Graphite

Graphite is the most stable form of carbon in nature. This black mineral is very brittle and can easily be broken by hand. The name derives from the Greek word grapho (to write), since graphite is the material used to make pencils. Graphite occurs naturally in different types of ores; crystalline graphite usually shows hexagonal or angular edges when freshly broken. This reflects the crystalline structure in which the carbon atoms are arranged in honeycomb layers stacked on top of each other. The atomic bonds of atoms within the layers are extremely strong, whereas those bonds between the layers are extremely weak. Graphene, a single layer of graphite, can be made by the “Scotch tape method”; peeling sticky tape from a lump of graphite is enough to break the weak bonds in between layers, and by repeating this on the result, it’s possible to detach a single layer. This was how graphene was discovered by Andrei Geim and Kostya Novoselov at the University of Manchester, which got them the Nobel Prize in Physics in 2010.

This lamellar atomic structure gives graphite its many uses. Apart from pencils, graphite can be used as a solid lubricant, typically used in machines that operate at high temperatures.

In a graphite layer, each carbon atom is only bonded to three others, out of a possible total of four. This leaves an electron spare, and these spare electrons are free to flow in the layer, making graphite highly conductive of electricity and heat. These properties see graphite used as electrodes in batteries and industrial processes like melting scrap iron in electric arc furnaces or aluminium smelting, and in carbon microphones. Graphite control rods are vital for the safety and workings of nuclear reactors, to moderate the neutrons involved in nuclear fission.