Diamond
A Diamond is the only gem made of a single element, carbon. Diamond forms under high temperature and pressure conditions that exist only within a specific depth range (about 100 miles) beneath the earth’s surface. Diamond’s crystal structure is isometric, which means the carbon atoms are bonded in essentially the same way in all directions. Because of this formation process diamonds are so hard that you can only scratch it with another diamond. Diamonds have a hardness of 10 on the MOH's scale of hardness.
