Amethyst(kecubung)


Amethyst

Amethyst

Amethyst cluster from Magaliesburg, South Africa. A Wikipedia:Featured picture
General
Category Mineral variety
Chemical formula Silica (silicon dioxide, SiO2)
Identification
Color Purple, 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 (+)
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 insoluble in common solvents
Other characteristics Piezoelectric

Amethyst is a violet variety of quartz often used in jewelry. The name comes from the Ancient Greek a- (“not”) and μέθυστος 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 19th 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 amethyst’s coloration is due to ferric iron impurities.[1] Further study has shown a complex interplay of iron and aluminium is responsible for the color.

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.

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.

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 jewelry.

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%, 15–20% blue and (depending on the light source) red secondary hues.[4] Green quartz is sometimes called green amethyst. Other names for green quartz are prasiolite, vermarine or lime citrine.

Faceted amethyst

The inside of an amethyst geode

Faceted green amethyst

History

Roman intaglio engraved gem of Caracalla in amethyst, once in the Treasury of Sainte-Chapelle.

Amethyst was used as a gemstone by the ancient Egyptians and was largely employed in antiquity for intaglio engraved gems.[5]

The Greeks believed amethyst gems could prevent intoxication,[6] while medieval European soldiers wore amethyst amulets as protection in battle. The reason for this being that amethysts are believed to heal people and keep them cool-headed. Beads of amethyst were found in Anglo-Saxon graves in England.

A large geode, or “amethyst-grotto”, from near Santa Cruz in southern Brazil was presented at the 1902 exhibition in Düsseldorf, Germany.

Amethyst is the traditional birthstone for February.

Mythology

The Greek word “amethystos” may be translated as “not drunken”, from Greek a-, not + methustos, intoxicated.[7] 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,and wine, 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.[8] Another variation involves the titan Rhea presenting Dionysus with the amethyst stone to preserve the wine-drinker’s sanity.[9]

Geographic distribution

An amethyst cluster from Artigas, Uruguay. Size: 15.9×15.6×10.6 cm.

Amethyst is produced in abundance from the state of Minas Gerais 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 exceeding in quantity Minas Gerais, as well as Mato Grosso, Espirito Santo, Bahia, and Ceará states, all amethyst producers of importance in Brazil.

It is also found and mined in South Korea. The largest opencast amethyst vein in the world is in Maissau, Lower Austria. 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 south India yield amethyst. One of the largest global amethyst producers is Zambia in southern Africa with an annual production of about 1000 tonnes.

Amethyst occurs at many localities in the United States. Among these may be mentioned: the Mazatzal Mountain region in Gila and Maricopa Counties, Arizona; 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, Michigan, and Ontario in Canada. Amethyst is relatively common in Ontario, and in various locations throughout Nova Scotia. The largest amethyst mine in North America is located in Thunder Bay, Ontario.[10]

Value

Up to 18th century amethyst was included in the cardinal, or most valuable, gemstones (along with diamond, sapphire, ruby, and emerald). However since the discovery of extensive deposits in locations such as Brazil it has lost most of its value.

Collectors look for depth of color, possibly with red flashes if cut conventionally. 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).

Comments
3 Responses to “Amethyst(kecubung)”
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