In 1998, C3, Inc. (Charles and Colvard) [Nasdaq: CTHR], a subsidiary of Cree Research, Inc., introduced gem-quality synthetic silicon carbide onto the market under the name “moissanite,” marketing it as a lower-cost alternative to diamond. For example, a 1 carat (200 mg) moissanite gem sells for about $600 (2005 USD), while a diamond of similar size and color typically runs for upwards of $4500. Synthetic moissonite is almost as hard as diamond, with a slightly higher index of refraction and greater dispersion; these qualities make SiC a decent and durable diamond simulant. Moissanite’s greater dispersion and index of refraction gives it more fire and brilliance than diamond.

Source: Wikipedia

While some properties of moissanite are closer to those of diamond than to cubic zirconia, another synthetic diamond simulant, once its properties are known, moissanite is perhaps even easier to identify, as it is doubly refractive and has a slight green tint to it. Jewellers were at first fooled by moissanite’s thermal conductivity, which is close to that of diamond, rendering older thermal testers useless; what worked with cubic zirconia did not work with moissanite.

Moissanite is harder than cubic zirconia (9 1/4 vs. 8 1/2), lighter (SG 3.33 vs. 5.6), and much more resistant to heat. This results in a stone of higher lustre, sharper facets and good resilience: loose moissanites may be placed directly into ring moulds, as the stones remain undamaged by temperatures up to twice the 900 °C melting point of 18k gold.