Sapphire refers to gem varieties of the mineral corundum, an aluminum oxide (Al2O3), when it is a color other than red. It can be found naturally or manufactured in large crystal boules for varied applications, including infrared optical components, watch faces, high-durability windows, and wafers for the deposition of semiconductors such as GaN nanorods.
The mineral corundum consists of pure aluminum oxide. Trace amounts of other elements such as iron, titanium and chromium give corundum their blue, yellow, pink, purple, orange or greenish color. Sapphire includes any gemstone quality varieties of the mineral corundum except the fully saturated red variety, which is instead known as ruby, and the pinkish-orange variety known as padparadscha.
General
Category Mineral Variety
Chemical formula aluminum oxide, Al2O3
Identification
Color Every color except red (which is ruby)
Crystal habit massive and granular
Crystal system Trigonal
Cleavage None
Fracture Conchoidal, splintery
Mohs Scale hardness 9.0
Luster Vitreous
Refractive index 1.762-1.778
Pleochroism Strong
Streak White
Specific gravity 3.95-4.03
Fusibility infusible
Solubility insoluble
Other Characteristics Coefficient of thermal expansion 5e-6–6.6e-6/K
Category Mineral Variety
Chemical formula aluminum oxide, Al2O3
Identification
Color Every color except red (which is ruby)
Crystal habit massive and granular
Crystal system Trigonal
Cleavage None
Fracture Conchoidal, splintery
Mohs Scale hardness 9.0
Luster Vitreous
Refractive index 1.762-1.778
Pleochroism Strong
Streak White
Specific gravity 3.95-4.03
Fusibility infusible
Solubility insoluble
Other Characteristics Coefficient of thermal expansion 5e-6–6.6e-6/K
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