Diamond and graphite both consist of pure carbon, but their materials properties vary
considerably. These differences arise from differences in the arrangements of the atoms
in the solids and differences in the bonding between atoms. Covalent bonding in
diamond leads to high strength and stiffness, excellent thermal conductivity, and poor
electrical conductivity. The atoms in graphite are arranged in sheets. Within the sheets,
the bonding between atoms is covalent, but between the sheets, the bonds are less
strong. Thus graphite can easily be sheared off in sheets as occurs when writing with a
pencil. Graphite’s thermal conductivity is much lower than that of diamond, and its
electrical conductivity is much higher.