Properties
| Category | Corundum variety |
|---|---|
| Formula | α-Al2O3 |
| Crystal system | Trigonal |
| Color | Commonly blue; also colorless and other colors |
| Crystal habit | Prismatic, dipyramidal, tabular, or rhombohedral crystals; also massive and granular |
| Cleavage | None; parting may occur |
| Fracture | Uneven to conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 9 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent to opaque |
| Specific gravity | Approximately 4.00 |
From the Wikipedia article
Sapphire is a gemstone variety of the mineral corundum, the crystalline form of aluminium oxide (α-Al2O3). Pure corundum is colorless, while trace elements in its crystal structure produce a wide range of colors. Blue is the best-known, but sapphires also occur in yellow, green, purple, pink, orange, gray, black, and colorless forms. Red gem-quality corundum is classified as ruby rather than sapphire. The boundary between ruby and pink sapphire is based on color appearance and varies among gemological and trade conventions. Sapphire has a Mohs hardness of 9, making it highly resistant to scratching and abrasion.
Source
Source record: crystal-compendium/sapphire/minerals.json. Fetched from English Wikipedia by the operator 2 October 2026.
https://en.wikipedia.org/wiki/Sapphire — revision id 1377304079. Text and properties from Wikipedia, licensed CC BY-SA 4.0.