Part I
Turquoise has always been a much desired stone. Its history is long, dating back to about 7000 BC, and mined in areas all over the world. At the end of this article is a brief internet bibliography that gives some of the history and significance. I am not a turquoise expert, but what I have observed about turquoise should be useful to those who are buying turquoise jewelry and would like to know more about it.
In today's fashion it is in and out every several years, and the best time to buy higher end turquoise of course is when it is less in favor.
But what are we buying? The buying challenge is even greater now than it used to be as there are more imitations out there and clever ways to make them appear more like the real thing.
The golden rules are quite simple.
Let price and your own judgment guide you when you are buying from retail stores, department stores, discount jewelry outlets and the like. In most cases they will not have much, if any information on the turquoise. But you can always ask.
Ask the vendor for specific information on origin and treatments. Reputable vendors will tell you what they know about it. They should tell you if it is from a specific mine, the Southwest, China, Tibet or otherwise and what has been done to it.
You may find that they don't know. A lot can be learned from its price. If it is very expensive, make sure you are buying from a reputable dealer. Natural, untreated turquoise of good color and size is rare and jewelry made from it is beyond the budget of most of us. In most cases the natural turquoise will have its mine or region included in its description.
Next is stabilized but undyed natural turquoise. This includes turquoises from specific mines that were too soft to use without stabilization. If they have been stabilized this information should be supplied.
Since turquoise is a soft stone, and will vary greatly in softness even from the same mine, you can expect that it has been treated in some way. Stabilization, a process to make the stone more durable by the addition of resin or other adhesive is extremely common. Without this process, there would be very little turquoise to buy. Even centuries ago turquoise all over the world was treated with various kinds of oil, wax or fat to stabilize it.
The price, of course, is less than for natural untreated turquoise.
Left- broken samples of Chinese turquoise, middle- two samples of Tibetan/Chinese, right - dogbone shaped stabilized turquoise, probably Chinese.
Then there is white turquoise matrix, a white stone that is the same composition as natural turquoise but without the copper and other elements that specifically give it the color of turquoise.* This "chalk turquoise" is dyed as well as stabilized.
White stones that take dye well are also sometimes erroneously called chalk turquoise. The most common are magnesite and howlite, but new ones such as marble, dolomite, calcite and other white stones are beginning to appear on the market.
Samples of magnesite, the one on right dyed to imitate turquoise
Lookalikes, other stones that naturally have a turquoise-like color are sometimes mistaken for turquoise. The most common examples are African jasper, variscite, chrysocholla, amazonite and apatite. The colors vary a lot but they are visually distinguishable from the color of true turquoise.
Further down the ladder is reconstituted turquoise, which is ground up bits of turquoise mixed with glassy material and then heated and formed into blocks that are then turned into various bead shapes, seed beads and heishi.
Last and least in terms of value are the imitations, such as glass, faience, ceramic and plastic. The dead giveaway here is the weight. They are much lighter than stone. In addition plastic melts if you pierce it with a hot needle.
Faience is an interesting medium in itself. It has a very long history as a replacement or imitation of turquoise. The ancient faience is a whitish clay coated with an alkaline glaze containing copper to give it the turquoise color.
Ancient Egyptian faience is a good example. Somewhere after the first millenium the knowlege of using alkaline glaze with copper was lost in the ancient Near and Middle East.
It was rediscovered around 1100-1200 AD, when ceramics in Persian and other ceramic products along the silk road began to appear with a beautiful turquoise color.
Turquoise from the various mines and regions often have typical colors or patterns in the matrix.
Traditionally the most favored sky blue turquoise comes from Iran and various mines in Arizona. The Sleeping Beauty mine in Globe, Arizona produces much of this most valued color.
Not all of these mines are still producing. However, turquoise from some of these defunct mines can still be found on the market. In Tibet the greenish turquoise is more favored, and you can find some beautiful green stones. Greenish turquoise is also typical of mines in Nevada and other parts of the Southwest, Mexico and the Hubei mines in China.
