Sapphire
Varietyof Corundum
Sapphire is gem corundum of any color other than red, classically blue. As a variety of Corundum, it shares that species' composition (Al2O3), crystal structure, and hardness; the distinction is the appearance defined above.
Photos
About Corundum
Full reference data — crystallography, X-ray diffraction, and cited physical properties — is on the Corundum species page.
| Formula | Al2O3 |
|---|---|
| Hardness (Mohs) | 9 |
| Density (calculated) | 3.983 |
| Crystal system | trigonal |
| Streak | white |