The elusive colors of Alexandrite

It is a common misconception that alexandrite changes color from green to red. In fact, the best alexandrites are teal, vanadium green, greenish blue, or blue-green under natural daylight or fluorescent and change to purple-red or red under incandescent light. The more apparent the color change, and the more vivid the colors, the more valuable the gem.

Alexandrite is that variety of chrysoberyl that can exhibit a color change as a function of the light source. Chrysoberyl is an obscure mineral in itself but, when we consider the percentage of chrysoberyl that actually shows a color change, we begin to realize just how small the chance of finding alexandrite is at all.

Every alexandrite is unique and it is unusual to find two that display exactly the same colors under a variety of light conditions unless they’re cut from the same crystal. There are stones that will exhibit some shade of green in daylight and other stones that reflect a shade of red under incandescent light, but finding a stone that changes completely from green to red would be nearly impossible. But this isn’t really the point. More important is that the colors and brilliance are attractive in every kind of light. Some people like green, and some like blue while others prefer pink over purple. Moreover, many alexandrites are likely to change color throughout the day and with the weather.

"Alexandrite was discovered in 1840 and associated with the last of the Russian czars. Its adoption into Victorian and Edwardian styles from the contemporaneous period was simply a natural progression. This one of a kind David Wein style ring features a 2.05-carat alexandrite parallelogram set in an evocative Victorian setting. "

Color change is the most important factor determining the quality and value of an alexandrite but the light source is a critical factor. Alexandrite should not be expected to change color from indoors to outdoors as some guides may suggest. The color change is a response to specific qualities of light which are measured and quantified as color temperature or degrees Kelvin.

Natural outdoor light can range from between 2000 to 20,000K and artificial lights generally range from between 3300 to 6500K. Incandescent light or warm light is gauged in a range around 3300K and candlelight at 2000K and these are the kinds of light that will affect a reddish response. Going in and out of your house won’t affect the colors unless your home uses incandescent lighting and that kind of lighting is nowadays uncommon because it uses more energy.

The largest alexandrite crystal weighing 5724 grams was discovered in the Takovaya district of the Ural mountains in 1840. This deposit continued to be mined for over 60 years and produced both emeralds and alexandrites until the turn of the century.

It was the only source of alexandrite for nearly 100 years and the Russian stones set the original standard for this extremely rare and valuable gemstone.

Everything changed in 1987 when alexandrites were found in Brazil. While the best Russian stones were known to exhibit a strong and attractive color change, we can surmise from the few available photographs that they must not have been very clean. Although the Russian deposit was said to have produced some 2000 kg of rough material in its 60 year history, the Brazilian deposits in Hematita have produced much more.

Today, there is no commercial production of Russian alexandrites and almost all of the original Russian stones are in museums or private collections. Even in Russia, most of the alexandrites sold today are from deposits outside of the country. Occasionally a few low quality crystals or very small and included supposedly Russian stones do appear, but they are insignificant compared to alexandrite production from other sources. From a historical prospective, the Russian stones always attract the most interest, but they are hardly ever available and as a result largely irrelevant in the current market.

Aside from Russia, alexandrites have been unearthed in Sri Lanka, Brazil, Tanzania, Madagascar, Zimbabwe, and India. The only significant discoveries occurred in Tanzania, Brazil, and India, but only Brazil and Tanzania continue to yield small quantities of stones.

In Brazil the alexandrite is a part of the mother rock and an entire hillside has been excavated in the search for gem bearing veins. In Tanzania, the deposition is alluvial and the stones have been carried by ancient rivers from some other source rock that has never been found and may lie thousands of miles away on another continent. Some Indian stones are still available, but most of them have been sold and the mining has almost stopped due to a lack of new material as well as government restrictions.

"Brazilian alexandrites are known for their strong color change and daylight colors that often appear more blue than green. "

Technically, the Hematita mine in Minas Gerais, Brazil, is the main source for current production, but the production of large sizes is limited. Large Brazilian alexandrites are very expensive, even if they are dark. Brazilian alexandrites appear reddish purple-to-purple red under incandescent light while their daylight colors are often more blue than green. The incandescent colors of Brazilian stones usually possess a strongly purplish secondary hue and the best colors are considered to be purplish red or raspberry red.

Most African alexandrites come from the from Tunduru area, in Southern Tanzania. Unlike Brazilian alexandrites, which are somewhat uniform in color and size, their African cousins occur in broad range of colors and sizes. And while many of the stones appear to be khaki or yellowish green or brownish in daylight, some magnificent blue green or green blue stones with an excellent color change have also been observed.

"African alexandrites are available in a broad range of colors and qualities. The earthy tones of this stone are common among stones of Tanzanian origin."

The Andrapradesh deposit in India was a significant source for Alexandrite from 2000 to 2010. The stones were well known for their outstanding daylight bluish green colors along with their relatively good clarity.

Under incandescent light they appear plumb reddish purple. And, although Brazilian stones generally show a superior color change, many Indian stones are outstanding and the daylight colors are exceptional.

"Indian alexandrites are significant for transparency and vibrant blue-green daylight colors."

Every alexandrite deposit can and has produced exceptional stones from time to time, but they are extremely uncommon and rarely very large. Along with diamonds, rubies, and emeralds, fine alexandrites are among the most valuable gemstones in the world.

In larger sizes over 4.00 carats, Burmese rubies are more expensive, but in weight ranges below 1.00 carat, fine alexandrites are more valuable and top stones rival the prices of even the finest white diamonds in a similar size. Even melee sized alexandrites are rarely available and in consequence priced almost like diamonds. Stones weighing less than 0.50 carat can be worth several thousand dollars at retail prices and stones over one carat may retail for ten times more.

All photographs courtesy of Multicolour Gems at www.multicolour.com