Sapphire is a precious gemstone, a variety of the mineral corundum. It is the third hardest mineral, after diamonds and moissanites. Sapphire is the birthstone for September and the gem of 45th wedding anniversaries. Commonly known for their striking blue color, Sapphires may come in other color varieties, except red, which instead are known as rubies. This gem is the most valuable and precious of the blue gemstones.