Alexandrite
The chameleon gem — green in daylight, red under incandescent light.
Alexandrite is the color-change variety of chrysoberyl, famous for its remarkable ability to shift from bluish-green in daylight to purplish-red under incandescent light. First discovered in Russia's Ural Mountains in 1830, it was named after Czar Alexander II. Fine alexandrite with strong, clean color change is among the rarest and most expensive gemstones in the world — often exceeding ruby and emerald in per-carat price. The phenomenon is caused by chromium impurities that absorb specific wavelengths differently depending on the light source.
Physical Properties
| Hardness (Mohs) | 8.5 |
| Refractive Index | 1.746–1.755 |
| Specific Gravity | 3.73 |
| Crystal System | Orthorhombic |
| Chemical Formula | BeAl₂O₄ (with Cr) |
Color Varieties
Major Sources
Brazil · Sri Lanka · East Africa · Russia (historical, mostly depleted) · India
Pricing Factors
Color Change Strength
The more dramatic and complete the color change, the higher the value. A stone that shifts 100% from green to red is exponentially more valuable than one showing partial change.
Color Quality
The best stones show vivid bluish-green in daylight and vivid purplish-red in incandescent light, without brownish or grayish modifiers.
Size
Fine alexandrites over 1 carat are rare. Stones over 3 carats with strong color change are museum-quality pieces.
Origin
Russian alexandrites carry the highest premiums due to historical significance and superior color change, though fine Brazilian material is also highly valued.
Care Instructions
Do
- Clean with warm soapy water and a soft brush
- Safe for ultrasonic cleaning in most cases
- Store separately to avoid scratching softer stones
Don't
- Don't expose to extreme heat
- Avoid harsh chemicals
- Don't buy without viewing under both daylight and incandescent light
Cleaning Method
Warm soapy water is the safest method. Ultrasonic is generally safe for untreated alexandrite.
Insider Buying Tips
Always view alexandrite under both daylight-equivalent and incandescent lighting before purchasing.
Be extremely cautious of 'alexandrite' sold at low prices — most is actually synthetic or color-change sapphire.
Lab-grown alexandrite exists and is significantly cheaper — demand a lab report for natural origin.
Expect to pay more per carat than ruby or sapphire for fine natural alexandrite with strong color change.
Brazilian alexandrite offers the best availability of fine material — Russian stones are essentially all vintage.
Did You Know?
Alexandrite was discovered on the same day Czar Alexander II came of age, and its red/green colors matched Russia's military colors.
Fine alexandrite was described as 'emerald by day, ruby by night.'
A 65.7-carat alexandrite in the Smithsonian is the largest faceted example on public display.
Related Resources
Related Gemstones
Garnet
A family of gems spanning every color — not just the deep reds.
Sapphire
Corundum in every color except red — the most versatile precious stone.
Spinel
The great imposter — historically mistaken for ruby and sapphire, now prized in its own right.
Tourmaline
The rainbow gem — no other mineral occurs in as many colors.