Question

In the diamond modification of solid carbon each atom is covalently bonded to exactly four nearest neighbors that are configured in a tetrahedral pattern around it. In the graphite modification of carbon the carbon atoms form planar sheets that are relatively widely separated from one another. Each carbon atom is bonded to three near neighbors in the plane, and has a weak interaction with atoms in adjacent planes. Diamond is an electrical insulator and is one of the hardest substances known. Interpret these properties in terms of its bonding.