Properties
| Category | Oxide mineral – Hematite group |
|---|---|
| Formula | Al2O3 |
| Crystal system | Trigonal |
| Color | Colorless, gray, golden-brown, brown; purple, pink to red, orange, yellow, green, blue, violet; may be color zoned, asteriated mainly grey and brown |
| Crystal habit | Steep bipyramidal, tabular, prismatic, rhombohedral crystals, massive or granular |
| Cleavage | None – parting in 3 directions |
| Fracture | Conchoidal to uneven |
| Tenacity | Brittle |
| Mohs scale hardness | 9 (defining mineral) |
| Luster | Adamantine to vitreous |
| Streak | Colorless |
| Diaphaneity | Transparent, translucent to opaque |
| Specific gravity | 3.95–4.10 |
From the Wikipedia article
Corundum is a crystalline form of aluminium oxide typically containing traces of iron, titanium, vanadium, and chromium. It is a rock-forming mineral. It is a naturally transparent material, but can have different colors depending on the presence of transition metal impurities in its crystalline structure. Corundum has two primary gem varieties: ruby and sapphire. Rubies are red due to the presence of chromium, and sapphires exhibit a range of colors depending on what transition metal is present. A rare type of sapphire, padparadscha sapphire, is pink-orange.
Source
Source record: crystal-compendium/corundum/minerals.json. Fetched from English Wikipedia by the operator 2 October 2026.
https://en.wikipedia.org/wiki/Corundum — revision id 1377168195. Text and properties from Wikipedia, licensed CC BY-SA 4.0.