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Russian Gemstones Encyclopedia

Vladimir Bukanov. Russian Gemstones Encyclopedia

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

MOISSANITE


MOISSANITE (Moissanit—Moissanite—ћуассанит) (Kunz, G.F. 1905), after Ferdinand F. Henri Moisson (1852-1907), a Professor of chemistry at the Sorbonne, Paris, who discovered the mineral in the Canyon Diablo meteorite, Coconino Co., Arizona, U.S.A.

Composition & Properties. Carbide – α-SiC, hexagonal system. Hardness 9.5. Density 3.2. Diamond luster to metal one. Dissoluble in acids. A rare analogue of synthetic silicon carbide, which was received through synthesis, at first, and then, it has been found in nature. It is found in meteorites, kimberlites in the form of lamellar crystals of greenish-gray color, sometimes it is found as an accessory mineral in sedimentary rocks. Natural crystals are of no practical importance because of their small size.

Synthesis. Synthetic moissanite, under the trade name carborundum, has been received with the method of melting in electric furnaces for usage as an abrasive material since 1915. It displays bright blueing on the surface of fine-crystalline aggregates of synthetic carborundum and sometimes it was used in jewelries. Since 1997, in the U.S.A. and later in Russia, they have begun to produce synthetic moissanite with the method of vacuum sublimation in the form of blocks up to 400 ct. Because its stability ups to the temperature of 2020°C, this material was used as a mat in electronic schemes, and then in jewelry for the imitation of brilliants. Moissanite with the admixture of nitrogen displays green color, with the admixture of boron – light blue, with graphite – light gray. They use the last variety the most often, it looses its color after the annealing. For gem-quality moissanite grayish-green color is typical as well as fine thread-like inclusions in the shape of channels. In faceted stone, they can be observed through the magnifying glass from the side of culet.

In hardness and thermal conductivity synthetic moissanite is close to diamond, for which it was set up sometimes. In Russia, they produce imitations of brilliants up to 4 ct. from this material in significant volumes. In rings big moissanits are mounted among small brilliants. Nowadays, they produce crystals of moissanite from colorless to black ones, but the best for jewelry purposes are yellow-green and dark green ones, which resemble chrysolite. In brilliant pattern of faceting they reach 12 ct. Moissanite is easily differed from diamond because of its bright yellow luminescence in ultra-violet rays, while diamond usually displays other colors of luminescence.

SynonymTairite, after Yu.M. Tairov, a Russ. inventor of the method of synthesis of moissanite.

Beside moissanite, among synthetic carbides we should mention tungstate carbide. Its gems faceted in the pattern of “rose” were used in jewelry under the trade name marcasite. Another carbide is boron carbide, composition – B4C, which was used as an abrasive material under the trade name norbide. Because of its high hardness 9.5, it can be supposed to be a potential jewelry stone.

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