Alexandrite is a rare variety of the mineral chrysoberyl, known for its pleochroism or changing color. Often described as “emerald by day, ruby by night,” alexandrite will exhibit an emerald like green to bluish-green that shifts to red or purplish-red depending on whether the gem is viewed in artificial or natural light.
Originally named after the Russian tsar Alexander II, alexandrite was first discovered in the Ural mountains in 1834. Though the original supply of alexandrite has long since been exhausted, there are some modern sources in Sri Lanka, Brazil, and some deposits in Africa, but fine quality alexandrite remains rare and highly prized.
Alexandrite is evaluated like most gemstones, using the classic 4 Cs that are used to judge diamonds: color, clarity, cut, and carat. Like most colored gemstones, the quality of the color of alexandrite is the most important factor when determining its value. Because alexandrite displays two distinct colors, identifying and evaluating the gemstone is accordingly complex.
How Alexandrite Color Affects Value
Not all varieties of chrysoberyl that change color are considered alexandrite—color change chrysoberyl and alexandrite are actually two different varieties of chrysoberyl. In order to be considered alexandrite, the gemstone must display a color shift that is not only dramatic and obvious, but it has to change to and from specific colors.
When viewed in daylight and moved to incandescent light, alexandrite will change color in the following manner: from blue-green to orange-red, from slightly blue-green to red, from green to slightly purple-red, from slightly green to purple-red, or from yellow-green to red-purple.
Stones that change color in combinations other than those listed above can be quite dramatic looking and may sell for high prices, but will not be identified as alexandrite when sent to a gemological laboratory. Good examples of color change chrysoberyl might sell for $2,500-$4,500 per carat for 1-2 carat stones, but true alexandrite in that size might sell for $6,000 per carat. Highly saturated alexandrite with a dramatic color change might fetch as much as $60,000 per carat.
The most prized alexandrite is red to purplish-red in artificial light, and green to bluish-green in daylight. The intensity of the primary hue, also known as color saturation, ranges from strong to moderately strong in the most valuable alexandrites. Stones with lower color intensities and those that are lacking in brightness do not match the quality of the finest alexandrite, and are accordingly lower in price.
Russian alexandrite remains in extremely short supply, but it exhibits the finest intensity of color, and is the standard against which most alexandrite is judged. Alexandrite mining in Sri Lanka has produced some larger gemstones, but they tend to be of less desirable colors.
When compared to Russian stones, the reds of Sri Lankan alexandrite tend to be more brownish-red than the finer purplish-red, and the greens tend to be yellowish rather than the blue-green of their Russian counterparts. Alexandrite from Brazil sometimes rivals the color of Russian gems, but it is also in extremely short supply and quite highly prized.
Evaluating Alexandrite Clarity
Due to its crystal structure and the geologic mechanisms that produce it, alexandrite tends to have few inclusions, or visible imperfections. Any presence of visible inclusions will dramatically lower the value of the stone. Clean examples with good color change and strong colors will always be the most valuable.
Occasionally, certain types of inclusions are oriented parallel to each other in alexandrite, and lead to a visual phenomenon known as chatoyancy, or a cat’s eye effect. When these thin, needle-like inclusions are present, the value of the stone can rise dramatically.
How Alexandrite Cut Affects Value
Cutting alexandrite presents a special challenge to the stone cutter. Because of its pleochroism, the cut of alexandrite is crucial to its overall look. To take full advantage of the color-change nature of the rough stone, alexandrite must be cut to show the strongest color change through the crown. The gem cutter needs to orient the rough stone in a way that highlights both colors when viewed in its face-up position.
Alexandrite is usually fashioned with step-cut pavilions and brilliant-cut crowns, in what are known as “mixed cuts.” The brilliant cut crowns feature triangular, kite-shaped facets, and the pavilions are normally cut with parallel facets in concentric rows.
Alexandrite Carat Weight
As with most all precious stones, larger alexandrites are more valuable than small ones. While most alexandrites are relatively small, weighing less than one carat, larger sizes are sometimes available, and command accordingly high prices.
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