Moissanite

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Chemical composition -- Silicon carbide.

Color -- Near colorless, usually slightly greenish or grayish.

Optics -- R.I. 2.65-2.69. Uniaxial.

Durability -- Hardness 9.25-9.5 (second in hardness to diamond).

Crystal structure -- Hexagonal.

Specific Gravity-- 3.22.

Moissanite, which has been found naturally in tiny amounts in meteorites, is the most recently touted manmade diamond imitation. Developed from material produced by Cree Research, C3 Inc. began to market it through selected retailers in mid-1998. In October 1999, C3 announced that they would change their business name to Charles & Colvard. If properly oriented and well cut, moissanite strongly resembles diamond, due to its high refractive index and dispersion. As it has similar thermal conductivity to diamond, moissanite can pass as diamond on a standard diamond thermal probe, so the vendor is also marketing a special instrument that measures relative transparency in the near-ultraviolet range (diamond absorbs and moissanite transmits light in these wavelengths).

Moissanite is most convincing as a diamond substitute in small sizes. Larger stones still show slight greenish or grayish tones that are difficult to eliminate. Careful examination through the crown facets (not through the table, since that's oriented on the optic axis) under a loupe or microscope should easily reveal facet doubling caused by double refraction, as well as very non-diamondlike surface polish and inclusions, so there seems to be little excuse for misidentification by a trained gemologist.

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Last updated 6 November 1999.