Turquoise

Turquoise is an opaque, blue-to-green mineral that is a hydrated phosphate of copper and aluminium, with the chemical formula Cu Al6(PO4)4(OH)8·4H2O. It is rare and valuable in finer grades and has been prized as a gemstone and ornamental stone for thousands of years owing to its unique hue. In recent times, turquoise has been devalued, like most other opaque gems, by the introduction onto the market of treatments, imitations and synthetics.

The gemstone has been known by many names. Pliny the Elder referred to the mineral as callais (from Ancient Greek κάλαϊς) and the Aztecs knew it as chalchihuitl.[4] The word turquoise dates to the 17th century and is derived from the French turquois for "Turkish" because the mineral was first brought to Europe through Turkey, from mines in the historical Khorasan Province of Persia.[2][3][4][5]

Turquoise
Turquoise-40031
General
CategoryPhosphate minerals
Formula
(repeating unit)
CuAl6(PO4)4(OH)8·4H2O
Strunz classification8.DD.15
Crystal systemTriclinic
Crystal classPinacoidal (1)
(same H–M symbol)
Identification
ColourTurquoise, blue, blue-green, green
Crystal habitMassive, nodular
CleavageGood to perfect_usually N/A
FractureConchoidal
Mohs scale hardness5–6
LusterWaxy to subvitreous
StreakBluish white
Specific gravity2.6–2.9
Optical propertiesBiaxial (+)
Refractive indexnα = 1.610
nβ = 1.615
nγ = 1.650
Birefringence+0.040
PleochroismWeak
FusibilityFusible in heated HCl
SolubilitySoluble in HCl
References[1][2][3]

Properties

The finest of turquoise reaches a maximum Mohs hardness of just under 6, or slightly more than window glass.[2] Characteristically a cryptocrystalline mineral, turquoise almost never forms single crystals, and all of its properties are highly variable. X-ray diffraction testing shows its crystal system to be triclinic.[3][6] With lower hardness comes lower specific gravity (2.60–2.90)[3] and greater porosity; these properties are dependent on grain size. The lustre of turquoise is typically waxy to subvitreous, and its transparency is usually opaque, but may be semitranslucent in thin sections. Colour is as variable as the mineral's other properties, ranging from white to a powder blue to a sky blue, and from a blue-green to a yellowish green. The blue is attributed to idiochromatic copper while the green may be the result of either iron impurities (replacing aluminium) or dehydration.

The refractive index of turquoise (as measured by sodium light, 589.3 nm) is approximately 1.61 or 1.62; this is a mean value seen as a single reading on a gemological refractometer, owing to the almost invariably polycrystalline nature of turquoise. A reading of 1.61–1.65 (birefringence 0.040, biaxial positive) has been taken from rare single crystals. An absorption spectrum may also be obtained with a hand-held spectroscope, revealing a line at 432 nm and a weak band at 460 nm (this is best seen with strong reflected light). Under longwave ultraviolet light, turquoise may occasionally fluoresce green, yellow or bright blue; it is inert under shortwave ultraviolet and X-rays.

Turquoise is insoluble in all but heated hydrochloric acid. Its streak is a pale bluish white and its fracture is conchoidal,[3] leaving a waxy lustre. Despite its low hardness relative to other gems, turquoise takes a good polish. Turquoise may also be peppered with flecks of pyrite or interspersed with dark, spidery limonite veining.

Formation

Big turquoise from Cananea
"Big Blue", a large turquoise specimen from the copper mine at Cananea, Sonora, Mexico

As a secondary mineral, turquoise forms by the action of percolating acidic aqueous solutions during the weathering and oxidation of pre-existing minerals. For example, the copper may come from primary copper sulfides such as chalcopyrite or from the secondary carbonates malachite or azurite; the aluminium may derive from feldspar; and the phosphorus from apatite. Climate factors appear to play an important role as turquoise is typically found in arid regions, filling or encrusting cavities and fractures in typically highly altered volcanic rocks, often with associated limonite and other iron oxides. In the Southwestern United States turquoise is almost invariably associated with the weathering products of copper sulfide deposits in or around potassium-feldspar-bearing porphyritic intrusives. In some occurrences alunite, potassium aluminium sulfate, is a prominent secondary mineral. Typically turquoise mineralization is restricted to a relatively shallow depth of less than 20 metres (66 feet), although it does occur along deeper fracture zones where secondary solutions have greater penetration or the depth to the water table is greater.

Turquoise is nearly always cryptocrystalline and massive and assumes no definite external shape. Crystals, even at the microscopic scale, are exceedingly rare. Typically the form is vein or fracture filling, nodular, or botryoidal in habit. Stalactite forms have been reported. Turquoise may also pseudomorphously replace feldspar, apatite, other minerals, or even fossils. Odontolite is fossil bone or ivory that has been traditionally thought to have been altered by turquoise or similar phosphate minerals such as the iron phosphate vivianite. Intergrowth with other secondary copper minerals such as chrysocolla is also common.

Occurrence

Turquoise with quartz
Massive Kingman blue turquoise in matrix with quartz from the Mineral Park mine, Arizona, US

Turquoise was among the first gems to be mined, and many historic sites have been depleted, though some are still worked to this day. These are all small-scale operations, often seasonal owing to the limited scope and remoteness of the deposits. Most are worked by hand with little or no mechanization. However, turquoise is often recovered as a byproduct of large-scale copper mining operations, especially in the United States.

