Editing Turquoise

{{Short description|Opaque, blue-to-green mineral}}
{{About|the mineral|the color|Turquoise (color)|5=Turquoise (disambiguation)}}
{{more citations needed|date=June 2022}}
{{Infobox mineral
| name        = Turquoise
| category    = [[Phosphate mineral]]s
| boxwidth    =
| boxbgcolor  =#00CED1
| image       = Turquoise-40031.jpg
| caption     = 
| formula     = {{chem2|CuAl6(PO4)4(OH)8*4H2O}}
| IMAsymbol   = Tqu<ref>{{cite journal |last=Warr|first=L. N. |date=2021 |title=IMA–CNMNC approved mineral symbols |journal=[[Mineralogical Magazine]] |volume=85 |issue=3 |pages=291–320 |doi=10.1180/mgm.2021.43 |bibcode=2021MinM...85..291W |s2cid=235729616|doi-access=free }}</ref>
| strunz      = 8.DD.15
| system      = [[triclinic crystal system|Triclinic]]
| class       = Pinacoidal ({{Overline|1}}) <br /><small>(same [[H–M symbol]])</small>
| colour      = [[turquoise (color)|Turquoise]], blue, [[blue-green]], green
| habit       = Massive, nodular
| twinning    =
| cleavage    = Perfect on {001}, good on {010}, but cleavage rarely seen
| fracture    = [[conchoidal fracture|Conchoidal]]
| mohs        = 5–6
| luster     = Waxy to subvitreous
| refractive  = ''n<sub>α</sub>'' = 1.610<br />''n<sub>β</sub>'' = 1.615<br />''n<sub>γ</sub>'' = 1.650
| opticalprop = Biaxial (+)
| birefringence = +0.040
| pleochroism = Weak
| streak      = Bluish white
| gravity     = 2.6–2.9
| melt        =
| fusibility  = Fusible in heated [[hydrochloric acid|HCl]]
| diagnostic  =
| solubility  = Soluble in [[hydrochloric acid|HCl]]
| diaphaneity = [[opacity (optics)|Opaque]]
| references  =<ref name="Hurlbut">{{cite book |last1=Hurlbut|first1=Cornelius S. |last2=Klein|first2=Cornelis |year=1985 |title=Manual of Mineralogy |edition=20th |publisher=[[Wiley (publisher)|John Wiley & Sons]] |location=New York |isbn=978-0-471-80580-9 |url-access=registration |url=https://archive.org/details/manualofmineralo00klei}}</ref><ref name="mindat">{{Mindat |id=4060 |name=Turquoise |access-date=2006-10-04}}. {{Cite web |url=http://www.mindat.org/min-4060.html |title=Turquoise: Turquoise mineral information and data |access-date=2006-10-04 |archive-date=2006-11-12 |archive-url=https://web.archive.org/web/20061112155323/http://www.mindat.org/min-4060.html |url-status=bot: unknown }}.</ref><ref name="rruff">{{cite book |editor1-last=Anthony |editor1-first=John W. |editor2-last=Bideaux |editor2-first=Richard A. |editor3-last=Bladh |editor3-first=Kenneth W. |editor4-last=Nichols |editor4-first=Monte C. |title=Handbook of Mineralogy |publisher=[[Mineralogical Society of America]] |location=[[Chantilly, Virginia]] |chapter-url=http://rruff.info/doclib/hom/turquoise.pdf |chapter=Turquoise |isbn=978-0-9622097-3-4 |volume=IV |year=2000 |url-status=live |archive-url=https://web.archive.org/web/20120211163838/http://rruff.geo.arizona.edu/doclib/hom/turquoise.pdf |archive-date=2012-02-11 }}</ref>
}}

'''Turquoise''' is an [[opacity (optics)|opaque]], [[blue-green|blue-to-green]] [[mineral]] that is a [[hydrate|hydrous]] [[phosphate]] of [[copper]] and [[aluminium]], with the [[chemical formula]] {{chem2|[[copper|Cu]][[aluminium|Al]]6([[phosphate|PO4]])4([[hydroxide|OH]])8*4[[water|H2O]]}}. It is rare and valuable in finer grades and has been prized as a [[gemstone]] for millennia due to its hue.

