Amethyst is the birthstone for February and the gem for the 6th and 17th wedding anniversaries. Amethyst has been the most prized purple variety of the quartz mineral species for centuries. The ancient Greeks thought it had magical and medicinal properties. Its characteristic purple results from color centers caused by natural irradiation acting on trace elements of iron in its crystal structure. Amethyst is sold in a variety of grades based mainly on color. So, dealers describing the four amethyst quality categories might vary.
1) 1st grade: A strongly saturated, medium-dark to dark reddish-purple or purple, with no visible face-up color zoning. This grade might be described as "AAA" or "super". Some dealers also use " African" or "Zambian" amethyst.
2) 2nd grade: A little less saturated,medium-dark color, some might show face-up color zoning or might be slightly included. Dealers often call "AA" or "A" grade.
3) 3rd grade: Considerably lighter in tone and saturation, a light lilac rather than an intense purple color. Dealers might call a"B" grade.
4) 4th grade: Hues are less saturated, a grayish to slightly grayish pale purple color, and not very attractive. Dealers often call " C" Grade.
Refractive Index: 1.544 to 1.553
Specific Gravity: 2.66
Hardness: 7 on the Mohs scale.
Sources: Brazil, Zambia, Uruguay, and Namibia.
Stability: Abrupt temperature changes can cause amethyst to fracture. Some amethyst colors can fade with prolonged exposure to intense light. Amethyst can also be damaged by hydrofluoric acid, ammonium fluoride, and alkaline solutions. Cleaning:Amethyst can be safely cleaned with warm soapy water. Ultrasonic cleaners are usually safe. Steam cleaning is not recommended.
Treatments: Heat treatment is the most common technique for improving the color and marketability of natural amethyst. Heating also removes undesirable brownish hues.