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The black, brown, or light veining in turquoise is referred to as its matrix, which can be called "cobweb," "edisonite," "egg-shell," or "spiderweb," depending on its characteristic pattern. Originally thought to be amorphous, Turquoise is cryptocrystalline, forming in the tetragonal crystal system with a pinacoid crystal form. Typically turquoise mineralization is restricted to a relatively shallow depth of less than 60 to 70 feet, although it does occur along deeper fracture zones where secondary solutions have greater penetration. Turquoise is typically found in arid regions of Australia, China, Chile, Iran, Mexico, Sinai, anf the Southwestern United States in Arizona, Nevada and New Mexico. Turquoise is found either filling, or encrusting cavities and fractures in volcanic rock, and is often associated with limonite or other iron oxides. As a secondary mineral, turquoise forms by the action of percolating acidic aqueous solutions during the weathering and oxidation of pre-existing minerals. American southwestern turquoise is associated with weathered by-products of copper sulfide deposits in or around potassium feldspar bearing porphyritic intrusives. In some occurrences alunite, potassium aluminium sulfate, is a prominent secondary mineral. Due to its total opacity, turquoise is cut and shaped into beads or a cabochon cut. Turquoise Crystallography, Chemistry, Physical Properties
Turquoise Optical Properties
Persian TurquoiseThe ancient Persians mined turquoise as far back as 2000 BC. Persian turquoise was sometimes referred to as Meshhed Turquoise or Meshed Turquoise, referring to the mines that were located at Nishâpur (Nishapur), in the Khorassan province (in the Alimersai Mountain region of what is now the north-eastern part of Iran). Turquoise was categorized based on quality, with the finest being called Anqushtari. Lesser stones were referred to as Arabi or Barkhaneh. American TurquoiseTurquoise has been used by the Native American Indians for over 2000 years. Pre-Columbian artifacts from the Anasazi, Aztec, and Hohokam tribes show the importance of the stone in art, religious rituals, and trade. Turquoise beaded jewelry, referred to as 'heishi,' (strung beads or shells) was popularized by the Santo Domingo and San Felipe Pueblo Indians of the American Southwest.
Sleeping Beauty TurquoiseThe term "sleeping beauty turquoise" (aka "Persian turquoise") refers to a rare, matrix-free variety of turquoise that occurs in association with granite host-rock. One of the few sources for this pure-colored stone is the 'Sleeping Beauty Mountain Mine', located in Globe, Arizona. The color range for this variety is described as darker 'Royal Blue' or lighter 'Sky Blue.' The majority of 'Sleeping Beauty' material coming from the mine may have been altered or enhanced is some manner, so you should always inquire with your jeweler (see 'Enhancements' below).  Turquoise EnhancementsTurquoise is a gemstone material that is commonly enhanced to improve appearance and durability. When in doubt, you should assume that a given piece of turquoise has been treated and/or altered in some manner. The typical methods of treatment are:
Turquoise that has been treated with the 'Zachary Process' is difficult to differentiate from untreated material. The process is designed to strengthen the material, then heat it to dissipate any traces of residual chemicals used in the treatment. Natural material can also be strengthened by impregnating it with vaporized quartz. The up-side of 'Enhanced' or 'Natural Processed' turquoise is that the color remains stable over time as opposed to natural, untreated turquoise which can oxidize, turning green over a long period of time. Natural stone is porous, which can be detected under a loupe, as opposed to enhanced material which will be totally smooth.
1. USGS, Donald W. Olson, Turquoise from the American Southwest 2. GIA, Turquoise Treatments | Copyright © 2009 AllAboutGemstones.com. All rights reserved. | | | ||||||||||||||||||||||||||||||||||||||||||||
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: Turquoise 
