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.
Properties
| Refractive index | 1.746 to 1.755 |
|---|---|
| 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 | Strong: green, orange, purple-red |
| Absorption spectrum | Chromium line in the red, 680 nm (Cr3+); broad band in the yellow that gives the color change (GIA G&G gives about 589 nm), 580 nm (Cr3+) |
Published values. They change a little from stone to stone. Our tools do not model alexandrite yet. Sources: GIA · International Gem Society
In more detail
It was found in Russia's Ural Mountains in the 1830s and named for the future Czar Alexander II. Today most alexandrite comes from Sri Lanka, East Africa and Brazil. It has excellent toughness and no cleavage, and it is usually not treated. GIA runs infrared spectroscopy on every alexandrite to tell natural from synthetic material.
On a grading report
LMHC wording: Color: [color] in daylight, [color] in incandescent light. Species: (natural) chrysoberyl. Variety: alexandrite.
Related terms
- Chrysoberyl: Chrysoberyl is a gem mineral of beryllium, aluminum and oxygen. Its best-known varieties are alexandrite and cat's-eye chrysoberyl.
- Color change: Color change is a visible change of a gem's main hue between daylight and incandescent light.
- Synthetic gemstone: A synthetic gemstone is made in a laboratory and has essentially the same chemistry and properties as the natural gem. A synthetic ruby is ruby, made by people.
- Toughness: Toughness is a gem's resistance to chipping and breaking. It differs from hardness, which is resistance to scratching.
- 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.