Sapphire is the most precious and expensive gemstone. It is a very popular gemstone due to its excellent colour, hardness, stability, and lustre. In the gem business, Sapphire without any colour prefix refers to the blue, yellow, pink, white type of the mineral Corundum. However, the term Sapphire includes all other gem varieties and colours of Corundum as well, excluding Ruby, the red kind of Corundum, which has its own name since ancientness.