|Dimensions (mm)||not provided|
|Weight (carats)||not provided|
This is a natural rough piece ready for cutting.This specimen is with its matrix and it has been stabilized so it is ready for cutting.Mined in a cooper mine in Nevada.
We have taken the photo with the slab wet.
Weight 67.50 cts app
Size 57 x 22 x 7 mm app
The tonal range of this extremely rare and hard-to-find turquoise will vary from light to medium with occasional matrix.
Turquoise is an opaque, blue-to-green mineral that is a hydrous phosphate of copper and aluminium. 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 Southwest United States is a significant source of turquoise; Arizona, California (San Bernardino, Imperial, and Inyo counties), Colorado (Conejos, El Paso, Lake, and Saguache counties), New Mexico (Eddy, Grant, Otero, and Santa Fe counties) and Nevada (Clark, Elko, Esmerelda County, Eureka, Lander, Mineral County and Nye counties) are (or were) especially rich. The deposits of California and New Mexico were mined by pre-Columbian Native Americans using stone tools, some local and some from as far away as central Mexico. Cerrillos, New Mexico is thought to be the location of the oldest mines; prior to the 1920s, the state was the country's largest producer; it is more or less exhausted today. Only one mine in California, located at Apache Canyon, operates at a commercial capacity today.
The turquoise occurs as vein or seam fillings, and as compact nuggets; these are mostly small in size. While quite fine material—rivalling Iranian material in both colour and durability—is sometimes found, most American turquoise is of a low grade (called "chalk turquoise"); high iron levels mean greens and yellows predominate, and a typically friable consistency precludes use in jewellery in the turquoise's untreated state. Arizona is currently the most important producer of turquoise by value. Two mines exist in the state, one is the Sleeping Beauty Mine in Globe, the other is the Kingman Mine that operates alongside a copper mine outside of the city.
Nevada is the country's other major producer, with more than 120 mines which have yielded significant quantities of turquoise. Unlike elsewhere in the US, most Nevada mines have been worked primarily for their gem turquoise and very little has been recovered as a byproduct of other mining operations. Nevada turquoise is found as nuggets, fracture fillings and in breccias as the cement filling interstices between fragments. Because of the geology of the Nevada deposits, a majority of the material produced is hard and dense, being of sufficient quality that no treatment or enhancement is required. While nearly every county in the state has yielded some turquoise, the chief producers are in Lander and Esmerelda Counties. Most of the turquoise deposits in Nevada occur along a wide belt of tectonic activity that coincides with the state's zone of thrust faulting.
|Starts||19th Jul 2017 12:02am PDT|
|Ends||21st Jul 2017 12:00am PDT|
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