can be made from carbon atoms only under special conditions of high
temperature and pressure. Artificial diamond-making in the laboratory
is a recent art, and still inferior to the natural subterranean processes.
An easier form of pure carbon to obtain is graphite, which has the
structure shown on the right. In graphite the carbon atoms are arranged
in layers of hexagons, with each atom bonded to three others. Each
carbon atom has one leftover electron, as in benzene. These electrons
are decolorized and are free to move about within one layer of atoms.
This helps to make graphite more stable. It also allows graphite to
conduct electricity, but only along the separate planes of hexagons.
The electrons cannot jump from one layer to another. In effect, graphite
is a "two-dimensional metal." The layers themselves are held together
only by van der Waals forces, and are relatively free to slip past
one another. It is this slippage of layers that makes powdered graphite
a good lubricant.