White Sapphire: Aluminium Oxide (alumina) Al2O3; crystal system: Trigonal; from the Indian Sanskrit Kuruvinda meaning hard stone; Hardness:9 ; Relative Density 3.99-4.05; cleavage: none; refractive Index 1.765-1.773; Birefringence: 0.008 ; Dispersion: Weak.
This is often used as a diamond substitute in cheaper jewellery without intent to deceive. Usually found in round brilliant cut form surrounding larger coloured stones in rings. A refractometer test will immediately establish its identity if the table facets are unobstructed. Also sapphire is doubly refracting and will show four extinction positions when rotated between crossed polarized filters. Visually lacking in life compared to diamond.