Moissanite

Moissanite was first found in 1893 as a small component of a meteorite in Arizona by Dr. Ferdinand Henri Moissan, after whom the material was named. Naturally occurring moissanite is exceedingly rare, having an appearance similar to that of diamond and a tetrahedral crystalline structure.

In 1998 C3, Inc. (Charles and Colvard), a subsidiary of Cree Research, Inc., introduced gem-quality moissanite (SiC; silicon carbide) onto the market. Touted as the best, most convincing diamond simulant to date, moissanite kicked up quite a stir: Journalists and programmes such as Nova reported on the troubling ease of misidentification between moissanite and diamond, citing incidents of fraud.

While some properties of moissanite are closer to diamond than those of cubic zirconia, another synthetic diamond simulant, once its properties are known, moissanite is perhaps even easier to identify. Jewellers were at first fooled by moissanite's thermal conductivity which approximates that of diamond, rendering older thermal testers useless; what worked with cubit zirconia did not work with moissanite.

Moissanite is much harder than cubic zirconia (9.5 vs. 8.5), lighter (SG 3.33 vs. 5.6), and much more resistant to heat. This results in a stone of higher lustre, sharper facets and extraordinary resilience: Loose moissanites may be placed directly into ring moulds, the stones surviving unscathed from temperatures up to twice the 900°C melting point of 18k gold.

Gem quality moissanite is manufactured exclusively by Charles and Colvard and is sold as a lower cost alternative to diamonds. In its gem form, moissanite has an index of refraction between 2.65 and 2.69, somewhat higher than a diamond at 2.42.

Despite its mechanical superiority, there are several factors preventing moissanite from dethroning cubic zirconia as queen of diamond simulants:

• Anisotropy. Unlike isometric diamond and cubic zirconia, the polytype of moissanite presently synthesized is hexagonal: being doubly refractive, the stones are easily detected with a polariscope or even by eye, the strong birefringence being seen as a doubling of the stone's back facets. Moissanite is usually cut with its optic axis perpendicular to the table of the stone in order to minimize this "drunk vision" effect, but even a slight tilt will betray the stone's true nature.

• Dispersion. Moissanite has a dispersive power nearly 2.5 times greater than diamond (0.104 vs. 0.044); this means the fire of moissanite is viewed as excessive by some, yet more beautiful by others.

• Colour. To date all moissanites have been plagued by a muddy tinge, usually green or gray. Lacking the brilliant whiteness of cubit zirconia, most moissanites would grade within the I-K colour range of diamond. However, it should be noted at least two fancy varieties of moissanite have been produced: a blue not unlike natural blue diamonds, and a rich green somewhat resembling tsavorite.

• Cost. Due its relatively expensive manufacturing process and because C3, Inc. is its only supplier, moissanite is a costly alternative to cubic zirconia, yet it remains a very affordable alternative to diamond at one tenth the price per carat.

External References

http://www.moissanite.com/unique_properties.cfm