Turquoise is an opaque , blue-to-green mineral that is a hydrous phosphate of copper and aluminium , with the chemical formula Cu Al 6 ( PO 4 ) 4 ( OH ) 8 ·4 H 2 O . It is rare and valuable in finer grades and has been prized as a gemstone for millennia due to its hue.
94-559: Like most other opaque gems, turquoise has been devalued by the introduction of treatments, imitations, and synthetics into the market. The robin egg blue or sky blue color of the Persian turquoise mined near the modern city of Nishapur , Iran , has been used as a guiding reference for evaluating turquoise quality. The word turquoise dates to the 17th century and is derived from the Old French turquois meaning "Turkish" because
188-399: 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 . With lower hardness comes greater porosity . The lustre of turquoise is typically waxy to subvitreous, and its transparency is usually opaque, but may be semitranslucent in thin sections. Colour
282-515: 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. In Navajo culture it
376-473: 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
470-482: 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
564-477: 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
658-663: A color name in English was in 1873, though earlier references in English to colors similar to that of robin's eggs were made as early as 1844. The "robin's egg" glaze appeared during the Yongzheng Emperor ’s reign (1722-35) in China, and Yixing potter Hua Fengxiang made works with "robin's egg" glaze. Tiffany Blue is the trademarked name for the light medium tone of robin egg blue associated with Tiffany & Co. ,
752-979: A copper deposit. The level of displacement is usually shallow at less than two kilometers below surface in an active volcanic area. An example for a typical arc-island porphyry deposit is described as follows: Finally, volcanic activity ceased and erosion removed the upper portions of the volcano and exposed the intrusive rocks and stockwork mineralization that used to lie within. In contrast, those that occur in continental orogenic belts are typically rhyolitic in composition and carry copper, molybdenum and gold, and in some cases tin and/or tungsten . The primary silicate minerals such as feldspar and amphibole are replaced by hydrothermal minerals stable at temperatures of about 400 °C or less such as chlorite , epidote , muscovite and quartz . Alteration assemblages typically include proximal potassic , intermediate phyllic or QSP, and more distal propylitic and argillic alteration. Where veinlets are close together,
846-965: 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 viewed turquoise as an embodiment of fire and gave it properties such as heat and smokiness. They inlaid turquoise, together with gold , quartz , malachite , jet , jade , coral , and shells , into provocative (and presumably ceremonial) mosaic objects such as masks (some with
940-486: A general rule. MVT deposits commonly lie in close proximity to evaporites . A mineral ore deposit is the volume of rock that can be mined at a profit. Therefore, there are many variants that can define whether a mineral deposit is profitable or not, such as price, tonnage, or location. Mineral commodities can be classified as metals or non-metals. Metals refer to elements of the periodic table which include base , ferrous , minor fissionable and precious metals . On
1034-402: 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. Turquoise is treated to enhance both its colour and durability (increased hardness and decreased porosity ). As
SECTION 10
#17327722464581128-419: A historical 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
1222-741: A lack of evidence for profitable extraction. Hydrothermal mineral deposits are divided into six main subcategories: porphyry , skarn , volcanogenic massive sulfide (VMS), sedimentary exhalative (SEDEX), and epithermal and Mississippi Valley-type (MVT) deposits. Each hydrothermal mineral deposit has different distinct structures, ages, sizes, grades, geological formation, characteristics and, most importantly, value. Their names derive from their formation, geographical location or distinctive features. Generally, porphyry-type mineral deposits form in hydrothermal fluid circulation systems developed around felsic to intermediate magma chambers and/or cooling plutons . However, they did not precipitate directly from
1316-416: A long period of time and have a relatively high grade in valuable minerals. The main minerals in this deposit are sulphide minerals such as pyrite , sphalerite , chalcopyrite and galena . The term “massive sulfide” deposit refers to any deposit containing more than 50% sulfide minerals. The modifier “volcanogenic” indicates that the massive sulfides are believed to be genetically related to volcanism that
1410-432: 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
1504-402: A profit by mining. Discovery of mineral deposits consumes considerable time and resources and only about one in every one thousand prospects explored by companies are eventually developed into a mine. A mineral deposit is any geologically significant concentration of an economically useful rock or mineral present in a specified area. The presence of a known but unexploited mineral deposit implies
1598-480: A rockmass. They are commonly epithermal in origin, that is to say they form at relatively high crustal levels and moderate to low temperatures. They are epigenetic since they form after their host rocks. Hydrothermal vein deposits fall into three main categories: There are two main possibilities for the origin of the ore, both of which are hydrothermal: One possibility, the rise of a small body of felsic magma may have led to either the: Elements were leached from
