Moissanite
Moissanite 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. Wikipedia
Birefringence: 0.313 (6H form)
Category: Mineral species
Cleavage: (0001) indistinct
Color: Colorless, green, yellow
Crystal class: 6H polytype: dihexagonal pyramidal (6mm); H-M symbol: (6mm)
Crystal habit: Generally found as inclusions in other minerals
Crystal system: 6H polytype, most common: hexagonal