Green in sunlight. Red in lamplight. Color-changing alexandrite is nature’s magic trick.Often described by gem aficionados as “emerald by day, ruby by night,” alexandrite is the very rare color-change variety of the mineral chrysoberyl. Originally discovered in Russia’s Ural Mountains in the 1830s, it’s now found in Sri Lanka, East Africa, and Brazil, but fine material is exceptionally rare and valuable.
Alexandrite, with its chameleon-like qualities, is a rare variety of the mineral chrysoberyl. Its color can be a lovely green in daylight or fluorescent light, changing to brownish or purplish red in the incandescent light from a lamp or candle flame. This is a result of the complex way the mineral absorbs light.Alexandrite’s 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.
COLOR: Bluish green in daylight, purplish red in incandescent light
REFRACTIVE INDEX: 1.746 to 1.755
BIREFRINGENCE: 0.008 to 0.010
SPECIFIC GRAVITY: 3.73
MOHS HARDNESS: 8.5
WHY WE LOVE THIS GEMSTONE
Making alexandrite change color from green to red is the world’s most fun use of a penlight.
This gem provides dramatic proof of how much the light source affects color in gems.
Alexandrite can show both color change and a cat’s-eye: two phenomena in one gem.