The Blue Sapphire is a gem of the corundum family. Sometimes white sapphires, rubies, and blue sapphires are found in the same mine, and that is why there is a mixture of colors in the crystals of these gems. Ruby is harder than white sapphire (known as pukhraj), and blue sapphire is harder than ruby and it is the hardest of all. Sapphire is one of the two varieties of Corundum, the other variety being Ruby. Sapphire includes all colors of Corundum except for red stones, which are referred to as Ruby. Sapphire is the most highly valued of the blue gemstones.