Alexandrite is the traditional birthstone for the month of June.
Green chromian variety of chrysoberyl (intermediate member of Chrysoberyl-Mariinskite series) that exhibits a color change in natural and artificial light from green (in daylight) to amethystine (under tungsten light) (Alexandrite effect). Some rare pleochloric sapphires that appear blue in daylight and reddish or violet in artificial light are called alexandrine or alexandrite sapphires. The term "alexandrite effect" is used to describe the color change effect that specific varieties or minerals display.
Although crystals of chrysoberyl are not uncommon, the gemstone variety, alexandrite, is one of the rarest and most expensive gems. A beryllium aluminum oxide, chrysoberyl is hard and durable, inferior in hardness only to corundum and diamond. It generally occurs in granites or granitic pegmatites, although alexandrites are usually found in mica schists. The largest faceted chrysoberyl, from Russia, weighs 66 carats, while alexandrites weighing more than 10 carats are rare.
Originally reported from Emerald mines in 1830 (Izumrudnye Kopi; Malyshevskoye deposit), Malyshevo, Ekaterinburg (Yekaterinburg; Sverdlovsk), Sverdlovskaya Oblast', Urals Region, Russia. Those first alexandrites were of very fine quality and displayed vivid hues and dramatic color change. The gem was named in 1842 by Nils Adolf Erik Nordenskiöld after the young Alexander II, because it was discovered on the future czar’s birthday. It caught the country’s attention because its red and green colors mirrored the national military colors of imperial Russia.
The spectacular Ural Mountain deposits didn’t last forever, and now most alexandrite comes from Sri Lanka, East Africa, and Brazil. The newer deposits contain some fine-quality stones, but many display less-precise color change and muddier hues than the nineteenth-century Russian alexandrites. You’ll still find estate jewelry set with some of the famed Ural Mountain alexandrites. They remain the quality standard for this phenomenal gemstone. Synthetic alexandrite has been made for a number of years. Chromium is the color-producing trace element in alexandrite, replacing some of the aluminum in its structure.