Graphite

Graphite is a soft, crystalline polymorph of carbon, and while it shares the same chemistry as diamond the two have very different physical properties (see diamond for examples). Graphite exhibits both metallic and non-metallic properties. The metallic properties include thermal and electrical conductivity, while the non-metallic properties include inertness, high thermal resistance, and lubricity. Some of the major end uses of graphite are in high-temperature lubricants, brushes for electrical motors, friction materials, battery and fuel cells, and pencil "lead".

While most graphite is formed through the metamorphism of organic material in rocks, it also occurs in igneous rocks and is found as nodules inside of iron meteorites.

Chemical composition - C
Hardness - 1-2
Specific gravity - 2.2
Transparency - Opaque
Colour - Silver-black
Streak - Shiny black
Lustre - Metallic to earthy
Cleavage/fracture - Perfect in one direction / sectile (curved shavings as though peeled by a knife)
Crystal habit/mode of occurrence - Tabular / massive, scales, lumps