Corundum
Chemical Formula	Al2O3
Species	Oxides & Hydroxides
Crystal System	Trigonal
Mohs Scale	9
Specific Gravity	3.95-4.10
Color	Colorless, gray, brown; pink to pigeon-blood-red, orange, yellow, green, blue to cornflower blue, Purple; may be color zoned, asteriated mainly grey and brown
Streak	White
Luster	Adamantine, Vitreous, Pearly
Refractive Index	n = 1.767 - 1.772 n = 1.759 - 1.763
Diaphaneity	Transparent, Translucent, Opaque
Cleavage	None Observed
Fracture	Irregular/Uneven, Conchoidal
Crystal Habit：Steep bipyramidal, tabular, prismatic, rhombohedral crystals, massive or granular
Geological Setting：Silica-poor rocks, such as Nepheline-Syenites, alkali igneous undersaturated rocks, contact aureoles in altered aluminous shales, aluminous xenoliths in high temperature plutonic and hypabyssal rocks, metamorphosed bauxite deposits, and as a detrital material in sediments.