Tips: Selecting Turquoise

Many people love the bright colors, texture and silky, cool feel of turquoise!

Primary source countries

Only a few mines are still active in the USA today; mostly in Arizona and Nevada. Turquoise was most often mined by families or individuals over the centuries. Variations of turquoise are often known by the mine from which they originated: Blue Gem, Orvil Jack, Easter Blue, Fox, Indian Mountain, Kingman, Lander Blue, Lone Mountain, Pilot Mountain, Royston, Sleeping Beauty, etc. Persian turquoise (Iran) is often known as the gold standard for quality in turquoise and was mined possibly as long ago as 2100 B.C.

Formation

Turquoise is a porous mineral which contains phosphates, and various amounts of copper, aluminum, iron, chromium and oxygen. These affect the color of the turquoise found.

Colors of Turquoise

Turquoise often has “matrix” materials which form lines & cracks (also called “webbing”) in it’s texture or structure. This matrix material is usually from the host rock through which the turquoise was formed. This can enhance the attractiveness of some turquoise, but can also allow the turquoise to crack or crumble along these vein-like structures. If you drop some pieces of turquoise they may break, crack or crumble.

Dark black matrix is often formed from iron pyrite. Golden brown matrix from iron oxides and yellow to brown matrix from rhyolite.

Generally speaking, of the turquoise found in U.S. mines, the most highly valued have more spider-like dark webbing. Most other forms of turquoise today require some form of treatment. With the enormous market demand for turquoise today, most turquoise is color treated or stabilized in some way.

Types of Turquoise

Turquoise being a relatively softer material (Moh’s hardness of 5 to 6) can be readily scratched by glass/quartz (hardness of 7), emeralds, rubies, sapphires (hardness of 9) or diamond (hardness 10). Turquoise is also porous and can absorb chemicals with prolonged exposure over time. Turquoise with a “chalky” appearance is softer than that found at or on the surface and must be treated so that it can be cut and used.

It is perfectly okay to ask what type of turquoise is being used in your jewelry piece. The merchant should know or be able to find out for you. Price is often an indicator of quality, but not always!

When purchasing turquoise that has been cut into thin strips and glued onto a silver piece with epoxy glue; ask the merchant to replace it if the stone comes away from the mounting. Often a weaker epoxy glue may have been used. If the silver piece bends (such as in a wrist cuff bracelet), the pressure exerted against the stones can crack or break out the turquoise.

Cleaning Turquoise

References

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Gem photo credits: Most of the photos of gemstones and minerals shown here are reproduced with kind permission of Roger Weller, Professor of Geology at Cochise College, AZ. Mr. Weller has many more beautiful photos of gemstones, minerals and rock examples. The Cochise College science and geology website is an excellent source of information for those that would like to learn more about the wonderful treasures and geologic evolution of the planet we live on.