The [[robin egg blue]] or [[sky blue]] color of the [[Iran|Persian]] turquoise mined near the modern city of [[Nishapur]], [[Iran]], has been used as a guiding reference for evaluating turquoise quality.<ref>{{cite web |title=Turquoise Quality Factors |url=https://gia.edu/turquoise-quality-factor |publisher=[[Gemological Institute of America]]}}</ref>

Like most other opaque gems, turquoise has been devalued by the introduction of treatments, imitations, and synthetics into the market. 

==Names==
The word ''turquoise'' dates to the 17th century and is derived from the [[Old French]] ''turquois'' meaning "Turkish" because the mineral was first brought to Europe through the [[Ottoman Empire]].<ref name="Beale-1973">{{Cite journal|last=Beale|first=Thomas W.|date=October 1973|title=Early trade in highland Iran: A view from a source area|url=http://www.tandfonline.com/doi/abs/10.1080/00438243.1973.9979561|journal=World Archaeology|language=en|volume=5|issue=2|pages=133–148|doi=10.1080/00438243.1973.9979561|issn=0043-8243|url-access=subscription}}</ref><ref name="mindat" /><ref name="rruff" /><ref name=Dana>{{cite book|last1=Palache|first1=C.|first2=H.|last2=Berman|first3=C.|last3=Frondel|date=1951|title=Dana's System of Mineralogy|publisher=Wiley|edition=7th|volume=II|pages=946–951}}</ref><ref name=USGS>[http://minerals.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/turquoise.html Turquoise] {{webarchive|url=https://web.archive.org/web/20070520223504/http://minerals.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/turquoise.html |date=2007-05-20 }}. minerals.usgs.gov</ref> 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.<ref>{{cite web |title=Turquoise - Etymology, origin and meaning of turquoise by etymonline |url=https://www.etymonline.com/word/turquoise |website=Online Etymology Dictionary (Etymonline) |publisher=Online Etymology Dictionary |archive-url=https://web.archive.org/web/20211208140515/https://www.etymonline.com/word/turquoise |access-date=8 December 2021|archive-date=2021-12-08 }}</ref> [[Pliny the Elder]] referred to the mineral as ''callais'' (from [[Ancient Greek]] {{lang|grc|κάλαϊς}}) and the [[Aztec]]s knew it as ''chalchihuitl''.<ref name="Dana" />

In professional mineralogy, until the mid-19th century, the scientific names ''kalaite''<ref name="Edinburgh">The Edinburgh Encyclopaedia, 1st American ed., Volume 13. — J. and E. Parker edition, 1832.</ref>{{rp|571-572}} or [[azure spar]] were also used, which simultaneously provided a version of the mineral origin of turquoise.<ref name="Brit">Encyclopaedia Britannica, Volume fifth. — Edinburgh: printed for Archibald Constable and Company, 1824.</ref>{{rp|452}} However, these terms did not become widespread and gradually fell out of use.

== History ==
Turquoise mining in New Mexico's [[Cerrillos Hills State Park|Cerrillos Hills]] began with Native Americans, later attracting brief European interest in the late 1800s. Prices peaked in 1890, then collapsed by 1912, ending large-scale operations.<ref>https://www.cerrilloshills.org/history/turquoise-mining-history</ref> During [[Mohammad Khodabanda]] reign (1578-1587), accumulated turquoise dust from fifty years of mining in [[Safavid Iran]] was squandered lavishly, reflecting royal excess amid economic hardship, political discord, and rising factionalism among the qezelbash elite.<ref>{{cite book |last=Munshi |first=Eskandar Beg |author-link=Iskandar Beg Munshi |date=1629 |title=History of Shah 'Abbas the Great (Tārīkh-e ‘Ālamārā-ye ‘Abbāsī) / Roger M. Savory, translator |edition= |url=https://archive.org/details/monshi-shah-abbas-english/Monshi_Shah-Abbas_English/page/341/mode/1up |access-date=May 10, 2025|page=341}}</ref>