1692-462: A similar four-dimensional geodynamic context. The formation of deposits of a particular type can vary in time and location, but different deposit types may also form synchronously, but spatially separated within the same broad orogen. Hydrothermal mineral deposits play a key role in nearly all modern industrial activities. According to some authors, the hydrothermal solutions can have four origins, although any single volume of hydrothermal solution
1786-428: A typical turquoise deposit begins with hydrothermal deposition of copper sulfides . This takes place when hydrothermal fluids leach copper from a host rock, which is typically an intrusion of calc-alkaline rock with a moderate to high silica content that is relatively oxidized . The copper is redeposited in more concentrated form as a copper porphyry , in which veins of copper sulfide fill joints and fractures in
1880-458: 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 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
1974-441: 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.) Since finer turquoise
SECTION 20
#17327722464582068-462: 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 iron impurities (replacing copper.) The refractive index of turquoise varies from 1.61 to 1.65 on the three crystal axes, with birefringence 0.040, biaxial positive, as measured from rare single crystals. Crushed turquoise
2162-450: Is commonly a mixture of two or more types: Ore minerals can form at the same time and from the same processes as the host rock, also termed as syngenetic , they can form slightly after the formation of the host rock, perhaps during weathering or compaction, also termed as diagenetic , or they can form much later than the host rock or epigenetic. Host rock is the rock surrounding the ore deposit. Porphyry deposits account for most of
2256-434: Is less common, and much less convincing. Other natural materials occasionally confused with or used in lieu of turquoise include: variscite and faustite ; 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
2350-517: Is liable to fade or discolour over time and will not hold up to normal use in jewellery. Robin egg blue Robin egg blue , also called eggshell blue or robin's-egg blue , is a shade of teal (a blue-green color), approximating the shade of the eggs laid by the American robin , an abundant songbird of North America . The egg pigment is biliverdin , a product of the breakdown of heme . The first recorded use of robin egg blue as
2444-406: 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 jewelry . Arizona is currently the most important producer of turquoise by value. Several mines exist in the state, two of them famous for their unique colour and quality and considered the best in the industry:
2538-544: 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
2632-468: 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 . 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
2726-428: 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. Historically, light waxing and oiling were the first treatments used in ancient times, providing
2820-434: Is soluble in hot hydrochloric acid . Its streak is white to greenish to blue, and its fracture is smooth to conchoidal . 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. Turquoise is nearly always cryptocrystalline and massive and assumes no definite external shape. Crystals, even at
2914-610: 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. The epoxy binding technique
Turquoise - Misplaced Pages Continue
3008-458: 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
3102-482: 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
3196-540: 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
3290-437: Is treated only for porosity, the treatment is undetectable. 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, especially since some dyes may fade or rub off on the wearer. Dyes have also been used to darken the veins of turquoise. Material treated with plastic or water glass
3384-772: 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. 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
3478-473: Is used for "a spiritual protection and blessing." 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
3572-630: 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 . 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
3666-448: The Aztecs knew it as chalchihuitl . In professional mineralogy, until the mid-19th century, the scientific names kalaite or azure spar were also used, which simultaneously provided a version of the mineral origin of turquoise. However, these terms did not become widespread and gradually fell out of use. The finest of turquoise reaches a maximum Mohs hardness of just under 6, or slightly more than window glass . Characteristically
3760-708: The Cerrillos Hills in New Mexico, are typical supergene deposits formed from copper porphyries. The deposits in Cochise County, Arizona , are found in Cambrian quartzites and geologically young granites and go down at least as deep as 54 meters (177 ft). 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
3854-563: The Earth's surface ) percolates through the copper porphyry. Dissolved oxygen in the water oxidizes the copper sulfides to soluble sulfates, and the acidic, copper-laden solution then reacts with aluminum and potassium minerals in the host rock to precipitate turquoise. This typically fills veins in volcanic rock or phosphate-rich sediments. Deposition usually takes place at a relatively low temperature, 90–195 °C (194–383 °F), and seems to occur more readily in arid environments. Turquoise in
