A fabulous, objective and very informative website I often use, called The Turquoise Guide, provides some great factual information on Turquoise.
I have excerpted large parts of this site here for the GURHAN blog-reader and customer who has a curiosity as to Turquoise and wishes to better understand the stone that Gurhan so commonly uses.
Background Information on Turquoise
In current usage, "natural turquoise" is used in two ways. First, the phrase is used to describe turquoise that has not been treated in any way with dyes, stabilizing epoxies, or other chemical treatments intended to alter the color, hardness or luster of the stone. Natural turquoise cannot be easily found in the marketplace. The purist who seeks it is advised to buy direct from the mine. It has been claimed that as little as 3-10 percent of turquoise mined is of sufficient hardness to be used in jewelry without stabilization. Natural turquoise is rare, indeed.
The term has also been used to describe turquoise that has not been treated with dyes or epoxies, but has been given a wax or oil coating for protection. Since the porosity of turquoise can lead to discoloring, staining and dehydration, only the most conservative purist would object to wax coatings.
"Natural Processed Turquoise"
"Natural processed" seems like an oxymoron to us, but the phrase is now starting to appear in the marketplace. This is a proprietary method, so we know very little about it. Apparently, turquoise is soaked in nontoxic chemicals to increase luster and color. The method is also claimed to leave no physical evidence of alteration. One advantage is that turquoise subjected to this secret treatment is less likely to turn green over time.
Most of the turquoise on the market has been treated in some way to deal with two problems intrinsic with this gemstone. First, turquoise is soft, sometimes even brittle, and thus susceptible to facture. Second, turquoise is porous. As a result, it is susceptible to staining, discoloration and fading. These two problems can be addressed in several ways, but most commonly are managed by stabilizing the turquoise (discussed below).
Another problem is that quality turquoise is getting harder to find. Many mines have been depleted and are now closed. The turquoise coming out of other mines is of lower quality than was once produced. As a result, methods have been developed to create turquoise with the appearance of quality by dying pale shades and by creating stones out of "chalk turquoise" (called reconstituted turquoise).
It should be noted that turquoise has been treated for thousands of years, usually with waxes and oils. Modern techniques represent "advances" on old solutions. Furthermore, many of the various types of gemstones sold these days have been treated in some way to harden them and create clearer crystals; heat treating is especially common.
Zachery Enhancement Method
There is another method that is often used called the Zachery Method. The method is named after its developer, James E. Zachery, an electrical engineer and active trader of turquoise.
This is a proprietary enhancement method, the specifics of which are not public. The method can only be used on turquoise that is of moderate quality. The turquoise is soaked in a non-toxic, secret chemical brew. When dried, the stone is easier to polish and the colors may be slightly more vivid. The only way to determine if a stone has been treated with this method is by destroying it and subjecting it to a chemical analysis. In a study by Fritsch et al., published in Gems and Gemology, it is reported that turquoise that has been treated with the Zachery method has more potassium than natural turquoise. What other chemicals might be used in the process is unknown.
This method is regarded highly by many in the trade because it is largely undetectable, even through the eyes of an expert; leads to a stone with greater luster; and does not involve the use of dyes and hardening agents. However, since it does not strengthen the stone in any substantial way, its use is restricted to good quality turquoise.
Virtually all turquoise on the market has been treated with a clear epoxy, resin or some other form of liquid plastic. A simple approach is to soak turquoise rough (the raw stone) for a long period of time in a hardening solution. Newer approaches involve "pressurized impregnation," in which pressure is used to force the hardening solution deep into the turquoise rough.
After drying, the stone can be cut, formed into cabochons or other shapes, polished and sold. The final product will look like a shinier and smoother version of natural turquoise. It will keep its color and be more resistant to scratches and dirt.
Stabilization is clearly much further removed from nature than simple waxing and oiling. It does have an advantage, however. Stabilization not only protects the stone from dirt, but also reduces the chances of fracturing. Second, waxing and oiling do not solve the problem of "bloom," in which materials from within the stone leak out over time to create an outer white deposit.
Our position on stabilization is simple: Given the nature of turquoise, together with the growing shortage of gemstone quality turquoise, stabilization is often necessary. We object only when the consumer is not informed that the turquoise they are buying has been treated in this fashion.
Much of the stabilized turquoise has also been color-treated. Dyes have been used to bring a stone closer to the Persian Blue that we all value. Another strategy is to dye the matrix a darker color to enhance contrast. Stabilization and dying is often accomplished simultaneously by adding a dye to the clear epoxy or resin used to harden the stone.
