A variety of Corundum, a mineral of aluminum oxide, the Violet Sapphire, gets its violet hue due to the presence of vanadium, which creates shades from lavender to violet to deep purple.

Corundum comes from many places around the world and is extensively used in industry cutting. Most notably and popular sapphires come from Sri Lanka and Kashmir with the most prominent violet ones coming from Madagascar and Sri Lanka.

Mineral Purple Sapphire
Chemistry Al2O3
Refractive Index 1.762 to 1.770
Birefringence 0.008 to 0.010
Specific Gravity  4.00
Mohs Hardness 9