• Sapphire is the most precious and valuable blue gemstone.
• It is a very desirable gemstone due to its excellent color, hardness, durability, and luster.
• 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, excluding Ruby, the red variety of Corundum, which has its own name since antiquity.
• Chemical Formula: Al2O3
• Color: Blue
• Hardness: 9
• Crystal System: Hexagonal
• Refractive Index: 1.76 - 1.77
• SG: 3.9 - 4.1
• Transparency: Transparent to opaque
• Double Refraction: .0008
• Luster: Vitreous to adamantine
• Cleavage: None, but may exhibit parting
• Mineral Class: Corundum