A violet-to-purple form of quartz. It is prized as a precious stone.
Amethyst (SiO2) is a violet or purple variety of quartz often used as an ornament. the ancient Greeks and Romans wore amethyst and made drinking vessels of it in the belief that it would prevent intoxication.
Chemistry
In the 20th century, the color of amethyst was attributed to the presence of manganese.
On exposure to heat, amethyst generally becomes yellow, and much of the citrine, cairngorm, or yellow quartz of jewelry is said to be merely "burnt amethyst".
Composition
Amethyst is composed of an irregular superposition of alternate lamellae of right-handed and left-handed quartz. As a consequence of this composite formation, amethyst is apt to break with a rippled fracture, or to show "thumb markings", and the intersection of two sets of curved ripples may produce on the fractured surface a pattern something like that of "engine turning". Some mineralogists, following Sir David Brewster, apply the name of amethyst to all quartz which exhibits this structure, regardless of color.
Because it has a hardness of 7 on the Mohs scale, amethyst is treasured for its use in jewelry.
History
Amethyst was used as a gemstone by the ancient Egyptians and was largely employed in antiquity for intaglios. Beads of amethyst are found in Anglo-Saxon graves in England. Many of the hollow agates of Brazil and Uruguay contain a crop of amethyst crystals in the interior. Much fine amethyst comes from Russia, especially from near Mursinka in the Ekaterinburg district, where it occurs in drusy cavities in granitic rocks. Many localities in India yield amethyst;
Alternate terminology
Due to its popularity as a gemstone, several descriptive terms have been coined in the gem trade to describe the varying colors of amethyst. In more recent times, certain gems (usually of Bolivian origin) that have shown alternate bands of amethyst purple with citrine orange have been given the name ametrine.
Purple corundum, or sapphire of amethystine tint, is called Oriental amethyst, but this expression is often applied by jewellers to fine examples of the ordinary amethystine quartz, even when not derived from eastern sources. Professional gemological associations, such as the Gemological Institute of America (GIA) or the American Gemological Society (AGS), discourage the use of the term "Oriental amethyst" to describe any gem, as it may be misleading.
Geographic distribution
Amethyst occurs at many localities in the United States, but these specimens are rarely fine enough for use in jewelry. Among these may be mentioned Amethyst Mountain, Texas; Amethyst is relatively common in northwestern Ontario, but uncommon elsewhere in Canada;
Value
Traditionally included in the cardinal, or most valuable, gemstones (along with diamond, sapphire, ruby and emerald), amethyst has lost much of its value due to the discovery of extensive deposits in locations such as Brazil.
Amethyst in folklore and astrology
Amethyst is the birthstone associated with February. Ranking members of the Roman Catholic Church traditionally wear rings set with a large amethyst as part of their office. Amethyst was considered to be a strong antidote against drunkenness, which is why wine goblets were often carved from it.
Or: "The legend of the origin of amethyst comes from Greek myths. Along came unsuspecting Amethyst, a beautiful young maiden on her way to pay tribute to the goddess Diana. Diana turned Amethyst into a stature of pure crystalline quartz to protect her from the brutal claws.
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