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.
REFRACTIVE INDEX 1.544 - 1.553
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."