Cutting and grinding turquoise in Meshed, Iran. 1973
Cutting and grinding turquoise in Nishapur, Iran, 1973

Iran

Iran has been an important source of turquoise for at least 2,000 years. It was initially named by Iranians "pērōzah" meaning "victory", and later the Arabs called it "fayrūzah", which is pronounced in Modern Persian as "fīrūzeh". In Iranian architecture, the blue turquoise was used to cover the domes of palaces because its intense blue colour was also a symbol of heaven on earth.

Persian Turquoise
Persian turquoise from Iran

This deposit is blue naturally and turns green when heated due to dehydration. It is restricted to a mine-riddled region in Nishapur, the 2,012 m (6,601 ft) mountain peak of Ali-mersai near Mashhad, the capital of Khorasan Province, Iran. A weathered and broken trachyte is host to the turquoise, which is found both in situ between layers of limonite and sandstone and amongst the scree at the mountain's base. These workings are the oldest known, together with those of the Sinai Peninsula.[5] Iran also has turquoise mines in Semnan and Kerman provinces.

Sinai

Since at least the First Dynasty (3000 BCE) in ancient Egypt, and possibly before then, turquoise was used by the Egyptians and was mined by them in the Sinai Peninsula. This region was known as the Country of Turquoise by the native Monitu. There are six mines in the peninsula, all on its southwest coast, covering an area of some 650 km2 (250 sq mi). The two most important of these mines, from a historic perspective, are Serabit el-Khadim and Wadi Maghareh, believed to be among the oldest of known mines. The former mine is situated about 4 kilometres from an ancient temple dedicated to the deity Hathor.

The turquoise is found in sandstone that is, or was originally, overlain by basalt. Copper and iron workings are present in the area. Large-scale turquoise mining is not profitable today, but the deposits are sporadically quarried by Bedouin peoples using homemade gunpowder. In the rainy winter months, miners face a risk from flash flooding; even in the dry season, death from the collapse of the haphazardly exploited sandstone mine walls is not unheard of. The colour of Sinai material is typically greener than Iranian material, but is thought to be stable and fairly durable. Often referred to as "Egyptian turquoise", Sinai material is typically the most translucent, and under magnification its surface structure is revealed to be peppered with dark blue discs not seen in material from other localities.

Chacoan turquoise with argillite
A selection of Ancestral Pueblo (Anasazi) turquoise and orange argillite inlay pieces from Chaco Canyon, New Mexico, US (dated c. 1020–1140) show the typical colour range and mottling of American turquoise. Some likely came from Los Cerrillos.

United States

Turquoise Cerillos Smithsonian
A fine turquoise specimen from Los Cerrillos, New Mexico, US, at the Smithsonian Museum. Cerrillos turquoise was widely used by Native Americans prior to the Spanish conquest.
Turquoisecollection
Bisbee turquoise commonly has a hard chocolate brown coloured matrix.
Turq mcGuin bunker
Untreated turquoise, Nevada, US. Rough nuggets from the McGinness Mine, Austin. Blue and green cabochons showing spiderweb, Bunker Hill Mine, Royston

The Southwest United States is a significant source of turquoise; Arizona, California (San Bernardino, Imperial, Inyo counties), Colorado (Conejos, El Paso, Lake, Saguache counties), New Mexico (Eddy, Grant, Otero, Santa Fe counties) and Nevada (Clark, Elko, Esmeralda County, Eureka, Lander, Mineral County and Nye counties) are (or were) especially rich. The deposits of California and New Mexico were mined by pre-Columbian Native Americans using stone tools, some local and some from as far away as central Mexico. Cerrillos, New Mexico is thought to be the location of the oldest mines; prior to the 1920s, the state was the country's largest producer; it is more or less exhausted today. Only one mine in California, located at Apache Canyon, operates at a commercial capacity today.

The turquoise occurs as vein or seam fillings, and as compact nuggets; these are mostly small in size. While quite fine material is sometimes found, rivalling Iranian material in both colour and durability, most American turquoise is of a low grade (called "chalk turquoise"); high iron levels mean greens and yellows predominate, and a typically friable consistency in the turquoise's untreated state precludes use in jewellery.

Arizona is currently the most important producer of turquoise by value.[5] Several mines exist in the state, two of them famous for their unique colour and quality and considered the best in the industry: the Sleeping Beauty Mine in Globe ceased turquoise mining in August 2012. The mine chose to send all ore to the crusher and to concentrate on copper production due to the rising price of copper on the world market. The price of natural untreated Sleeping Beauty turquoise has risen dramatically since the mine's closing. The Kingman Mine as of 2015 still operates alongside a copper mine outside of the city. Other mines include the Blue Bird mine, Castle Dome, and Ithaca Peak, but they are mostly inactive due to the high cost of operations and federal regulations. The Phelps Dodge Lavender Pit mine at Bisbee ceased operations in 1974 and never had a turquoise contractor. All Bisbee turquoise was "lunch pail" mined. It came out of the copper ore mine in miners' lunch pails. Morenci and Turquoise Peak are either inactive or depleted.

