Physical Properties of Turquoise

Turquoise is opaque and has a Mohs scale hardness that varies remarkably. If silicification has not occurred, the turquoise will likely be chalky, porous, and soft. The specific gravity of turquoise is 2. The color of turquoise can vary from deep blue to deep green, with every variation of color in between, because of its chemical composition. Generally, the more copper in the molecule, the bluer the turquoise. Turquoise specimens from various mines have been analyzed to determine their chemical compositions. Turquoise can also change color naturally, usually becoming greener when exposed to moisture. Man, too, can change the color of turquoise artificially by submerging the stone in animal fat. Although turquoise must consist of copper, aluminum, and phosphorus, other elements can replace them (in various percentages), thereby changing the molecular structure. For example, two very rare minerals, chalcosiderite (where iron replaces the aluminum) and faustite (where zinc replaces the aluminum) exist in turquoise environments. However, more frequently, iron and zinc will partially replace the aluminum, leaving turquoise altered only in color, specific gravity, and of course, chemical composition. Most turquoise is concentrated more near the copper-aluminum end of this spectrum than the iron or zinc-aluminum end; therefore, most turquoise is blue or blue-green. A great many variables exist in this stone; it is sill turquoise. A series of chemical tests were conducted on turquoise from 21 different mines in several countries. There were marked differences in the composition of the oxides forming these turquoise samples. These tests, if nothing else, show just how complex a mined turquoise is; turquoise simply does not always follow the accepted generalizations. For example, the tests show that a Persian mine noted for its blue turquoise had the lowest copper and highest iron content. Brown, Blue Gold, The Turquoise Story, Main Street Press, Anaheim, CA, 1975. The International Turquoise Annuals, vol. Allen Penick, “Turquoise, the Mineral that’s an Accident. D, The Turquoise, A report to the National Academy of Science, vol. (This reprint includes a foreword and details on Southwestern turquoise mines by Rex Arrowsmith and an excellent reference list. Northrop, Turquoise and Spanish Mines in New Mexico, University of New Mexico, Press, 1975. Snow, Turquoise, reprinted by General Printing and Paper Co.