== Properties ==
The finest of turquoise reaches a maximum [[Mohs scale of mineral hardness|Mohs 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. [[X-ray diffraction]] testing shows its [[crystal system]] to be [[triclinic]].<ref name="rruff" /><ref>{{cite web |url=http://rruff.info/Turquoise/R050554 |publisher=RRUFF Project |title=Turquoise R050554 |url-status=dead |archive-url=https://web.archive.org/web/20170502182409/http://rruff.info/Turquoise/R050554 |archive-date=2017-05-02 |access-date=2017-10-19 }}</ref> With lower hardness comes greater [[porosity]].<ref  name=Sinkankas1964>{{cite book |last1=Sinkankas |first1=John |title=Mineralogy for amateurs. |date=1964 |publisher=Van Nostrand |location=Princeton, N.J. |isbn=0442276249 |pages=425–426}}</ref> The [[Lustre (mineralogy)|lustre]] of turquoise is typically waxy to subvitreous, and its [[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 [[Minerals#Colour and streak|idiochromatic]] copper<ref name=Rossman1981>{{cite journal|last1=Rossman |first1=G. R. |year=1981 |title=Color in gems: The new technologies |journal=Gems & Gemology |volume=17 |number=2 |pages=60–71 |doi=10.5741/GEMS.17.2.60 |url=https://www.gia.edu/doc/SU81.pdf |access-date=13 August 2022}}</ref> while the green may be the result of [[iron]] impurities (replacing copper.)<ref name="VigierEtal2019">{{cite book |editor1-last=Vigier |editor1-first=Emmanuelle |editor2-last=Querré |editor2-first=Guirec |editor3-last=Cassen |editor3-first=Serge |title=La parure en callaïs du néolithique européen |date=2019 |publisher=Archaeopress Publishing Ltd. |location=Oxford |isbn=9781789692815 |url=https://books.google.com/books?id=-vIYEAAAQBAJ |access-date=13 August 2022}}</ref>{{rp|29}}

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.<ref name=Hurlbut/>

Crushed turquoise is soluble in hot [[hydrochloric acid]].<ref name=Sinkankas1964/> Its [[Streak (mineralogy)|streak]] is white to greenish to blue, and its [[fracture]] is smooth to [[conchoidal fracture|conchoidal]].<ref name="rruff"/> 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 the microscopic scale, are rare. Typically the form is a vein or fracture filling, nodular, or [[botryoidal]] in [[crystal habit|habit]].<ref name="Hurlbut"/> [[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 historically been 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. Turquoise is distinguished from chrysocolla, the only common mineral with similar properties, by its greater hardness.<ref name="Hurlbut"/>

Turquoise forms a complete [[solid solution]] series with '''chalcosiderite''', {{chem2|CuFe6(PO4)4(OH)8*4H2O}}, in which [[ferric]] iron replaces aluminium.<ref name=Hurlbut/>

== Formation ==
[[File:Big turquoise from Cananea.jpg|thumb|"Big Blue", a large turquoise specimen from the [[copper mine]] at [[Cananea]], [[Sonora]], Mexico]]
Turquoise deposits probably form in more than one way.<ref>{{cite web|last=Dietrich|first=R. V.|date=2004|title=Turquoise|access-date=November 20, 2004|url=http://www.cst.cmich.edu/users/dietr1rv/turquoise.htm|publisher=University of Central Michigan|archive-url=https://web.archive.org/web/20041220062508/http://www.cst.cmich.edu/users/dietr1rv/turquoise.htm|archive-date=December 20, 2004|url-status=dead}}</ref> However, a typical turquoise deposit begins with [[hydrothermal mineral deposit|hydrothermal deposition]] of [[copper sulfide]]s. This takes place when hydrothermal fluids leach copper from a host rock, which is typically an [[Igneous intrusion|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 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 [[mica]]s at a temperature of {{convert|400-600|C|F|sp=us}}<ref name="rruff"/><ref>{{cite journal |last1=Watanabe |first1=Yasushi |last2=Sato |first2=Ryuya |last3=Sulaksono |first3=Adi |title=Role of Potassic Alteration for Porphyry Cu Mineralization: Implication for the Absence of Porphyry Cu Deposits in Japan: Role of potassic alteration in porphyry system |journal=Resource Geology |date=April 2018 |volume=68 |issue=2 |pages=195–207 |doi=10.1111/rge.12165|doi-access=free }}</ref><ref>{{cite web |title=Hydrothermal Alteration |url=https://geologyscience.com/applied-geology/mining-geology/hydrothermal-alteration/ |website=Geology Science |access-date=11 November 2020 |date=2020}}</ref>

