The structure of diamond is shown above. Each black dark circle represents a carbon atom and each line representing a single bond.
In diamond, each carbon atom is bonded to four other carbon atoms in a tetrahedral arrangement as shown above. As a consequence, this arrangement forms a large complex rigid structure resulting in diamond having the following properties:
-Diamond is the hardest natural substance known
-Diamond does not conduct electricity because all the electrons found in the outer shell of the carbon atoms, are used in bonding. As such, there is no motion of free electrons which would result in electricity.
-Diamond has a very high melting and boiling point because of this rigid giant structure (large amount of energy needed to overcome these bonds).