Turquoise

The turquoise or calaite is a mineral of class 8 (phosphates), according to the Strunz classification, with a bluish-green color. It is a phosphate of aluminum and copper. Its formula is: CuAl₆(PO₄)₄(OH)₈·/b >4H₂O. It is a relatively rare mineral, and when compact and of good quality, it has been highly prized as a precious and ornamental stone for thousands of years due to its unique color. At present, like many other gems, it is apparently much more common in the jewelry market, due to the introduction of treatments and imitations, some of which are very difficult to detect even by experts.

The word "turquoise"' It is very old and of indeterminate origin. Derived from the French pierre turquoise, meaning "Turkish stone". It is thought that this arises from a confusion, since in Turkey there are no turquoise deposits, but they were traded there, and then the gem was associated with that country.

Properties

Even the finest turquoise is quite brittle, peaking in hardness just below 6 on the Mohs scale, or slightly less than ordinary window glass. It is generally found as cryptocrystalline masses, and its properties are quite variable. The lower the hardness, the lower the specific weight (oscillating between 2.9 and 2.3) and higher porosity. Turquoise's luster is waxy to almost vitreous, and is generally opaque, although it can be slightly translucent in small sections. The color is as variable as the rest of its properties, ranging from white to dark blue and sky blue, and from blue-green to yellowish-green. The blue color is attributed to copper, while the green may be the result of iron impurities or dehydration. Turquoise almost always appears in a compact form, with millimeter-sized crystals being very rare.

Deposits and exploitation

It is a rare mineral, of secondary formation and is found mainly in desert regions. Turquoise is among the first gemstones to be mined, and while many historic sites have been depleted, some remain in operation to this day. These are all on a small scale, generally operating temporarily due to the remoteness of the deposits among other reasons. Most are extractions by hand, with little or no mechanization. However, turquoise is sometimes obtained as a by-product of large-scale copper mining, especially in the United States.

Spain

In the prehistoric variscite exploitations of Palazuelo de las Cuevas, in the municipality of San Vicente de la Cabeza (Zamora) and Can Tintorer, in Gavá (Barcelona), there is also turquoise, but in small quantities. It has appeared occasionally in the tungsten mines of San Finx, in Lousame (La Coruña). Turquoises, associated with quartz and amblygonite, were also found in the old San José mine, in Valdeflores (Cáceres), in blue-green specimens. Millimeter crystals have been found in Castrocalbón (León)

Iran

For at least 2,000 years, the region once known as Persia has remained the most important source of turquoise supply. These "perfect color" they are only found in a mine located on top of the 2012-meter Ali-mersai mountain, 25 km from Mashhad, the capital of Khorasan province, Iran.

Sinai

Since at least the First Dynasty (c. 3000 BC), turquoise was used by the ancient Egyptians who mined it from the Sinai Peninsula, called "Country of Turquoises" by the natives. There are six mines in the region, all on the southwestern coast of the peninsula, covering an area of approximately 650 km². The two most important mines, from a historical perspective, are at Serabit el-Hadim and Wadi Maghara, and are among the oldest known deposits. The mine is located about four kilometers from an ancient temple dedicated to the goddess Hathor.

United States

Significant deposits of turquoise are found in the southwestern United States: Arizona, California, Colorado, New Mexico and Nevada are or were especially rich in this mineral.

Deposits in California and New Mexico were mined with stone tools by natives before the discovery of America. Cerrillos in New Mexico is among the oldest mines in the region. Before the 1920s, the state was the largest producer in the country, but today its operation is almost nil. Only one deposit in California, located in Apache Canyon (San Bernardino County) is operating at commercial capacity.

Other deposits

The ornamental and currency use (through barter) of turquoise has been widespread in India, along the caravan routes of Asia, and among nomadic peoples such as the Mughals. In mountainous areas such as the Hymalayas and Altai, they are used to adorn the hair of men and women. China has been a minor-order site for 3,000 years or more. Quality gems, in the form of compact nodules, are found in Yunxian and Zhushan, in Hubei province. Furthermore, Marco Polo reported finding turquoise in Sichuan. Most of the Chinese turquoise is exported, but they also produce small carvings by working the material in a similar way to jade. Russia, Mongolia, Nepal, Bhutan, Afghanistan, Turkestan, India and the Indochinese peninsula are prominent buyers of turquoise, used above all in traditional clothing and celebrations.

In Tibet, where green turquoises are highly prized, deposits of good quality gemstones are believed to exist in the mountains of Derge and Nagari-Khorsum, in the east and west of the region respectively. However, the existence of these mines is doubted by some due to the lack of verification.