Turquoise - Misplaced Pages Continue
3948-521: 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
4042-635: The New York City jewelry company. This color-related article is a stub . You can help Misplaced Pages by expanding it . Hydrothermal mineral deposit Hydrothermal mineral deposits are accumulations of valuable minerals which formed from hot waters circulating in Earth's crust through fractures. They eventually produce metallic -rich fluids concentrated in a selected volume of rock, which become supersaturated and then precipitate ore minerals. In some occurrences, minerals can be extracted for
4136-558: The Sinai Peninsula is found in lower Carboniferous sandstones overlain by basalt flows and upper Carboniferous limestone . The overlying beds were presumably the source of the copper, which precipitated as turquoise in nodules, horizontal seams, or vertical joints in the sandstone beds. The classical Iranian deposits are found in sandstones and limestones of Tertiary age were intruded by apatite -rich porphyritic trachytes and mafic rock. Supergene alteration fractured
4230-685: The Sinai Peninsula . Iran also has turquoise mines in Semnan and Kerman provinces. 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 km (250 sq mi). The two most important of these mines, from
4324-429: The contact aureole of a pluton. Typical calc-silicate minerals are garnet , epidote, pyroxene , chlorite, amphibole and quartz – magnesian minerals dominate if dolomite is replaced whereas calcic minerals dominate where limestone is replaced. Skarn deposits are of economic interest, since they are the source of numerous metals as well as minerals of industrial application. Skarn formation, as illustrated in
4418-578: The copper and molybdenum world production, 60 and 95 percent of its supply respectively. Porphyry-type ore deposits form in hydrothermal fluid circulation systems developed above and around high-level, subvolcanic felsic to intermediate magma chambers and/or cooling plutons . The ore is temporally and genetically related to the intrusions, but did not precipitate directly from the magma. Porphyry mineral deposits are formed when two plate tectonic plates collide in an advanced subduction zone , then cools off reacting with existing rocks and finally forming
4512-618: The 1980s to improve the stability of medium to high-grade turquoise. The process can be applied in several ways: either through deep penetration on rough turquoise to decrease porosity, by shallow treatment of finished turquoise to enhance color, or both. The treatment can enhance color and improve the turquoise's ability to take a polish. Such treated turquoise can be distinguished in some cases from natural turquoise, without destruction, by energy-dispersive X-ray spectroscopy , which can detect its elevated potassium levels. In some instances, such as with already high-quality, low-porosity turquoise that
4606-577: The American Southwest. The pre-Columbian Aztec and Maya also considered it to be a valuable and culturally important stone. 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
4700-563: 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 . In many cultures of the Old and New Worlds, this gemstone has been esteemed for thousands of years as a holy stone,
4794-600: The Navajo and other Southwestern Native American tribes today is a rather modern development, thought to date from around 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
SECTION 50
#17327722464584888-611: The Nevada deposits were first worked by Native Americans, the total Nevada turquoise production since the 1870s has been estimated at more than 600 short tons (540 t), including nearly 400 short tons (360 t) 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,
4982-655: The Pilot Mountain Mine in Mineral County , and several properties in the Royston and Candelaria areas of Esmerelda County. In 1912, the first deposit of distinct, single-crystal turquoise was discovered at Lynch Station in 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
5076-578: 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
5170-426: The already solidified portions of the pluton. The fluids would have migrated upward and outward, following fractures in the solidified part of the granite pluton, precipitating ore minerals in veins and altering the wallrocks. The other possibility, a regional shearing event developed in the crust. Shearing take place at temperatures on the order of 300–400 °C. Thus, the shearing event may have been accompanied by
5264-402: 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. The goddess Hathor was associated with turquoise, as she was the patroness of Serabit el-Khadim , where it
5358-485: The bottom of the basin, which are heated by the geothermal gradient, and later ascends by convective currents (red arrows). Model for the origin of the Red Sea sulfide deposits. Cold seawater (blue arrows) enters the seafloor via deep-seated fractures. As it descends, it heats up and leaches silicon, metals and other solutes from the seafloor basalts . The source of sulfur can be by bacterial reduction of marine sulfate
5452-719: The buyer on sale of the material. Turquoise prehistoric artifacts (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 lead–zinc ore field. In Spain, turquoise has been found as a minor mineral in the variscite deposits exploited during prehistoric times in Palazuelos de las Cuevas (Zamora) and in Can Tintorer, Gavá (Barcelona). China has been
5546-514: 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
5640-452: 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 may occur. The colour of Sinai material is typically greener than that of Iranian material but is thought to be stable and fairly durable. Often referred to as "Egyptian turquoise", Sinai material
