Moissanite

Moissanite (/ˈmɔɪsənaɪt/) is naturally occurring silicon carbide and its various crystalline polymorphs. It has the chemical formula SiC and is a rare mineral, discovered by the French chemist Henri Moissan in 1893. Silicon carbide is useful for commercial and industrial applications due to its hardness, optical properties and thermal conductivity. Moissanite (/ˈmɔɪsənaɪt/) is naturally occurring silicon carbide and its various crystalline polymorphs. It has the chemical formula SiC and is a rare mineral, discovered by the French chemist Henri Moissan in 1893. Silicon carbide is useful for commercial and industrial applications due to its hardness, optical properties and thermal conductivity. Mineral moissanite was discovered by Henri Moissan while examining rock samples from a meteor crater located in Canyon Diablo, Arizona, in 1893. At first, he mistakenly identified the crystals as diamonds, but in 1904 he identified the crystals as silicon carbide. Artificial silicon carbide had been synthesized in the lab by Edward G. Acheson just two years before Moissan's discovery. The mineral form of silicon carbide was named moissanite in honor of Moissan later on in his life. The discovery in the Canyon Diablo meteorite and other places was challenged for a long time as carborundum contamination from man-made abrasive tools. Until the 1950s, no other source for moissanite than meteorites had been encountered. Then, in 1958, moissanite was found in the Green River Formation in Wyoming and, the following year, as inclusions in kimberlite from a diamond mine in Yakutia. Yet the existence of moissanite in nature was questioned as late as 1986 by the American geologist Charles Milton. Moissanite, in its natural form, remains very rare. It has been discovered only in a few rocks, from upper mantle rock to meteorites. Discoveries show that it occurs naturally as inclusions in diamonds, xenoliths, and such ultramafic rocks as kimberlite and lamproite. It has also been identified as presolar grains in carbonaceous chondrite meteorites. Analysis of silicon carbide grains found in the Murchison meteorite has revealed anomalous isotopic ratios of carbon and silicon, indicating an origin from outside the solar system. 99% of these silicon carbide grains originate around carbon-rich asymptotic giant branch stars. Silicon carbide is commonly found around these stars, as deduced from their infrared spectra. All applications of silicon carbide today use synthetic material, as the natural material is very scarce. Silicon carbide was first synthesized by Jöns Jacob Berzelius, who is best known for his discovery of silicon. Years later, Edward Goodrich Acheson produced viable minerals that could substitute for diamond as an abrasive and cutting material. This was possible, as moissanite is one of the hardest substances known, with a hardness below that of diamond and comparable with those of cubic boron nitride and boron. Pure synthetic moissanite can be made from thermal decomposition of the preceramic polymer poly(methylsilyne), requiring no binding matrix, e.g., cobalt metal powder.