In Mexico, turquoise is sometimes found in the Cananea and Nacozari copper mines in the state of Sonora, but the company that owns those mines does not exploit them commercially and they are generally lost in the copper extraction process.

Other places where this mineral is exploited are: Afghanistan, Australia, northern Chile and Turkestan.

History of use

Tutankamon gold mask, embedded with lapislázuli, cornalin and glass paste.

Hues of turquoise have been prized in many important ancient cultures: they have adorned the rulers of Ancient Egypt, the Incas, Moches, Chimúes, Aztecs (and possibly other pre-Columbian Mesoamerican cultures), the Persians, Mesopotamia, Indus Valley Civilization, and China since at least the Shang Dynasty. Despite being one of the oldest gemstones, and probably the first to be introduced to Europe via Turkey, along with other products from the Silk Road, turquoise did not become an important ornamental stone until the 17th century. XIV. It was apparently unknown in India until the Muhgal period, and in Japan until the 18th century. A belief shared by many of these civilizations maintains that turquoise has certain prophylactic qualities: it was thought that it changed color according to the state of health of the wearer and that it protected from evil forces.

The Aztecs inlaid turquoise along with gold, quartz, malachite, jet, jade, coral, and shells into possibly ceremonial objects such as masks (some of which were based on skulls), knives, and shields. Natural resins, bitumen and wax were used to bond the turquoise to the base material, which was generally wood, although bone and seashells were also used.

Currently it is widely used in jewelry, goldsmithing and costume jewellery.

Courage and care

The purity of color is the determining factor in the value of a turquoise: in general, the most prized color is dark blue, with the value decreasing with the increase in greenish hues, color fading and spots. However, in Tibet they are preferred in a more greenish blue color. Whatever the color, turquoise should not be excessively soft or chalky, even if 'cured', such material (which most turquoises possess) is capable of fading or discoloration after a certain time and will not It is appropriate for use in jewelry.

The parent rock in which turquoise is found can sometimes be seen as an irregular stain or as a network of brown or black veins that cut through the stone. These veins can increase the value of the stone, or decrease it. Veined turquoise is highly prized in the Southeastern United States, but not in Asia, as purity and veinless stones are preferred. The uniformity of the color is highly appreciated, and in the finished pieces, the quality of the work is also a positive factor: like the shine and symmetry of the stone. Adjusted or calibrated stones -stones attached to jewelry adjusting its size- are usually the most coveted. Like coral and other opaque gemstones, turquoise is commonly priced by millimeter size rather than by carat.

Turquoises can be treated in a variety of ways, some more radically and permanently than others. There are controversies about whether some of these treatments should be acceptable, but the most accepted is one that improves the coloration and luster of the gem by applying wax or oil: if it is of high quality, it absorbs little wax or oil, and turquoise does not need this treatment to preserve its color and beauty. All things being equal, turquoise that has not been treated will always be the most expensive.

As a phosphate material, turquoise is inherently brittle and sensitive to solvents; perfumes and other cosmetics can alter its color, just like oily skin. Prolonged exposure to sunlight can also discolor or dehydrate it. Certain care should be taken when used as jewelry: cosmetics, including sunscreen or sunscreen, and hairspray should be applied before accessorizing, and it should not be worn on the beach or other sunny places. After use, the turquoise should be cleaned with a soft cloth to avoid the accumulation of residues, and it should be stored in a container, isolated from other pieces, to avoid scratches caused by other harder and better polished gems.

Turquoise engraving

The inconsistent hardness of turquoise must have prevented the ancients from frequently engraving this stone at the same time that the specimens from antiquity must have altered when they came to us. Be that as it may, there are few known turquoise engravings. However, there are a few:

• An amulet of the Genevosio collection, convex on one side and plane on the other, representing on one side Diana with two branches on the hands and on another kind of sister, a star and a bee, with Greek words on both sides
• The cabinet of the Duke of Orleans had two turquoises recorded, one representing Diana with his carcaj behind her back and another to Faustina, the mother
• It is also quoted in the gallery of Florence, a turquoise as a pool ball in which a head is recorded. He had thought of seeing Caesar's in it, but it seems he represents Tiberius.

Symbols

In Central Asia it is considered a valuable talisman symbolizing courage and hope, as well as bringing success to men in love and virtue to girls. Another belief says that it protects the nose and from respiratory ailments. It is located under the sign of Taurus.