The Origin and Occurrence of Turquoise

The Origin and Occurrence of Turquoise
An article by Lee Anderson
http://www.americana.net/jewelry_turquoise_origin_article.html
Turquoise consists of the chemical elements copper (Cu), aluminum (Al), phosphorus (PO4), and water (H2O). It is described as a “hydrous basic aluminum phosphate of copper” or a “hydrous aluminum phosphate colored by copper salts.” Its chemical formula is:

CuAl6 (PO44)8 4H2O,

although this varies widely. This molecular structure permits the inclusion of other elements, principally iron (Fe), calcium (Ca), magnesium (Mg), manganese (Mn), silicon (Si), and zinc (Zn). These additional elements, when incorporated in the molecular structure of turquoise, influence its color and hardness.

Turquoise is formed when the proper minerals, present in the proper proportions, are subjected to certain physical and chemical processes. These minerals are broken down, or “weathered,” from nearby “source” rocks and then dissolved, transported, and deposited in cracks, openings, and hollows in “host” rocks that lie beneath the surface. This mineral “solution” must remain in these host rocks for millions of years, at just the right pressures and temperatures, to form turquoise. (Keep in mind that over these enormous periods of time, mountains rise and wear away, and seas advance and recede.) It’s remarkable that a specific grouping of minerals could be subjected to the forces of pressure and temperature for such long periods, eventually forming something as beautiful as turquoise!