AMETHYST: Amethyst is the most highly valued stone in the quartz group. The name means “not drunken” (Greek), as amethyst was worn as an amulet against drunkenness. Crystals are always grown onto a base. Prisms are usually not well developed, therefore are often found as crystal points (pointy amethyst) with the deepest color. These parts are broken off at the base for further treatment.
Heat treatment between 878-1382 degrees F (470-750 degrees C) produces light yellow, red-brown, green, or colorless varieties. There are some amethysts that lose some color in daylight. The original color can be restored by X-ray radiation. The coloring agent is iron. In artificial light, amethyst does not display as desirable qualities.
Found in geodes in alluvial deposits. The most important deposits are in Brazil (“Palmeira” amethyst of Rio Grande do Sul, “Maraba” amethyst of Para), Madagascar, Zambia, Uruguay, as well as in Burma ( Myanmar), India, Canada, Mexico, Namibia, Russia, Sri Lanka, and the United States ( Arizona). The best stones are faceted; others are tumbled or worked into ornaments. Formerly amethyst was a favorite gemstone of high officials of the Christian church. Can be confused with precious beryl, fluorite, kunzite, spinel, topaz, tourmaline, an tinted glass. Synthetic amethyst is abundant on gemstone market.
CITRINE: The name is derived from its lemon yellow color. The coloring agent is iron. Natural citrines are rare. Most commercial citrines are heat-treated amethysts or smoky quartzes. Brazilian amethyst turns light yellow at 878 degrees F (470 degrees C) and dark yellow to red-brown at 1022-1040 degrees F (550-560 degrees C). some smoky quartzes turn into citrine color already at about 390 degrees F (200 degrees C).
Almost all heat-treated citrines have a reddish tint. The natural citrines are mostly pale yellow. Names for citrine such as Bahia, Madeira, or Rio Grande topaz are improper and no longer accepted in the trade as they are deceptive. On the other hand, when one, for example, speaks of Madeira color and/or Madeira citrine, this is a correct usage; the expert properly connects a certain color with the locality name.
Deposits of natural-colored citrines are found in Brazil, Madagascar, and the United States, as well as in Argentina, Burma (Myanmar), Namibia, Russia, Scotland, and Spain. Well-colored citrines are used as ring stones and pendants; less attractive stones are made into necklaces or ornaments.
Can be confused with many yellow gemstones, especially apatite, golden beryl, orthoclase, topaz, and tourmaline, as well as tinted glass.