Graphite is a single element crystal composed solely of carbon, and thus is a polymorph of diamond. Like diamond, graphite is a completely covalent mineral, however, here the structure is isometric with tetrahedral symmetry. Each carbon atom is surrounded by three other carbon atoms in 3-fold planar coordination due to the sp2 coordination of the carbon atoms. The individual sheets are bonded to each other by covalent bonding among the pi orbitals. These relatively weak bonds allow the sheets to easily slide past each other, providing the greasy feel common to graphite, as well as its lubricating properties. Crystals are commonly hexagonal tablets; sometimes foliated, scaly, granular and earthy; usually massive. The color is steel-gray to iron black; metallic; often shiny.
Graphite results from the metamorphism of carbonaceous materials in sedimentary deposits and is found with quartz and muscovite in schists of regional metamorphic rocks and in marbles. Good and fairly pure specimens are scarce. Fine crystals have been found in marbles in New Jersey, Alabama and New York (USA). Large deposits occur in Finland and Germany. Its principal use is in lubricants. The name is derived from the Greek “graphein”, meaning “write” in allusion to its use as a crayon.
Chesterman, C.W. 1978. The Audubon Society Field Guide to North American Rocks and Minerals. A.A. Knopf, Chanticleer Press Inc., New York. USA.
Kukesh, J.S., L. Pauling L. 1950. The problem of the graphite structure. American Mineralogist. 35:125.