Turquoise
Turquoise is typically formed as a byproduct from the interaction of percolating solutions and pre-existing minerals. It is typically found in arid regions, filling or encrusting shallow (<20m) cavities and fractures, typically in highly altered volcanic rocks.
Turquoise is mainly found in Persia, Sinai, United States, Mexico and China. For at least 2,000 years, the region once known as Persia, has remained the most important source of turquoise, for it is here that fine material is most consistently recovered. Turquoise is also found in Sinai. Since at least the First Dynasty (3000 BCE), and possibly before then, turquoise was used by the Egyptians. The color of Sinai material is typically greener than Iranian material. China has been a minor source of turquoise for 3,000 years or more. Other significant source areas include: Afghanistan; Australia, northern Chile, Cornwall, Saxony, Silesia, and Turkestan. The Southwest United States is a significant source of turquoise; Arizona, California, Colorado, New Mexico and Nevada are (or were) especially rich. The deposits of California and New Mexico were historically mined by Native Americans using stone tools, some local and some from as far away as central Mexico. While turquoise of fine color and durability is sometimes found in the United States, most American turquoise is of a low grade (called "chalk turquoise") and is too friable for use in jewelry.
For more information about the geology of stones that are commonly used in semi-precious jewelry see out Geology page in www.annabloomdesigns.com.
Some of the above material description are cited directly from or based on information taken from www.wikipedia.org.
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