Any corundum that is not red is called sapphire. Some stones change color when viewed outdoors in the sun others display stars formations due to microscopic crystals arranged in a hexagonal pattern inside them. Occasionally, corundum is even bi-colored or multi-colored. (In ancient times almost any blue gem was called sapphire, only more recently has the advance of gemological science allowed us to more easily differentiate each kind of gem mineral from the others of the same color.)Ĭorundum comes in just about every color imaginable, orange, yellow, green, pink, purple, violet, brown, gray, and black. Traces of iron and vanadium can make corundum blue, and then it is named sapphire, which is derived from the Greek word sáppheiros denoting the blue stone lapis lazuli. Pure corundum is colorless, but when traces of chromium are present, corundum can be red, and is then called 'ruby,' a term derived from the Latin ruber meaning red. Rubies and sapphires may look very different, but they're the same mineral - corundum, which is just a combination of aluminum and oxygen (Al 20 3).

Black star sapphire price per carat