Blue Sky...Blue Stone
by Bob Jones, Senior Editor Rock&Gem Magazine
Turquoise is one of the world's earliest-used gem materials. Ranked with the jades of the Orient and lapis in the Near East, turquoise has been revered for thousands of years. In the Southwestern United States, no gemstone has been held in greater esteem. Diggings at Chaco Canyon and other ancient sites have revealed tens of thousands of pieces of turquoise in various stages of lapidary treatment. Where ancient leaders were buried, the amount of turquoise present in the grave sites indicates that it was a stone of significance long ago. Hardly a deposit of turquoise was left undiscovered by the ancient ones. Today, the gem material's popularity reaches from the Southwestern United States across the entire world.
Turquoise depends on the whims of nature for its formation. It is not a material that originated deep within the earth as a primary mineral. Rather, it relies on weathering and the ingredients of the earth's crust for its formation.
The ancient Egyptians sent slave convoys deep into the Arabian Desert to extract fragments of this blue gem from the sedimentary rocks where it occurred as a late-forming secondary mineral. The world-famous Persian turquoise (Persia is now Iran), also formed by weathering and chemical reaction, is still considered by many to be the finest ever mined.
The chemistry of turquoise reveals its origins. It is found only in or near copper deposits, as it depends on the presence of copper ions for its formation. Turquoise is a hydrous hydrate of copper, aluminum and phosphorus. The latter element is combined with oxygen, and called the phosphate radical. Radicals act as single chemical units, though they may be made up of two or more elements. The hydrous hydrate designation indicates the presence of water in the lattice structure of the turquoise molecule.
Turquoise also depends on its host rock to provide two other critical ingredients in addition to the copper ion. They are aluminum ions and the phosphate radical. A trace of water completes the structure. When the rocks in and around a copper deposit are weathered, the necessary ingredients for turquoise may be released. If feldspar is present, and it almost always is, an abundance of aluminum ions will occur. If a mineral containing phosphorus occurs there, that ion is released. Usually the mineral apatite, a calcium phosphate, serves that purpose. Any number of copper minerals can supply the necessary main ingredient.
The internal atomic arrangement of turquoise is such that iron can substitute for the aluminum, resulting in a color variation. Iron-free material is an intense sky-blue. As iron enters the structure, the color shades toward green. If the iron completely replaces the aluminum, the mineral takes on a new identity, chalcosiderite (chalco indicates the presence of copper and siderite is a term for an iron compound). Since iron and aluminum can replace each other gradually, a whole series of color shadings from pure-blue turquoise to stark-green chalcosiderite occurs in nature. The demand for turquoise as it shades toward green tends to diminish next to the rich blue of pure turquoise that is always more popular.
Another color feature in turquoise, which is exceedingly popular here in the Southwest, is spiderweb turquoise. The name alludes to a pattern of tracings of color, ranging from black to red, due to infillings of another mineral--iron oxide. Turquoise of pure-blue color without patterns of any kind are the most sought after in the Near East. In the Southwest and the Far East, however, spiderweb turquoise is very popular and commands the highest prices.
Spiderwebbing occurs when iron oxide, which can range in color from black to reddish, fills in cracks in turquoise. The pattern is always random, with the individual strands ranging in thickness from hair-thin to coarse bands. There is no pattern to spiderwebbing, as the contrasting lines wander through the turquoise, crossing, curving and ending abruptly. Such contrasting lines are attractive and raise the value of the turquoise. Sometimes the contrasting iron oxide is seen in small rounded blotches or thick bands or layers. A good lapidary artist can use such contrast to his or her advantage, incorporating it into the overall artistic effect of the stone.
There was a time when turquoise could be collected by rockhounds. Small deposits were accessible, mainly near the huge copper porphyries that are common in the Southwest. Now it is nearly impossible to go into the field and dig turquoise. Any spot that produces the stone has long since been claimed, mined out or incorporated into a larger operation.