With or without matrix? The turquoise of highest value is an even color throughout and free of any matrix (the background material in which the turquoise nodules form). Stones with a bluish turquoise color have the greatest value , for instance the robin's egg blue of Sleeping Beauty turquoise.
Turquoise with matrix is desired by many people, particularly where a Southwestern or ethnic look is in fashion. In contrast in Middle Eastern and many Asian countries the turquoise without matrix is preferred. Turquoise for this market is often set in gold rather than in silver and also with diamonds and other gems for a completely different look.
The matrix can be a good marker for real turquoise as its appearance is very typical for turquoise from specific locations, and also as a marker for stones such as magnesite, which has its own distinctive patterns.
The matrix patterns can take a delicate webbed appearance or a deep colored ground in which round nodules or irregular patches of turquoise appear.
Color: Unless you can see the kinds of turquoise side by side it is difficult to vizualize the subtle variations in color and texture, but the next best thing is to check photos of the natural turquoises and compare the colors, matrix or lack thereof, and the characteristics of the matrix.
This is labeled yellow turquoise, but as you can see, some of it is not very yellow! Jasper is one of the common stones found in "yellow turquoise".
A site I have visited often for examples of different types of turquoise is http://nevadagem.com/pages/turquoise.html. They sell only natural turquoise, so the examples they show are a good start to turquoise education.
The major mines, both active and closed are represented, along with concise descriptions of the stone, a little history and several photos for each type. Once you become familiar with these differences you will be more able to distinguish a good or bad buy when purchasing turquoise.
Another with a good variety of samples from mines and their general information is: http://www.skystonetrading.com/turquoise.asp
The most well known turquoise regions include: The Southwest, (Arizona, Utah, Nevada), Mexico, Iran (Nishapur), Tibet, China (Hubei mines), and the Sinai peninsula (source of the ancient Egyptian turquoise).
Turquoise mine names you are most likely to see include Kingman and Sleeping Beauty, but there are many others you should know about.
The sites mentioned above give very good information on many more mines and the varieties of turquoise that come from them.
But don't expect to become a turquoise expert! this is just to help you become aware of the many characteristics of turquoise and its imitations.
Even experts cannot always tell by eye whether turquoise has been treated, or is an imitation. There are simple tests to supplement visual information. You really can't assume anything about the source of turquoise depending solely on where it is bought and its surface appearance.
In the past Chinese turquoise usually had a glassy surface. Now I hear from turquoise vendors that they are producing turquoise with a matte surface as well.
I observed some Navajo women at this past year's Tucson show buying stabilized Chinese turquoise. Many mines in the Southwest are no longer producing, and fine gem quality turquoise has never been in great supply.
Hearsay has it that In Iran they now sell turquoise from Arizona. The mines in Iran are said to be depleted.
One great thing about life is the chance to learn new things. Certainly the subject of turquoise will supply us with new things to learn for a long time to come.
* Correction. the "real" chalk turquoise does have copper but in very small amounts. It is very whitish in appearance. This chalk turquoise is found in the Southwest and in China as well, and presumably wherever turquoise deposits are found. My thanks to Russ Nobbs of Ring & Things for clarifying this point. See more on the issue in Part II.
Additional turquoise references:
http://www.rockhounds.com/rockgem/articles/turquoise.html
http://www.bwsmigel.info/GEOL.115.ESSAYS/Gemology.Turquoise.html
http://minerals.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/turquoise.html
http://www.rings-things.com/gemstone/index.html look under Turquoise
http://www.jewelrysupplier.com/2_turquoise/turquoisel_properties.htm
http://www.collectorsguide.com/fa/fa098.shtml
http://www.lapidaryjournal.com/feature/may03str.cfm
http://nevadagem.com/pages/turquoise.html
http://www.khulsey.com/jewelry/semi-precious_gems_turquoise.html
http://www.luckygemstones.com/turq_informed_buyer.htm
http://www.silversun-sf.com/turquoise_info/turquoise_page.htm
http://www.metmuseum.org/toah/hi/hi_sttu.htm
The next section will include information on testing, characteristic, composition and some of my personal experiences with turquoise.
To be continued in Part II
I'd love to hear your comments.
Thanks.
