Turquoise 55693 move=:edit= 225825217 2008-07-15T16:01:28Z Onorem 622881 Reverted edits by [[Special:Contributions/Pink!Teen|Pink!Teen]] ([[User talk:Pink!Teen|talk]]) to last version by 78.161.78.127 {{otheruses}} {{Infobox mineral | name = Turquoise | category = | boxwidth = | boxbgcolor = | image = turquoise.pebble.700pix.jpg | caption = Turquoise pebble, one inch (2.5 cm) long. This pebble is greenish and therefore low grade | formula = CuAl<sub>6</sub>(PO<sub>4</sub>)<sub>4</sub>(OH)<sub>8</sub>·4H<sub>2</sub>O | color = Blue, blue-green, green | habit = Massive, nodular | system = [[Triclinic]] | twinning = | cleavage = Good to perfect - usually N/A | fracture = Conchoidal | mohs = 5-6 | luster = Waxy to subvitreous | refractive = 1.61-1.65 | opticalprop = | birefringence = +0.040 | pleochroism = | streak = Bluish white | gravity = 2.6-2.9 | melt = | fusibility = Fusible in heated [[hydrochloric acid|HCl]] | diagnostic = | solubility = Soluble in HCl | diaphaneity = | melting point = None. | references =<ref name="Hurlbut">Hurlbut, Cornelius S.; Klein, Cornelis, 1985, ''Manual of Mineralogy'', 20th ed., John Wiley and Sons, New York ISBN 0-471-80580-7</ref><ref name="mindat">{{cite web|url=http://www.mindat.org/min-4060.html|title=Turquoise:turquoise mineral information and data|publisher=mindat.org| accessdate = 2006-10-04}}</ref><ref name="rruff">http://rruff.geo.arizona.edu/doclib/hom/turquoise.pdf Handbook of Mineralogy</ref> }} '''Turquoise''' is an opaque, blue-to-green [[mineral]] that is a [[hydrate|hydrous]] [[phosphate]] of [[copper]] and [[aluminium]], with the [[chemical formula]] [[copper|Cu]][[aluminium|Al]]<sub>6</sub>([[phosphorus|P]][[oxygen|O]]<sub>4</sub>)<sub>4</sub>(O[[hydrogen|H]])<sub>8</sub>'''·'''4[[water|H<sub>2</sub>O]]. It is rare and valuable in finer grades and has been prized as a [[gemstone|gem]] and [[ornamental stone]] for thousands of years owing to its unique hue. In recent times turquoise, like most other opaque gems, has been devalued by the introduction of treatments, imitations, and synthetics onto the market, some difficult to detect even by experts. The substance has been known by many names, but the word ''turquoise'' was derived around 16th century from the [[French language]] either from the word for ''Turkish'' (''Turquois'') or ''dark-blue stone'' (''pierre turquin'').<ref name="GT">{{cite journal|author=King, R. J.|date=2002|title=Turquoise|journal=Geology Today|volume=18|issue=3| pages= 110–111|accessdate= 24 November|accessyear=2004|url=http://www.blackwell-synergy.com/links/doi/10.1046/j.1365-2451.2002.00345.x/full/ | doi = 10.1046/j.1365-2451.2002.00345.x/full/ <!--Retrieved from URL by DOI bot--> }}</ref> This may have arisen from a misconception: turquoise does not occur in [[Turkey]] but was traded at Turkish bazaars to Venetian merchants who brought it to Europe.<ref name="GT"/> The colour, however, has been employed extensively in the decorative tiles adorning Turkish places of worship and homes for hundreds of years, beginning with the [[Seljuq dynasty|Seljuk]]s, or was derived from the colour of the Mediterranean Sea on the southern Turkish coast and the association quite possibly has caused the name to take root. == Properties of turquoise == Even the finest of turquoise is fracturable, reaching a maximum [[Mohs scale of mineral hardness|hardness]] of just under 6, or slightly more than window glass.<ref name="mindat"/> Characteristically a [[cryptocrystalline]] mineral, turquoise almost never forms single [[crystal]]s and all of its properties are highly variable. Its [[crystal system]] is proven to be [[triclinic]] via [[X-ray diffraction]] testing. With lower hardness comes lower [[specific gravity]] (high 2.90, low 2.60) and greater [[porosity]]: These properties are dependent on grain size. The [[Lustre (mineralogy)|lustre]] of turquoise is typically waxy to subvitreous, and [[Transparency (optics)|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]] (as measured by [[sodium]] light, 589.3 nm) of turquoise is approximately 1.61 or 1.62; this is a mean value seen as a single reading on a [[gemology|gemmological]] [[refractometer]], owing to the almost invariably polycrystalline nature of turquoise. A reading of 1.61&ndash;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 nanometres and a weak band at 460 nanometres (this is best seen with strong reflected light). Under longwave [[ultraviolet]] light, turquoise may occasionally [[fluorescence|fluoresce]] green, yellow or bright blue; it is inert under shortwave ultraviolet and [[X-ray]]s. Turquoise is insoluble in all but heated [[hydrochloric acid]]. Its [[Mineral#Streak|streak]] is a pale bluish white and its [[fracture]] is [[conchoidal fracture|conchoidal]], 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 == As a secondary [[mineral]], turquoise apparently 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 American southwest turquoise is almost invariably associated with the weathering products of copper sulfide deposits in or around potassium feldspar bearing porphyritic [[intrusive]]s. 