Turquoise is a [[secondary mineral|secondary]] or [[supergene (geology)|supergene]] mineral, not present in the original copper porphyry.<ref name="rruff"/> It forms when [[meteoric water]] (rain or snow melt infiltrating 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.<ref name="king-2002">{{cite journal |last1=King |first1=R. J. |title=Turquoise |journal=Geology Today |date=May 2002 |volume=18 |issue=3 |pages=110–114 |doi=10.1046/j.1365-2451.2002.00345.x|s2cid=241236951 }}</ref> This typically fills veins in volcanic rock or phosphate-rich sediments.<ref name="rruff"/> Deposition usually takes place at a relatively low temperature, {{convert|90-195|C|F|sp=us}}, and seems to occur more readily in arid environments.<ref name="king-2002"/>

Turquoise in the [[Sinai Peninsula]] is found in [[lower Carboniferous]] [[sandstone]]s 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]] [[trachyte]]s and [[mafic]] rock. Supergene alteration fractured 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 {{convert|9|m|feet|sp=us}} below the surface.<ref name="king-2002"/>

Turquoise deposits are widespread in North America. Some deposits, such as those of [[Saguache County, Colorado|Saguache]] and [[Conejos County, Colorado|Conejos]] Counties in Colorado<ref name="king-2002"/> or the [[Cerrillos Hills State Park|Cerrillos Hills]] in New Mexico,<ref>{{cite web |last1=Kretzmann |first1=John A. |last2=Moiola |first2=Lloyd A. |year=2014 |citeseerx=10.1.1.505.2557 |title=Historic preservation in the Cerrillos mining district |url=http://www.emnrd.state.nm.us/Mmd/AML/documents/CerrillosSouthAMLConferencePaper.pdf |access-date=9 June 2020}}</ref><ref>{{Cite web |title=Turquoise Mining History: Cerrillos Hills |url=https://www.cerrilloshills.org/history/turquoise-mining-history |access-date=2023-09-27 |website=www.cerrilloshills.org}}</ref> are typical supergene deposits formed from copper porphyries. The deposits in [[Cochise County, Arizona]], are found in [[Cambrian]] [[quartzite]]s and geologically young [[granite]]s and go down at least as deep as {{convert|54|m|feet|sp=us}}.<ref name="king-2002"/>

== Occurrence ==
[[File:Turquoise with quartz.jpg|left|thumb|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.<ref>{{Cite journal |last=King |first=R. J. |date=2002 |title=Turquoise |url=http://www.blackwell-synergy.com/links/doi/10.1046/j.1365-2451.2002.00345.x/full/ |journal=Geology Today |volume=18 |issue=3 |pages=110–111}}</ref>
[[File:Turquoise of Nishapur - village of Ma'dan 14.JPG|alt=Turquoise of Madan-e Olya of Nishapur|thumb|Turquoise of [[Madan-e Olya]] of [[Nishapur]]]] Deposits typically take the form of small [[Vein (geology)|veins]] in partially decomposed volcanic rock in arid climates.<ref name=Hurlbut/>

