Turquoise is a relatively soft stone ranging in color from light sky blues to deep rich blues, blue greens and green. The color of turquoise is determined by the amount of copper (blue) verses iron (green) found in the stone. Turquoise is mined in many places throughout the world: southwest US, China, Iran, Afghanistan, Argentina, Brazil, Australia and Mexico to name a few. Experience with the stone and familiarity with the colors can help in identifying where the turquoise was mined. Around 80% of turquoise available today is mined in China and Tibet much of the remainder is mined in the US.
Turquoise is a problematic stone due to the number of dyed imitations, synthetics and treatments used on poor or low-grade turquoise to create a stone with a more valuable appearance. Additionally processes of grinding chalk turquoise and mixing with dye and resin to create reconstituted turquoise and out and out synthetic imitations in plastic and polymer clay. There is nothing wrong with any of the processes as long as the end product is sold with full disclosure. When dealing in finer turquoise I recommend using experience and your best judgment or that of someone trusted.
Stabilization of a softer turquoise stone that otherwise couldn’t be cut or polished is considered an acceptable practice, as long as the natural appearance of the stone is not altered. The majority of turquoise available today is stabilized. Lower grade, nearly colorless, turquoise is generally stabilized using dyed resins and therefore altering the natural look of the stone. This should be revealed by the dealer selling the stone, however may not be. Turquoise treated this way should be inexpensive. Next ‘lower’ quality of turquoise is a reconstituted mix of chalk turquoise mixed with dye and resin, this being the least desirable and basically a synthetic stone. Additionally stones containing no turquoise at all are sometimes dyed to look like turquoise, this is mainly done with Howlite. Beyond these are completely synthetic turquoise looking materials made from polymer clays, resins, plastics, etc. These can be easily identified with a heated pin or needle. When heated and applied to the material it will melt, unlike real turquoise.
The pieces in the photograph above are old Navajo. The top bracelet is set with Kingman turquoise, the middle bracelet is set with Sleeping Beauty turquoise, the bottom bracelet is set with turquoise mined in the Globe/Miami area of Arizona, USA. The photograph below is of a dyed howlite bead.