Turquoise gemstones are very often enhanced, and good quality natural, untreated stones are no longer the norm. Other types of stone which have been dyed are also frequently seen.

The best quality Turquoise is usually found near the surface, where it hardens and is exposed to mineralization by other  materials. As mining goes deeper, softer stone is encountered. Some turquoise is very soft, almost chalk-like. This stone is porous and unusable as-is, and must be Stabilized by being infused with chemicals or resins. The softer stone is also frequently ground to a powder and mixed with resin and tinted to form so-called Reconstituted Turquoise. Turquoise ranges in hardness from 5 to 6 on the Mohs scale (as a comparison, window glass has a hardness of about 6 to 7, so glass will scratch all but the hardest Turquoise, while Turquoise will not scratch most glass).

Some Turquoise is also subject to severe color fading with exposure to light. In many cases, Turquoise will also form a desirable patina with age and wear.

Hard, natural stones are prized. Due to the small supply of completely natural Turquoise, stabilized stones have also found acceptance in many circles.

What Is Out There...

Dyed Turquoise:  This process is used to add more desirable color to lackluster, faded, low-grade stones. Unless the stone has been sealed, some dyes can be detected by rubbing with a white cloth. Tinting is also sometimes used to highlight spiderwebbing and matrix, where that would produce a more desirable stone. Dyed Turquoise is not considered to be gem quality.

Other Dyed Stone: Limestone, Howlite, Steatite, Calcite, Magnesite and other materials are frequently dyed to imitate Turquoise, and deceptively sold as such. Turquoise purportedly from China, Tibet and certain other localities often consists of an artifical mixture of these materials.

Bonded or Reconstituted Turquoise: This is really just powdered, low-grade Turquoise which has been mixed with resin and colorant to form a plastic/stone hybrid material.

Fake Spiderwebbed Turquoise: A product assembled from low-grade chunks of natural Turquoise, glued together using an epoxy adhesive. When cut, this can resemble natural spiderwebbed Turquoise. This material is often dyed as well.

Stabilizing Processes: Stabilizing involves treatment to seal and harden soft and porous stones. There are several processes and materials which are used...

• Plastic Hardening. A process which involves forcing a plastic material to fill the pores throughout softer stones. Plastic hardening is often combined with dye to enhance the color of the "stone." The plastic/stone hybrid produced is similar to the Reconstituted Turquoise (see above). Most inexpensive "Turquoise" is produced by this method.
• Silica Treatment. This process forces silica into the pores of softer stone, resulting in a stone which imitates naturally hard, better quality Turquoise. This is difficult to detect.
• Chemical Treatments. These can be used both to stabilize and color soft stones. In some cases, a second heat treatment is used to dissipate any chemical residues, making the treatment more difficult to detect.
• Waxing. This process is used to seal porous stones. Some of the waxes used are similar to those used to wax Emeralds. The treatment can prevent staining, but can sometimes be used to add coloring and fill voids. Unless waxing is repeated, wear can lead to uneven aging on the stone. Waxing using a non-colored wax does not usually affect value, though it can make it more difficult to detect other treatments.
• Resin Sealing. Used to harden the surface of soft, porous stones. However, this process is often used to disguise dyed stones, preventing the dye from rubbing or wearing off.

What to Look For...

There is no easy and foolproof way for the average person to detect dyed, stabilized, reconstituted and chemically enhanced forms of Turquoise. However, there are some things you can look for...

1. Weird colors do exist in natural Turquoise. But some shades that look artificial should cause you to question. The same can be said for coloring that is too even.
2. Lower quality Turquoise which has only been dyed or waxed can often be detected by its softness relative to better Turquoise.
3. Veining and webbing used to be good indicators against reconstituted stones. Veins and spiderwebbing also were areas to look for indications of dye. But the fakers have become increasingly good at reproducing these features.
4. Some heavily waxed, plastic treated and resin-stabilized stones are too shiney in comparison to natural Turquoise. These sometimes also have an unnatural transluscency in strong light, due to the artificial material filling the pores.
5. A hot needle will sometimes (not always) detect plastic, resin and wax treated stones. Touch a glowing hot needle (or soldering iron) to an area of the stone which will not be visible when worn. If you look through a loupe or strong magnifying glass while doing this, you should be able to see any indication of melting wax, plastic or resin. The smell given off will be chemical. Note: this test may mar portions of stabilized Turquoise.
6. Under high magnification, natural Turquoise will have small pits. In stabilized and reconstituted Turquoise, these pits will me missing, or all the holes will be full of glassy looking material. Some high-quality Turquoise does have quartz-type inclusions, and you don't want to mistake resin for that.

The hot needle will not detect other types of stone which have been dyed or treated to resemble Turquoise. The dye will sometimes rub off, but be aware that lower quality Turquoise can be very soft and rub off also. Also, some dyes used to treat stone don't come off so easily.

If your suspicions are not satisfied by the simple methods above, the definitive way to authenticate a piece of Turquoise is to take or send the piece to a gemologist who has access to the laboratory equipment to do a proper test. This involves looking at the stone through a microscope, performing a spectral analysis, determining the relative density of the stone in comparison with known examples of natural stone, etc.

Please let me know if there are new treatments, simulants, or methods of detecting treatments that should be included here.

Subjects on which I've written recent Guides...
Other Gemstones
Coin Collecting

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