Amethyst is a violet variety of quartz. The name comes from the Koine Greek αμέθυστος amethystos from α- a-, "not" and μεθύσκω (Ancient Greek) methysko / μεθώ metho (Modern Greek), "intoxicate", a reference to the belief that the stone protected its owner from  drunkenness. Ancient Greeks wore amethyst and carved drinking vessels from it in the belief that it would prevent intoxication. Amethyst, a semiprecious stone, is often used in jewelry and is the traditional birthstone for February. Structure
Amethyst is a purple variety of quartz (SiO2) and owes its violet color to irradiation, impurities of iron and in some cases other transition metals, and the presence of other trace elements, which result in complex crystal lattice substitutions. The hardness of the mineral is the same as quartz, thus making it suitable for use in jewelry. Hue and tone
Amethyst occurs in primary hues from a light lavender or pale violet, to a deep purple. Amethyst may exhibit one or both secondary hues, red and blue. High quality amethyst can be found in Siberia, Sri Lanka, Brazil, Uruguay, and the Far East. The ideal grade is called "Deep Siberian" and has a primary purple hue of around 75–80%, with 15–20% blue and (depending on the light source) red secondary hues. ‘Rose de France’ is defined by its markedly light shade of the purple, reminiscent of a lavender/lilac shade.
In ancient China, it was also used as a powerful tool to remove negative energies and drive away the hazards of daily life. Synthetic amethyst
Synthetic (laboratory-grown) amethyst is produced by a synthesis method called hydrothermal growth, which grows the crystals inside a high-pressure autoclave. Synthetic amethyst is made to imitate the best quality amethyst. Its chemical and physical properties are the same as that of natural amethyst and it can not be differentiated with absolute certainty without advanced gemmological testing (which is often cost-prohibitive). One test based on "Brazil law twinning" (a form of quartz twinning where right and left hand quartz structures are combined in a single crystal) can be used to identify most synthetic amethyst rather easily. Synthesizing twinned amethyst is possible, but this type is not available in large quantities in the market.Treated amethyst is produced by gamma ray, X-ray, or electron-beam irradiation of clear quartz (rock crystal), which has been first doped with ferric impurities. Exposure to heat partially cancels the irradiation effects and amethyst generally becomes yellow or even green. Much of the citrine, cairngorm, or yellow quartz of jewelry is said to be merely "burnt amethyst". Cultural history
Ancient Greece
The Greek word "amethystos" may be translated as "not drunken", from Greek a-, "not" + methustos, "intoxicated". Amethyst was considered to be a strong antidote against drunkenness, which is why wine goblets were often carved from it.