While we would never buy color-treated turquoise, we have no objection to it provided that the consumer is told what they are purchasing. Much dyed turquoise is sold fraudulently as the real thing, sadly.
Taking yet another huge step away from natural turquoise, we find reconstituted Turquoise. Other sites refer to this as "stove-top" turquoise. We are not sure who the clever person is who coined this phrase, but it is quite appropriate.
With this method, turquoise stones too small to be used for cabochons, beads or freeform nuggets are powered. This powered "turquoise trash," as we like to refer to it, is then mixed with a binding agent, poured into a mold, and then dried. This reconstituted turquoise is then cut into slabs and then used as natural turquoise slabs might be used in jewelry production.
Reconstituted turquoise is quite inexpensive and thus might be suitable for use in low-priced jewelry. We personally object to the idea of reconstituted turquoise; more objectionable is the selling of reconstituted turquoise as the real thing.
There is an imitation turquoise called "block turquoise" that contains no turquoise stone whatsoever. We mention it here because it is often sold as "reconstituted turquoise." The difference is important: reconstituted turquoise contains turquoise power; block turquoise is completely synthetic.
Often Mother Nature creates stunning, high quality turquoise in thin veins that are too slight for stand alone use. These slender pieces of turquoise are thus glued to a base consisting of stone or another material for added strength, then cut, shaped and polished. Sometimes a thin vein of turquoise can be cut with its host stone serving as the supportive base. We like the idea of taking full advantage of what Mom Nature has provided, as long as the consumer knows that the hidden base in his or her jewelry is not turquoise.
Matrix in Turquoise
Turquoise is often marked with dark veins that run through it called "matrix." In some regions such markings are considered to be beautiful. This seems to be so in the U.S. Southwest and the Far East. In other areas, such as the Middle East, these markings are thought of as imperfections and the stones that carry them are valued less.
For Gurhan, the matrix patters are an intensely beautiful part of the stone and he will often buy a stone because of those very lines of character and personality.
Turquoise matrix is essentially the remnants of the rock that "hosted" the turquoise as it formed through weathering and oxidation processes over millions of years.
Turquoise matrix can take on different colors, depending on the host rock (sometimes called "the mother rock").
Black matrix tends to be favored, as it creates a nice contrast. Matrix of this color is often iron pyrite (iron sulfide).
Yellow matrix is often rhyolite, an igneous, volcanic rock. Since turquoise usually forms in rock with a volcanic origin, the presence of rhyolite should not be surprising.
Brown matrix usually consists of an iron oxide, of which there are sixteen different types. The best known of the iron oxides is probably hematite.
The term "spider webbing" is used to describe turquoise with thin lines of matrix running throughout them, much like a spider's web.
Where Turquoise Comes From
In his gold jewelry, Gurhan primarily uses Turquoise from the Sleeping Beauty and Kingman mines in the U.S., and when he has found it, rarely, from Persia. In both silver and gold jewelry, he uses Turquoise from China. And if ever he sees an extraordinary piece from somewhere else, he'll use it too!
Turquoise from Iran
Turquoise of stunning beauty has been mined in Iran (formerly known as Persia) for over 5000 years. Although Iranian production accounts for just a small proportion of the world's total output, its turquoise still sets the standard for quality.
In Iran, turquoise is called “Ferozah," which translated means "victory." It is Iran's national gemstone.
The best of Iranian turquoise is rich blue, with less matrix than most turquoise mined elsewhere. It is also distinguished by white patches. Turquoise is never a hard mineral, but Iranian turquoise is usually harder than turquoise mined in other locations. Today, only the turquoise coming from the Southwest U.S. comes close to Iranian turquoise in color richness and beauty.
The Persians classified turquoise into three quality groups:
Angushtari. This is first quality, suitable for the finest jewelry. These stones had the rich blue "Persian turquoise" color with little marking or matrix.
Barkhaneh. This is second-quality turquoise, much like Angushtari but with more markings and matrix.
Arabi. These stones were considered third-rate due to a pale blue or green shade or unwanted speckles. (Spots in Persian turquoise tend to be white, not black.)
Turquoise is commercially mined in Iran in just one location: a section of the Ali-mersai mountain range, outside of the city of Mashhad, the capital of the Khorasan province.
Turquoise from China
The Chinese have been mining turquoise for at least 3700 years. This estimate is based on the find of bronze work with turquoise overlays that date back to 1700 B.C. It is believed, however, that ancient Chinese civilizations imported most of their turquoise, probably from Persia (Iran). Turquoise was used to carve statues and other art pieces, preferring jade for their jewelry.
