Graphite

Graphite is a giant covalent structure made of layers of carbon atoms. Each carbon atom forms three strong covalent bonds to other carbon atoms, producing a network of linked hexagonal rings within each layer.

The forces between the layers are weak, so the layers can slide over one another. This makes graphite useful as a lubricant, reducing friction between surfaces.

Each carbon atom has a fourth outer electron that is not used in a covalent bond. These electrons are delocalised: they can move through a layer and carry charge. Graphite therefore conducts electricity and can be used as an electrode to carry current into or out of a substance.

Diamond

Diamond is made of carbon atoms joined in a continuous three-dimensional network. Each carbon atom forms four covalent bonds to four other carbon atoms. A covalent bond holds atoms together through shared electrons.

This network is a giant covalent structure: strong covalent bonds extend throughout it. The bonds hold the atoms firmly in place, making the structure rigid and diamond very hard. This hardness makes diamond suitable for use in cutting tools.