One of the most distinctive properties of chrysoberyl is its exceptional hardness. With a Mohs hardness of 8.5, it is the third-hardest gemstone and the third-hardest mineral that is even occasionally found at Earth’s surface. Although chrysoberyl is extremely hard, it does break with distinct cleavage in one direction and indistinctly or poorly in two others. It also has a brittle tenacity.
Most specimens of chrysoberyl are nearly colorless or fall into the brown to yellow to green color range. Red specimens are occasionally found.
Chrysoberyl often occurs in tabular or prismatic crystals with distinct striations (see photo below). It also occurs in twinned crystals with distinct star and rosette shapes. These crystals usually persist well and retain their shape during stream transport because of the mineral’s exceptional hardness. This makes them easy to identify in gem gravels, but the twinning often interferes with their usefulness as gems.
| Physical Properties of Chrysoberyl | |
| Chemical Classification | Oxide |
| Color | Usually ranges from brown to pale yellow, yellow-green and green |
| Streak | Colorless |
| Luster | Vitreous |
| Diaphaneity | Transparent to translucent |
| Cleavage | Poor, prismatic |
| Mohs Hardness | 8.5 |
| Specific Gravity | 3.7 to 3.8 |
| Diagnostic Properties | Hardness, color |
| Chemical Composition | Beryllium aluminum oxide, BeAl2O4 |
| Crystal System | Orthorhombic |
| Uses | As a gemstone: chrysoberyl when transparent, “cat’s-eye” when chatoyant, and “alexandrite” in specimens that exhibit color change. |