The ancient Greeks called diamond "adamas," meaning invincible, theorizing that something so beautiful must be the crystallized teardrops of the gods. Diamonds are known for their prismatic beauty and hardness, and they are highly valued for these and other qualities. At one time, it was even thought that if you took a diamond into bed with you, it would cure your illness! Diamond is the birthstone for April and the gem of the 10th and 60th anniversary.