Some turquoise comes from the Shanghai region, where the Ma'ashan turquoise mine is located, but most is produced in the Hubei Province where it sometimes obtains the brilliant blues long favored by turquoise enthusiasts.
One often reads that China produces 80 percent of the world's current output of turquoise. We have found no independent confirmation for this figure. We do not doubt it, given our own familiarity with the operations of turquoise wholesale suppliers. (However, it is not verified)
Chinese turquoise is usually stabilized with a clear epoxy to harden and seal it.
Turquoise from the United States
Most quality turquoise from the United States is found in the Southwest, particularly in Arizona, New Mexico, Nevada, Colorado, and California. Turquoise was sacred to Native Americans even before the arrival of Columbus. Most of the mines in these states have run dry and few are operating commercially these days. Even more difficult to find is gem-quality turquoise. Most turquoise today probably comes from Arizona, and is recovered as a byproduct from copper mining operations. The presence of copper is what makes turquoise blue.
Most of the mines in Arizona are deleted of their turquoise and are not being commercially mined. Here are a few mines that are significant, either for historical reasons or because turquoise is still being produced. Most of the Arizona mines are open pit copper mines, with turquoise being retrieved by others under contract.
Birdseye Mine. This mine has been closed for many years, but produced collector's quality stone.
Castle Dome. Located in Inspiration, this mine operated from 1943 through 1953.
Cave Creek. Located to the NE of Cave Creek, Arizona. There are reports of beautiful turquoise coming from this mine today, but we are still investigating for the details.
Kingman Mine. Kingman turquoise is well know in turquoise circles because of the beautiful blue coloration and black matrix of the stones coming from the mine.
Lavender Pit. This famous mine is located near Bisbee, Arizona. The mine is an open copper mine. Bisbee Blue turquoise is a rich blue, often with brown matrix. Green turquoise is also found in the mine. Little turquoise comes out of the mine these days. Most Bisbee blue turquoise jewelry comes from previously found supplies. It has been reported that the copper company, the Phelps Dodge Corporation, made few efforts to mine the turquoise. The stone in which it was embedded was hauled away as the company dug to reach the copper deep below. The turquoise would then be "harvested" by third parties under lease from the dump. It has also been reported that the copper miners should "borrow" the turquoise they came upon, stashing it into their lunch boxes, and then selling it on the open local market.
Morenci Mine. Located in the southeastern part of Arizona, this mine produces turquoise of a light blue color. The mine is no longer producing significant quantities of turquoise.
Sleeping Beauty. One of the most beautiful turquoise stones found in the U.S., "Sleeping Beauty Turquoise" is light blue in color and has little or no matrix. This mine is still operating, producing beautiful but expensive gem-quality turquoise.
In comparison with Arizona, California is a small player in the turquoise world. Turquoise has been found in the Llanada copper mine in San Benito County; and the Baker, Gove and Apache Canyon mines in San Bernardino County.
Turquoise has been found in fifteen mines, according to mindat.org, although not always in commercial quantities or qualities.
Mindat.org lists over 140 locations within Nevada where turquoise has been found. These include mines in 14 of Nevada's 16 counties.
New Mexico is home to 30 turquoise-hosting mines, according to mindat.org. Turquoise is found in the mines located in 7 of New Mexico's 33 counties. With the exception of Santa Fe County, these are located in the southern half of the state.
While most turquoise from the United States is mined in just a few states in the Southwest -- namely Arizona, New Mexico, Nevada, and Colorado -- turquoise has been found in mines (although not in commercially profitable concentrations) in many more states.
Turquoise from Mexico
Turquoise has been a prized gem in Mexico for a very long time, probably longer than can be documented. For example, a Teotihuacan mask that might date back as far as 300 A.D. has been unearthed. The Toltec civilization is known to have traded turquoise with northern civilizations in the 8th Century. When the Toltec civilization died out, only to be replaced by the Aztecs, turquoise gained even greater prominence. One of the most stunning pieces in Montezuma's famed treasure (now in British museum) includes a carved serpent that is decorated with turquoise tiles.
Today most of the turquoise mined in Mexico comes from the northern state of Sonora, which shares a border with the U.S. state of Arizona. Mexican turquoise can be of high quality, and comes in both shades of blue and green. The very best Mexican turquoise is every bit as good as that found in the Southwestern U.S. states.