A black solid compound, SiC, insoluble in water and soluble in molten alkali; r.d. 3.217; m.p. c. 2700°C. Silicon carbide is made by heating silicon(IV) oxide with carbon in an electric furnace (depending on the grade required sand and coke may be used). It is extremely hard and is widely used as an abrasive. The solid exists in both zinc blende and wurtzite structures. There is a clear form known as moissanite, used as a diamond substitute.