Turquoise mines are found in many parts of the world, including the United States, China, Iran, the Sinai Peninsula, Bulgaria, Persia,  Tibet,  Afghanistan; Australia (Victoria and Queensland), northern India, northern Chile (Chuquicamata), Cornwall, Saxony, Silesi, and Turkestan. 

This gemstone has been known by many names. Pliny the Elder referred to the mineral as callais and the Aztecs knew it as chalchihuitl. 

The word turquoise dates to the 17th century and is derived from the French turquois for "Turkish" because the mineral was first brought to Europe through Turkey, from mines in the historical Khorasan Province of Persia.

In the United States, the earliest Turquoise Mine was what is now known as Cerrillos, NM. Turquoise Beads have been found at the Chaco Canyon Site dating back prior to 900 A.D. The Cerrillos Turquoise mines are still being mined on occasion, but not in commercial production.

In the late 1800's, the Navajo Indians started using Turquoise in their silver Jewelry and shortly after a market for Southwest Native American Turquoise Jewelry was born.

Soon after that the demand for Turquoise grew exponentially and prospectors began opening Turquoise mines in Arizona, Nevada, New Mexico and Colorado.

Turquoise Properties

The finest of turquoise reaches a maximum Mohs hardness of just under 6, or slightly more harder window glass. 

Characteristically a cryptocrystalline mineral, turquoise almost never forms single crystals, and all of its properties are highly variable.

Color 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.

Turquoise may also be peppered with flecks of pyrite or interspersed with dark, spidery limonite veining.

Other colors such as red, pink and purple that are marketed as rare colors of turquoise are actually dyed howlite or magnesite.

 Despite its low hardness relative to other gems, turquoise takes a good polish.

Turquoise Formation

As a secondary mineral, turquoise forms by the action of percolating acidic aqueous solutions during the weathering and oxidation of preexisting minerals. It is usually found in junction with copper deposits.

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 in the formation of turquoise, because 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. 

Typically turquoise mineralization is restricted to a relatively shallow depth of less than 66 feet (20 metres), although it does occur along deeper fracture zones where secondary solutions have greater penetration or the depth to the water table is greater.

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 habit. Stalactite forms have been reported. 

Turquoise Mining

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. It is often recovered from discarded tailings above ground.

The Southwest United States is a significant source of turquoise. Arizona, California (San Bernardino, Imperial, Inyo counties), Colorado(Conejos, El Paso, Lake, Saguache counties), New Mexico (Eddy, Grant, Otero, Santa Fe counties) and Nevada (Clark, Elko, Esmeralda County, Eureka, Lander, Mineral County and Nye counties) are (or were) especially rich.

The deposits of California and New Mexico were mined by pre-Columbian Native Americans using stone tools, some local and some from as far away as central Mexico. 

Cerrillos, New Mexico is thought to be the location of the oldest mines. Prior to the 1920s, the state was the United States' largest producer. It is more or less exhausted today. Only one mine in California, located at Apache Canyon, operates at a commercial capacity today.

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 unless it is "stabilized", a process where it is injected with plastic polymers to harden it.

Arizona is currently the most important producer of turquoise by value. Several mines exist in the state, two of them famous for their unique colour and quality and considered the best in the industry. The Sleeping Beauty Mine in Globe, Arizona ceased turquoise mining in August 2012.

This mine then chose to send all ore to the crusher and to concentrate on copper production due to the rising price of copper on the world market. The price of natural untreated Sleeping Beauty turquoise has risen dramatically since the mine's closing.

The Kingman Mine as of 2015 still operates alongside a copper mine outside of the city. Other mines include the Blue Bird mine, Castle Dome, and Ithaca Peak, but they are mostly inactive due to the high cost of operations and federal regulations.

The Phelps Dodge Lavender Pit mine at Bisbee ceased operations in 1974 and never had a turquoise contractor. All Bisbee turquoise was "lunch pail" mined. It came out of the copper ore mine in miners' lunch pails.

Morenci and Turquoise Peak are either inactive or depleted.

Nevada 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 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 faulting. It strikes about N15°E and extends from the northern part of Elko County, southward down to the California border southwest of Tonopah.

Nevada has produced a wide diversity of colours and mixes of different matrix patterns, with turquoise from Nevada coming in various shades of blue, blue-green, and green. Some of this unusually coloured turquoise may contain significant zinc and iron, which 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.