Editing Turquoise (section)

== 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"/>