A Guide to Amethyst
History, Lore and Appreciation
Enthusiasts who appreciate quartz’s diverse family of gems often single out amethyst as the most significant variety of the quartz mineral. Amethyst has been used in personal adornment for millennia, often sought out by royalty or important members of the clergy.
In Medieval Europe particularity, the color purple was worn in rare dyed textiles that could only be afforded by the very wealthy. Amethyst’s bold purple color, and rare reddish flashes, coupled with the fact that only a few mines for it existed in ancient times, further contributed to its selection as a “royal” or “bishop’s gem”. Important amethysts feature prominently in British regalia. The name amethyst has a peculiar derivation. It comes from the Greek word amethystos, which translates to “not intoxicated.” A belief based in Classical mythology says that amethyst protected its wearer from inebriation (even following copious consumption of alcohol) consequently made the gem highly desirable by those so inclined.
Birthstones and Anniversaries
Amethyst is the birthstone for February. It is also considered to be a 6th wedding anniversary gem.
Description and Properties
Amethyst is a variety of quartz that crystallizes in the trigonal system and is composed of silica, with the chemical composition: SiO2.
Color(s): Transparent to translucent lilac to purple through bluish purple, with a reddish purple color-shift that is sometimes visible in incandescent light. Ametrine is an unusual form of quartz mined from southeastern Bolivia, principally at the Anahí mine. The colors are both yellow and purple in areas of crystal growth-related zoning. Such gems are sometimes cut or carved in a way that mixes the colors, and at other times to show the division of colors.
Refractive Index: 1.544 to 1.553
Specific Gravity: 2.66 (+0.03, -0.02)
Cause(s) of color: Iron-related color centers, natural irradiation of geological origin.
Mohs Hardness: 7
Internal identifying characteristics: Amethyst often contains areas of color next to areas that have no color, called color zoning. Amethyst, which has a hydrothermal geologic formation, often has liquid inclusions containing solids and gases, so-called two– and three-phase inclusions. Inclusions of other minerals such as rutile and hematite sometimes can be found in amethyst as well. Amethyst might show a bull’s eye effect viewed with crossed polarizing filters.
Amethyst is sometimes subject to heat treatment, which in a controlled environment may cause overly dark amethyst to be lightened. Heating amethyst from some sources may turn them yellow, known as citrine. Some amethyst can be heated to turn green, a color referred to in the trade as “oro verde.”
Collectors of amethyst look for depth of the purple color with red flashes if the gem is cut conventionally. Many famous lapidaries (cutters) work with amethyst to make unusual carvings or cuts, which are also highly prized. Because commercial quantities of ametrine come from only one region in the world, it is sometimes collected if the depth of color and the division of color is strong, or if it has been skillfully or cleverly carved.
The Ural Mountains in Russia is considered the “classic” source for amethyst because that it is a known historical source. “Uralian” amethyst, often called “Siberian” in the trade
(a curious trade name because there are no known deposits in Siberia) at their best, exhibit deep reddish purple, to purple red colors. Other important sources include Brazil and Uruguay, Bolivia, the United States (Arizona), Morocco, DR Congo, Rwanda, Myanmar and Zambia.
Cutting, Care and Cleaning
Amethyst – once considered rare – today has thankfully become one of the world’s most plentiful gems. It is available in many sizes, different cutting styles and carvings. Amethyst is fairly resilient and can be worn extensively. Care should be taken not to knock the gem during use, as small fissures or cracks may develop, especially along facet junctions. It can be cleaned with warm, sudsy water or a dampened cloth. Some amethyst may lighten in tone over time after prolonged exposure to bright light.
Source: CIBJO Retailer Reference Guide, cibjo.org. Image: American Gem Trade Association