Diamonds are a mineral form of carbon but are very different from graphite. Unlike graphite, diamond is very hard, with a hardness of 10 on the Moh's scale. This is due to its strong covalent bonds. Good quality diamonds are clear and strong. Diamonds are excellent conductors of heat energy which makes them cold to the touch.
Diamonds occur in various forms, including the diamond proper, bort, ballas, and carbonado.
Bort is hard and dark and is an imperfect type of crystallized diamond. Ballas is a spherical mass of tiny diamond crystals. Carbonado, or black diamond or carbon, is a grayish-black form of diamond with no cleavage. This is a model of the atomic structure of a diamond crystal. Another form of carbon is C60, which is buckminsterfullerene.