A mineral consisting of a low-pressure allotropic form of carbon; it is soft, black, and lustrous and has a greasy feeling; it occurs naturally in hexagonal crystals or massive or can be synthesized from petroleum coke; hardness is 1-2 on Mohs scale, and specific gravity is 2.09-2.23; used in pencils, crucibles, lubricants, paints, and polishes. Also known as black lead; plumbago.