How common is an amethyst



amethyst
A mineral grade with grown amethysts
Chemism SiO2+ (Al, Fe, Ca, Mg, Li, Na)
Mineral grade Oxides; Metal to oxygen = 1: 2
see quartz (after Strunz)
see quartz (after Dana)
Crystal system trigonal
Crystal class trigonal-trapezoidal
colour violet, partly blotchy-cloudy, also zonal color distribution (colorless-violet)
Line color White
Mohs hardness 7
Density (g / cm³) 2.65 g / cm3
shine Glass to greasy gloss
transparency transparent to translucent
fracture shell-like
Cleavage no
Habitus short to long, prismatic, pseudo-hexagonal crystals
Frequent crystal faces
Twinning
Crystal optics
Refractive index nO = 1,5442
ne = 1,5533
Birefringence
(optical orientation)
Δ = 0.0091; uniaxial positive
Pleochroism very faint, violet and gray-violet, rarely also distinctly violet and lighter cobalt blue (with a violet tinge)
Angle / dispersion
of the optical axes
2vz ~ 0-10° (0,013)
Other properties
Phase transitions
Melting point
Chemical behavior is etched by hydrofluoric acid (HF)
Similar minerals other quartz varieties, ametrine
radioactivity not radioactive
magnetism not magnetic
Special marks weak, greenish fluorescence

amethyst is a purple variety of the mineral quartz (SiO2).

Etymology and history

The origin of the name from the Greek αμεθυστoς (amethystos) - "counteracting the intoxication" - expresses the old belief that amethyst wearers are immune to the intoxicating effects of wine. Likewise, wine made from an amethyst goblet shouldn't make you drunk. Originally this (but) belief arose from the custom of diluting (red) wine with water, which then took on a reddish-purple (amethyst-colored) color. At the same time, of course, you could drink a lot more of it without getting drunk or even having to suffer a hangover.

Another variant of the naming is that Bacchus, the god of wine, poured wine into a nymph called amethyst that was transformed into a crystal, whereupon it turned purple.

The amethyst was also said to have an apotropaic effect against theft. This fact is proven by prehistoric grave finds. Merovingian tombs with amethyst show, if at all, traces of robbery not in the area where the stones were laid (necklace), even if gold pendants were also to be found here. It is possible that in this epoch of early history there was a further (and today no longer reconstructable) alleged (negative) effect of the amethyst on the thief.

colour

The purple color of the amethyst ranges from a very light, slightly pink to a very dark purple.

The distribution of color in the crystal is mostly irregular. Sectors of the crystal that are parallel to the main thrombohedron {10-11} are usually more intensely colored. There the purple color is concentrated in thin dark purple bands parallel to the {10-11} and, more rarely, the {01-11} areas.

In these sectors, amethysts have an irregular, fine-lamellar twinning according to Brazilian law and the intensely colored planes mark these twin planes.

Lattice defects, with one Fe, give the color4+-Ion in tetrahedral coordination, i.e. surrounded by four oxygen ions, so-called [FeO4] Centers. It is still controversial whether these defects occur on the silicon position (Fe4+ replaces Si4+) or on interstitial spaces (Fe4+ in a normally empty tetrahedral gap in one of the 6-sided channels of the quartz structure).

These defects arise from defects with Fe3+ in a tetrahedral gap by exposure to radioactive radiation. This removes an electron from the Fe ion and thus oxidizes Fe3+ to Fe4+. The radiation dose required to produce the amethyst color is z. B. in granitic rocks solely through the decay of naturally occurring 40K isotopes created in 6,000,000 years.

Amethysts can also be removed by artificial X-rays. B. be produced in nuclear reactors from colorless Fe-containing quartz.

Amethysts lose their color quite quickly under the influence of sunlight. The stones should therefore not be exposed to direct UV radiation.

Amethysts also lose their color when heated. They mostly develop a citrine color, caused by submicroscopic iron oxide mixtures, and more rarely a green prasiolite color or become completely colorless.

Education and Locations

Amethyst is a common mineral; large and clear specimens that are suitable for cutting and further processing as gemstones are limited to comparatively few sites. It occurs in Brazil, Uruguay, Madagascar, Russia and Sri Lanka. Such crystals are found mainly in cavities in hydrothermal veins and in volcanic rocks. So-called amethyst druses, in which the crystals have formed within a cavity, surrounded by a layer of chalcedony, are also frequently found in the trade. The most beautiful Druze usually come from Brazil and can be as tall as a man.

