other names: Turquoise
mineral class: Hydrous phosphates with foreign anions
chemical formula: CuAl6(PO4)4(OH)8 · 4H2O
Chemical elements: Copper, aluminum, phosphorus, oxygen, hydrogen
Similar minerals: Amazonite, Chrysocolla, Lazulith, Variscit
colour: green Blue
crystal structure: triclinic
mass density: approx. 2.8
magnetism: not magnetic
Mohs hardness: 6
stroke color: green white
transparency: transparent to opaque
General to the turquoise:
Of the turquoise describes a mineral that is composed of aluminum and copper and has a comparatively high water content. It forms warty, grape-shaped or kidney-shaped crusts or masses, whereas crystals are quite rare in this mineral and usually so small that they are barely visible to the naked eye. Turquoise is usually opaque, but can also crystallize completely transparent. Often there is an adhesion with chrysocolla, a mineral of the silicate group. Turquoise is a mussel to uneven fracture and may have a dull or waxy luster. According to its name, turquoise appears in different bluish, pale blue-green and greenish hues, and yellow variants are occasionally found in the United States. As a coveted semi-precious stone turquoise must be pretreated because of its porous structure. The Mohs' hardness of turquoise varies widely and can range between 2 and 6, due to the fact that specimens found on the surface of the earth are dried out and thus much harder than those that are mined several meters in depth. Soft turquoises are very similar in their consistency to conventional chalk and can easily be scratched with a fingernail.
The turquoise used today developed from the French term "pierre turquoise" for "Turkish stone", although the stones transported to Europe from the 15th century came from Iran and were only traded in Turkey.
Origin, occurrence and localities:
Turquoise is formed as secondary mineral in the course of weathering processes and oxidation of other minerals and magmatic rocks and develops mainly in cracks and cavities. While the aluminum content is mostly due to feldspar, the copper in turquoise comes from rock types such as malachite or azurite. Often in the turquoise black or dark brown spots and veins, which are caused by a chemical admixture with limonite. Turquoise is common worldwide, but is considered very rare due to the small number of economically significant sites. Most mines that mine turquoise today in significant quantities are located in the United States, especially in the southwestern states such as Arizona and Colorado. Iran, the Sinai Peninsula and China, Mexico, China and Australia also have economically significant deposits.
History and usage:
The turquoise looks back on a five millennia long history of targeted promotion and use as a gem stone. Already in the early dynasties of ancient Egypt turquoise was used for the production of precious jewelery and faience works. Inlaid with turquoise adorned especially golden bracelets, masks and grave goods of important pharaohs. As early as the third millennium BC, turquoise was so sought after in Egypt that imitations were made from dyed earthenware. Turquoise also played an important role among the people of the indigenous peoples of Central America as a prestige object and gemstone. Archaeological evidence shows that the semi-precious stone was used to process human skulls with turquoise ornaments to ceremonial masks, which served as burial objects of the rulers. Turquoise finally reached Europe via the Silk Road in the late Middle Ages and experienced a veritable boom as a gem in the Renaissance. He is considered one of the oldest semi-precious stones used in European crafts. Even today, turquoise is processed worldwide into chains, bracelets, rings and brooches.