Chrysoberyl
Chrysoberyl is beryllium aluminum oxide, BeAl2O4, an orthorhombic mineral notable for exceptional hardness ranking just below corundum and diamond among natural gem minerals. Despite the beryl in its name, chrysoberyl is chemically unrelated to true beryl, which is a beryllium aluminum silicate rather than an oxide. Its most famous varieties, alexandrite and cat's eye chrysoberyl, are prized gemstones known respectively for dramatic color change and a sharp band of reflected light.
Chrysoberyl properties at a glance
| Type | Minerals |
|---|---|
| Chemical formula | BeAl2O4 |
| Mohs hardness | 8.5 |
| Crystal system | Orthorhombic |
| Luster | Vitreous |
| Streak | White |
| Cleavage | Distinct/good on {110}, poor on {010} |
| Fracture | Conchoidal |
| Specific gravity | 3.65–3.8 |
| Transparency | Transparent to translucent |
| Common colors | Yellow, Greenish-yellow, Green, Brown, Colorless, Color-change green/red (alexandrite) |
| Rarity | common |
Geology & background
Chrysoberyl crystallizes in granite pegmatites and mica schists where beryllium-rich fluids interact with aluminum-bearing rock during late-stage cooling, and it also occurs in placer gravels eroded from such source rocks. The alexandrite variety, which shifts from green in daylight to red under incandescent light, was first discovered in Russia's Ural Mountains in 1830 and later found in Sri Lanka, Brazil, and Tanzania. Ordinary yellow-green chrysoberyl and cat's eye material come chiefly from placer deposits in Sri Lanka and Brazil, historically among the most productive sources.
Collectors value chrysoberyl for both rarity and practical durability, since its hardness makes finished gems highly resistant to everyday scratching, a real advantage over softer colored stones. Fine alexandrite remains one of the most expensive colored gemstones per carat due to the scarcity of strongly color-changing material, while cat's eye chrysoberyl depends on parallel rutile inclusions to produce its sharp chatoyant band. Rough crystals are often twinned into distinctive pseudo-hexagonal trilling shapes, themselves collectible curiosities apart from any gem value.
How to identify Chrysoberyl
Chrysoberyl typically appears yellow, greenish-yellow, brown, or, in the alexandrite variety, green shifting to red under different lighting. It has a vitreous luster, a white streak, and a hardness of 8.5, letting it scratch quartz and topaz with ease, a quick field test that separates it from softer look-alikes. Cleavage is distinct in one direction but often not obvious in rounded river-worn pebbles, which instead show conchoidal fracture. Twinned crystals form pseudo-hexagonal trillings. It is commonly confused with yellow beryl or topaz, but its superior hardness sets it apart.
- Compare the specimen's color, luster, crystal habit, grain size, streak, and locality before confirming.
- Use multiple photos when possible, including a fresh surface and a close view of texture.
Where Chrysoberyl is found
Reported from multiple localities worldwide; verify locality against specimen provenance when available.
How much is Chrysoberyl worth?
| Entry-level specimen | $2 |
|---|---|
| Typical collector specimen | $20 |
| Premium specimen | $150+ |
Value depends on size, crystal quality, color, locality, rarity, damage, and provenance.
Common uses
- Collector specimens
- Education
- Field identification
- Industrial or lapidary use when suitable
Interesting facts
- Alexandrite, a variety of chrysoberyl, appears green in daylight and red under candlelight or incandescent bulbs, a shift first documented in Russia.
- Chrysoberyl ranks 8.5 on the Mohs scale, making it the third-hardest common gem mineral after diamond and corundum.
- Cat's eye chrysoberyl owes its sharp band of light to parallel fibrous inclusions of rutile aligned inside the crystal.
Care & safety
Handle as a collector specimen until hardness, cleavage, and fracture are verified.
Avoid inhaling dust. Do not cut, grind, or polish unknown specimens without eye protection and a proper respirator.
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