Turquoise

Big turquoise from Cananea

Turquoise with quartz

Turquoise of Nishapur - village of Ma'dan 14

Persian Turquoise

Chacoan turquoise with argillite

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Turquoise Cerillos Smithsonian

Turquoise is a phosphate mineral that is prized for its unique blue to green color. It has been valued as a gemstone and ornamental stone for thousands of years owing to its distinctive hue. The name "turquoise" is derived from the French word turquois meaning "Turkish," because the mineral was first brought to Europe through Turkey from mines in the historical Khorasan region of Persia (now Iran).

Properties

Turquoise is an opaque, blue-to-green mineral that is a hydrated phosphate of copper and aluminium, with the chemical formula CuAl6(PO4)4(OH)8·4H2O. It is rare and valuable in finer grades and has been prized as a gemstone and ornamental stone for thousands of years due to its unique hue. Turquoise may form as crusts, nodules, or veins in spaces of weathered volcanic rocks, often in arid climates. Its color varies from blue to green, depending on the amounts of copper and iron within the mineral.

Formation and Sources

Turquoise forms by the process of sedimentation where water percolates through rocks containing copper, aluminium, and phosphorus minerals. Over time, the water evaporates, leaving behind the minerals that form turquoise. This process requires specific conditions, such as the presence of acidic, copper-rich groundwater and a suitable host rock.

The most significant turquoise mines are located in the Southwestern United States, Iran, Sinai Peninsula in Egypt, and China. Each region produces turquoise with characteristics unique to the local geology, which can sometimes be used to identify the source of a particular specimen.

History and Cultural Significance

Turquoise has been esteemed by various cultures for millennia. Ancient Egyptians mined turquoise in the Sinai Peninsula as early as 3000 BCE, where it was used in jewelry, amulets, and in the decoration of objects. The Ancient Persians valued turquoise highly, using it to cover the domes of palaces because its sky-blue color represented heaven. In the Southwestern United States, Native American tribes such as the Navajo, Zuni, and Hopi have been using turquoise in their jewelry and ceremonial items for hundreds of years.

Uses

Turquoise is primarily used in jewelry and as an ornamental stone. It is often cut into cabochons or beads and set in silver or gold. Due to its relative softness (Mohs hardness of 5 to 6), it requires care in handling and storage to avoid scratching. Turquoise may also be treated to enhance its color and durability. Common treatments include impregnating the stone with wax or resin, which improves its color and luster.

Imitations and Enhancements

Due to its value, turquoise has been imitated by various materials, including dyed howlite and synthetic compounds. It is important for buyers to be aware of the distinctions between natural, treated, and imitation turquoise. Enhancements such as stabilization can improve the durability and color of the stone but may affect its value.

Conservation

The extraction of turquoise can have environmental impacts, including habitat destruction and water pollution. As with many gemstones, ethical sourcing and conservation efforts are important to ensure the sustainability of turquoise mining practices.