Chrysoberyl is a gem mineral of beryllium, aluminum and oxygen. Its best-known varieties are alexandrite and cat's-eye chrysoberyl.
Properties
| Refractive index | 1.746 to 1.755 (GIA, mineral chrysoberyl); spot readings about 1.74 to 1.75 |
|---|---|
| Birefringence | 0.008 to 0.010 |
| Optic character | Doubly refractive (biaxial) |
| Dispersion | 0.015 |
| Specific gravity | 3.73 |
| Hardness (Mohs) | 8.5 |
| Crystal system | Orthorhombic |
| Pleochroism | Distinct: yellow, brown, green |
| Absorption spectrum | Strong band in the blue-violet, diagnostic in yellow to green stones, 444 nm (Fe) |
Published values. They change a little from stone to stone. Our tools do not model chrysoberyl yet. Sources: International Gem Society · GIA
In more detail
Chrysoberyl is often yellow, yellowish green or brown. Studies link its yellow and brown colors to small amounts of iron. The chromium-bearing variety that changes color is alexandrite. Aligned needle-like inclusions reflect light as a band, best seen in a cabochon. GIA calls cat's-eye chrysoberyl the most valuable and sought-after chatoyant gem.
Related terms
- Alexandrite: Alexandrite is the chromium-bearing, color-change variety of chrysoberyl. It is green in daylight and changes to purplish or brownish red in incandescent light.
- Chatoyancy: Chatoyancy is a single band of light that glides across a gem, like the slit eye of a cat. Light reflects from many aligned, needle-like inclusions.
- Cabochon: A cabochon is a gem polished to a smooth, convex dome, with no facets. It is one of the oldest and simplest cuts.
- Color change: Color change is a visible change of a gem's main hue between daylight and incandescent light.
- Needle: A needle is a thin, elongated crystal inclusion that looks like a tiny rod at 10x.