graphite

A naturally occurring crystalline form of carbon dimorphous with diamond. Graphite has a layered structure that consists of rings of six carbon atoms arranged in widely spaced horizontal sheets, and thus crystallizes in the hexagonal system, in contrast to the same element crystallizing in the octahedral or tetrahedral system as diamond, resulting in very different characteristics in each. Graphite is opaque, soft, greasy to the touch, and iron black to steel gray in color; it occurs as crystals, flakes, scales, veins, bedded masses, or disseminations in metamorphic rocks.