Vitreous (polycrystalline or glassy) or pyrolytic graphitic structures of relatively hard, inert, and stable compounds that are conductors of thermal and electrical energy. Characterized by ionic and Van der Waals type atomic bonding. Primarily carbon or carbon-silicon compounds. Once used in endosseous dental implant system and as implant coatings.

A flaw on the surface of a diamond that looks like a very small black dot.