=== Iran ===
[[Iran]] has been an important source of turquoise for at least 2,000 years. It was initially named by [[Iranian peoples|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 [[dome]]s of [[palace]]s because its intense blue colour was also a symbol of heaven on earth.<ref name="Beale-1973" /><ref>Farmani, Anousheh (2015) ''"Precious and semi-precious minerals and their roots in ancient Persian texts"'', Second International Congress of Science and Earth, Tehran [https://web.archive.org/web/20231028133214/https://fa.seminars.sid.ir/ViewPaper.aspx?ID=35943]</ref><ref>{{Cite book|last=zawush|first=Muhammad|title=mineralogy in Ancient Iran|publisher=Institute of Humanities and Cultural Studies|year=1996|isbn=9789644260315|location=tehran|pages=156}}</ref>
[[File:Persian Turquoise.jpg|thumb|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 {{convert|2012|m|ft|adj=on|abbr=on}} 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 the [[Sinai Peninsula]].<ref name=USGS /> Iran also has turquoise mines in [[Semnan Province|Semnan]] and [[Kerman]] provinces.<ref name="Beale-1973" />

=== Sinai ===
Since at least the [[First Dynasty of Egypt|First Dynasty]] (3000&nbsp;[[Common Era|BCE]]) in [[ancient Egypt]], and possibly before then, turquoise was used by the [[Egyptians]] and was [[mining|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 {{convert|650|km2|abbr=on}}. The two most important of these mines, from 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 the deposits are sporadically quarried by [[Bedouin]] peoples using homemade [[gunpowder]].{{Citation needed|date=March 2014}} 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 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.

[[File:Chacoan turquoise with argillite.jpg|right|thumb|A selection of [[Ancestral Puebloans|Ancestral Pueblo]] (Anasazi) turquoise and orange [[argillite]] inlay pieces from [[Chaco Canyon]], [[New Mexico]], US (dated {{circa}} 1020–1140) show the typical colour range and mottling of American turquoise. Some likely came from [[Los Cerrillos, New Mexico|Los Cerrillos]].]]

=== United States ===
[[File:Turquoise Cerillos Smithsonian.jpg|thumb|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.]]
[[File:turquoisecollection.jpg|thumb|Bisbee turquoise commonly has a hard chocolate brown coloured matrix.]]
[[File:Turq mcGuin bunker.jpg|thumb|right|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 County, California|San Bernardino]], [[Imperial County, California|Imperial]], [[Inyo County, California|Inyo]] counties), [[Colorado]] ([[Conejos County, Colorado|Conejos]], [[El Paso County, Colorado|El Paso]], [[Lake County, Colorado|Lake]], [[Saguache County, Colorado|Saguache]] counties), [[New Mexico]] ([[Eddy County, New Mexico|Eddy]], [[Grant County, New Mexico|Grant]], [[Otero County, New Mexico|Otero]], [[Santa Fe County, New Mexico|Santa Fe]] counties) and [[Nevada]] ([[Clark County, Nevada|Clark]], [[Elko, Nevada|Elko]], [[Esmeralda County, Nevada|Esmeralda County]], [[Eureka, Nevada|Eureka]], [[Lander County, Nevada|Lander]], [[Mineral County, Nevada|Mineral County]] and [[Nye County, Nevada|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 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 [[jewelry]].

[[Arizona]] is currently the most important producer of turquoise by value.<ref name=USGS /> 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, Arizona|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, Arizona|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, Arizona|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 [[wikt:nugget|nugget]]s, fracture fillings and in [[breccia]]s 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 County, Nevada|Lander]] and [[Esmeralda County, Nevada|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 fault]]ing. It [[Strike and dip|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|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,{{which|date=April 2019}} the total [[Nevada]] turquoise production since the 1870s has been estimated at more than {{convert|600|ST}}, including nearly {{convert|400|ST}} 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, Nevada|Mineral County]], and several properties in the Royston and [[Candelaria, Nevada|Candelaria]] areas of Esmerelda County.<ref>{{cite book|title=Minerals of Nevada|publisher=Nevada Bureau of Mines|series=Special Publication 31|pages=78–81, 443–445}}</ref>

