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Turquoise

A blue to blue-green mineral of aluminum and copper, mainly CuAl₆(PO₄)₄(OH)₈·4H₂O, prized as a gemstone in its polished blue form.

Natural turquoise may have been cut and polished, but no artificial changes have been made to the gems. Color may change over time as body oils and other sources of moisture are absorbed into the stones. Only high quality turquoise can be used in its natural state. Natural turquoise means a stone with no alteration to its composition. Such stones are merely polished and cut into shapes before being mounted in jewelry. Natural turquoise remains porous, as all natural stone is to varying degrees, and may tend to change color over time as it is worn and handled.

The colour of turquoise ranges from blue through various shades of green to greenish and yellowish gray. A delicate sky-blue, which provides an attractive contrast with precious metals, is most valued for gem purposes. The blue in turquoise is enhanced when copper is present. If the area where turquoise is formed contains more aluminum, the turquoise will shade to green. When zinc is present, the deposits are a yellow-green color, a rare combination that so far has been found in only a few areas, including the Carico Lake and Blue Ridge mines in Nevada.

Numerous deposits of turquoise in the southwestern U.S. have been worked for centuries by American Indians. The mineral also occurs in Iran, northern Africa, Australia, and Siberia.

Not likely to be confused with many other minerals. Turquoise can be distinguished from more glassy chrysocolla by the phosphorus test, from fine grained quartz (with copper stain) by its solubility in acid, and from similar, but green, variscite by the color shift with heat. It is hard to tell from prosopite and ceruleite without a phosphorus test. Indians because of their considerable use and wearing of turquoise found that backing increased the wearability of the turquoise. They found if the stone was not backed it would for the most part end up cracking.

Early backing materials were the cassing of old model T batteries and progressed to old phonograph records and then to the final use of epoxy steel resins. This is a very helpful way of determening the age of old Indian jewelry.

Turquoise forms when water percolates through rocks that contain copper, aluminum and other minerals. A chemical reaction takes place that results in deposits of what we know as turquoise. That's a simplified way of describing a process that takes millions of years and only happens when a complex set of conditions come together.

Hardness of turquoise used for jewelry usually varies from 5-6 on the Mohs scale. The hardest turquoise is usually found nearest the surface of the earth, where it's had a chance to dry, or cure. Softer turquoise is chalk-like -- too soft and porous to be used unless it's treated.

Care Tips:

Handle your turquoise jewelry carefully to avoid scratching it. Don't store turquoise with harder gemstones or other materials that might rub against it and cause damage.
Keep turquoise away from high heat and chemicals such as oils, perfumes, and household cleaners. Even stabilized turquoise can be affected by a constant bombardment of chemicals.

Clean your turquoise in warm, sudsy water and dry it immediately with a soft cloth. Avoid commercial jewelry cleansers.