Question

why diamond is the hardest natural substance known

Answer 1

Because diamond is made up carbon atom sharing which covalant bond between atom and elements

Answer 2

Diamond has a giant molecular structure. Each carbon atom is covalently bonded to four other carbon atoms. A lot of energy is needed to separate the atoms in diamond. This is because covalent bonds are strong, and diamond contains very many covalent bonds. This makes diamond's melting point and boiling point very high.