Colour: Variations from violet to blue.
Hardness: 6½ (on Moh’s hardness scale.)
Specific Gravity: 3.35. 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: 1.69 to 1.70. This is a measure of the amount light is bent from its original path when passing through a stone.
Chemical composition: Calcium aluminium hydroxysilicate. Part of the Zoisite family of minerals.
Principal sources: Tanzania.