| Formula |
|Silica (silicon dioxide, Si O 2)|
|Crystal class||Trapezohedral (32)|
|Space group||P3221 (no. 154)|
|Color||Purple, violet, dark purple|
|Crystal habit||6-sided prism ending in 6-sided pyramid (typical)|
|Twinning||Dauphine law, Brazil law, and Japan law|
|Mohs scale hardness||7–lower in impure varieties|
|Diaphaneity||Transparent to translucent|
|Specific gravity||2.65 constant; variable in impure varieties|
|Optical properties||Uniaxial (+)|
|Refractive index||nω = 1.543–1.553 |
nε = 1.552–1.554
|Birefringence||+0.009 (B-G interval)|
|Pleochroism||Weak to moderate purple/reddish purple|
|Melting point||1650±75 °C|
|Solubility||Insoluble in common solvents|
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.
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.
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, called "Deep Siberian", 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. These pale colors were once considered undesirable, but have recently become popular due to intensive marketing. 
Green quartz is sometimes incorrectly called green amethyst; this is a misnomer and not an appropriate name for the material, as the proper terminology is prasiolite.  Other names for green quartz are vermarine or lime citrine.
Amethyst frequently shows color zoning, with the most intense color typically found at the crystal terminations. It is the most prized variety of quartz.  One of a gem cutter’s tasks is to make a finished product with even color. Sometimes, only a thin layer of a natural, uncut amethyst is violet colored, or the color is very uneven. The uncut gem may have only a small portion that is suitable for faceting.  
The color of amethyst has been demonstrated to result from substitution by irradiation of trivalent iron (Fe3+) for silicon in the structure,   in the presence of trace elements of large ionic radius,  and to a certain extent, the amethyst color can naturally result from displacement of transition elements even if the iron concentration is low. Natural amethyst is dichroic in reddish violet and bluish violet,  but when heated, turns yellow-orange, yellow-brown, or dark brownish and may resemble citrine,  but loses its dichroism, unlike genuine citrine. When partially heated, amethyst can result in ametrine.
Amethyst can fade in tone if overexposed to light sources, and can be artificially darkened with adequate irradiation.  It does not fluoresce under either short-wave or long-wave UV light.
Amethyst is found in many locations around the world. Between 2000 and 2010, the greatest production was from Marabá and Pau d'Arco, Pará, and the Paraná Basin, Rio Grande do Sul, Brazil; Sandoval, Santa Cruz, Bolivia; Artigas, Uruguay; Kalomo, Zambia; and Thunder Bay, Ontario. Lesser amounts are found in many other locations in Africa, Brazil, Spain, Argentina, Russia, Afghanistan, South Korea, Mexico, and the United States. 
Amethyst is produced in abundance in the state of Rio Grande do Sul in Brazil where it occurs in large geodes within volcanic rocks.     Many of the hollow agates of southwestern Brazil and Uruguay contain a crop of amethyst crystals in the interior. Artigas, Uruguay and neighboring Brazilian state Rio Grande do Sul are large world producers, with lesser quantities mined in Minas Gerais and Bahia states. 
The largest amethyst geode found to date was the Empress of Uruguay, found in Artigas, Uruguay in 2007. It stands at a height of 3.27 meters, lays open along its length, and weighs 2.5 tons.
Amethyst is also found and mined in South Korea.  The large opencast amethyst vein at Maissau, Lower Austria, was historically important,  but is no longer included among significant producers.  Much fine amethyst comes from Russia, especially near Mursinka in the Ekaterinburg district, where it occurs in drusy cavities in granitic rocks.   Amethyst was historically mined in many localities in south India,  though these are no longer significant producers.  One of the largest global amethyst producers is Zambia in southern Africa, with an annual production around 1000 tons. 
Amethyst occurs at many localities in the United States. The most important production is at Four Peaks, Gila and Maricopa Counties, Arizona, and Jackson's Crossroads, Wilkes County, Georgia. 
Smaller occurrences have been reported in the Red Feather Lakes, near Fort Collins, Colorado; Amethyst Mountain, Texas; Yellowstone National Park; Delaware County, Pennsylvania; Haywood County, North Carolina; Deer Hill and Stow, Maine, and in the Lake Superior region of Minnesota, Wisconsin, and Michigan. 
Amethyst is relatively common in the Canadian provinces of Ontario and Nova Scotia. The largest amethyst mine in North America is located in Thunder Bay, Ontario. 
Amethyst is the official state gemstone of South Carolina. Several South Carolina amethysts are on display at the Smithsonian Museum of Natural History. 
Amethyst was used as a gemstone by the ancient Egyptians and was largely employed in antiquity for intaglio engraved gems. 