5734-616: The distribution and ore grade of the skarn zones. Many orebodies are elongate along structural weaknesses such as faults and bedding planes The largest and thickest orebodies tend to occur where carbonate beds lie immediately above gently inclined pluton contacts. Together, they comprise the single largest copper-gold mine in the world, with reserves of 2.8 billion tonnes grading 1.1% Cu and 1.1 g/t Au. Hydrothermal vein ore deposits consist of discrete veins or groups of closely spaced veins. Veins are believed to be precipitated by hydrothermal solutions travelling along discontinuities in
SECTION 60
#17327722464585828-411: The figure on the right, can be explained in three stages: There is a very close spatial association with the granite, the skarn occurs only within marble which is known to be a very reactive rock type, and the skarn has a chemical composition that is unlike any known igneous or sedimentary rock type. Furthermore, various structures such as flexures in the contact or impermeable hornfels beds affected
5922-419: The generation and movement of hydrothermal fluid as the crust was subjected to prograde devolatilization. This fluid might have leached the ore elements from one part of the granite pluton and reprecipitated them in veins in another part of the same pluton, effectively concentrating them. Epithermal ore deposits form at shallow depth and are typically tabular (two-dimensional) in geometry. Good examples are
6016-453: 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
6110-635: The gold-silver veins in northwestern Nevada and large ion veins such as the fluorspar veins in the St. Lawrence mine in Newfoundland and the tin-bearing veins that made up the East Kemptville Mine in southwestern Nova Scotia. Volcanogenic massive sulfide (VMS) are responsible for almost a quarter of the world's zinc production while contributing for lead, silver and copper as well. VMS deposits tend to be of great size since they form over
6204-474: The iron phosphate vivianite . Intergrowth with other secondary copper minerals such as chrysocolla is also common. Turquoise is distinguished from chrysocolla, the only common mineral with similar properties, by its greater hardness. Turquoise forms a complete solid solution series with chalcosiderite , CuFe 6 (PO 4 ) 4 (OH) 8 ·4H 2 O , in which ferric iron replaces aluminium. Turquoise deposits probably form in more than one way. However,
6298-412: 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
6392-485: 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. Deposits typically take the form of small veins in partially decomposed volcanic rock in arid climates. Iran has been an important source of turquoise for at least 2,000 years. It
6486-629: The magma. While, a skarn deposit is an assemblage of ore and calc-silicate minerals , formed by metasomatic replacement of carbonate rocks in the contact aureole of a pluton. Volcanogenic massive sulfide deposits form when mafic magma at depth, (perhaps a few kilometers beneath the surface), acts as a heat source, causing convective circulation of seawater through the oceanic crust . The hydrothermal fluid leaches metals as it descends and precipitates minerals as it rises. Sedimentary exhalative deposits, also called sedex deposits, are lead-zinc sulfide deposits formed in intracratonic sedimentary basins by
6580-404: The microscopic scale, are rare. Typically the form is a 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 historically been thought to have been altered by turquoise or similar phosphate minerals such as
6674-462: 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
6768-570: The mineral was first brought to Europe through the Ottoman Empire . However, according to Etymonline , the word dates to the 14th century with the form turkeis , meaning "Turkish", which was replaced with turqueise from French in the 1560s. According to the same source, the gemstone was first brought to Europe from Turkestan or another Turkic territory. Pliny the Elder referred to the mineral as callais (from Ancient Greek κάλαϊς ) and
6862-490: The minerals comes from the volcanic rocks through which the sea water flows, taking with it the minerals of the volcanic rock. The sea water is heated, convection currents are formed and they ascend carrying the minerals which are discharged at the bottom of the sea or immediately below the surface in the form of black smokers. Magma rises up from the mantle and then cools off in the crust and then releases volatile fluids that contain metals that are eventually transported up to
6956-421: The mountains of Derge and Nagari-Khorsum in the east and west of the region respectively. Other notable localities include: Afghanistan ; Australia ( Victoria and Queensland ); north India ; northern Chile ( Chuquicamata ); Cornwall ; Saxony ; Silesia ; and Turkestan . The pastel shades of turquoise have endeared it to many great cultures of antiquity: it has adorned the rulers of Ancient Egypt ,
7050-422: The other hand, non-metals refer to industrial minerals such as gypsum , diamonds, oil, coal and aggregate . Hydrothermal deposits of economically valuable and recoverable minerals are generally considered scarce, meaning such deposits are very small relative to the total area of earth's surface. Each of these deposit types is usually considered to represent a distinctive deposit group with common features and in
