Sketch of carbon atoms, 1990s.
© Science Museum / Science & Society Picture Library
Carbon atoms drawn in graphite, with pencils lying on top of the paper. Graphite is an allotrope of carbon in which each carbon atom is linked to three other carbon atoms by strong bonds which results in the formation of planar sheets of carbon atoms. These sheets are joined together by weak residual forces. Graphite is soft, greasy, black and marks paper readily. It is used in pencil lead and amongst its many other uses, in lubricants, paints, electrodes and crucibles.