Nevada is the country's other major producer, with more than 120 mines which have yielded significant quantities of turquoise. Unlike elsewhere in the US, most Nevada mines have been worked primarily for their gem turquoise and very little has been recovered as a byproduct of other mining operations. Nevada turquoise is found as nuggets, fracture fillings and in breccias as the cement filling interstices between fragments. Because of the geology of the Nevada deposits, a majority of the material produced is hard and dense, being of sufficient quality that no treatment or enhancement is required. While nearly every county in the state has yielded some turquoise, the chief producers are in Lander and Esmeralda counties. Most of the turquoise deposits in Nevada occur along a wide belt of tectonic activity that coincides with the state's zone of thrust faulting. It strikes about N15°E and extends from the northern part of Elko County, southward down to the California border southwest of Tonopah. Nevada has produced a wide diversity of colours and mixes of different matrix patterns, with turquoise from Nevada coming in various shades of blue, blue-green, and green. Some of this unusually coloured turquoise may contain significant zinc and iron, which is the cause of the beautiful bright green to yellow-green shades. Some of the green to green yellow shades may actually be variscite or faustite, which are secondary phosphate minerals similar in appearance to turquoise. A significant portion of the Nevada material is also noted for its often attractive brown or black limonite veining, producing what is called "spiderweb matrix". While a number of the Nevada deposits were first worked by Native Americans, the total Nevada turquoise production since the 1870s has been estimated at more than 600 tons, including nearly 400 tons from the Carico Lake mine. In spite of increased costs, small scale mining operations continue at a number of turquoise properties in Nevada, including the Godber, Orvil Jack and Carico Lake mines in Lander County, the Pilot Mountain Mine in Mineral County, and several properties in the Royston and Candelaria areas of Esmerelda County.[7]

In 1912, the first deposit of distinct, single-crystal turquoise was discovered in Lynch Station, Campbell County, Virginia. The crystals, forming a druse over the mother rock, are very small; 1 mm (0.04 in) is considered large. Until the 1980s Virginia was widely thought to be the only source of distinct crystals; there are now at least 27 other localities.

In an attempt to recoup profits and meet demand, some American turquoise is treated or enhanced to a certain degree. These treatments include innocuous waxing and more controversial procedures, such as dyeing and impregnation (see Treatments). There are however, some American mines which produce materials of high enough quality that no treatment or alterations are required. Any such treatments which have been performed should be disclosed to the buyer on sale of the material.

Other sources

Turquoise prehistoric artefacts (beads) are known since the fifth millennium BCE from sites in the Eastern Rhodopes in Bulgaria – the source for the raw material is possibly related to the nearby Spahievo Ph-Zn ore field.[8]

China has been a minor source of turquoise for 3,000 years or more. Gem-quality material, in the form of compact nodules, is found in the fractured, silicified limestone of Yunxian and Zhushan, Hubei province. Additionally, Marco Polo reported turquoise found in present-day Sichuan. Most Chinese material is exported, but a few carvings worked in a manner similar to jade exist. In Tibet, gem-quality deposits purportedly exist in the mountains of Derge and Nagari-Khorsum in the east and west of the region respectively.[9]

Other notable localities include: Afghanistan; Australia (Victoria and Queensland); north India; northern Chile (Chuquicamata); Cornwall; Saxony; Silesia; and Turkestan.

History of use

Chacoan turquoise pendant
Trade in turquoise crafts, such as this freeform pendant dating from 1000–1040, is believed to have brought the Ancestral Puebloans of the Chaco Canyon great wealth.
Turqoise nose ornament
Moche turquoise nose ornament. Larco Museum Collection, Lima, Peru
Drevnosti RG v3 ill094 - Palash
Backswords, inlaid with turquoise. Russia, 17th century.
Xiuhtecuhtli (mask)
Turquoise mosaic mask of Xiuhtecuhtli, the Aztec god of fire.
Tutmask
The iconic gold burial mask of Tutankhamun, inlaid with turquoise, lapis lazuli, carnelian and coloured glass.

The pastel shades of turquoise have endeared it to many great cultures of antiquity: it has adorned the rulers of Ancient Egypt, the Aztecs (and possibly other Pre-Columbian Mesoamericans), Persia, Mesopotamia, the Indus Valley, and to some extent in ancient China since at least the Shang Dynasty.[10] Despite being one of the oldest gems, probably first introduced to Europe (through Turkey) with other Silk Road novelties, turquoise did not become important as an ornamental stone in the West until the 14th century, following a decline in the Roman Catholic Church's influence which allowed the use of turquoise in secular jewellery. It was apparently unknown in India until the Mughal period, and unknown in Japan until the 18th century. A common belief shared by many of these civilizations held that turquoise possessed certain prophylactic qualities; it was thought to change colour with the wearer's health and protect him or her from untoward forces.

The Aztecs inlaid turquoise, together with gold, quartz, malachite, jet, jade, coral, and shells, into provocative (and presumably ceremonial) mosaic objects such as masks (some with a human skull as their base), knives, and shields. Natural resins, bitumen and wax were used to bond the turquoise to the objects' base material; this was usually wood, but bone and shell were also used. Like the Aztecs, the Pueblo, Navajo and Apache tribes cherished turquoise for its amuletic use; the latter tribe believe the stone to afford the archer dead aim. Among these peoples turquoise was used in mosaic inlay, in sculptural works, and was fashioned into toroidal beads and freeform pendants. The Ancestral Puebloans (Anasazi) of the Chaco Canyon and surrounding region are believed to have prospered greatly from their production and trading of turquoise objects. The distinctive silver jewellery produced by the Navajo and other Southwestern Native American tribes today is a rather modern development, thought to date from circa 1880 as a result of European influences.

In Persia, turquoise was the de facto national stone for millennia, extensively used to decorate objects (from turbans to bridles), mosques, and other important buildings both inside and out, such as the Medresseh-I Shah Husein Mosque of Isfahan. The Persian style and use of turquoise was later brought to India following the establishment of the Mughal Empire there, its influence seen in high purity gold jewellery (together with ruby and diamond) and in such buildings as the Taj Mahal. Persian turquoise was often engraved with devotional words in Arabic script which was then inlaid with gold.

Cabochons of imported turquoise, along with coral, was (and still is) used extensively in the silver and gold jewellery of Tibet and Mongolia, where a greener hue is said to be preferred. Most of the pieces made today, with turquoise usually roughly polished into irregular cabochons set simply in silver, are meant for inexpensive export to Western markets and are probably not accurate representations of the original style.

