Colour: Found in a multitude of fancy colours, though associated with blue when not specified.
Hardness: 9 (on Moh’s hardness scale). Second only to diamond.
Specific Gravity: 3.99/4. This is an indication of the stone's density, calculated by comparing the stone's weight with the weight of an equal volume of water.
Refractive Index: 1.76 to 1.77. This is a measure of the amount light is bent from its original path when passing through a stone.
Chemical composition: Aluminium oxide, Al2O3. Part of the corundum family of minerals.
Principal sources: Mynmar (Burma), Sri Lanka, India, Thailand, Australia and Nigeria.