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Roger Weller, geology instructor
Bisbee Lavender Pit mine and Turquoise
Courtesy R. Weller/Cochise College
The discovery of Bisbee turquoise was a result of copper mining operations in the Mule Mountains of south-central Cochise County. The Phelps Dodge Corporation operated in Bisbee Arizona between 1951 and 1974, extracting copper ore from the first, large, open mine, called the “Lavender Pit.” Through the mid 50s and 60s, the primary goal of the Lavender pit mining operation was to retrieve copper ore; because of this, there was no sizable effort to retrieve turquoise. The turquoise was simply a byproduct of this copper mining operation.
“Lavender Pit”, Phelps Dodge Mining Corp. mine 1958
most of the finest specimens found their way out of the mines in the pockets and
lunch pails of the miners. Despite the lack of effort to retrieve it,
throughout the mid 50s and mid 60s, the turquoise that made it out of the mine
was some of the first turquoise to be marketed and subsequently, Bisbee
turquoise is one of the most famous American turquoises. Bisbee turquoise is
some of the rarest and highest quality turquoise available. The turquoise found
in Bisbee vary in quality, hardness, and color, ranging from a soft low-quality
green and pale blue to the hardest, brightest blue. Often referred to as
Bisbee-Blue, this rich colored, hard, turquoise is the finest turquoise
available. Brilliant blue color and fine wisps of webbing are often
these fine gems. Today, the physical qualities and scarcity of Bisbee
turquoise make them prized gems to behold.
Note: By the 70s, the mining operations were over; the mines of Bisbee had produced
“3 million ounces of gold, 97 million ounces of silver, 8 billion tons of copper, 273 tons
of zinc, and 304 million pounds of lead. There is no comprehensive record of secondary
minerals, since mining operations were focused on retrieving precious metals.
Turquoise in general
For thousands of years and throughout the world, Turquoise has been appreciated for its beauty and purported mystic qualities. Valued and treasured as a good luck talisman to ward off unnatural death, the oldest proof of the use of turquoise is amongst the artifacts of the Egyptians around 3000 B.C. Various cultures believe turquoise has unique and holy abilities to ward off evil, danger, or accidents. It has been said that turquoise is endowed with special powers to relax the mind, giving spiritual clarity, and also enhancing understanding and happiness. The designation, “Turquoise,” is believed to come from French, pierre turquoise, meaning Turkish stone. The mineral originally found its way from Iran, through turkey and on to Europe.
Courtesy of David H. Garske
Turquoise is a porous mineral deposit of copper hydroxi phosphate of aluminum, copper, phosphorus hydrogen and oxygen. This phosphate class gemstone occurs in igneous rocks and forms as water trickles through a host stone for millions of years, gradually leaving a deposit. The more copper within its structure will create a color in the blue range, more aluminum, iron or chromium will form colors in the green to white range. Additionally zinc will yield a yellow-green color. Other colors that are found in a turquoise come from the host stone, known as a matrix; these colors sometimes form thin evenly spaced webbing. A dark, black, matrix is usually formed by iron pyrite, gold-brown by iron oxides, and yellow to brown from rhyolite. Quality turquoise is hard, about a six on the Mohs scale, and normally ranges from blue to medium green.
(Mohs scale of mineral hardness: http://www.minsocam.org/MSA/collectors_corner/article/mohs.htm )
Typically, turquoise has an opaque waxy luster and can have an almost glasslike appearance with thin semi-translucent sections. The minerals crystals are very fine and usually cannot be seen, even microscopically. The gemstone fractures in a concoidal (shell like), break and when exposed to long wave ultraviolet light and can fluoresce green, yellow or bright blue.
In selecting a gemstone, one should be aware of the nature of turquoise. Turquoise used for jewelry varies from 5 to 6 on the Mohs scale, relatively soft compared to a diamond. Turquoise found near the surface of the earth is usually hardest because it has had a chance to dry, or cure. There is softer, chalky turquoise; however it is too soft and porous to be used unless treated. Use caution when choosing a turquoise, since it may be found in various grades which affect the value of the gemstone. There are a few terms to beware of when shopping for Bisbee or ay other turquoise. These terms include natural, stabilized, color treated, reconstituted and, simulated. A natural, porous, stone is usually polished into a cabochon (rounded) or cut and shaped. Over time, the stone may change color due to handling and exposure to sunlight and moisture. A stabilized gemstone is chemically treated to harden the stone with a coating in an epoxy resin. This finish seals the stone and prevents discoloration. Color treated turquoise is substandard in hardness and color and is chemically treated to change or enhance color and hardness. Reconstituted turquoise is soft unusable dust and chips; mixed with resins and pressed into form it resembles natural turquoise. Simulated turquoise is imitation turquoise, usually a dyed plastic made to resemble natural turquoise. Whether you’re choosing Bisbee blue turquoise or any other gemstone, make a purchase because it “speaks to you,” buy the best you can afford and simply enjoy it.
Care and cleaning
Avoid scratching or cracking your turquoise by carefully handling it. Do not store it with other jewelry that may damage your gemstone. Clean it in warm soapy water, dry immediately with a soft cloth. Avoid chemicals, heat, perfumes, cosmetics and cleaners as much as possible. Natural oils and acids will cause turquoise to change color over time.
Bisbee turquoise is still available today however is usually prized by their owners. There are many other varieties of turquoise however those extracted from the Lavender pit are said to be very distinctive in color and webbing. Many grades of turquoise are also available so one must be careful and knowledgeable. After selecting a gem, use caution, paying attention to care and cleaning. Bisbee blue or any other variety, should last a lifetime and if it is chosen because you love it, it will bring you years of enjoyment.