Williamsite

Williamsite is a variety of Antigorite that has oil-green colour and is often included with black crystals of chromite or magnetite.

Williamsite is cut into cabochons and beads. It is also used as Jade simulant.
General Information
A variety or type of:Antigorite, which is a variety of Serpentine
Chemical Formula
(Mg,Fe
2+
 
)
 
3
Si
 
2
O
 
5
(OH)
 
4
Anthony et al, Handbook of mineralogy (2001)
Photos of natural/un-cut material from mindat.org
Physical Properties of Williamsite
Mohs Hardness4
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) +/-4
Specific Gravity2.51 to 2.63
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Cleavage QualityPerfect
Anthony et al, Handbook of mineralogy (2001)
FractureConchoidal,Splintery
Anthony et al, Handbook of mineralogy (2001)
Optical Properties of Williamsite
Refractive Index1.530 to 1.575
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Optical CharacterBiaxial/-
Anthony et al, Handbook of mineralogy (2001)
Colour
Colour (General)Intense green
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Causes of ColourGreen, Cr3+ around chromite inclusions
W. William Hanneman, Pragmatic Spectroscopy For Gemologists (2011)
TransparencyTranslucent
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
LustreWaxy,Silky,Resinous,Greasy,Dull (Earthy)
Anthony et al, Handbook of mineralogy (2001)
Fluorescence & other light emissions
Fluorescence (Long-Wave UV)Weak whitish-green
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Crystallography of Williamsite
Crystal SystemMonoclinic
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Inclusions in Williamsite
Black octahedral chromite crystals - Blue Chart Gem Identification, Herve Nicolas Lazzarelli, 2010, p 6
Further Information
Mineral information:Williamsite information at mindat.org
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