The Egyptian use of turquoise stretches back as far as the First Dynasty and possibly earlier; however, probably the most well-known pieces incorporating the gem are those recovered from Tutankhamun's tomb, most notably the Pharaoh's iconic burial mask which was liberally inlaid with the stone. It also adorned rings and great sweeping necklaces called pectorals. Set in gold, the gem was fashioned into beads, used as inlay, and often carved in a scarab motif, accompanied by carnelian, lapis lazuli, and in later pieces, coloured glass. Turquoise, associated with the goddess Hathor, was so liked by the Ancient Egyptians that it became (arguably) the first gemstone to be imitated, the fair structure created by an artificial glazed ceramic product known as faience.

The French conducted archaeological excavations of Egypt from the mid-19th century through the early 20th. These excavations, including that of Tutankhamun's tomb, created great public interest in the western world, subsequently influencing jewellery, architecture, and art of the time. Turquoise, already favoured for its pastel shades since around 1810, was a staple of Egyptian Revival pieces. In contemporary Western use, turquoise is most often encountered cut en cabochon in silver rings, bracelets, often in the Native American style, or as tumbled or roughly hewn beads in chunky necklaces. Lesser material may be carved into fetishes, such as those crafted by the Zuni. While strong sky blues remain superior in value, mottled green and yellowish material is popular with artisans.

Cultural associations

In many cultures of the Old and New Worlds, this gemstone has been esteemed for thousands of years as a holy stone, a bringer of good fortune or a talisman. The oldest evidence for this claim was found in Ancient Egypt, where grave furnishings with turquoise inlay were discovered, dating from approximately 3000 BCE. In the ancient Persian Empire, the sky-blue gemstones were earlier worn round the neck or wrist as protection against unnatural death. If they changed colour, the wearer was thought to have reason to fear the approach of doom. Meanwhile, it has been discovered that the turquoise certainly can change colour, but that this is not necessarily a sign of impending danger. The change can be caused by the light, or by a chemical reaction brought about by cosmetics, dust or the acidity of the skin.[11]

The goddess Hathor was associated with turquoise, as she was the patroness of Serabit el-Khadim, where it was mined. Her titles included "Lady of Turquoise", "Mistress of Turquoise", and "Lady of Turquoise Country".[12]

In Western culture, turquoise is also the traditional birthstone for those born in the month of December. The turquoise is also a stone in the Jewish High Priest's breastplate, described in Exodus 28. The stone is also considered sacred to the indigenous peoples of the Southwestern United States[13] Zuni and Pueblo peoples of the American Southwest,[14] The pre-Columbian Aztec and Maya also considered it to be a valuable and culturally important stone.[15]

Imitations

Chrysocolla USA
Some natural blue to blue-green materials, such as this botryoidal chrysocolla with drusy quartz, are occasionally confused with or used to imitate turquoise.

The Egyptians were the first to produce an artificial imitation of turquoise, in the glazed earthenware product faience. Later glass and enamel were also used, and in modern times more sophisticated porcelain, plastics, and various assembled, pressed, bonded, and sintered products (composed of various copper and aluminium compounds) have been developed: examples of the latter include "Viennese turquoise", made from precipitated aluminium phosphate coloured by copper oleate; and "neolith", a mixture of bayerite and copper(II) phosphate. Most of these products differ markedly from natural turquoise in both physical and chemical properties, but in 1972 Pierre Gilson introduced one fairly close to a true synthetic (it does differ in chemical composition owing to a binder used, meaning it is best described as a simulant rather than a synthetic). Gilson turquoise is made in both a uniform colour and with black "spiderweb matrix" veining not unlike the natural Nevada material.

The most common imitation of turquoise encountered today is dyed howlite and magnesite, both white in their natural states, and the former also having natural (and convincing) black veining similar to that of turquoise. Dyed chalcedony, jasper, and marble is less common, and much less convincing. Other natural materials occasionally confused with or used in lieu of turquoise include: variscite and faustite;[5] chrysocolla (especially when impregnating quartz); lazulite; smithsonite; hemimorphite; wardite; and a fossil bone or tooth called odontolite or "bone turquoise", coloured blue naturally by the mineral vivianite. While rarely encountered today, odontolite was once mined in large quantities—specifically for its use as a substitute for turquoise—in southern France.

These fakes are detected by gemologists using a number of tests, relying primarily on non-destructive, close examination of surface structure under magnification; a featureless, pale blue background peppered by flecks or spots of whitish material is the typical surface appearance of natural turquoise, while manufactured imitations will appear radically different in both colour (usually a uniform dark blue) and texture (usually granular or sugary). Glass and plastic will have a much greater translucency, with bubbles or flow lines often visible just below the surface. Staining between grain boundaries may be visible in dyed imitations.

Some destructive tests may, however, be necessary; for example, the application of diluted hydrochloric acid will cause the carbonates odontolite and magnesite to effervesce and howlite to turn green, while a heated probe may give rise to the pungent smell so indicative of plastic. Differences in specific gravity, refractive index, light absorption (as evident in a material's absorption spectrum), and other physical and optical properties are also considered as means of separation.

Treatments

Madan Turquoise Mines
An early turquoise mine in the Madan village of Khorasan, Iran

Turquoise is treated to enhance both its colour and durability (i.e., increased hardness and decreased porosity). As is so often the case with any precious stones, full disclosure about treatment is frequently not given. Gemologists can detect these treatments using a variety of testing methods, some of which are destructive, such as the use of a heated probe applied to an inconspicuous spot, which will reveal oil, wax or plastic treatment.

