Editing Turquoise (section)

=== 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.