Each carbon atom in a graphite layer is joined to three other carbon atoms by strong covalent bonds to form flat hexagonal rings. The various layers of carbon atoms in graphite are quite far apart so that no covalent bonds can exist between them. The various layers of carbon atoms in graphite are joined by weak forces, they can slide over one another. Due to the sheet like structure graphite is a soft substances. That is why it is used as dry lubricant for machine parts.