Noun
moissanite (countable and uncountable, plural moissanites)
(mineralogy) Naturally-occurring silicon carbide, having various crystalline polymorphs.
Among the natural gems only moissanite and diamond are harder, with diamond having a Mohs hardness of 10.0 and moissanite falling somewhere in between corundum (ruby) and diamond in hardness. Source: Internet
The gemstone moissanite (silicon carbide) can be treated as a diamond simulant, though more costly to produce than cubic zirconia. Source: Internet