Alexandrite (the gem version of Beryllium) is one of the world’s most expensive gemstones. It’s prized because it has color changing-properties. In natural light it can look blue to blue-green, but under indoor light it looks red. Its hardness, 8.5 on the Mohs scale, makes it particularly appropriate for jewelry, and its relative rarity also creates high demand for the stone.
There’s a wonderful legend attached to how Alexandrite was discovered, and also how it came by its present name. As the myth goes, the gem was discovered in 1834 on the sixteenth birthday of the later Russian Czar, Alexander II. The gem was thus named after Alexander by its discoverer, Nils Gustoff Nordenskjold, a Finnish geologist.
This myth proves not to be true, and it appears Nordenskjold was sent some samples from another geologist. Nordenskjold thought he was looking at emeralds, but couldn’t understand how an emerald could have such a different hardness. Emeralds typically have a hardness of 7.5 to 8 on the Mohs scale. He then probably discovered the color changing properties of the stone, but did not name the stone alexandrite. Instead records show he called the stone diaphanite.
Count Lev Alekseevich Perovskii is credited with bringing the stone to the Russian royal family and possibly renaming it. This occurred well after Alexander II’s sixteenth birthday. Perhaps the Tsar had a right to demand the name change since the earliest supply of alexandrite was found in the Ural Mountains. Today, mines in India, Brazil, Zimbabwe, and Myanmar have found good deposits of alexandrite. Myanmar’s mines are particularly noted for the strong color-changing properties of their gems, though the stones mined there hardly ever exceed a carat in size.
Price on alexandrite is exceptionally high. One-half to a full carat alexandrite of top quality can cost as much as $15,000 US Dollars (USD). Quality is determined not only by lack of flaws but also the amount to which the stone changes color. Therefore you’ll probably find the best stones, especially in smaller sizes come from Myanmar. Stones exceeding the one-carat size have sold for as much as $100,000 USD. These gemstones rarely are larger than five carats, especially in unflawed form.
Most people are interested in the color-changing abilities of alexandrite, and especially want to know why it changes colors. The crystalline structure of the gem explains its special ability. The stone has what are called doubly refractive crystals, which create different light refraction under natural or artificial light conditions. This is called pleochroism. Light is refracted (bent) and follows through different pathways depending upon its type or polarization. Thus sunlight creates a different path through the stone than does indoor light and creates what is called a diochroic effect (two colors exhibited at different times).