Sapphire is the non-red variety of corundum, the second hardest natural mineral known to mankind. The red variety of corundum is Ruby. Sapphires are well known among the general public as being blue, but it can be nearly any color. The blue color is by far the most popular color for sapphire but orange-pink, golden, white, and even black have generated much interest in the gem trade. Oriented rutile crystal inclusions cause a six-pointed-star light effect (called asterism to form the popular Star Sapphire.