Chemistry: SiO2

Crystallography: Hexagonal

Refractive index: 1.544 - 1.553

Hardness: 7

Specific gravity: 2.651

Cleavage: None

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.

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 a particularly rich purple color that glowed with reddish and/or bluish highlights. 

The term Siberian is no longer a place designated as the mines are long worked out, but instead, it is used 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 special 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 or blue flashes 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.