Sapphire is the most precious and valuable gemstone in blue. It is a very desirable gemstone due to its excellent color, luster, durability and hardness. In the gem trade, Sapphire without any color prefix refers to the blue variety of the mineral Corundum. However, the term Sapphire encompasses all other gem varieties and colors of Corundum as well (yellow, green, violet, orange etc.), except Ruby which has hes own name since ancient times