In 1912, the first deposit of distinct, single-crystal turquoise was discovered at [[Lynch Station, Virginia|Lynch Station]] in [[Campbell County, Virginia|Campbell County]], [[Virginia]]. The crystals, forming a [[Druse (geology)|druse]] over the mother rock, are very small; {{convert|1|mm|in|2|abbr=on}} 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.{{citation needed|date=May 2015}}

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 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 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.<ref>{{cite journal|last1=Kostov|first1=R. I.|first2=J.|last2=Chapman|first3=B.|last3=Gaydarska|first4=I.|last4=Petrov|first5=A.|last5=Raduntcheva|date=2007|title=Turquoise – archaeomineralogical evidences from the Orlovo prehistoric site (Haskovo district, Southern Bulgaria)|journal=Geology and Mineral Resources|volume=14|issue=7–8|pages=17–22}}</ref> 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).<ref>{{Cite book |last=Calvo Rebollar |first=Miguel |title=Minerales y Minas de España. Vol. VII. Fosfatos, Arseniatos y Vanadatos. |publisher=Escuela Técnica Superior de Ingenieros de Minas de Madrid. Fundación Gómez Pardo. |year=2015 |isbn=978-84-95063-96-0 |location=Zaragoza, Spain |pages=347–348 |language=es |trans-title=Minerals and mines of Spain}}</ref>

[[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 [[Yun County, Hubei|Yunxian]] and [[Zhushan County|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.<ref name="dharamsalanet.com">{{cite web|url=http://www.dharamsalanet.com/links/articles/turquoise.htm |title=Turquoise – The Gemstone of Tibet|first=Martin|last=Watson |access-date=2007-06-01 |url-status=dead |archive-url=https://web.archive.org/web/20070319222057/http://www.dharamsalanet.com/links/articles/turquoise.htm |archive-date=March 19, 2007 }}</ref>

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

== History of use ==
[[File:Chacoan turquoise pendant.jpg|left|thumb|Trade in turquoise crafts, such as this freeform pendant dating from 1000 to 1040, is believed to have brought the [[Ancestral Pueblo]] people of the [[Chaco Canyon]] great wealth.]]
[[File:Turqoise nose ornament.jpg|right|thumb|[[Moche culture|Moche]] turquoise nose ornament. [[Larco Museum]] Collection, Lima, Peru]]
[[File:Drevnosti RG v3 ill094 - Palash.jpg|left|thumb|Backswords, inlaid with turquoise. Russia, 17th century]]
[[File:Xiuhtecuhtli (mask).jpg|right|thumb|Turquoise mosaic mask of [[Xiuhtecuhtli]], the [[Aztec]] god of fire. The Aztecs differentiated turquoise based on quality: ''xihuitl'', a more mundane version used for decoration such as in mosaics, and ''teoxihuitl'', a special version embued with qualities of ''[[Teotl]]'' and valued for its beauty.<ref>{{cite book |last1=Bassett |first1=Molly H. |title=The fate of earthly things : Aztec gods and god-bodies |date=2015 |location=Austin |isbn=9780292760882 |page=105 |edition=First}}</ref>]]
[[File:CairoEgMuseumTaaMaskMostlyPhotographed.jpg|right|thumb|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 [[Aztec]]s (and possibly other Pre-Columbian [[Mesoamerica]]ns), [[Greater Iran|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, DC |url=http://www.nga.gov/exhibitions/china1999/096_053.htm |title=China Exhibition |year=1999 |access-date=2006-09-23 |url-status=dead |archive-url=https://web.archive.org/web/20060930014758/http://www.nga.gov/exhibitions/china1999/096_053.htm |archive-date=2006-09-30 }}</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 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 (lignite)|jet]], [[jade]], [[Coral (precious)|coral]], and [[Exoskeleton|shells]], into provocative (and presumably ceremonial{{Clarify|date=November 2019}}) [[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. In Navajo culture it is used for "a spiritual protection and blessing."<ref>{{Cite web |date=2022-02-03 |title=How turquoise became synonymous with New Mexico |url=https://www.nationalgeographic.com/travel/article/how-turquoise-became-synonymous-with-new-mexico |archive-url=https://web.archive.org/web/20220203152409/https://www.nationalgeographic.com/travel/article/how-turquoise-became-synonymous-with-new-mexico |url-status=dead |archive-date=February 3, 2022 |access-date=2023-09-27 |website=Travel |language=en}}</ref> 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 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 [[turban]]s to [[bridle]]s), [[mosque]]s, and other important buildings both inside and out,{{citation needed|date=June 2014}} such as the [[Shah Mosque (Isfahan)|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.

