It is made primarily of graphite composite material. It is an impure form of polycrystalline diamond consisting of diamond, graphite, and amorphous carbon. The Graphite Metallic color is discontinued. The lead of the pencil is a mix of finely ground graphite and clay powders. They exhibit structures analogous to various allotropes of carbon, including graphite, diamond, and nanotubes. He discovered that overheating carborundum, as opposed to pure carbon, produced almost pure graphite. An example of this is solid carbon, which can exist as graphite or diamond. More durable brushes can be made of graphite or liquid metal. Electrodes of metal, graphite and semiconductor material are widely used. He then had special boron-free graphite produced. Sonora is the leading producer of gold, copper, graphite, molybdenum, and wollastonite. The iron is recycled on site, leaving a mixture of graphite and slag. It used a mixture of graphite, sulphur, and antimony. France was also unable to import the inferior German graphite pencil substitute. Soot is produced by laser ablation of graphite or pyrolysis of aromatic hydrocarbons.