Diamonds are a girl's best friend because of its spellbinding charm and dazzling sparkles. What should you know when shopping for a diamond? How do you take care of the precious stone? Diamonds are natural mineral formed deep in the earth crust. Under high pressure and high temperature, carbon atoms are re-arranged to give the rare gem. Diamond is the hardest natural substance on earth, yet it is brittle. It may still crack if subject to heavy stress.