Occurrences of turquoise were known to the Native Americans of the Southwest long before copper mining was a fact. Fine deposits like at Cripple Creek, Colorado; Chaco Canyon, New Mexico; and many places in Arizona were held in high regard by the Native Americans as sources for their precious blue stone. In Arizona, for example, a very active trade developed between the coastal tribes who gathered shells and the interior tribes who dug turquoise in several places, as well as salt from the Campo Verde region of central Arizona. The salt mines are still a collecting site for rockhounds today.
When the Spaniards came to the New World, turquoise was seen as a common component of ceremonial and royal robes and jewelry. With their lust for gold, the Spaniards paid little heed to this revered gemstone. This is certainly not true today, as turquoise has taken its place on the list of highly regarded non-crystalline gem materials.
Bisbee material ranks as some of Arizona's finest turquoise (above left). Solid blue turquoise without spiderwebbing is a variety highly prized in the Near East (above right).
With the advent of copper mining in the New World, turquoise became more available. Since turquoise has no ore value of consequence, and it occurs in minor amounts in copper deposits, it was possible to collect it without any significant backlash from mining companies. Miners could easily gather small fragments of turquoise rock and take them home without hassle, as turquoise remained largely unknown as a gem material outside the Southwestern United States. That has changed dramatically in the last three decades.
As mining progressed, some copper mines developed a reputation for producing the better-quality stones. Even today, Bisbee Blue is sought for its rich color that is often spiderwebbed and especially hard. Bisbee is now past history, but the mines in the Globe-Miami district of Arizona continue to produce. The Sleeping Beauty Pit in Miami, a source of choice turquoise, is still producing. An independent contractor works with the company to mine turquoise without interfering with copper production.
The same is true of the Duval Pit, north of Kingman, which is probably the largest producer of turquoise in the country. Turquoise mining by Colbaugh Processing Company of Kingman supplies a major portion of the market today. As supplies of gem-grade turquoise inevitably dwindled--even as mining proceeded--the price of the finest natural turquoise climbed out of sight for most lapidaries. Consequently, it has become necessary to treat lower-grade turquoise so that it can be a usable gem material.
The earliest successful treatment method was developed by Colbaugh Processing in the 1950s. Recognizing that it was wasteful to cast aside the lower-grade turquoise, the Colbaughs developed a scientific process for strengthening the softer grades of the gem. The process, called stabilizing, brings out the natural color of the gem, while giving it sufficient hardness and strength to survive lapidary treatment. The process is still not public knowledge, but Marty Colbaugh did take me through his plant to reveal the general techniques used.
The turquoise has to be thoroughly dried. This is done by intense and prolonged heating. It is then infused under pressure with epoxy so that the epoxy penetrates the stone. Afterwards, the turquoise is sealed in small metal containers and cooled very slowly. The entire process takes months. Sometimes, the canisters explode and entire lots are destroyed. If successful, the resulting turquoise shows a nice natural color, is easily polished, and is strong enough to be worked by the lapidary. Best of all, it can be obtained at a price the lapidary can afford.
If this and other processes had not come along, the supply of useful turquoise would have dried up long ago, and turquoise would never have achieved the popularity it has developed since the 1970s. People like the Colbaughs deserve a lot of credit for the continued widespread use of turquoise today.
Now, Native American-style turquoise jewelry is popular all over the world. At the Munich Show each fall, Native American jewelry is available and sells very well. It is not uncommon to see people wearing fine Native American jewelry with turquoise wherever you travel abroad. Such is the popularity of this lovely stone.
If you want to collect turquoise today, the only option is to go to an operating mine, where permission is a must. Rarely is it possible for the individual collector to obtain good rough on his or her own. The vast amount of turquoise being mined is obtained under contract with one of the big copper companies operating an open pit. The turquoise is mined by contract miners who suffer the costs and share the profits with the mining company. Despite the difficulty of collecting turquoise, rough material remains widely available to fill the high demand. The striking material that has been so long prized will remain an integral ingredient in human adornment.
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