[[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 [[Ancient Egypt]]ian use of turquoise stretches back as far as the [[First Dynasty of Egypt|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 (Ancient Egypt)|pectorals]]''. Set in gold, the gem was fashioned into beads, used as inlay, and often carved in a [[scarab (artifact)|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{{Clarify|date=November 2019}}) the first gemstone to be imitated, the fair structure created by an artificial glazed [[ceramic]] product known as [[Egyptian faience|faience]].

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 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 [[Fetishism|fetishes]], such as those crafted by the [[Zuni people|Zuni]]. While strong sky blues remain superior in value, mottled green and yellowish material is popular with [[artisan]]s.

== Cultural associations ==

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".<ref>{{cite book|title=Bulletin of the Egyptian Museum|date=2007|author=The Supreme Council of Antiquities|page=24}}</ref>

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 [[Kohen Gadol|High Priest]]'s [[breastplate]], described in [[Book of Exodus|Exodus]] chapter 28. The stone is also considered sacred to the indigenous [[Zuni people|Zuni]] and [[Pueblo]] peoples of the American Southwest.<ref>{{cite book |last1=Lowry |first1=Joe Dan |title=Turquoise : the world story of a fascinating gemstone |location=Layton, Utah |isbn=978-1423650898 |date=2018 |pages=36–41 |edition=Updated |url=https://books.google.com/books?id=gRkkACkgN2AC&q=Lowry%2C+Joe+Dan.+Turquoise.+p.%C2%A036%E2%80%9341.&pg=PA6 |access-date=11 November 2020}}</ref><ref>{{cite book|series=Collector's Guide|volume=17|title=Sharing the Art of New Mexico|date=2003|page=184}}</ref> The pre-Columbian [[Aztec]] and [[Maya people|Maya]] also considered it to be a valuable and culturally important stone.{{sfn|Lowry|2018|page=34}}

== Imitations ==
{{unreferenced section|date=April 2019}}
[[File:Chrysocolla USA.jpg|left|frame|Some natural blue to blue-green materials, such as this [[botryoid]]al [[chrysocolla]] with [[Drusy stones|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 [[Egyptian faience|faience]]. Later glass and [[vitreous enamel|enamel]] were also used, and in modern times more sophisticated [[porcelain]], [[plastic]]s, and various assembled, pressed, bonded, and [[Sintering|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 [[Chemical 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.

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 name=USGS /> [[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 [[gemology|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 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 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 ==
{{more citations needed section|date=June 2022}}
[[File:Madan Turquoise Mines.jpg|thumb|An early turquoise mine in Madan, [[Khorasan Province]], Iran]]
Turquoise is treated to enhance both its colour and durability (increased [[hardness]] and decreased [[porosity]]). As is so often the case with any precious stones, full disclosure about treatment is frequently not given. [[Gemology|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.)

=== Backing ===
Since finer turquoise is often found as thin seams, it may be [[adhesive|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 Americans in the United States|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. Backing of turquoise is not widely known outside of the [[Indigenous peoples of the Americas|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.{{Citation needed|date=June 2007}}

