That beautiful, blue stone turquoise is iconically identified with the Southwest. But it occurs all over the world and has been prized by other cultures like the Persians, Turks, and Chinese. (The name “turquoise” comes from a French word meaning “Turkish”).
In the New World, turquoise was known by other names including the Nahuatl (Aztec)”chalchihuitl” (cha-che-wee-til) but equally prized.
The formation of turquoise is almost capricious. Water passes through porous weathered rock, usually volcanic, to become charged with phosphate. When it encounters copper and aluminum in the correct range of proportions, the compound CuAl6(PO4)4(OH)8•4H2O may result. This substance will deposit out of solution either in veins through the cracks in host rock or as non-crystalline nuggets in larger openings. These deposits are tiny compared with the amount of host rock which surrounds them. Deposition occurs in shallow ground, usually no deeper than 200 feet.
Deposits begin whitish, soft and chalky—far too crumbly for cutting. As more and more turquoise material is deposited, the material becomes harder and richer in color. Most natural turquoise is chalk turquoise or that of poor quality, so the percentage of gem-quality stone is very, very small compared with the amount of rock which must be broken and sorted to find those pieces. (In both modern and ancient times, we humans have been very clever at enhancing poorer turquoise to resemble the better stuff. Much of the turquoise currently on the market is infused with plastics or resins to make it seem gem-quality.)
In New Mexico, we’ve had a number of mines which have yielded small amounts of beautiful stone. Mines in the Cerrillos area (just south of Santa Fe) are most famous, but others in the Silver City, Hatchita, and Ruidoso areas have produced excellent gem-quality turquoise. Because of the vagaries of formation, the turquoise from each mine has a typical “look” : a range of color, pattern between host rock (matrix) and turquoise, inclusions like pyrite or quartz, and general appearance that a well-experienced person may likely identify. But the range of turquoise appearance from a single mine is part of what makes it interesting.
Along with other items like obsidian and pottery, turquoise was probably traded prehistorically. Certainly it shows up in areas far from any known deposits but as yet there is no way to scientifically assure that a particular piece of turquoise originated from a particular mine. And the smaller the piece (like small beads), the less likely it is that it will be possible—thus adding to the mystery.
If you find yourself in Albuquerque’s Old Town area, stop into the small, unassuming Turquoise Museum (2107 Central Ave.) for an in-depth, fascinating look at these “pieces of the sky”.