Amethyst has been the most-prized quartz variety for centuries. Once available only to royalty, relatively plentiful supplies have made amethyst more widely available in modern times. Today, because of its availability and affordability, amethyst is used in mass-market jewelry as well as custom designer pieces. This makes amethyst one of the world’s most popular colored gems and the most commercially important gem-quality quartz variety.
The finest amethyst color is a strong reddish purple or purple with no visible color zoning. Dealers prefer strongly saturated reddish purple to dark purple, as long as the stone is not so dark that it reduces brightness. If the color is too dark, an amethyst might look black under dim lighting conditions.
Any brownish or bronze-colored tints in an amethyst’s purple color, or any noticeable color zoning, lower its value dramatically. Buyers of loose amethysts view color zoning by placing the gems table-down against a white background.
Many amethysts display a weak, light color or have strong zones of lighter and darker purple color. These factors lower the value of these stones.
Heat treatment can lighten the color of very dark amethyst. Lower-quality light-colored amethyst and even light-colored quartz have been dyed to impart a purple color.
Much of the faceted amethyst in the market is eye-clean, meaning it lacks eye-visible inclusions. African material, especially from Zambia, can be a highly saturated raspberry color. It tends to have more inclusions than Brazilian material. However, due to its remarkable color, this is considered acceptable in a faceted stone. Eye-clean material of the same color is more valuable.