A well-known German site is the Steinkaulenberg in Idar-Oberstein. The unique and well-known blue-violet color is given there by the metals in the mountain range. After huge deposits were found in Brazil and these crystals can also be colored, mining in the Steinkaulenberg was stopped. Mineral mining is now prohibited there. The color of the amethysts from Idar-Oberstein can only be achieved with Brazilian crystals by appropriate dyeing.

Europe's largest amethyst deposit is located near the Lower Austrian city of Maissau. The site of the Amethyst from Maissau, discovered around 150 years ago, is located around 60 km northwest of Vienna, 1 km after the village of Maissau on Horner Strasse in the direction of Horn. The occurrence in Maissau has a secured course of approx. 400 m, of which approx. 40 m is accessible in the open-air gallery, shows a maximum width of 2 m and is almost vertical (dip between 80 and 90 ° after SSW or NNE). The first targeted excavations took place in 1986 under the supervision of the Krahuletz Museum Eggenburg. In 1999 the Maissau Amethyst Society (MAG) began to systematically excavate the corridor. This impressive disclosure of an amethyst corridor is unique in the world. In addition, a continuation of the corridor for a distance of 1 km can be assumed.

Another rich occurrence of amethyst has been known since the 19th century in the area around the Eggenburg cemetery. Johann Krahuletz was able to make valuable finds here.

Use as a gem stone

Gem-quality amethyst is a popular and widespread gemstone that is cut into various faceted shapes (brilliant, navette, briolette) or cabochon for trade.

Dark purple stones are considered particularly valuable. In addition, the varieties ametrine (combination of amethyst and citrine in one stone) or the opaque variety amethyst quartz with violet and white bands are valued as gemstones.

Manipulations and imitations

By Burn Amethyst (approx. 400 ° C) produces the yellow to golden color of the citrine variety. Many of the misleadingly sold "gold or Madeira opase" in the gemstone trade are actually burnt amethysts. In the case of some amethysts, the firing also produces a greenish hue similar to the prasiolite, as which the fired amethyst is then also sold. Sometimes the color disappears completely in the flame and white quartz remains.

Fired stones usually get significantly more cracks and cracks, which are noticeable due to their sheen. Often the crystal tips and surfaces burst as well. As a rule, only low quality amethysts are burned in order to "enhance" them. A widespread misconception is that burned gemstones, which are then referred to as citrines, do not have to be declared as burned. However, this is also a fake, since essential properties are changed by human intervention. Real citrine is usually only lightly colored and always has a long, rock-crystal-like shape. Citrine does not form drusen and is also a lot rarer than amethyst.

A cheap, if not very durable, method of enhancing the color of amethyst is to treat it with colored wax, as amethyst, unlike agate, can only be colored superficially.

Be since the 19th and 20th centuries Syntheses different gemstones, including amethyst, which can only be distinguished from natural amethysts by deviations in structure and purity.

For fashion jewelry, the amethyst is used through purple glass imitates or offered in composite form as a duplicate.

→ see also main article Gemstone - manipulations and imitations

Esoteric

In esotericism, the amethyst is used as a healing stone against drunkenness and addictions. In addition, it is said to have cleansing, inspiring and insightful properties. Hildegard von Bingen used amethyst as a healing stone for various diseases such as skin blemishes, swellings, insect and spider bites and against lice. There is no scientific evidence for such an effect.

As a zodiac stone, the amethyst is assigned to the zodiac sign Pisces, according to other sources to the zodiac sign Sagittarius or Capricorn and as a planetary stone to the planet Neptune or Pluto.

Amethyst druses are often used for energetic cleansing and charging of other healing stones.

See also

literature

  • Walter Schumann: Precious and semi-precious stones. 13th edition. BLV Verlags GmbH, 1976/1989, ISBN 3-405-16332-3
  • Bernhard brother: Finished stones, Neue Erde Verlag (1998), ISBN 3-89060-025-5
  • Rossman, G.R .: Colored Varieties of the Silica Minerals in: Heaney, Prewitt & Gibbs (Editors) 1994: Silica, Reviews in Mineralogy Vol. 29, ISBN 0-939950-35-9

Categories: Gemstone | Variety (mineralogy) | Rhombohedral crystal system