REFRACTIVE INDEX 1.544 – 1.553
HARDNESS 7 SPECIFIC GRAVITY 2.651
HEAT SENSITIVE No
WEARABILITY* Very Good
SPECIAL CARE INSTRUCTIONS None
ENHANCEMENTS Amethyst can be heat treated to improve the color or change it to citrine. Not common.
*Wearability is graded as Excellent, Very Good, Good, Poor, and Forget It! For more details see the article on “Hardness and Wearability.”
Crystalline quartz in colors ranging from pale lilac to deep reddish purple and ranging from transparent to translucent is known as amethyst. Siberian mines once produced the world’s finest stones with particularly rich purple color that glowed with reddish and/or bluish highlights. Today the term Siberian no longer is a place designation as the mines are long since worked out, but instead is used a a “grade” term, implying colors similar to the original stones from Siberia.
Today’s major sources are Brazil, Bolivia and Uruguay in South America and Zambia in Africa. Brazilian stones can be found in huge sizes, but generally are moderate in color. They often suffer from color-banding, which sometimes is visible despite efforts of the cutter to minimize it.
Many amethyst lovers prefer the usually smaller, but more richly colored stones coming from Zambia and, more recently, from Uruguay.
Very light amethyst which once was considered low grade, has gained a recent boost in popularity by intensive marketing on TV shopping programs and the clever marketing strategy of calling it “Rose de France”. To my mind these light stones have their greatest appeal when given fancy and unusual cuts, where the artistry of cutting is more on display than the material itself.
At hardness 7 and with no particular warnings on care necessary, amethyst makes a fine jewelry gem for all purposes. Lower grades of material are cabbed, carved, and made into a great variety of beads and other ornamental objects.
Value per carat in amethyst, unlike many gems, doesn’t rise exponentially with weight as it is readily available in large sizes; but depends almost entirely on color. The “Siberian” deep purple with red and blue flash commands the highest prices. As the stone is plentiful, there is little reason to pay top dollar for stones with visible inclusions or inferior cutting.
Sinkankas gives a wholesale price range for medium sized, medium to deep purple stones, as $8-25/carat for commercial cuts. Federman insists that African stones should bring about 25% more per carat than Brazilian ones.
Text and photos courtesy of Barbara Smigel at Artistic Colored Stones.