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 m, although it does occur along deeper fracture zones where secondary solutions have greater penetration or the depth to the water table is greater. Although the features of turquoise occurrences are consistent with a secondary or [[Supergene (geology)|supergene]] origin, some sources refer to a [[hypogene]] origin. The ''hypogene'' hypothesis, which holds that the aqueous solutions originate at significant depth, from [[hydrothermal]] processes. Initially at high temperature, these solutions rise upward to surface layers, interacting with and leaching essential elements from pre-existing minerals in the process. As the solutions cool, turquoise precipitates, lining cavities and fractures within the surrounding rock. This hypogene process is applicable to the original copper sulfide deposition; however, it is difficult to account for the many features of turquoise occurrences by a hypogene process. That said, there are reports of two phase [[fluid inclusions]] within turquoise grains that give elevated homogenization temperatures of 90 to 190 <sup>o</sup>C that require explanation. 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 [[crystal habit|habit]]. [[Stalactite]] forms have been reported. Turquoise may also [[pseudomorph]]ously replace feldspar, apatite, other minerals, or even [[fossil]]s. [[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 == [[Image:Turquoise with quartz.jpg|right|thumb|250px|Massive turquoise in matrix with [[quartz]] from [[Mineral Park]], [[Arizona]].]] Turquoise was among the first gems to be mined, and while many historic sites have been depleted, some are still worked to this day. These are all small-scale, often seasonal operations, 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]]. === Iran === [[Image:Cutting and grinding turquoise in Meshed, Iran. 1973.jpg|thumb|250px|Cutting and grinding turquoise in [[Meshed]], Iran. 1973.]] For at least 2,000 years, the region once known as [[Persia]], has remained the most important source of turquoise, for it is here that fine material is most consistently recovered. This "perfect colour" deposit, which is blue naturally, and turns green when heated due to dehyration, is restricted to a mine-riddled in [[Neyshabur]],<ref>Microsoft Encarta 2007. © 1993-2006 Microsoft Corporation. All rights reserved.</ref><ref>[http://www.answers.com/topic/neyshabur Answer of Answers.com site from Columbia university press encyclopedia]</ref><ref>[http://www.firoozeh-iran.com/history_en.asp Persian turquoise]</ref> the 2,012-metre mountain peak of [[Ali-mersai]], which is tens of kilometers from [[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, together with those of the [[Sinai Peninsula]], are the oldest known. Iranian turquoise is often found replacing feldspar. Although it is commonly marred by whitish patches, its colour and hardness are considered superior to the production of other localities. Iranian turquoise has been mined and traded abroad for centuries, and was probably the source of the first material to reach Europe. === Sinai === Since at least the [[First Dynasty]] (3000 [[Common Era|BCE]]), and possibly before then, turquoise was used by the [[Egyptians]] and was [[mining|mined]] by them in the [[Sinai Peninsula]], called "Country of Turquoise" by the native [[Monitu]]. There are six mines in the region, all on the southwest coast of the peninsula, covering an area of some 650 km². 