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| Sapphire | |
|---|---|
 The 422.99-carat Logan sapphire | |
| General | |
| Category | Oxide mineral |
| Formula (repeating unit) | aluminium oxide, Al2O3 |
| Identification | |
| Color | Every color except for red – which is called a ruby – or pinkish-orange (the padparadscha) |
| Crystal habit | massive and granular |
| Crystal system | Trigonal Symbol (32/m) Space Group: R3c |
| Cleavage | none |
| Fracture | conchoidal, splintery |
| Mohs scale hardness | 9.0 |
| Luster | vitreous |
| Streak | white |
| Specific gravity | 3.95–4.03 |
| Optical properties | Abbe number 72.2 |
| Refractive index | nω=1.768–1.772 nε=1.760–1.763, Birefringence 0.008 |
| Pleochroism | Strong |
| Melting point | 2030–2050 °C |
| Fusibility | infusible |
| Solubility | Insoluble |
| Other characteristics | coefficient of thermal expansion (5.0–6.6)×10−6/K |
Sapphire is a type of the mineral corundum, an aluminium oxide (Al2O3). Sapphires are the same as rubies, except that they are not red.
Sapphire can be found in the ground or it can be made in large crystal. Blue sapphires are the most famous kind, but they can be many different colors, like amber and orange.
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