Why can graphite conduct electricity but diamond can’t even though they are both purely made of carbon?

Though graphite and diamond are made of only carbon, they both have a different structure. The structure of Graphite consists of carbon atoms covalently bonded to 3 other carbon atoms. Each carbon atom therefore has an electron in its outer shell that is delocalised and free to move around the graphite structure. As a result, electrical charge can be carried by these delocalised electrons and hence graphite can conduct electricity. On the other hand, the structure of diamond consists of each carbon atom covalently bonded to four other carbon atoms. Therefore each carbon atom has all of its electrons in its outer shell bonded, for this reason there are no free electrons that can move around the diamond structure and conduct electricity.