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
| Color | often blue, but varies |
| Mohs scale hardness | 9.0 |
| Specific gravity | 3.95 – 4.03 |
| Refractive index | 1.768 – 1.772 |
| Pleochroism | Strong |