Alexandrite is a birthstone for June, along with pearl and moonstone. Alexandrite is also the gem for the 55th wedding anniversary.
Alexandrite, with its chameleon-like qualities, is a rare variety of the mineral chrysoberyl. Its dramatic color change is sometimes described as “emerald by day, ruby by night.” Other gems also change color in response to a light-source change, but this gem’s transformation is so striking that the phenomenon itself is often called “the alexandrite effect.”
Alexandrite is also a strongly pleochroic gem, which means it can show different colors when viewed from different directions. Typically, its three pleochroic colors are green, orange, and purple-red. However, the striking color change doesn’t arise from the gem’s pleochroism, but rather from the mineral’s unusual light-absorbing properties.
Because of its scarcity, especially in larger sizes, alexandrite is a relatively expensive member of the chrysoberyl family. It shares its status as a June birthstone with cultured pearl and moonstone. The gem was named after the young Alexander II, heir apparent to the throne. It caught the country’s attention because its red and green colors mirrored the national military colors of imperial Russia.
Change is the most important quality factor for alexandrite.
The most-prized alexandrites show a strong color change from bluish green in daylight and red to purplish red in incandescent light, with moderately strong to strong color saturation.
Alexandrites tend to contain few inclusions. There’s a dramatic rise in value for clean material with good color change and strong hues. Rarely parallel needle-like inclusions create a cat’s-eye phenomenon, increasing the alexandrite’s value.
Alexandrites are most often fashioned as mixed cuts, which have brilliant-cut crowns and step-cut pavilions. When cutting alexandrite, cutters orient the gem to show the strongest color change through the crown.
Most fashioned alexandrites are small, weighing less than one carat. Larger sizes and better qualities rise in price dramatically: Fine-quality stones in sizes above 5.0 carats are very expensive.
TIPS & ADVICE
- If it seems too good to be true, it probably is. Natural alexandrite is rare and valuable. An inexpensive gem with a strong red-green color change is likely to be a synthetic or simulant.
- Judging the quality of alexandrite requires expertise. Look for gemological credentials. A jeweler who knows and loves alexandrite will welcome the challenge to find one that’s right for you.
- When in doubt, get a lab report. For a significant purchase an independent laboratory report can confirm that the alexandrite you are buying is natural.
- Don’t expect to be able to match alexandrites easily.
Creating pairs or suites of alexandrite for earrings, a three stone ring, or a necklace is very challenging. Matching size, shape, color, and color change is particularly difficult.
- MINERAL: Chrysoberyl
- CHEMISTRY: BeAl2O4
- COLOR: Bluish green in daylight, purplish red in incandescent light
- REFRACTIVE INDEX: 746 to 1.755
- BIREFRINGENCE:008 to 0.010
- SPECIFIC GRAVITY:73
- MOHS HARDNESS:5
(Gem Encyclopedia Alexandrite)