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 [[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. In proximity to nearby [[Eilat]], [[Israel]], an attractive intergrowth of turquoise, malachite, and chrysocolla is found. This [[rock (geology)|rock]] is called ''Eilat stone'' and is often referred to as ''Israel's national stone'': it is worked by local artisans for sale to tourists. === United States === [[Image:Chacoan turquoise with argillite.jpg|right|thumb|250px|A selection of [[Ancient Pueblo Peoples|Ancestral Puebloan]] (Anasazi) turquoise and orange [[argillite]] inlay pieces from [[Chaco Canyon]] (dated ca. 1020&ndash;1140 CE) show the typical colour range and mottling of American turquoise.]] [[Image:turquoisecollection.jpg|thumb|250px|Bisbee turquoise commonly has a hard chocolate brown coloured matrix, and is considered some of the finest in the world.]] The [[Southwest United States]] is a significant source of turquoise; [[Arizona]], [[California]] ([[San Bernardino County, California|San Bernardino]], [[Imperial County, California|Imperial]], and [[Inyo County, California|Inyo]] counties), [[Colorado]] ([[Conejos County, Colorado|Conejos]], [[El Paso County, Colorado|El Paso]], [[Lake County, Colorado|Lake]], and [[Saguache County, Colorado|Saguache]] counties), [[New Mexico]] ([[Eddy County, New Mexico|Eddy]], [[Grant County, New Mexico|Grant]], [[Otero County, New Mexico|Otero]], and [[Santa Fe County, New Mexico|Santa Fe]] counties) and [[Nevada]] ([[Clark]], [[Elko]], [[Esmerelda 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 in the United States|Native Americans]] using stone tools, some local and some from as far away as central [[Mexico]]. [[Cerrillos, New 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&mdash;rivalling Iranian material in both colour and durability&mdash;is sometimes found, most American turquoise is of a low grade (called "chalk turquoise"); high iron levels mean greens and yellows predominate, and a typically friable consistency precludes use in [[jewellery]] in the turquoise's untreated state. Arizona is currently the most important producer of turquoise by value, with the vivid [[Bisbee Blue]] being a good example of the state's natural endowment; much of the Arizona material is recovered as a byproduct of copper mining. 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 Esmerelda Counties. Most of the turquoise deposits in Nevada occur along a wide belt of [[tectonics|tectonic]] activity that coincides with the state's zone of thrust faulting. It strikes about N15E 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. Nevada produces some unique shades of bright mint to apple to neon yellow 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.<ref>Minerals of Nevada - Nevada Bureau of Mines Special Pub. 31 Pages 78-81; 443-445 </ref>[[Image:Turq mcGuin bunker.jpg|thumb|right|250px|Untreated turquoise, Nevada USA. Rough nuggets from the McGuinness Mine, Austin; Blue and green cabochons showing spiderweb, Bunker Hill Mine, Royston]] In 1912, the first deposit of distinct, single-crystal turquoise was discovered in [[Lynch Station]], [[Campbell County, Virginia|Campbell County]], [[Virginia]]. The crystals, forming a druse over the mother rock, are very small; 1 mm (0.04 inches) 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.<ref name="EFO">{{cite web|url=http://www.element51.com/article1.htm|title=Turquoise Crystal Localities| accessdate = 2006-09-23|publisher=Element 51}}</ref> The specimens are highly valued by collectors. 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|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 === [[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]], where green turquoise has long been appreciated, gem-quality deposits purportedly exist in the mountains of [[Derge]] and [[Nagari-Khorsum]] in the east and west of the region respectively.<ref>{{cite web|url=http://www.dharamsalanet.com/links/articles/turquoise.htm|title="Turquoise – The Gemstone of Tibet ", Article by Gemmologist Martin Watson| accessdate = 2007-06-01}}</ref> Other notable localities include: [[Afghanistan]]; [[Australia]] ([[Victoria (Australia)|Victoria]] and [[Queensland]]); northern [[Chile]] ([[Chuquicamata]]); [[Cornwall]]; [[Saxony]]; [[Silesia]]; and [[Turkestan]]. == History of its use == [[Image:Chacoan turquoise pendant.jpg|left|thumb|250px|Trade in turquoise crafts, such as this freeform pendant dating from 1000&ndash;1040 [[Anno Domini|CE]], is believed to have brought the Ancestral Puebloans of the Chaco Canyon great wealth.]] The pastel shades of turquoise have endeared it to many great cultures of antiquity: it has adorned the rulers of [[Ancient Egypt]], the [[Aztec]]s (and possibly other Pre-Columbian [[Mesoamerica]]ns), [[Persian Empire|Persia]], [[Mesopotamia]], the [[Indus Valley Civilization|Indus Valley]], and to some extent in ancient [[China]] since at least the [[Shang Dynasty]].<ref name="NGA">{{cite web|publisher=National Gallery of Art|location=Washington D.C.