Graphite

Graphite, Plumbago, or Black Lead, is a form of carbon (q.v.) which has no connection with lead, save in colour and lustre. It is black, but has a silvery metallic lustre, is unctuous to the touch, soiling the fingers, and has a hardness of 0-5 to 1, and a specific gravity of 1-9 to 2-3. It generally occurs in scales disseminated through limestones, slate, or mica-schist, or in more considerable beds in a massive form, as in the Laurentian rocks (q.v.) of Canada, where the total thickness of the beds is said to exceed that of the coal-seams in the Coal-measures of England. Very rarely it occurs in six-sided crystalline scales, which are believed to belong to the Oblique system. It does so at New Cumnock, in Ayrshire, where its formation is owing to the penetration of a coal seam by an igneous dyke, and it does so also on the surface of the pigs of inferior or "mottled" cast iron when too much coal has been added to the ore at the top of the blast furnace. The graphite of Borrowdale, near Keswick, is practically exhausted, and we draw our supplies from Ceylon, Siberia, and Finland, our annual imports being about 14,500 tons, of the value of £192,000.

Graphite is used for "black-lead" pencils, for polishing ironwork, so as to protect it from rust and in the manufacture of crucibles.