They say 3 of graphite's electrons are covalently bonded and the other one is delocalised. But it shares among the other carbon atoms as well as having it itself because no carbon atom is charged in graphite. But that means it is very much covalent in nature? Why not have a double bond somewhere to explain the extra delocalised electron in every carbon atom in graphite? Or is it the case that they want to say that this electron is not fixed so can double bond with any of the three neighbouring carbon atoms? Is that different to saying it forms a double bond since a double bond in reality means a reasonance structure where the bonding is not fixed anyway.