Turquoise Information on Grades

The Grading Of Turquoise

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High Grade Natural Turquoise: found in all shades from sky blue to apple green. It is the hardest grade and takes the best polish. The contrast between the color of turquoise and the color of matrix {or mother rock} enhances the beauty of each stone. Many mines produce distinctive stones whose origin can be identified by an experienced person.
Enhanced turquoise: The Zachery or Foutz process impregnates turquoise with vaporized quartz. This makes the stone harder, darkens the color and takes a good polish. This process is hard to detect by normal methods because quartz occurs naturally with some turquoise.
Stabilized or Treated Turquoise: American manufacturers have perfected a process using pressure and heat to fill the microscopic gaps in the stone with plastic resin. When cured the product is a treated stone hard enough to cut and polish. Most nugget and some heishi products are made from real turquoise that has been stabilized. Stabilization allows genuine but lower grade turquoise to be used in jewelry.
Wax Treated: Much of the turquoise from China is wax impregnated. The paraffin treatment deepens and stabilizes the color but only affects the surface.
Reconstituted: This term describes pulverized turquoise scrap from stone cutting mixed with blue dye and plastic binder. Most products marketed under this name should really by labeled as simulated “block”. Compressed Nugget is a similar product made from larger pieces.
Block: A mixture of plastic resin and dyes that is produced in loaf sized blocks. We used to call this reconstituted because we were told it was made from ground up turquoise scraps. In reality there is no actual rock of any sort in block turquoise; it is entirely man-made and should be labeled “simulated”. Block is produced in many colors, simulating many different stones and shells. Except for occasional batches of Lapis Block that contain ground up iron pyrite, these are entirely simulated. Block is used heavily for inlay and heishi.
Dyed Stones: There are several naturally occurring stones that look similar to turquoise when they are dyed blue. These include Howlite, a white rock with black or gray markings, and Magnite or Magnesite, a chalky white mineral that forms in rough nodules looking faintly like the vegetable cauliflower. Other simulations include glass, plastic, faience ceramic and polymer clay.
This information on the treatments and grades was originally written by Homer Milfred published by the New Mexico Abandoned Mine Land Bureau in the Report 1994 – 1 – November 15, 1995. We feel that this is the most accurate and simplistic information on the grades of turquoise. We would like to add that there are some lesser grades of natural turquoise in smaller pieces that are used in small settings and inlay work. These come in varying grades of hardness. The “block turquoise” referred to here is really imitation or plastic and is quite often marketed as the real thing. They can even create a matrix in it. Plastic turquoise or other block stones can melt, fade and become quite less attractive after purchase and wear. Imitation stones are quite often used in machine stamped silver jewelry made overseas and marketed here as Native American jewelry.

Collection of Natural American Turquoise Cabochons