Alexandrite is an unusual gemstone featuring distinct and fascinating phenomena which set the standard for all color change gems. It is a rare variety of the mineral chrysoberyl that changes color under different lighting conditions. This extraordinary gem can change from a vivid green or bluish-green to an intense red to purplish-red hue or a greenish-blue to purple. Most alexandrite gems are under one carat; stones of larger sizes are rare and command some of highest prices of all colored gemstones.
This beautiful gem was discovered by chance in the 1830s. Finnish miners were mining emeralds near the Tokovaya River in the Ural Mountains of Russia and collected what they thought were vivid green emeralds, but upon returning to the campsite at the end of the day they were astonished to see their “emeralds” were now a bright red hue. When morning came and the gems had returned to their bright green color, they knew they had found something very special. The gems were named alexandrite after Alexander II (1818-1881), the heir to the Russian throne.
Alexandrite’s colors of red and green mirrored the military colors of Tsarist Russia and thus were highly sought after among the Russian aristocracy. Appreciation for this rare gem quickly spread beyond Europe. In 1891, George Kunz, Tiffany’s master gemologist, travelled to Russia on a buying trip. Among the gems procured was a large stockpile of alexandrite. No one knows the exact quantity he acquired, but Tiffany and Co. had reserves large enough for them to corner the market on alexandrite for decades to come. Supplies of alexandrite in the Ural Mountains were soon depleted and for many decades there were no more discoveries of this gem until a new source was found in Minas Gerais, Brazil in the 1980s. While many of these stones show moderate color change, only a small number rival the spectacular gems from Russia.
Alexandrite has three trace elements in its crystal structure producing this color change phenomenon: vanadium, iron and, most importantly, chromium. When two different light sources (incandescent and daylight) carrying different spectrum emissions illuminate the gem, it absorbs different color wavelengths and emits a different color. Interestingly, the spectrum is similar to that of emerald and ruby. An alexandrite’s value is based primarily on the intensity of the color change as well as the hues it exhibits; stronger color changes and purer hues lead to higher values. Alexandrite often has some inclusions and for very clean stones the value rises exponentially. These gems are often cut in mixed cuts with the crown having a brilliant-cut and the pavilion a step-cut. Gem cutters have a challenging job as they must orient the stone to maximize the color change in the face up position in addition to retaining as much weight as possible.
