Chemical Composition: CuAl
6((OH)
2/PO
4)
4.4H
2O
Mohs' Hardness: 5-6
Specific Gravity: 2.90-2.80
Cleavage: None
Transparency: Opaque
Refractive Index: 1.61-1.65
Double Refraction: +.0.04
Dispersion: None
The mineralogical name for turquoise is calaite, which is derived from a name used by Pliny to describe the stone. However, this name is rarely used, it is more commonly called Oriental Turquoise, true or mineral Turquoise or Turquoise de la vieille roche, or just plain turquoise. The name, turquoise, means Turkish stone, as this stone came to Europe through various trade routes, origionating in Persia, the Sinai Peninsula or further east, all of which went through Turkey.
Turquoise is always opaque and varies in color from a light sea green to a deep blue. The color comes from Copper and Iron sulfate found throughout the stone. The coloration comes from various colored bands spread evenly across defined spaces in the stone. When a heat of 482°F (250°c) is applied to the stone discoloration occurs, as blues change to a dull green color. Very thin sections of the gem are colorless to a light yellow in hue. Turquoises are also known to lose their color in sunlight. A dying technique has been formed to counteract this bleaching effect. But the technique does not work perfectly, and the dye on the stone can be chipped off with a knife.
Turquoise is found in cracks and cevices of other rocks. It is found in irregularly shaped masses. While turquoise was thought to be amorphous for a long time, it actually consists of an array of very small microcrystals. Geographically, turquoise is found all over the globe, from Mexico and New Mexico to Iran and Afghanistan, Tibet, Israel, eastern Austrailia and Virginia. One of the first clutches of turquoise was found on the Sinai Peninsula, but this was mined out over 4,000 years ago.
Today, the more blue a turquoise is, the more expensive it is considered. However, Mexicans and southwestern Native Americans did not share this belief. They considered both the blue and the green variations equally valuable. In fact, they called all blue/green stones that were similar to turquoise, chalchihuitl. This included jadeite, turquoise and amazonite.
In ancient Tibet, turquoise, along with gold, was the most common offering to gods and demons. Thrones for kings and Lamas were often adorned with turquoise, as was a special cape the Lamas wore. In early 17th century Europe, turquoise was thought to change its opacity as the health of the wearer changed. One author at the time claimed "A true wife should be like a turquoise stone, clear in heart in her husband's health, and cloudy in his sickness."
Sources:
Precious Stones, by Dr. Max Bauer. Charles E. Tuttle Company: Rutland Vermont and Tokyo, Japan, 1969
Gemstones of the World, by Walter Schumann. Sterling Publishing Co., New York, 1979
Simon and Schuster's guide to Rocks and Minerals, Simon and Schuster Inc. New York, 1978
The Magic of Jewels and Charms, Dr. George Frederick Kunz. J.B. Lippincott company, Philadelphia and London, 1915