translucency
Degree of lustre
Description of texture
Specific Gravity (hydrostatic balance)
Refractive index (spot reading with refractometer)
Polycristalline anisotropic (Polariscope)
Fluorescence (LW and SW UV-lamp)
Chelsea Filter
Microscope (texture, polish, treatment, etc.)
UV-Vis Spectrometer (natural colour vs dyed)
FTIR spectrum (treatment detection , A-, B-, C-Jade)
Raman microspectrometry (identification, treatment detection , A-, B-, C-Jade)
X-ray fluorescence (chemical composition, chromium concentration)
Every jadeite is independently tested by at least two gemmologists!
Colour description
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Colour distribution
Jadeite Testing
Specific gravity measurement
Polariscope examination
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Jadeite Testing
Jadeite granular texture
Polariscope examination
Jadeite Testing
Observation of UV reaction
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Jadeite Testing: UV-Vis
UV-Vis spectrometer:
From heavyweight......to very small.
Jadeite UV-Vis spectrum
Fe
Cr
Cr
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Jadeite Testing: Infrared
Our recent acquisition,
a portable FTIR spectrometer for
gemstone testing (Bruker Alpha).
Jadeite infrared spectrum
before treatment: A-jadeite
after treatment:
B-jadeite
A-jadeite with finger fat
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Jadeite infrared spectrum
before treatment: A-jadeite
after treatment:
B-jadeite
A-jadeite with finger fat
Wax peaks in a IR spectrum of a paraffin treated jadeite
Jadeite Testing: Raman
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Raman spectra of Jadeite
... eternal values
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Important jadeite jewellery
SSEF launches new Jadeite
report in January 2009
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Jadeite
Testing
SSEF will introduce a new and detailed
jadeite report beginning of 2009.
Thank you for your attention
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Jade - SSEF

Transcription

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