Waxing and oiling

Historically, light waxing and oiling were the first treatments used in ancient times, providing a wetting effect, thereby enhancing the colour and lustre. This treatment is more or less acceptable by tradition, especially because treated turquoise is usually of a higher grade to begin with. Oiled and waxed stones are prone to "sweating" under even gentle heat or if exposed to too much sun, and they may develop a white surface film or bloom over time. (With some skill, oil and wax treatments can be restored.)

Stabilization

Material treated with plastic or water glass is termed "bonded" or "stabilized" turquoise. This process consists of pressure impregnation of otherwise unsaleable chalky American material by epoxy and plastics (such as polystyrene) and water glass (sodium silicate) to produce a wetting effect and improve durability. Plastic and water glass treatments are far more permanent and stable than waxing and oiling, and can be applied to material too chemically or physically unstable for oil or wax to provide sufficient improvement. Conversely, stabilization and bonding are rejected by some as too radical an alteration.[16]

The epoxy binding technique was first developed in the 1950s and has been attributed to Colbaugh Processing of Arizona, a company that still operates today. The majority of American material is now treated in this manner although it is a costly process requiring many months to complete.

Dyeing

The use of Prussian blue and other dyes (often in conjunction with bonding treatments) to "enhance” its appearance, make uniform or completely change the colour, is regarded as fraudulent by some purists,[16] especially since some dyes may fade or rub off on the wearer. Dyes have also been used to darken the veins of turquoise.

Reconstitution

Perhaps the most extreme of treatments is "reconstitution", wherein fragments of fine turquoise material, too small to be used individually, are powdered and then bonded with resin to form a solid mass. Very often the material sold as "reconstituted" turquoise is artificial, with little or no natural stone, made entirely from resins and dyes. In the trade "reconstituted" turquoise is often called "block" turquoise or simply "block."

Backing

Since finer turquoise is often found as thin seams, it may be glued to a base of stronger foreign material for reinforcement. These stones are termed "backed," and it is standard practice that all thinly cut turquoise in the Southwestern United States is backed. Native indigenous peoples of this region, because of their considerable use and wearing of turquoise, have found that backing increases the durability of thinly cut slabs and cabochons of turquoise. They observe that if the stone is not backed it will often crack. Early backing materials included the casings of old model T batteries, old phonograph records, and more recently epoxy steel resins. Backing of turquoise is not widely known outside of the Native American and Southwestern United States jewellery trade. Backing does not diminish the value of high quality turquoise, and indeed the process is expected for most thinly cut American commercial gemstones.

Valuation and care

Turquoise-slab
Slab of turquoise in matrix showing a large variety of different colouration

Hardness and richness of colour are two of the major factors in determining the value of turquoise; while colour is a matter of individual taste, generally speaking, the most desirable is a strong sky to robin egg blue (in reference to the eggs of the American robin).[9] Whatever the colour, for many applications, turquoise should not be soft or chalky; even if treated, such lesser material (to which most turquoise belongs) is liable to fade or discolour over time and will not hold up to normal use in jewellery.

The mother rock or matrix in which turquoise is found can often be seen as splotches or a network of brown or black veins running through the stone in a netted pattern; this veining may add value to the stone if the result is complementary, but such a result is uncommon. Such material is sometimes described as "spiderweb matrix"; it is most valued in the Southwest United States and Far East, but is not highly appreciated in the Near East where unblemished and vein-free material is ideal (regardless of how complementary the veining may be). Uniformity of colour is desired, and in finished pieces the quality of workmanship is also a factor; this includes the quality of the polish and the symmetry of the stone. Calibrated stones—that is, stones adhering to standard jewellery setting measurements—may also be more sought after. Like coral and other opaque gems, turquoise is commonly sold at a price according to its physical size in millimetres rather than weight.

Turquoise is treated in many different ways, some more permanent and radical than others. Controversy exists as to whether some of these treatments should be acceptable, but one can be more or less forgiven universally: This is the light waxing or oiling applied to most gem turquoise to improve its colour and lustre; if the material is of high quality to begin with, very little of the wax or oil is absorbed and the turquoise therefore does not "rely" on this impermanent treatment for its beauty. All other factors being equal, untreated turquoise will always command a higher price. Bonded and "reconstituted" material is worth considerably less.

Being a phosphate mineral, turquoise is inherently fragile and sensitive to solvents; perfume and other cosmetics will attack the finish and may alter the colour of turquoise gems, as will skin oils, as will most commercial jewellery cleaning fluids. Prolonged exposure to direct sunlight may also discolour or dehydrate turquoise. Care should therefore be taken when wearing such jewels: cosmetics, including sunscreen and hair spray, should be applied before putting on turquoise jewellery, and they should not be worn to a beach or other sun-bathed environment. After use, turquoise should be gently cleaned with a soft cloth to avoid a buildup of residue, and should be stored in its own container to avoid scratching by harder gems. Turquoise can also be adversely affected if stored in an airtight container.

