Turquoise
Turquoise is one of the first gem materials used by humankind, and was held in high esteem by many cultures. Egyptian royalty were wearing turquoise jewelry as early as 5500 BC. It is the national gem of Tibet, and was an important material to the Native American tribes in the Southwestern U.S., who used turquoise as a ceremonial gem and as a medium of exchange. Historically, turquoise was believed to guarantee health, good fortune, and protection from evil.
Turquoise can be semitranslucent to opaque, and its color usually ranges from light to medium blue or greenish blue. It is often mottled, and sometimes has dark splotches or veins of matrix. Some turquoise has fine seams of matrix which form a spiderweb pattern. The most valuable turquoise is an even medium blue, with no matrix, and the ability to take a good polish. Turquoise is one of the birthstones for December.
 Hardness & Toughness
Turquoise has a hardness of 5 to 6 on the Mohs scale, and its toughness is generally fair to good.
Stability
High heat can cause discoloration and surface damage to turquoise. The gem is normally stable to light, but dissolves slowly in hydrochloric acid. Turquoise tends to be porous, and can be discolored by chemicals, cosmetics, and even skin oils or perspiration which tend to turn blue turquoise a more greenish color.
| Treatments |
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| Treatment |
Purpose |
Stability |
Prevalence |
Detection |
| Impregnation with wax or plastic (sometimes with dye added) |
Improves the color and luster of pale material; plastic also improves durability |
Excellent to fair. Plastic is stable under normal conditions, but wax may gradually deteriorate and discolor |
Common |
Detectable by a trained gemologist or a gemological laboratory |
| Painting matrix with black shoe polish or similar colorants |
Makes the matrix a more desirable color |
Fair. Solvents can damage or destroy the treatment |
Common |
Detectable by a trained gemologist or a gemological laboratory |
| Backing with epoxy resin |
Adds thickness, strength, and weight to pieces otherwise too thin to cut |
Good under normal conditions. Heat or solvents can damage or destroy the epoxy backing |
Common |
Detectable by a trained gemologist or a gemological laboratory if the stone is unmounted |
| Filling cavities with metal-loaded epoxy |
Hides cavities and imitates pyrite inclusions |
Fair. Heat or solvents can damage or destroy the fillings, and they may eventually separate even under normal conditions. |
Occasional |
Detectable by a trained gemologist or a gemological laboratory |
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Zachery Treatment*
*Click here for more information on this treatment.
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Strengthens the gems, and sometimes darkens color slightly |
Good to excellent. May be affected by some acids. |
Unknown |
Detectable by a gemological laboratory using EDXRF spectroscopy |
| Surface coating with lacquer, epoxy, etc. |
Adds color and/or seals underlying dye or paint |
Variable, depending on material used |
Rare |
Detectable by a trained gemologist or a gemological laboratory |
Sources
Historically, the finest material was mined in Iran and is known as Persian turquoise. This source is no longer commercially important. Today, the United States is the major source of turquoise. Other sources are China, Chile, Australia, and Mexico.
Care & Cleaning
Only warm soapy water should be used to clean turquoise. Turquoise should never be cleaned in an ultrasonic or steam cleaner.
Imitations
Glass and plastic are both used to imitate turquoise. "Reconstructed turquoise," is usually made of various powdered minerals - not turquoise - dyed and bonded with plastic, epoxy resin, or similar substances.
 Synthetics
Synthetic turquoise was produced on a limited basis in the 1980s, but was never widely available on the market.
Alternatives
Some alternatives to turquoise include agate, chrysocolla chalcedony, jadeite jade, lapis lazuli, malachite and nephrite jade.
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