A Guide to Buying Alexandrite

Alexandrite is a variety of chrysoberyl that changes color from green to red depending upon the light source. It was originally discovered in Russia, and was named after the former Russian czar Alexander II, by mineralogist Nordenskjold. Some think that the stones red and green colors coinciding with the Russian imperial colors may have influenced the decision to name it such. Since its discovery it has also been found in Brazil, Burma, India, Madagascar, Sri Lanka, Tanzania and Zimbabwe.

The determining factor of whether a chrysoberyl is considered to be alexandrite is based upon its distinct color change. Although it is pleochroic, its color change is not the result of it as with most color change gems. Instead it is because the stone transmits nearly equal amounts of the blue-green and red portions of the light spectrum, while absorbing mostly yellow. Since incandescent light is more towards the red end of the spectrum it will appear reddish. Daylight is more equal through the spectrum, and our eyes are more sensitive to green light so the stone will appear green. The severity of color change in the stone is based upon the difference in the areas of transmission relative to absorption of yellow, more difference results in more color change.

The quality of color change is the largest factor in determining the value of alexandrite. An ideal stone (which hasn’t been found yet) would change from a rich emerald green to a velvety ruby red, but typically in fine specimens it is more from a slightly bluish green to a purplish red. The amount of color change is typically measured by dealers in percentage, 100% would be the ideal and anything less than 30% might not be considered alexandrite. As well, brown or gray in the stone will drastically lower its value.

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