See also

References

  1. ^ Hurlbut, Cornelius S.; Klein, Cornelis (1985). Manual of Mineralogy (20th ed.). New York, NY: John Wiley and Sons. ISBN 978-0-471-80580-9.
  2. ^ a b c "Turquoise: mineral information and data". mindat.org. Archived from the original on 2006-11-12. Retrieved 2006-10-04.
  3. ^ a b c d e Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C., eds. (2000). "Turquoise" (PDF). Handbook of Mineralogy. IV. Chantilly, VA: Mineralogical Society of America. ISBN 978-0-9622097-3-4. Archived (PDF) from the original on 2012-02-11.
  4. ^ a b Palache, C.; Berman, H.; Frondel, C. (1951). Dana's System of Mineralogy. II (7th ed.). Wiley. pp. 946–951.
  5. ^ a b c d Turquoise Archived 2007-05-20 at the Wayback Machine. minerals.usgs.gov
  6. ^ "Turquoise R050554". RRUFF™ Project. Archived from the original on 2017-05-02.
  7. ^ Minerals of Nevada. Special Publication 31. Nevada Bureau of Mines. pp. 78–81, 443–445.
  8. ^ Kostov, R. I., J. Chapman, B. Gaydarska, I. Petrov, A. Raduntcheva. 2007. Turquoise – archaeomineralogical evidences from the Orlovo prehistoric site (Haskovo district, Southern Bulgaria). – Geology and Mineral Resources, 14, 7-8, 17-22.
  9. ^ a b Watson, Martin. "Turquoise – The Gemstone of Tibet". Archived from the original on March 19, 2007. Retrieved 2007-06-01.
  10. ^ "China Exhibition". Washington, D.C.: National Gallery of Art. 1999. Archived from the original on 2006-09-30. Retrieved 2006-09-23.
  11. ^ Shepardson, Mathew. "Does Turquoise Change Color?". T. Skies. Archived from the original on 11 March 2018. Retrieved 11 March 2018.
  12. ^ Bulletin of the Egyptian Museum 2007, By The Supreme Council of Antiquities p.24
  13. ^ Turquoise By Joe Dan Lowry, p.36-41
  14. ^ Collector's Guide Volume 17, sharing the art of New Mexico. 2003, p. 184
  15. ^ Turquoise By Joe Dan Lowry, p.34
  16. ^ a b Harriss, Joseph A. "Tantalizing Turquoise". Archived from the original on 2008-02-01. Retrieved 2007-06-01.

Further reading

  • British Museum (2000). Aztec turquoise mosaics. Retrieved November 15, 2004 from www.thebritishmuseum.ac.uk
  • Dietrich, R. V. (2004). Turquoise. Retrieved November 20, 2004 from www.cst.cmich.edu/users/dietr1rv/turquoise.htm
  • Persian Turquoise Mine [1]
  • King, R. J. (2002). "Turquoise". Geology Today. 18 (3): 110–114. doi:10.1046/j.1365-2451.2002.00345.x.
  • Pogue, J. E. (1915). The turquoise: a study of its history, mineralogy, geology, ethnology, archaeology, mythology, folklore, and technology. National Academy of Sciences, The Rio Grande Press, Glorieta, New Mexico. ISBN 0-87380-056-7
  • Schadt, H. (1996). Goldsmith's art: 5000 years of jewelry and hollowware. Arnoldsche Art Publisher, Stuttgart, New York. ISBN 3-925369-54-6
  • Schumann, W. (2000). Gemstones of the world, revised edition. Sterling Publishing. ISBN 0-8069-9461-4
  • Webster, R. (2000). Gems: Their sources, descriptions and identification (5th ed.), pp. 254–263. Butterworth-Heinemann, Great Britain. ISBN 0-7506-1674-1

External links

Birthstone

A birthstone is a gemstone that represents a person's month of birth. Birthstones are often worn as jewelry or as a pendant.

Blue-green

Blue-green is a color that is a representation of the color that is between green and blue on a typical traditional old-fashioned RYB color wheel.

Blue-green belongs to the cyan family of colors.

Cosmic latte

Cosmic latte is a name assigned to the average color of the universe, found by a team of astronomers from Johns Hopkins University. In 2001, Karl Glazebrook and Ivan Baldry determined that the average color of the universe was a greenish white, but they soon corrected their analysis in a 2002 paper in which they reported that their survey of the light from over 200,000 galaxies averaged to a slightly beigeish white. The hex triplet value for cosmic latte is #FFF8E7.

Double-headed serpent

The Double-headed serpent is an Aztec sculpture kept at the British Museum. Composed of mostly turquoise pieces applied to a wood base, it is one of nine mosaics of similar material in the British Museum; there are thought to be about 25 such pieces from that period in the whole of Europe. It came from Aztec Mexico and might have been worn or displayed in religious ceremonies. It is possible that this sculpture may be one of the gifts given by the Aztec emperor, Moctezuma II, to Spanish conquistador Hernán Cortés when he invaded in 1519. The mosaic is made of pieces of turquoise, spiny oyster shell and conch shell.

Howlite

Howlite, a calcium borosilicate hydroxide (Ca2B5SiO9(OH)5), is a borate mineral found in evaporite deposits.

J Golf Phoenix LPGA International

The J Golf Phoenix LPGA International, in full the J Golf Phoenix LPGA International Presented by Mirassou Winery, was a women's professional golf tournament in Arizona on the LPGA Tour. Founded as the "Sun City Classic" in 1980, it was held annually in the Phoenix area through 2009, making it one of the longest-lasting events on the LPGA Tour.

Tournament Golf Foundation managed the tournament since its start and continues to manage the Safeway Classic tournament on the LPGA Tour. Proceeds from the event were donated to local medical charities; over $12 million was raised during the course of the tournament

The tournament had a variety of sponsors during its history, including Safeway Inc., a California-based supermarket chain.

It was at this tournament that Annika Sörenstam shot 59 in the second round in 2001, which stands as the record for the lowest scoring round ever shot for 18 holes in an LPGA Tour event. With thirteen birdies and no bogeys, she began the round with eight birdies, added four more over the next five holes, but managed only one over the final five. Sörenstam won the event with 261 (–27), two strokes ahead of runner-up Se Ri Pak.The LPGA Tour returned to the Phoenix area in 2011 with the Founders Cup.

