amethyst

Amethyst
General
Category	Mineral variety
Chemical formula	Silica (silicon dioxide, SiO2)
Identification
Color	Violet
Crystal habit	6-sided prism ending in 6-sided pyramid (typical)
Crystal system	rhombohedral class 32
Twinning	Dauphine law, Brazil law, and Japan law
Cleavage	None
Fracture	Conchoidal
Mohs Scale hardness	7–lower in impure varieties
Luster	Vitreous/glossy
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	2.65 constant; variable in impure varieties
Optical properties	Uniaxial (+) (Positive)
Refractive index	nω = 1.543–1.553 nε = 1.552–1.554
Birefringence	+0.009 (B-G interval)
Pleochroism	None
Melting point	1650±75 °C
Solubility	H2O insoluble
Other characteristics	Piezoelectric

Amethyst is a violet variety of quartz often used in jewelry. The name comes from the Ancient Greek a- ("not") and methustos ("intoxicated"), a reference to the belief that the stone protected its owner from drunkenness; the ancient Greeks and Romans wore amethyst and made drinking vessels of it in the belief that it would prevent intoxication.

Chemistry

Amethyst is the violet variety of quartz; its chemical formula is SiO₂.

In the 20th century, the color of amethyst was attributed to the presence of manganese. However, since it is capable of being greatly altered and even discharged by heat, the color was believed by some authorities to be from an organic source. Ferric thiocyanate was suggested, and sulfur was said to have been detected in the mineral.

More recent work has shown that amethysts' coloration is due to ferric iron impurities.^[1] Further study has shown a complex interplay of iron and aluminium is responsible for the color.^[2]

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". Veins of amethystine quartz are apt to lose their color on the exposed outcrop^{[citation needed]}.

Synthetic amethyst is made to imitate the best quality amethyst. Its chemical and physical properties are so similar to that of natural amethyst that it can not be differentiated with absolute certainty without advanced gemological testing (which is often cost-prohibitive). There is 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^[3]) which can be used to identify synthetic amethyst rather easily. In theory however it is possible to create this material synthetically as well, but this type is not available in large quantities in the market.^[4]

Composition

Amethyst is composed of an irregular superposition of alternate lamellae of right-handed and left-handed quartz. It has been shown that this structure may be due to mechanical stresses.

Because it has a hardness of seven on the Mohs scale, amethyst is suitable for use in jewelery.

Hue and tone

Amethyst occurs in primary hues from a light pinkish violet to a deep purple. Amethyst may exhibit one or both secondary hues, red and blue. The ideal grade is called "Deep Siberian" and has a primary purple hue of around 75–80 percent, 15–20 percent blue and (depending on the light source) red secondary hues.^[4]

The inside of an Amethyst Geode.

Cut Amethyst

Cut Green Amethyst

History

Amethyst was used as a gemstone by the ancient Egyptians and was largely employed in antiquity for intaglios. The Greeks believed amethyst gems could prevent intoxication, while medieval European soldiers wore amethyst amulets as protection in battle.^{[citation needed]} Beads of amethyst were found in Anglo-Saxon graves in England.^{[citation needed]}

A huge geode, or "amethyst-grotto", from near Santa Cruz in southern Brazil was exhibited at the Düsseldorf, Germany Exhibition of 1902.

Mythology

The Greek word "amethystos" may be translated as "not drunken". Amethyst was considered to be a strong antidote against drunkenness, which is why wine goblets were often carved from it. In Greek mythology, Dionysus, the god of intoxication, was pursuing a maiden named Amethystos, who refused his affections. Amethystos prayed to the gods to remain chaste, which the goddess Artemis granted and transformed her into a white stone. Humbled by Amethystos's desire to remain chaste, Dionysus 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 is 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.^[5] Another variation involves the goddess Rhea presenting Dionysus with the amethyst stone to preserve the wine-drinker's sanity.^[6]

Geographic distribution

Amethyst is produced in abundance from the state of Minas Gerais in Brazil where it occurs in large geodes within volcanic rocks. It is also found and mined in South Korea. The largest opencast amethyst vein in the world is in Maissau, Lower Austria. 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. One of the largest global amethyst producers is Zambia with an annual production of about 1,000 t.

Museum-quality piece of Amethyst

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; Yellowstone National Park; Delaware County, Pennsylvania; Haywood County, North Carolina; Deer Hill and Stow, Maine. It is found also in the Lake Superior region. Amethyst is relatively common in Ontario, and in various locations throughout Nova Scotia, 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. The highest grade amethyst (called "Deep Russian") is exceptionally rare and therefore its value is dependent on the demand of collectors when one is found. It is however still orders of magnitude lower than the highest grade sapphires or rubies (Padparadscha sapphire or "pigeon's blood" ruby).^[4]

See also

• List of minerals

Notes

References

• "Amethyst". part of a poster by the Juneau – John Rishel Mineral Information Center. Alaska office of the United States Bureau of Land Management. http://www.blm.gov/ak/jrmic/poster/amethyst.html. Retrieved on 2006-09-11. 
• Ure, Andrew (1827). A Dictionary of Chemistry. Printed for Thomas Tegg, (et al.). p. 141. http://books.google.com/books?vid=OCLC22415868&id=9YS0XNQU8x4C&pg=PA141&lpg=PA141&dq=Amethyst&as_brr=1. Retrieved on 2006-09-11. "The amethyst is a gem of a violet colour, and great brilliancy, said to be as hard as the ruby or sapphire, from which it only differs in colour. This is called the oriental amethyst, and is very rare. When it inclines to the purple or rosy colour, it is more esteemed than when it is nearer to the blue. These amethysts have the same figure, hardness, specific gravity, and other qualities, as the best sapphires or rubies, and come from the same places, particularly from Persia, Arabia, Armenia and the West Indies. The occidental amethysts are merely coloured crystal or quartz." 

External links

Wikimedia Commons has media related to: Amethyst

• http://mineral.galleries.com/minerals/gemstone/amethyst/amethyst.htm
• http://mindat.org/min-198.html
• http://gemstone.org/gem-by-gem/english/amethyst.html

This article incorporates text from the Encyclopædia Britannica, Eleventh Edition, a publication now in the public domain.