Graphite is an electrical conductor, hence useful in such applications as arc lamp electrodes. It can conduct electricity due to the vast electron delocalization within the carbon layers (a phenomenon called aromaticity). These valence electrons are free to move, so are able to conduct electricity.
The atomic structure of graphite results in a large number of electrons not being bonded, allowing them to migrate between the layers of graphite. It is this large number of free electrons (electron delocalization) that give graphite its excellent conductive properties. As well as being a good conductor, graphite is also cheap, robust and easily accessible.