Nishapur

Nishapur or Nishabur (pronunciation ; Persian: نیشابور‎, also Romanized as Nīshāpūr, Nišâpur, Nişapur, Nīshābūr, Neyshābūr, and Neeshapoor, from Middle Persian: New-Shabuhr, meaning "New City of Shapur", "Fair Shapur", or "Perfect built of Shapur") is a city in Razavi Khorasan Province, capital of the Nishapur County and former capital of Province Khorasan, in northeastern Iran, situated in a fertile plain at the foot of the Binalud Mountains. It had an estimated population of 239,185 as of 2011 and its county 433,105. Nearby are the turquoise mines that have supplied the world with turquoise for at least two millennia.

The city was founded in the 3rd century by Shapur I as a Sasanian satrapy capital. Nishapur later became the capital of Tahirid dynasty and was reformed by Abdullah Tahir in 830, and was later selected as the capital of Seljuq dynasty by Tughril in 1037. From the Abbasid era to the Mongol invasion of Khwarezmia and Eastern Iran, the city evolved into a significant cultural, commercial, and intellectual center within the Islamic world. Nishapur, along with Merv, Herat and Balkh were one of the four great cities of Greater Khorasan and one of the greatest cities in the middle ages, a seat of governmental power in eastern of caliphate, a dwelling place for diverse ethnic and religious groups, a trading stop on commercial routes from Transoxiana and China, Iraq and Egypt.

Nishapur reached the height of its prosperity under the Samanids in the 10th century, but was destroyed and the entire population slaughtered by Mongols in 1221. This massacre, combined with subsequent earthquakes and other invasions are believed to have destroyed the pottery industry the city was known for.

Opération Turquoise

Opération Turquoise was a French-led military operation in Rwanda in 1994 under the mandate of the United Nations.

Shades of cyan

This article is about notable tints and shades of the color cyan, a greenish blue. Cyan is one of the subtractive primary colors- cyan, magenta, and yellow.

The first recorded use of cyan blue ("cyan blue" was the name used for the color "cyan" in the 19th century) as a color name in English was in 1879.

Splendid fairywren

The splendid fairywren (Malurus splendens) is a passerine bird in the Australasian wren family, Maluridae. It also known simply as the splendid wren or more colloquially in Western Australia as the blue wren. The splendid fairywren is found across much of the Australian continent from central-western New South Wales and southwestern Queensland over to coastal Western Australia. It inhabits predominantly arid and semi-arid regions. Exhibiting a high degree of sexual dimorphism, the male in breeding plumage is a small, long-tailed bird of predominantly bright blue and black colouration. Non-breeding males, females and juveniles are predominantly grey-brown in colour; this gave the early impression that males were polygamous as all dull-coloured birds were taken for females. It comprises several similar all-blue and black subspecies that were originally considered separate species.

Like other fairywrens, the splendid fairywren is notable for several peculiar behavioural characteristics; birds are socially monogamous and sexually promiscuous, meaning that although they form pairs between one male and one female, each partner will mate with other individuals and even assist in raising the young from such trysts. Male wrens pluck pink or purple petals and display them to females as part of a courtship display.The habitat of the splendid fairywren ranges from forest to dry scrub, generally with ample vegetation for shelter. Unlike the eastern superb fairywren, it has not adapted well to human occupation of the landscape and has disappeared from some urbanised areas. The splendid fairywren mainly eats insects and supplements its diet with seeds.

The Fairy with Turquoise Hair

The Fairy with Turquoise Hair (Italian: La Fata dai Capelli Turchini, often simply referred to as La Fata Turchina) is a fictional character in Italian writer Carlo Collodi's 1883 book The Adventures of Pinocchio. She repeatedly appears at critical moments in Pinocchio's wanderings to admonish the little wooden puppet to avoid bad or risky behavior. Although the naïvely willful marionette initially resists her good advice, he later comes to follow her instruction. She in turn protects him, and later enables his assumption of human form, contrary to the prior wooden form.

The character is the inspiration for the Blue Fairy in Disney's adaptation of the story.

Turquoise-fronted amazon

The turquoise-fronted amazon (Amazona aestiva), also called the turquoise-fronted parrot, the blue-fronted amazon and the blue-fronted parrot, is a South American species of amazon parrot and one of the most common amazon parrots kept in captivity as a pet or companion parrot. Its common name is derived from the distinctive turquoise marking on its head just above its beak.

Turquoise (color)

Turquoise () is a blue/green color, based on the gem of the same name. The word turquoise comes from the French for "Turkish", as the gem was originally imported from Turkey. The first recorded use of turquoise as a color name in English was in 1573.The X11 color named turquoise is displayed on the right.

Turquoise (horse)

Turquoise (1825–1846) was a British Thoroughbred racehorse and broodmare who won the classic Oaks Stakes at Epsom Downs Racecourse in 1828. In a racing career which lasted from April 1828 until April 1830 she ran eighteen times, winning eleven races and finishing second on five occasions. As a three-year-old in 1828 she failed to attract a bid after winning a claiming race at Newmarket but then created an upset by winning the Oaks at odds of 25/1. She went on to prove herself a leading stayer, winning three more races before the end of the season. In 1829 she won five more races including three walkovers when no horses appeared to challenge her. She was retired after a single unsuccessful run in 1830.

Turquoise jay

The turquoise jay (Cyanolyca turcosa) is a species of bird in the family Corvidae.

The turquoise jay is a vibrant blue jay with a black face mask and collar. It is found exclusively in South America throughout southern Colombia, Ecuador, and northern Peru. The turquoise jay prefers a humid habitat of montane evergreen forests and elfin forests with both primary and secondary growth. This bird is omnivorous and is known to eat insects, berries, eggs, and young birds of other species. Turquoise jays are nonmigratory and tend to travel in mixed flocks.