7144-589: The rock and converted some of the minerals in the rock to alunite , which freed aluminum and phosphate to combine with copper from oxidized copper sulfides to form turquoise. This process took place at a relatively shallow depth, and by 1965 the mines had "bottomed" at a depth averaging just 9 meters (30 ft) below the surface. Turquoise deposits are widespread in North America. Some deposits, such as those of Saguache and Conejos Counties in Colorado or
7238-412: The rock. Deposition takes place mostly in the potassic alteration zone, which is characterized by conversion of existing feldspar to potassium feldspar and deposition of quartz and micas at a temperature of 400–600 °C (752–1,112 °F) Turquoise is a secondary or supergene mineral, not present in the original copper porphyry. It forms when meteoric water (rain or snow melt infiltrating
7332-676: The seafloor. The host rocks are mainly volcanic, with the felsic volcanic rocks pointing to a convergent setting such as an island arc or orogenic belt . Minor sedimentary beds such as chert and slate are found in VMS deposits and they indicate marine deposition, below the wave base . VMS deposits formed on the seafloor, in the same way that modern seafloor smokers are forming today. The most recent compilations of VMS deposits on land include about 1,100 deposits in more than 50 countries and 150 different mining camps or districts. Lenses of barite (BaSO 4 ), gypsum or anhydrite are associated with
7426-407: 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 Ancient Egyptian use of turquoise stretches back as far as
7520-457: The state's zone of thrust faulting . It strikes at a bearing of about 15° 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
7614-479: The stone is not backed it will often crack. 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. A proprietary process was created by electrical engineer and turquoise dealer James E. Zachery in
7708-434: The submarine venting of hydrothermal fluids. These deposits are commonly stratiform, tabular - lenticular and are typically hosted in shale however, sedimentary rocks detrictics or even carbonates could be the host. SEDEX deposits form in sedimentary basins under a regional tectonic extensional environment, under the ocean where cold seawater (blue arrows) is mixed with basin water and through sinsedimentary faults flow towards
7802-489: The submarine venting of hydrothermal fluids. These deposits are typically hosted in shale . Hydrothermal epithermal deposits consist of geological veins or groups of closely spaced geological veins. Finally, Mississippi Valley-type (MVT) are hosted in limestone or dolomite that was deposited in a shallow marine environment in a tectonically stable intraplate environment. As expected in such an environment, volcanic rocks , folding and regional metamorphism are absent as
7896-589: The sulfides in some deposits. Sedimentary exhalative (SEDEX) deposits account for 40% of total world zinc production, 60% of lead and a significant proportion of silver. Despite their economic importance however, sedex deposits are relatively rare. A worldwide compilation of sedex deposits indicates that about 70 are known, of which 24 have been or are being mined. The majority is uneconomic to mine because of relatively low grade or unusually fine grain size, making mill recovery rather low. SEDEX deposits are lead-zinc sulfide deposits formed in intracratonic rift basins by
7990-406: The surface and over time these accumulations become mineral deposits. As the high-temperature volatile fluids from the magma make contact with low-temperature liquids such as seawater that travel downwards via cracks and faults, producing, due to the large difference in temperature and chemical properties, mineral precipitation, yielding the black colour in the black smokers that end up showing up in
8084-519: The trade reconstituted turquoise is often called "block turquoise" or simply "block". 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 ). Whatever the colour, for many applications, turquoise should not be soft or chalky; even if treated, such lesser material (to which most turquoise belongs)
8178-404: The zones of alteration around each veinlet overlap, making the whole rock hydrothermally altered. Skarn Mineral Deposits tend to be small in size but high in mineral grade. Therefore, it is a balance and challenge to find a profitable skarn orebody. Geologically speaking, a skarn deposit is an assemblage of ore and calc-silicate minerals, formed by metasomatic replacement of carbonate rocks in
8272-480: Was first developed in the 1950s and has been attributed to Colbaugh Processing of Arizona, a company that still operates today. 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
8366-520: 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. This deposit is blue naturally and turns green when heated due to dehydration. It
8460-592: 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
8554-534: Was mined. Her titles included "Lady of Turquoise", "Mistress of Turquoise", and "Lady of Turquoise Country". 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 chapter 28. The stone is also considered sacred to the indigenous Zuni and Pueblo peoples of
8648-504: 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
8742-455: Was ongoing at the time of sulfide deposition. Thus, VMS deposits are believed to be syngenetic or perhaps slightly diagenetic in age relative to their host volcanic rocks. Deposition of VMS is due to mainly two reasons: VMS deposits form in zones of extension and active volcanism. The original fluid is mainly cold, alkaline, deficient-in-metals sea water and in some cases it can include a lesser proportion of magmatic fluid. The main source of
8836-549: 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 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
#457542