|FORMATION AND COLORS OF TURQUOISE|
THE FORMATION AND COLORS OF TURQUOISE
Chemically, the mineral turquoise is a hydrous basic phosphate of copper and aluminum. It is formed when water of the right chemistry trickles through a host stone over many, many centuries, gradually leaving behind a turquoise deposit. If you would like to know more about the geology of turquoise formation, check out our page on Nevada turquoise. It has considerable information on mining for turquoise and the regional geologic conditions that formed so many turquoise mines in our state. Nevada Turquoise - You can link to it HERE.
The vast majority of all turquoise world-wide is formed as one of two different types. They are nugget turquoise and vein turquoise.
Vein turquoise forms as solutions are deposited in open cracks and voids which are caused by small faults or other movement of the rock. Vein turquoise can either have a matrix pattern or not, but most of the clear turquoise that is found does originally form as veins. Veins can range all the way from very thin coatings less than 1/16th of an inch thick, to very unusual wide veins up to 5 or more inches thick. The widest veins tend to be made of more porous low quality turquoise material. Thin pieces of vein turquoise, too thin to be cut alone, are cut in one of two ways. They are either backed with a man made material like epoxy or hard plastic, or an amount of natural hard matrix is left attached to the thin vein, and the two cut as one piece. Either way, the backing strengthens the stone and makes it much less likely to break and easier to cut. Without some form of backing, they would otherwise be unusable. Sometimes turquoise will form surrounding and mixed in with angular fragments of broken country rock. This is called turquoise breccia and sometimes makes interesting gems of contrasting turquoise and mother rock, which in many places in Nevada is a black chert.
|The other common form of turquoise is the individual
nugget. Nuggets form as aggregates of small pieces of turquoise in clay filled openings.
Many commonly have a spider web type matrix, though some nuggets do form clear and free
from matrix patterns. Nuggets may form in clay filled shear zones, or along bedding planes
where the layers of the host rock may have gaps or space between the layers filled with
Since turquoise is a mineral that is deposited by water solutions, turquoise can take the shape of cavities left behind when the stems and parts of fossil plants are dissolved out of the harder host rock. This can also occur where fossil clams leave behind voids when sedimentary rocks host turquoise deposits. This is referred to as "Fossil" Turquoise, and it is very rare.
|The colors of turquoise cover a far wider range than most people think. In fact colors often vary considerably within various locations at the same mine. If the mix has more copper, the turquoise will be colored in the blue range; the addition of iron adds tones more in the green range; if more aluminum than normal is present, the stones are in the green to white range. The addition of zinc yields a yellow-green color and adds hardness to the stone. Turquoise from Nevada comes in various shades of blue, blue-green, green-blue, and green, all of which are considered desirable. Nevada also produces some unique shades of bright mint to apple to neon yellow green that are unequalled anywhere else on earth. Some of this unusual turquoise may contain significant zinc and iron, which is the cause of the beautiful bright green to yellow-green shades. Significant quantities of the mint to yellow-green colors have so far been found only in Lander County, specifically in the Carico Lake district, the Pixie mine at Cortez and at Damele and Orvil Jack mines. In some cases, stones from one mine resemble very closely those from another mine and can be virtually impossible for even a gemstone expert to tell the difference. No one can say that stones from a certain mine are all one color, as there is always some amount of variation, but in general the bulk of a mine's production shares some common qualities and characteristics. Turquoise can also come in varying grades, with the higher-quality generally being darker in color, harder and with very little porosity. Often the stones of a lighter color have a tendency to be softer and more porous, and this may give them the potential to change color with wear - however this is not always the case.|
|The other colors that appear in a turquoise gemstone come
from the matrix or host stone that the turquoise was formed in. The host rock matrix can
be golden, rust-red colored, black, brown or be darker shades of green or blue. In Nevada,
a black matrix is usually present from black chert (a common host rock); a yellow to gold
to brown shades of matrix form from iron oxide. Some turquoise matrix is hard and takes a
good polish while other forms can be soft and do not polish as well as the turquoise
itself. Matrix that is thin and evenly spaced over the surface of the stone is commonly
known as a "spider web" matrix. Spider web matrix usually enhances the
collectability and value of turquoise in the US, but in some other places, it
makes the stone less valuable. Spider web matrix patterns are fairly common in
some Nevada mines.
Turquoise is most commonly set in gold throughout the world, with the exception being the Southwestern US, where is is most commonly set in silver. Because yellow gold forms a quite different background for blue stones than does silver, light blue stones are favored for finer pieces, stones often so pale that they are not wanted by jewelry artists that work in silver. Most Persian Turquoise, offered at very high prices, is pale and almost always set in gold. It is impossibly difficult to find enough top level Gem-Grade Turquoise to set in gold on a large scale as this highest grade of material is actually much rarer than diamonds. World wide, only about 1/10 of one percent of all the Turquoise mined is of a high enough grade that can be set in gold.
Always remember that the 'best' color of turquoise is
largely a matter of personal choice. Most turquoise authorities in the world would agree
that the ideal color for turquoise is a bold copper blue shade often called "Royal
Blue". It is the most vivid and intense of all the pure blue turquoise shades.
It is rare - some
mines, even good mines, may never produce a single carat of it. Other mines may yield only
a few ounces of it in thousands of pounds of normally high-grade material. Beyond that,
however, many of the other tones are considered very attractive and are valued and
appreciated by their owners.
TURQUOISE INFORMATION PAGE
Please note that the author, Chris Ralph, retains all copyrights to this entire document and it may not be reproduced, quoted or copied without permission.
NEVADA OUTBACK GEMS TURQUOISE AND JEWELRY
Nevada Outback Gems
|Find out more by checking out All of Our links below:|
|View our Premium Contemporary Turquoise Jewelry - Wearable Artwork!||View our Unique Gem Quality Turquoise Cabochons|
|Premium Jewelry, with Gemstones of all types||Top Quality Loose Gemstones - Gemstones of all types|
|Rare Crystals and Gemstone Rough, all types including Turquoise||Check out our EBAY Auctions of Jewelry, Gemstones and Rough|
|How to make a purchase, information and terms||More information about us - Nevada Outback Gems|
|About Nevada Turquoise||Contact us - we want to help|
|More Info about Turquoise, the Beautiful Gem||Nevada Outback Gems Homepage|
|Take a virtual tour of our turquoise mines||Our Free Colored Gemstone Information Encyclopedia|
|Chris' Adventures Prospecting for Gold, Silver, Turquoise and other Gems||Nevada Outback Library and Bookstore - Learn more!|
|Nevada Outback Gems Website News||More Info about Gem Cutting|