Graphite forms as carbon compounds interact in veins, and in metamorphic rocks as organic material in limestone is altered by heat and pressure. It is one of the softest of all minerals, with a value of less than 2 on the Mohs scale of hardness. In fact, its softness along with its black colour make it the perfect material for pencils - which earned its name from grapbein, the Greek word for 'writing'. Yet despite its softness, graphite, like diamond, the hardest of all minerals, is a form of pure carbon, Graphite breaks into minute, flexible flakes that easily slide over one another. This 'basal cleavage' gives graphite a distinctive greasy feel that makes it a good dry lubricant. In nature, graphite is found in two distinct forms: flake graphiteand lump graphite. Lump graphite is compact and lacks graphite's normal flakiness.