Turquoise is an anglicized version of turkois, which is French for "Turkey stone." Originally mined in Persia (now Iran), turquoise arrived in Europe via Turkey, hence the name. Persian turquoise is noted for the purity of its blue color and experts regard it as the finest of all turquoise. Most turquoise today comes from China, Mexico and the United States; it's no longer mined in Iran.
Depending upon its origin, turquoise may vary in color from pale blue to bright green. Although pure sky blue is regarded as best by many people, there is no ideal color. Each hue has its devotees.
Turquoise is found close to the surface in arid climates. Phosphate and aluminum combine to form turquoise when surface waters seep into underlying rocks. The blue comes from small amounts of copper, while iron impurities yield a greenish color. Although sometimes found in veins, turquoise most often occurs as nuggets.
The rock in which turquoise is formed is called a matrix. Turquoise with parts of the rock still embedded in it is called matrix turquoise. Nuggets may also contain small bits (inclusions) of pyrite or other minerals. Iron oxide forms a webbed pattern of fine lines, leading to the name "spiderweb" turquoise. Veining or a mottled appearance in the stone is from the uneven distribution of copper.
Natural turquoise is turquoise which has had nothing done to it that changes or preserves the color, hardens or protects the surface or makes it easier to work with. It's usually just polished and placed in a setting.
Because it is porous, natural turquoise is absorbent. Perfumes, cosmetics, and perspiration can cause it to change color or become dull. Excessive heat will destroy turquoise. It's also a very soft stone that requires care in wearing.
Turquoise is frequently treated in several ways, some of which are nearly undetectable, even by experts. Treating turquoise often preserves the color and protects the stone. It also salvages otherwise unusable stones. Artificial, imitation and synthetic turquoise are also on the market. As with treated turquoise, buying these is only a problem if you think you're buying natural stones.
The most common treatments are stabilization and
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