Chrysoberyl
| Property | Details |
|---|
| Mineral | Chrysoberyl (beryllium aluminate) |
| Mohs Hardness | 8.5 |
| Refractive Index | 1.746 – 1.755 |
| Birthstone | Not a traditional birthstone |
| Major Sources | Sri Lanka, Brazil, Madagascar, Tanzania |
| Treatments | Rarely treated |
Overview
Chrysoberyl is one of the hardest gemstones available, ranking 8.5 on the Mohs scale—surpassed only by corundum (sapphire and ruby) and diamond. Despite sharing the word “beryl” in its name, chrysoberyl is a completely different mineral from the beryl family (emerald, aquamarine). It is best known for two extraordinary phenomena: the sharp “eye” of cat’s eye chrysoberyl (cymophane) and the dramatic color change of alexandrite, its most famous variety.
Cat’s Eye (Cymophane)
When gemologists say “cat’s eye” without further qualification, they mean chrysoberyl cat’s eye—the finest and most valuable example of the chatoyancy phenomenon. A single, sharp band of light glides across the cabochon-cut stone like a cat’s pupil, caused by parallel needle-like inclusions of rutile silk. The best specimens show a “milk and honey” effect: when a light source is positioned to one side, one half of the stone appears milky white while the other glows a rich honey gold. Fine cat’s eye chrysoberyl from Sri Lanka is exceptionally rare and valuable.
Relationship to Alexandrite
Alexandrite is the color-change variety of chrysoberyl, colored by chromium. While alexandrite is covered in its own dedicated guide, it is worth noting that ordinary chrysoberyl, cat’s eye chrysoberyl, and alexandrite are all the same mineral species. Transparent yellowish-green chrysoberyl without cat’s eye or color change is sometimes faceted and is an excellent, durable gemstone in its own right.
Colors & Varieties
Yellowish green: The most common color of transparent chrysoberyl, ranging from honey yellow to greenish yellow. Cat’s eye (cymophane): Usually honey to greenish, always cut as cabochons to display the eye. Alexandrite: Green in daylight, red-purple under incandescent light—the most valuable variety. Colorless: Extremely rare but occasionally found.
Quality & Value Factors
For cat’s eye chrysoberyl, the sharpness and centering of the eye, the strength of the milk-and-honey effect, body color (honey gold is most desirable), and size all determine value. For faceted chrysoberyl, look for vivid yellowish-green color, good clarity, and well-proportioned cuts. Chrysoberyl is rarely treated, so natural specimens are the norm—a significant advantage for buyers seeking untreated gemstones.
Care & Cleaning
At 8.5 on the Mohs scale, chrysoberyl is extremely durable and suitable for all types of jewelry, including daily-wear rings. It has no cleavage concerns and is resistant to chemicals. Clean safely with warm soapy water, ultrasonic cleaners, or steam. Chrysoberyl is one of the most worry-free gemstones you can own.