Moissanite

In gemology moissanite is classified as synthetic - although it is found in nature, but the natural crystals are of no practical importance because of their small size.

The natural mineral was first found as tiny crystals - small green platelets of silicon carbide, in iron meteorite fragments at Diablo Canyon in Arizona by Dr. Ferdinand H. Moissan. The mineral was named in his honour.

Synthetic moissanite is a Diamond simulant. Most of the properties of diamond are quite well imitated, but moissanite may be detected easily by a gemmologist with simple equipment. Synthetic moissanite is often colourless, sometimes brown, green, yellow and blue but the colours are not very strong.
General Information
Chemical Formula
SiC
Arthur Thomas, Gemstones (2009)
Photos of natural/un-cut material from mindat.org
Moissanite Treatments
A near-colourless moissanite has been heat-treated, causing a brownish colour across all the facets. Cleaning and hand-polishing the samples, using cerium oxide on leather, restored the reflectivity to 98% of the non-treated material. If heating forms part of any testing experiment on a suspected moissanite, the gemmologist should remember that surface oxidation could occur and keep the level of heating to a minimum. The colour of the surface might undergo alteration. - Michael O’Donoghue, Gems, Sixth Edition (2006), p. 89
Synthetic Moissanite
The method of synthesis is probably a modified form of the flux-melt process. - Gemstones, Arthur Thomas, 2009, p 207
Physical Properties of Moissanite
Mohs Hardness9 to 9.5
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Specific Gravity3.17 to 3.24
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Cleavage QualityNone
Arthur Thomas, Gemstones (2009)
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FractureConchoidal
Anthony et al, Handbook of Mineralogy (2001)
Heat SensitivityMay turn yellowish if heated (250 watt bulb)
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Optical Properties of Moissanite
Refractive Index2.648 to 2.691
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Optical CharacterUniaxial/+
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Birefringence0.043
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) DoublingMore from other references
PleochroismNil
Arthur Thomas, Gemstones (2009)
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Dispersion0.104
Arthur Thomas, Gemstones (2009)
Colour
Colour (General)Colourless, greenish, yellowish
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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TransparencyTransparent
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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LustreAdamantine
Arthur Thomas, Gemstones (2009)
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Fluorescence & other light emissions
Fluorescence (General)Usually dark orange or light blue
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Crystallography of Moissanite
Crystal SystemHexagonal
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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HabitTabular
Arthur Thomas, Gemstones (2009)
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Geological Environment
Where found:A rare mineral: formed in an iron meteorite; as inclusions in diamond; in diamondiferous kimberlites and lamproites, and in eclogite; in volcanic breccias and rhyolite; in alluvium.
Anthony et al, Handbook of Mineralogy (2001)
Inclusions in Moissanite
Inclusions: white needles - Gemmological Tables, Ulrich Henn and Claudio C. Milisenda, 2004, p 32
Further Information
Mineral information:Moissanite information at mindat.org
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