Turquoise

:This article is about the gem. For the colour, see turquoise (color) and cyan.

Occurrence

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.

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Iran

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 is restricted to a mine-riddled, 2,012-metre mountain peak of Ali-mersai, 25 km 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.

Related Topics:
Persia - Ali-mersai - Mashhad - Khorasan - Trachyte - Scree - Sinai Peninsula

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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.

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Sinai

Since at least the First Dynasty (3,000 BCE), and possibly before then, turquoise was used by the Egyptians and was 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.

Related Topics:
First Dynasty - BCE - Egyptians - Mined - Serabit el-Khadim - Wadi Maghareh - Hathor

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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.

Related Topics:
Basalt - Bedouin - Gunpowder - Flash flooding

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In proximity to nearby Eilat, Israel, an attractive intergrowth of turquoise, malachite, and chrysocolla is found. This 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.

Related Topics:
Eilat - Israel - Rock

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United States

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The Southwest United States is a significant source of turquoise; Arizona, California (San Bernardino, Imperial, and Inyo counties), Colorado (Conejos, El Paso, Lake, and Saguache counties), New Mexico (Eddy, Grant, Otero, and Santa Fe counties) and Nevada 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 country's largest producer; it is more or less exhausted today.

Related Topics:
Southwest United States - Arizona - California - San Bernardino - Imperial - Inyo - Colorado - Conejos - El Paso - Lake - Saguache - New Mexico - Eddy - Grant - Otero - Santa Fe - Nevada - Pre-Columbian - Native American - Mexico - Cerrillos - 1920

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Only one mine in California, located at Apache Canyon, operates at a commercial capacity today.

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The turquoise occurs as vein or seam fillings, and as compact nuggets; these are mostly small in size. While quite fine material—rivalling Iranian material in both colour and durability—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 an estimated 75–100 mines opened over the state's history. The Nevada material is noted for its often attractive brown or black limonite veining, producing what is called "spiderweb matrix".

Related Topics:
Jewellery - Bisbee Blue

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In 1912, the first deposit of distinct, single-crystal turquoise was discovered in Lynch Station, 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.http://www.element51.com/article1.htm The specimens are highly valued by collectors.

Related Topics:
1912 - Lynch Station - Campbell County - Virginia - 1980s

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In an attempt to recoup profits and meet demand, most 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).

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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. However, the existence of these deposits is doubted by some due to a lack of corroboration.

Related Topics:
China - Limestone - Yunxian - Zhushan - Hubei - Marco Polo - Sichuan - Jade - Tibet - Derge - Nagari-Khorsum

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

Related Topics:
Afghanistan - Australia - Victoria - Queensland - Chile - Chuquicamata - Cornwall - Saxony - Silesia - Turkestan

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