|url=http://www.nga.gov/exhibitions/china1999/096_053.htm|title=China Exhibition|date=1999| accessdate = 2006-09-23}}</ref> 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 empire|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 (lignite)|jet]], [[jade]], [[Coral (precious)|coral]], and [[animal shell|shells]], into provocative (and presumably ceremonial) [[mosaic]] objects such as [[mask]]s (some with a human [[skull]] as their base), [[knife|knives]], and [[shield]]s. Natural [[resin]]s, [[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 people|Pueblo]], [[Navajo Nation|Navajo]] and [[Apache (tribe)|Apache]] tribes cherished turquoise for its amuletic use; the latter tribe believe the stone to afford the [[Archery|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 [[Ancient Pueblo Peoples|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]] jewelry 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 [[turban]]s to [[bridle]]s), [[mosque]]s, and other important buildings both inside and out, such as the Medresseh-I Shah Husein Mosque of [[Isfahan (city)|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 [[engraving|engraved]] with devotional words in [[Arabic language|Arabic]] script which was then inlaid with gold. [[Image:Tutmask.jpg|right|thumb|The iconic gold burial mask of [[Tutankhamun]], inlaid with turquoise, [[lapis lazuli]], [[carnelian]] and coloured [[glass]].]] [[Cabochon]]s 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 [[Finger ring|rings]] and great sweeping [[necklace]]s called ''[[pectoral]]s''. 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 semblance created by an artificial glazed [[ceramic]] product known as [[faience]]. (A similar blue ceramic has been recovered from [[Bronze Age]] burial sites in the [[British Isles]].) The [[France|French]] conducted [[archaeology|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 c. 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 [[Fetishism|fetish]]es, such as those crafted by the [[Zuni]]. While strong sky blues remain superior in value, mottled green and yellowish material is popular with [[artisan]]s. In Western culture, turquoise is also the traditional [[birthstone]] for those born in the month of December. ===In Judeo-Christian scripture=== Turquoise may have significance in [[Judeo-Christian]] scripture: In the [[Book of Exodus]], the construction of a "breastplate of judgment" is described as part of the priestly vestments of [[Aaron]] (Exodus 28:15&ndash;30). Attached to the [[ephod]], the breastplate ([[Hoshen]]) was adorned with twelve [[gemstone]]s set in gold and arranged in four rows, each stone engraved with the name of one of the [[Israelite|Twelve Tribes of Israel]]. Of the four stones in the third row, the first and second have been translated to be turquoise by various scholars and English bible versions (usually not having both as turquoise at the same time); many others disagree, however.<ref name="NB">{{cite web|url=http://bible.ort.org/books/pentd2.asp?ACTION=displaypage&BOOK=2&CHAPTER=28|title=Navigating the Bible| accessdate = 2006-09-23}}</ref> In regard to the first of these stones, the translation is based on the [[Septuagint]] rendering the identity of the stone as ''chrysolithos'' (the [[masoretic text]] calls it ''tarshish'', which just refers to [[Tarshish]], a place, and gives no clue to the gem in question); at the time it was written ''chrysolithos'' did not mean [[Chrysolite]] specifically, but only ''golden stone'' (''chryso-lithos''). ''Chrysolithos'' is considered by scholars to possibly mean [[Topaz]], Chrysolite, yellow [[Jasper]], yellow [[Serpentine]], or Turquoise - the last of these on the basis that Turquoise contains golden flecks, and that [[targum]]s identified the stone as being ''sea coloured''. Scholars favour stones which are mostly yellow as being the more likely solution, and opaque stones (Jasper or Serpentine) as more likely than translucent ones, on the consideration of nearby stones in the Hoshen. In regard to the second of these stones, the masoretic text calls it ''shoham'', and the Septuagint calls it ''Beryllios'' ([[Beryl]]), though elsewhere it translates ''shoham'' as ''onychion'' ([[Onyx]]), or as ''smaragdos'' (''green stone''). ''Shoham'' is of uncertain meaning. Following the Septuagint, some people think the stone should be an onyx (and many more traditional English versions of the Bible take this translation), but scholars think that the stone is actually [[Malachite]] (because it