Jewellery Blog, Gemstone Information

June 5, 2009

Gemstone Knowledge – Amethyst

Filed under: Uncategorized — pangsheng @ 9:38 am

Amethyst

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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
Refractive index nω = 1.543–1.553 nε = 1.552–1.554
Optical Properties Uniaxial (+) (Positive)
Birefringence +0.009 (B-G interval)
Pleochroism None
Streak White
Specific gravity 2.65 constant; variable in impure varieties
Melting point 1650±75 °C
Solubility H2O insoluble
Diaphaneity Transparent to translucent
Other Characteristics Piezoelectric

Amethyst is a violet variety of quartz often used as an ornamental stone 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.

Birthstone

Amethyst is the birthstone associated with February. It is also associated with the astrological signs of Pisces, Aries (especially the violet and purple variety), Aquarius, and Sagittarius. Its the official zodiac stone of pisces. People born in February on the 19th or later have amethyst as both their birth and zodiac stone. It is a symbol of heavenly understanding, and of the pioneer in thought and action on the philosophical, religious, spiritual, and material planes. Ranking members of the Roman Catholic Church traditionally wear rings set with a large amethyst as part of their office.

Lore

The Greek word “amethystos” (αμέθυστος) 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. Another variation involves the goddess Rhea presenting Dionysus with the amethyst stone to preserve the wine-drinker’s sanity.

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.

Amethyst occurs at many localities in the United States, but these specimens are rarely fine enough for use in jewellery. 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.

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. 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”.

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 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 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/or 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.

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.

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

Alternate terminology

Several descriptive terms have been coined in the gem trade to describe the colors of amethyst. “Rose de France” is usually a pale pinkish lavender or lilac shade (usually the least-sought color). The most prized color is an intense violet with red flashes and is called “Siberian”, although gems of this color may occur from several locations other than Siberia, notably Uruguay and Zambia. 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 jewelers 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.

The Second Book of Pseudo-Albertus Magnus, Of the Vertues of Certaine Stones, refers to amethysts by the name Amarictus.

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).

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1 Comment »

  1. […] Gemstone Knowledge – Amethyst […]

    Pingback by Baby name meaning and origin for Delaware — June 12, 2009 @ 6:40 am | Reply


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