| Other names: | Varieties include emery (with magnetite), ruby (red) and sapphire (purple and colorless). |
| Mineral class: | Oxides and Hydroxides |
| Composition: | Al2O3 |
| Hardness: | 9 |
| Luster: | Adamantine, vitreous |
| Color: | Brown, Grey, pink or blue; varies considerably |
| Streak: | None |
| Cleavage: | Occasional cleavage-like fracture ("parting") |
| Specific Gravity: | 3.9-4.1 |
| Crystal form: | Hexagonal |
| Environment: | Accompanies igneous rocks that are relatively low in silica composition (e.g. syenites), and high-grade metamorphic rocks that are formed under extreme and intense levels of pressure (e.g., marbles, mica schists). |
| Uses: | Abrasives, gemstones, synthetic varieties used in mechanical precision engineering applications. |
| Comments: | Some varieties fluorescent yellow in UV light. Infusible. Insoluble in acids. Grey crystals up to 375 lbs have been found in South Africa. |