The diamond is the best known and the most heavily marketed gemstone. Diamond has an isometric crystallography. Commercial gem diamonds are colorless or pale, steely blue.
Diamonds can also be gray, yellow, brown, green, orange, lavender, and even black.
Diamond crystals frequently contain inclusions of other minerals. Many diamonds fluoresce blue to violet and the effect is sometimes strong enough to be seen in daylight. Diamond has a high specific gravity. At a high enough temperature in the presence of oxygen, diamond can burn.