is green like beryl and ''smaragdos'', cloudy as beryl can be, and in bands like onyx). Scholars also disagree as to which tribes of the [[Israelites]] each stone is meant to represent; traditional sources are in just as much disagreement. == Imitations == The Egyptians were the first to produce an artificial imitation of turquoise, in the glazed earthenware product [[faience]]. Later glass and [[vitreous enamel|enamel]] were also used, and in modern times more sophisticated ceramics, [[porcelain]], [[plastic]]s, and various assembled, pressed, bonded, and [[sinter]]ed 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 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 [[synthesis|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. [[Image:Chrysocolla USA.jpg|left|frame|Some natural blue to blue-green materials, such as this botryoidal [[chrysocolla]] with quartz drusy, are occasionally confused with, or used to imitate turquoise.]] 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]];<ref>{{cite web|url=http://minerals.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/turquoise.html|title=U.S. Geological Survey article on Turquoise| accessdate = 2007-06-01}}</ref> [[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&mdash;specifically for its use as a substitute for turquoise&mdash;in southern [[France]]. These fakes are detected by [[gemology|gemmologists]] 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 [[carbonate]]s odontolite and magnesite to [[effervescence|effervesce]] and howlite to turn green, while a heated probe may give rise to the acrid 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. Imitation turquoise is so prevalent that it likely outnumbers real turquoise by a wide margin. Even material used in ''authentic'' Native American and Tibetan jewellery is often fake or, at best, heavily treated. == Treatments == [[Image:Madan Turquoise Mines.jpg|thumb|300px|An early [[turquoise]] mine in the Madan village of Khorasan.]] 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. It is therefore left to [[Gemology|gemologists]] to detect these treatments in suspect stones using a variety of testing methods&mdash;some of which are necessarily destructive. For example, the use of a heated probe applied to an inconspicuous spot will reveal oil, wax, or plastic treatment with certainty. ===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 [[plastic]]s (such as [[polystyrene]]) and [[water glass]] 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.<ref name="Purists">{{cite web|url=http://www.geocities.com/harriss75007/turquois.htm|title="Turquoise", Article by Journalist Joseph A. Harriss| accessdate = 2007-06-01}}</ref> 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. Without such impregnation, most American mining operations would be unprofitable. ===Dyeing=== The use of [[Prussian blue]] and other dyes (often in conjunction with bonding treatments) to "enhance" &ndash; that is, make uniform or completely change &ndash; colour is regarded as fraudulent by some purists,<ref name="Purists">Purist Citation</ref> 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 radical of treatments is "reconstitution", wherein fragments of fine turquoise material, too small to be used individually, are powdered and then bonded to form a solid mass. Much, if not all, of this "reconstituted" material is likely artificial with no natural components, or may have foreign filler material added to it (see [[#Imitations|Imitations]] section). ===Zachery Processing=== Another treatment&mdash;the details of which remain undisclosed&mdash;is the so-called Zachery Process,<ref>{{cite web|url=http://www.khulsey.com/jewelry/semi-precious_gems_turquoise.html|title="Semi-Precious Gemstones - Turquoise", Kevin Hulsey Illustration, Inc.| accessdate = 2007-06-01}}</ref> named after its developer, [[electrical engineering|electrical engineer]] and turquoise trader James E. Zachery. This process claims to use only medium grade material at a minimum, leaving the turquoise harder and with a better colour and lustre. ===Backing=== Since finer turquoise is often found as thin seams, it may be [[adhesive|glue]]d to a base of stronger foreign material as a means of reinforcement. These stones are termed "Backed" and it is standard practice that all thinly cut turquoise in the Southwestern [[United States]] is backed. [[Native Americans in the United States|Native indigenous peoples]] of this region, because of their considerable use and wearing of turquoise, found that backing increased the durability of thinly cut slabs and cabs of turquoise. They observed that if the stone was not backed it would, for the most part, end up cracking. Early backing materials were the casings of old model T batteries and progressed to old phonograph records and most recently to the use of epoxy steel resins. Backing of turquoise is not known outside of the [[Indigenous peoples of the Americas|Native American]] and Southwestern United States jewelry trade. The value of turquoise of the highest quality is not discounted because it is backed and indeed the process is expected for most thinly cut American commercial gemstones.