Turquoise parrot

The turquoise parrot (Neophema pulchella) is a species of parrot in the genus Neophema native to Eastern Australia, from southeastern Queensland, through New South Wales and into North-Eastern Victoria. It was described by George Shaw in 1792. A small lightly built parrot at around 20 cm (8 in) long and 40 g (1 1⁄2 oz) in weight, it exhibits sexual dimorphism. The male is predominantly green with more yellowish underparts and a bright turquoise blue face. Its wings are predominantly blue with red shoulders. The female is generally duller and paler, with a pale green breast and yellow belly, and lacks the red wing patch.

Found in grasslands and open woodlands dominated by Eucalyptus and Callitris trees, the turquoise parrot feeds mainly on grasses and seeds and occasionally flowers, fruit and scale insects. It nests in hollows of gum trees. Much of its habitat has been altered and potential nesting sites lost. Predominantly sedentary, the turquoise parrot can be locally nomadic. Populations appear to be recovering from a crash in the early 20th century. The turquoise parrot has been kept in captivity since the 19th century, and several colour variants exist.

Variscite

Variscite is a hydrated aluminium phosphate mineral (AlPO4·2H2O). It is a relatively rare phosphate mineral. It is sometimes confused with turquoise; however, variscite is usually greener in color. The green color results from the presence of small amounts of chromium.

X11 color names

In computing, on the X Window System, X11 color names are represented in a simple text file, which maps certain strings to RGB color values. It was traditionally shipped with every X11 installation, hence the name, and is usually located in /lib/X11/rgb.txt. The web colors list is descended from it but differs for certain color names.Color names are not standardized by Xlib or the X11 protocol. The list does not show continuity either in selected color values or in color names, and some color triplets have multiple names. Despite this, graphic designers and others got used to them, making it practically impossible to introduce a different list. In earlier releases of X11 (prior to the introduction of Xcms), server implementors were encouraged to modify the RGB values in the reference color database to account for gamma correction.As of X.Org Release 7.4 rgb.txt is no longer included in the roll up release, and the list is built directly into the server. The optional module xorg/app/rgb contains the stand-alone rgb.txt file.

The list first shipped with X10 release 3 (X10R3) on 7 June 1986, having been checked into RCS by Jim Gettys in 1985. The same list was in X11R1 on 18 September 1987. Approximately the full list as is available today shipped with X11R4 on 29 January 1989, with substantial additions by Paul Ravelling (who added colors based on Sinclair Paints samples), John C. Thomas (who added colors based on a set of 72 Crayola crayons he had on hand) and Jim Fulton (who reconciled contributions to produce the X11R4 list). The project was running DEC VT240 terminals at the time, so would have worked to that device.In some applications multipart names are written with spaces, in others joined together, often in camel case. They are usually matched insensitive of case and the X Server source code contains spaced aliases for most entries; this article uses spaces and uppercase initials except where variants with spaces are not specified in the actual code.

Xiuhtecuhtli

In Aztec mythology, Xiuhtecuhtli [ʃiʍˈtekʷt͡ɬi] ("Turquoise Lord" or "Lord of Fire"), was the god of fire, day and heat. He was the lord of volcanoes, the personification of life after death, warmth in cold (fire), light in darkness and food during famine. He was also named Cuezaltzin [kʷeˈsaɬt͡sin] ("flame") and Ixcozauhqui [iʃkoˈsaʍki], and is sometimes considered to be the same as Huehueteotl ("Old God"), although Xiuhtecuhtli is usually shown as a young deity. His wife was Chalchiuhtlicue. Xiuhtecuhtli is sometimes considered to be a manifestation of Ometecuhtli, the Lord of Duality, and according to the Florentine Codex Xiuhtecuhtli was considered to be the father of the Gods, who dwelled in the turquoise enclosure in the center of earth. Xiuhtecuhtli-Huehueteotl was one of the oldest and most revered of the indigenous pantheon. The cult of the God of Fire, of the Year, and of Turquoise perhaps began as far back as the middle Preclassic period. Turquoise was the symbolic equivalent of fire for Aztec priests. A small fire was permanently kept alive at the sacred center of every Aztec home in honor of Xiuhtecuhtli.The Nahuatl word xihuitl means "year" as well as "turquoise" and "fire", and Xiuhtecuhtli was also the god of the year and of time. The Lord of the Year concept came from the Aztec belief that Xiuhtecuhtli was the North Star. In the 260-day ritual calendar, the deity was the patron of the day Atl ("Water") and with the trecena 1 Coatl ("1 Snake"). Xiuhtecuhtli was also one of the nine Lords of the Night and ruled the first hour of the night, named Cipactli ("Alligator"). Scholars have long emphasized that this fire deity also has aquatic qualities. Xiuhtecuhtli dwelt inside an enclosure of turquoise stones, fortifying himself with turquoise bird water. He is the god of fire in relation to the cardinal directions, just as the brazier for lighting fire is the center of the house or temple. Xiuhtecuhtli was the patron god of the Aztec emperors, who were regarded as his living embodiment at their enthronement. The deity was also one of the patron gods of the pochteca merchant class.Stone sculptures of Xiuhtecuhtli were ritually buried as offerings, and various statuettes have been recovered during excavations at the Great Temple of Tenochtitlan with which he was closely associated. Statuettes of the deity from the temple depict a seated male with his arms crossed. A sacred fire was always kept burning in the temples of Xiuhtecuhtli. In gratitude for the gift of fire, the first mouthful of food from each meal was flung into the hearth.

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