|MadSci Network: Physics|
If you ask what (man-made) materials have the largest value of index of refraction. I think it may be moissanite.It began to make a huge splash in the gem world as the latest and greatest diamond simulant in mid-1998 . This synthetic silicon carbide crystal was discovered by a materials scientist at North Carolina State University and is being developed by Charles & Colvard (formerly known as C3) and Cree Research. Its natural counterpart has been found only in meteorites and is deep green, but the synthetic moissanite is near colorless and will probably continue fool quite a few jewelers and jewelry buyers. Its high refractive index and extreme hardness (second only to diamond) make it an effective diamond simulant, and the popular diamond probes that test thermal conductivity fail to distinguish it from diamond. Charles & Colvard is also marketing a detector that can distinguish between moissanite and diamond. Another way to identify it is by its double refraction -- look through the stone from several different angles and you should see double images of facet lines or objects viewed through the stone. 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. Best Wishes,
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