{{Fact|date=June 2007}} == Valuation and care == [[Image:turquoise-slab.jpg|right|thumb|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's egg" blue (in reference to the eggs of the [[American Robin]]).{{Fact|date=June 2008}} In [[Tibet]], however, a greener blue is said to be preferred.{{Who|date=June 2008}} Whatever the colour, turquoise should not be excessively 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&mdash;that is, stones adhering to standard jewellery setting measurements&mdash;may also be more sought after. Like [[Coral (precious)|coral]] and other opaque gems, turquoise is commonly sold at a price according to its physical size in millimetres rather than weight. Turquoise is [[#Treatments|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'' [[wax]]ing or [[oil]]ing 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 jewelry 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 build up 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== {{portalpar|Gemology and Jewelry|AEW diamond solo white.gif|35}} {{commonscat|Turquoise (mineral)}} *[[List of minerals]] ==Notes== <!--This article uses the Cite.php citation mechanism. If you would like more information on how to add references to this article, please see http://meta.wikimedia.org/wiki/Cite/Cite.php --> {{reflist}} == References == <div class="references-small"> *British Museum (2000). ''Aztec turquoise mosaics''. Retrieved [[November 15]], [[2004]] from [http://www.thebritishmuseum.ac.uk/compass/ixbin/hixclient.exe?_IXDB_=compass&_IXSR_=wz2&_IXSS_=_IXFPFX_%3dgraphical%252ffull%252f%26_IXsearchterm%3dturquoise%26%257bUPPER%257d%253av2_free_text_tindex%3dturquoise%26_IXDB_%3dcompass%26_IXNOMATCHES_%3dgraphical%252fno_matches%252ehtml%26%2524%2b%2528with%2bv2_searchable_index%2529%2bsort%3d%252e&_IXFIRST_=41&_IXMAXHITS_=1&_IXSPFX_=graphical/full/&_IXsearchterm=turquoise&submit-button=summary www.thebritishmuseum.ac.uk] *Dietrich, R. V. (2004). ''Turquoise''. Retrieved [[November 20]], [[2004]] from [http://www.cst.cmich.edu/users/dietr1rv/turquoise.htm www.cst.cmich.edu/users/dietr1rv/turquoise.htm] *Persian Turquoise Mine [http://www.Persian-Turquoise.ir] *Hurlbut, Cornelius S.; Klein, Cornelis, 1985, ''Manual of Mineralogy'', 20th ed., John Wiley and Sons, New York ISBN 0-471-80580-7 *King, R. J. (2002) ''Turquoise''. ''Geology Today'' 18 (3), pp. 110-114. Retrieved [[November 24]], [[2004]], from: [http://www.blackwell-synergy.com/links/doi/10.1046/j.1365-2451.2002.00345.x/full/ www.blackwell-synergy.com/links/doi/10.1046/j.1365-2451.2002.00345.x/full/] *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, Stuttgard, New York. ISBN 3-925369-54-6 *Schumann, W. (2000). ''Gemstones of the world'', revised edition. Sterling Publishing. ISBN 0-8069-9461-4 *USGS (2002). ''Turquoise''. ''An overview of production of specific U.S. gemstones''. U.S. Bureau of Mines Special Publication 14-19. Retrieved [[November 15]], [[2004]] from http://minerals.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/turquoise.html *Webster, R. (2000). ''Gems: Their sources, descriptions and identification'' (5th ed.), pp. 254-263. Butterworth-Heinemann, Great Britain. ISBN 0-7506-1674-1 </div> {{FA_link|de}} [[Category:Phosphate minerals]] [[Category:Aluminium minerals]] [[Category:Copper minerals]] [[Category:Gemstones]] [[Category:Symbols of New Mexico]] {{Link FA|de}} [[ar:فيروز (حجر كريم)]] [[ca:Turquesa (Mineral)]] [[cs:Tyrkys]] [[de:Türkis (Mineral)]] [[et:Türkiis]] [[es:Turquesa]] [[eo:Turkiso]] [[eu:Turkesa]] [[fa:فیروزه]] [[fr:Turquoise (pierre)]] [[gl:Turquesa]] [[hi:फीरोजा़]] [[it:Turchese]] [[he:טורקיז]] [[ka:ფირუზი]] [[la:Turcica]] [[lt:Turkis]] [[hu:Türkiz]] [[nl:Turkoois (mineraal)]] [[ja:トルコ石]] [[pl:Turkus]] [[pt:Turquesa]] [[qu:Anqas umiña]] [[ru:Бирюза]] [[sk:Tyrkys]] [[fi:Turkoosi]] [[sv:Turkos]] [[vi:Ngọc lam]] [[tr:Turkuaz (mineral)]] [[uk:Бірюза]]