Graphite is made from layers of carbon which contain many 6-membered carbon rings (hexagonal). Each layer is held together by each carbon being covalently bonded to 3 other carbon atoms and this leaves a delocalised electron to move freely through the structure. Between layers are weak intermolecular forces which allows sliding of the layers on top of each other and so graphite is very slippery and used as a lubricant. The delocalisation of the electron in the layers also means that it is a good conductor of electricity as the free electrons can carry a charge.