Turquoise is an opaque, blue-to-green mineral that is a hydrous phosphate of copper and aluminium, with the chemical formula CuAl6(PO
4)4(OH)8·4H
2O. It is rare and valuable in finer grades and has been prized as a gem and ornamental stone for thousands of years owing to its unique hue.
In recent times, turquoise, like most other opaque gems, has been devalued by the introduction of treatments, imitations, and synthetics onto the market.
The substance has been known by many names, but the word turquoise, which dates to the 16th century, is derived from an Old French word for "Turkish", because the mineral was first brought to Europe from Turkey, from the mines in historical Khorasan Province of Iran.
Pliny the Elder referred to the mineral as callais, the Iranians named it "phirouzeh" and the Aztecs knew it as Teoxihuitl.
For at least 2,000 years, Iran, known before as Persia in the West, has remained an important source of turquoise which was named by Iranians initially “pirouzeh” (Arabic Firouzeh) meaning “victory”.In Iranian architecture, the blue turquoise was used to cover the domes of the Iranian palaces because its intense blue colour was also a symbol of heaven on earth.
Neyshabur Turquoise is the finest in the world. For at least 2,000 years, Iran and Neyshabur has remained an important source of turquoise which was named by Iranians initially “pirouzeh” (Arabic Firouzeh) meaning “victory”.
This deposit, which is blue naturally, and turns green when heated due to dehydration, is restricted to a mine-riddled region in Nishapur, the 2,012-metre (6,601 ft) mountain peak of Ali-mersai, which is tens of kilometers 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.
Reference:
http://en.wikipedia.org/wiki/Turquoise