The ancient Greeks believed amethyst gems could prevent intoxication,  while medieval European soldiers wore amethyst amulets as protection in battle in the belief that amethysts heal people and keep them cool-headed.  Beads of amethyst were found in Anglo-Saxon graves in England.  Anglican bishops wear an episcopal ring often set with an amethyst, an allusion to the description of the Apostles as "not drunk" at Pentecost in Acts 2:15. 
A large geode, or "amethyst-grotto", from near Santa Cruz in southern Brazil was presented at a 1902 exhibition in Düsseldorf, Germany. 
The meaning of amethyst varies from time to time and culture, which is why amethyst has different meanings in Feng Shui and focuses on increasing wealth. In ancient China, it was also used as a powerful tool to remove negative energies and drive away the hazards of daily life.[ self-published source? ]
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 those of natural amethyst, and it cannot 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".  
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.  In his poem "L'Amethyste, ou les Amours de Bacchus et d'Amethyste" (Amethyst or the loves of Bacchus and Amethyste), the French poet Rémy Belleau (1528–1577) invented a myth in which Bacchus, the god of intoxication, of wine, and grapes was pursuing a maiden named Amethyste, who refused his affections. Amethyste prayed to the gods to remain chaste, a prayer which the chaste goddess Diana answered, transforming her into a white stone. Humbled by Amethyste's desire to remain chaste, Bacchus poured wine over the stone as an offering, dyeing the crystals purple.  
Variations of the story include that Dionysus had been insulted by a mortal and swore to slay the next mortal who crossed his path, creating fierce tigers to carry out his wrath. The mortal turned out to be a beautiful young woman, Amethystos, who was on her way to pay tribute to Artemis. Her life was spared by Artemis, who transformed the maiden into a statue of pure crystalline quartz to protect her from the brutal claws. Dionysus wept tears of wine in remorse for his action at the sight of the beautiful statue. The god's tears then stained the quartz purple. 
This myth and its variations are not found in classical sources. However, the goddess Rhea does present Dionysus with an amethyst stone to preserve the wine-drinker's sanity in historical text. 
Tibetans consider amethyst sacred to the Buddha and make prayer beads from it.  Amethyst is considered the birthstone of February.  In the Middle Ages, it was considered a symbol of royalty and used to decorate English regalia.  In the Old World, amethyst was considered one of the cardinal gems, in that it was one of the five gemstones considered precious above all others, until large deposits were found in Brazil. 
Until the 18th century, amethyst was included in the cardinal, or most valuable, gemstones (along with diamond, sapphire, ruby, and emerald), but since the discovery of extensive deposits in locations such as Brazil, it has lost most of its value.  It is now considered a semiprecious stone. 
Collectors look for depth of color, possibly with red flashes if cut conventionally.  As amethyst is readily available in large structures, the value of the gem is not primarily defined by carat weight. This is different from most gemstones, since the carat weight typically exponentially increases the value of the stone. The biggest factor in the value of amethyst is the color displayed. 
The highest-grade amethyst (called "Deep Russian") is exceptionally rare. When one is found, its value is dependent on the demand of collectors. The highest-grade sapphires or rubies are still orders of magnitude more expensive than amethyst. 
The most suitable setting for gem amethyst is a prong or a bezel setting. The channel method must be used with caution. 
Amethyst has a good hardness, and handling it with proper care will prevent any damage to the stone. Amethyst is sensitive to strong heat and may lose or change its colour when exposed to prolonged heat or light. Polishing the stone or cleaning it by ultrasonic or steamer must be done with caution. 
Agate is the banded variety of chalcedony, with a wide variety of colors. Agates are primarily formed within volcanic and metamorphic rocks. The ornamental use of agate was common in Ancient Greece, in assorted jewelry and in the seal stones of Greek warriors, while bead necklaces with pierced and polished agate date back to the 3rd millennium BCE in the Indus Valley civilisation.
Beryl ( BERR-əl) is a mineral composed of beryllium aluminium silicate with the chemical formula Be3Al2Si6O18. Well-known varieties of beryl include emerald and aquamarine. Naturally occurring, hexagonal crystals of beryl can be up to several meters in size, but terminated crystals are relatively rare. Pure beryl is colorless, but it is frequently tinted by impurities; possible colors are green, blue, yellow, pink, and red (the rarest). It is an ore source of beryllium.
Emerald is a gemstone and a variety of the mineral beryl (Be3Al2(SiO3)6) colored green by trace amounts of chromium or sometimes vanadium. Beryl has a hardness of 7.5–8 on the Mohs scale. Most emeralds have lots of material trapped inside during the gem's formation, so their toughness (resistance to breakage) is classified as generally poor. Emerald is a cyclosilicate.
