Why can graphite conduct electricity but diamond cant?

Electricity is the movement of charge and therefore something charged must move to carry this charge. graphite carbon atoms make 3 covalent bonds with the adjacent atoms however carbon has 4 electrons in its outer shell (its in group 4) (if needed explain the periodic table and structure of the atom) which leaves one electron free to move across the molecule and carry the charge. diamond makes 4 bonds and therefore there are no free electrons to carry the charge.