|Turquoise is an opaque, blue-to-green mineral that is a hydrated phosphate of copper and aluminium. It is rare and valuable in fine grades and has been prized as a gem and ornamental stone for thousands of years owing to its unique hue.|
In recent times, turquoise has been greatly devalued, like most other opaque gems, by the introduction of treatments, imitations, and synthetics.
|The production of turquoise from deposits in California can be traced back to pre-Colombian Native Americans. Prehistoric mining tools have been found in some of the old workings of the turquoise mines. Over the years, the State's deposits have produced a substantial amount of turquoise. Deposits are located in San Bernardino, Imperial, and Inyo Counties. The material occurs as nodules and as vein filling.|
In the better grade materials, the color varies from a pale to a dark blue, poorer grade materials are greenish-blue and green in color.
|Historically, a number of turquoise mines operated in the State, several mines in each of the counties. Today, only a very few mines still produce commercial Turquoise, none of which is easy to find. |
California turquoise is no longer marketed in large commercial quantities, but high grade examples can still be found by amateur rock hunters.