A gemstone is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks and occasionally organic materials that are not minerals are also used for jewelry and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their luster or other physical properties that have aesthetic value. Rarity and notoriety are other characteristics that lend value to gemstones.
Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO2. Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar.
Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide (α-Al2O3) with trace amounts of elements such as iron, titanium, chromium, vanadium, or magnesium. The name sapphire is derived via the Latin "sapphirus" from the Greek "sappheiros", which referred to lapis lazuli. It is typically blue, but natural "fancy" sapphires also occur in yellow, purple, orange, and green colors; "parti sapphires" show two or more colors. Red corundum stones also occur, but are called rubies rather than sapphires. Pink-colored corundum may be classified either as ruby or sapphire depending on locale. Commonly, natural sapphires are cut and polished into gemstones and worn in jewelry. They also may be created synthetically in laboratories for industrial or decorative purposes in large crystal boules. Because of the remarkable hardness of sapphires – 9 on the Mohs scale (the third hardest mineral, after diamond at 10 and moissanite at 9.5) – sapphires are also used in some non-ornamental applications, such as infrared optical components, high-durability windows, wristwatch crystals and movement bearings, and very thin electronic wafers, which are used as the insulating substrates of special-purpose solid-state electronics such as integrated circuits and GaN-based blue LEDs. Sapphire is the birthstone for September and the gem of the 45th anniversary. A sapphire jubilee occurs after 65 years.
Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al2SiO4(F,OH)2. It is used as a gemstone in jewelry and other adornments. Common topaz in its natural state is colorless, though trace element impurities can make it pale blue or golden brown to yellow orange. Topaz is often treated with heat or radiation to make it a deep blue, reddish-orange, pale green, pink, or purple.
Tourmaline is a crystalline silicate mineral group in which boron is compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. This gemstone comes in a wide variety of colors.
Garnets are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives.
A ruby is a pinkish red to blood-red colored gemstone, a variety of the mineral corundum. Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called sapphires. Ruby is one of the traditional cardinal gems, alongside amethyst, sapphire, emerald, and diamond. The word ruby comes from ruber, Latin for red. The color of a ruby is due to the element chromium.
Opal is a hydrated amorphous form of silica (SiO2·nH2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Due to its amorphous property, it is classified as a mineraloid, unlike crystalline forms of silica, which are considered minerals. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl, and basalt.
Pleochroism is an optical phenomenon in which a substance has different colors when observed at different angles, especially with polarized light.
Benitoite is a rare blue barium titanium cyclosilicate, found in hydrothermally altered serpentinite. It forms in low temperature, high pressure environments typical of subduction zones at convergent plate boundaries. Benitoite fluoresces under short wave ultraviolet light, appearing bright blue to bluish white in color. The more rarely seen clear to white benitoite crystals fluoresce red under long-wave UV light.
Cordierite (mineralogy) or iolite (gemology) is a magnesium iron aluminium cyclosilicate. Iron is almost always present and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: (Mg,Fe)2Al3(Si5AlO18) to (Fe,Mg)2Al3(Si5AlO18). A high-temperature polymorph exists, indialite, which is isostructural with beryl and has a random distribution of Al in the (Si,Al)6O18 rings.
Demantoid is the green gemstone variety of the mineral andradite, a member of the garnet group of Minerals. Andradite is a calcium- and iron-rich garnet. The chemical formula is Ca3Fe2(SiO4)3 with chromium substitution as the cause of the demantoid green color. Ferric iron is the cause of the yellow in the stone.
Spessartine is a nesosilicate, manganese aluminium garnet species, Mn2+3Al2(SiO4)3. This mineral is sometimes mistakenly referred to as spessartite.
Sunstone is a microcline or oligoclase feldspar, which when viewed from certain directions exhibits a spangled appearance. It has been found in Southern Norway, Sweden, various United States localities and on some beaches along the midcoast of South Australia.
Ametrine, also known as trystine or by its trade name as bolivianite, is a naturally occurring variety of quartz. It is a mixture of amethyst and citrine with zones of purple and yellow or orange. Almost all commercially available ametrine is mined in Bolivia.
Prasiolite is a green variety of quartz.
Gemstone irradiation is a process in which a gemstone is artificially irradiated in order to enhance its optical properties. High levels of ionizing radiation can change the atomic structure of the gemstone's crystal lattice, which in turn alters the optical properties within it. As a result, the gemstone's color may be significantly altered or the visibility of its inclusions may be lessened.
Kostov, R. I. 1992. Amethyst. A Geological-Mineralogical and Gemmological Essay. Union of Scientists in Bulgaria, Sofia, 249 p. (in Bulgarian with English abstract)
Lieber, W. 1994. Amethyst. Geschichte, Eigenschaften, Fundorte. Christian Weise Verlag, München, 188 S.