=== Zachery treatment===
A proprietary process was created by electrical engineer and turquoise dealer James E. Zachery in 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 is treated only for porosity, the treatment is undetectable.<ref>{{cite journal |last1=Fritsch |first1=Emmanuel |last2=McClure |first2=Shane F. |last3=Ostrooumov |first3=Mikhail |last4=Andres |first4=Yves |last5=Moses |first5=Thomas |last6=Koivula |first6=John I. |last7=Kammerling |first7=Robert C. |title=The identification of Zachery-treated turquoise |journal=Gems & Gemology |date=Spring 1999 |volume=35 |pages=4–16 |doi=10.5741/GEMS.35.1.4 |url=https://www.gia.edu/doc/The-Identification-of-Zachery-Treated-Turquoise.pdf |access-date=14 May 2022}}</ref><ref name="Schwarzinger22017">{{cite journal |last1=Schwarzinger |first1=Bettina |last2=Schwarzinger |first2=Clemens |title=Investigation of turquoise imitations and treatment with analytical pyrolysis and infrared spectroscopy |journal=Journal of Analytical and Applied Pyrolysis |date=May 2017 |volume=125 |pages=24–31 |doi=10.1016/j.jaap.2017.05.002}}</ref>

=== 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,<ref name="Purists" /> especially since some dyes may fade or rub off on the wearer. Dyes have also been used to darken the veins of turquoise.

=== 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]] (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.<ref name="Purists">{{cite web |url=http://www.geocities.com/harriss75007/turquois.htm |title=Tantalizing Turquoise|last=Harriss|first= Joseph A. | access-date = 2007-06-01 |archive-url=https://web.archive.org/web/20080201025038/http://www.geocities.com/harriss75007/turquois.htm|archive-date=2008-02-01}}</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.

=== 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 [[#Imitations|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".

== Valuation and care ==
{{unreferenced section|date=April 2019}}
[[File:turquoise-slab.jpg|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 blue|sky]] to [[robin egg blue]] (in reference to the eggs of the [[American robin]]).<ref name="dharamsalanet.com" /> 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;<ref name=Hurlbut/> 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 (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 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. {{Citation needed|date=December 2020}}

== See also ==
* {{Annotated link|Bisbee Blue}}, with a deep blue color
* {{Annotated link|Lapis lazuli}}, with a deep blue color
* {{Annotated link|Lazurite}}, with a deep blue color
* [[List of minerals]]
* {{Annotated link|Variscite}} of pale green color due to trivalent chromium ({{Chem|Cr|3+}})

{{Clear}}

== References ==
{{Reflist}}

== Further reading ==
{{Refbegin}}
* {{cite web|author=British Museum|date=2000|title=Aztec turquoise mosaics|url=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%2Ffull%2F&_IXsearchterm=turquoise&submit-button=summary|access-date=November 15, 2004|url-status=dead|archive-url=https://web.archive.org/web/20070311072224/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%2Ffull%2F&_IXsearchterm=turquoise&submit-button=summary|archive-date=March 11, 2007|website=www.thebritishmuseum.ac.uk}}
* {{cite book| last=King| first=J.C.H., Max Carocci, Caroline Cartwright |date=2012|title=Turquoise in Mexico and North America: Science, Conservation, Culture and Collections| publisher= British Museum, London, UK.}}
* {{cite book|last=Pogue|first=J. E.|date=1915|title=The Turquoise: A study of its history, mineralogy, geology, ethnology, archaeology, mythology, folklore, and technology|publisher=National Academy of Sciences, The Rio Grande Press|location=Glorieta, NM|isbn=0-87380-056-7}}
* {{cite book|last=Schadt|first=H.|date=1996|title=Goldsmith's Art: 5000 Years of Jewelry and Hollowware|publisher=Arnoldsche Art Publisher|location=Stuttgart & New York, NY|isbn=3-925369-54-6}}
* {{cite book|last=Schumann|first=W.|date=2000|title=Gemstones of the World|url=https://archive.org/details/gemstonesofworld00schu|url-access=registration|edition=revised|publisher=Sterling Publishing|isbn=0-8069-9461-4}}
* {{cite book|last=Webster|first=R.|date=2000|title=Gems: Their Sources, Descriptions and Identification|edition=5th|pages=254–263|publisher=Butterworth-Heinemann|location=Great Britain|isbn=0-7506-1674-1}}
{{Refend}}

== External links ==
* {{Commons category-inline|Turquoise (mineral)}}

{{Phosphate minerals}}
{{Gemstones}}
{{Jewellery}}

{{Authority control}}

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