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.
Frequently Asked Questions
What is the milk and honey effect in cat's eye chrysoberyl?
The milk and honey effect is the most prized phenomenon in cat's eye chrysoberyl. When a single light source illuminates the stone from one side, the eye divides the cabochon into two halves: one side appears milky white (the milk) while the other glows a rich, warm honey gold (the honey). As you rotate the stone, the colors swap sides. This dramatic two-tone effect, combined with a sharp, well-centered eye, represents the pinnacle of cat's eye quality and commands the highest prices.
Is chrysoberyl the same as beryl?
No, despite the similar name, chrysoberyl and beryl are completely different minerals with different chemical compositions and crystal structures. Chrysoberyl is beryllium aluminate (BeAl2O4), while beryl is beryllium aluminum silicate (Be3Al2Si6O18). The beryl family includes emerald, aquamarine, and morganite. Chrysoberyl includes cat's eye chrysoberyl and alexandrite. The shared element is beryllium, but the minerals are otherwise unrelated.
How rare is cat's eye chrysoberyl?
Fine cat's eye chrysoberyl is quite rare, especially in larger sizes with a sharp, well-centered eye and strong milk-and-honey effect. Sri Lanka is the primary source of the finest specimens. Cat's eye chrysoberyl above 5 carats with exceptional eye quality is extremely scarce and commands premium prices among collectors. While the term cat's eye can apply to many minerals that display chatoyancy, chrysoberyl cat's eye is the most valuable and most sought-after.
Can chrysoberyl be used in engagement rings?
Chrysoberyl is an excellent choice for engagement rings. At 8.5 on the Mohs scale, it is harder than any gemstone except sapphire, ruby, and diamond. It has no cleavage concerns, excellent toughness, and is resistant to chemicals. Transparent yellowish-green chrysoberyl makes a unique and durable ring stone, while cat's eye chrysoberyl offers a distinctive, eye-catching alternative to traditional faceted gems. Both varieties will withstand decades of daily wear.
What is the relationship between chrysoberyl and alexandrite?
Alexandrite is the color-change variety of chrysoberyl. They are the same mineral species (beryllium aluminate) but alexandrite contains trace amounts of chromium that cause its famous color-change property: green in daylight and red under incandescent light. Ordinary chrysoberyl does not contain chromium and does not change color. Cat's eye chrysoberyl is another variety that displays a sharp eye effect. All three are chrysoberyl with different optical phenomena.
Specialty & Collector Gemstones