Alternate birthstone for July. From the olden days, it was a soft stone that could readily be formed as a piece of jewelry or talisman.
Chemical formula: CuAl6(PO4)4(OH)8·4H2O
Crystal system: Triclinic
Crystal Habit: Massive, nodular
Cleavage: Good to perfect
Mohs scale: 5-6
Specific gravity: 2.6- 2.9
A hydrated phosphate of copper and aluminum.
A hydrated phosphate of copper and aluminum.
Turquoise has been used for thousands of years; from Ancient Egypt to Pre-Columbian Mesoamericans, Persia, Mesopotamia, the Indus Valley and China. The Aztecs inlaid Turquoise, along with gold, quartz, malachite, jet, jade, coral and shells into mosaic objects like masks, knives and shields. The Pueblo, Navajo, and Apache Indians use turquoise for religious and social beliefs. They believed the turquoise would afford the archer dead aim so they wore the turquoise.
As a secondary mineral, turquoise forms by the action of percolating acidic aqueous solutions during the weathering and oxidation of preexisting minerals. For example, the copper may come from primary copper sulfides such as chalcopyrite or from the secondary carbonates malachite or azurite. The aluminum may derive from feldspar and the phosphorus from apatite. Climate factors appear to play an important role as the turquoise is typically found in arid regions, filling or encrusting cavitites and fractures in typically highly altered volcanic rocks, often associated limonite and other iron oxides. In the Southwestern United States turquoise is almost invariably associated with the weathering products of copper sulfide deposits in or around potassium-feldspar-bearing porphyritic intrusives. In some occurrences alunite, potassium aluminum sulfate, is a prominent secondary mineral. Typically turquoise mineralization is restricted to a relatively shallow depth of less than 20 meters, although it does occur along deeper fracture zones where secondary solutions have a greater penetration or the depth to the water table is greater.
Turquoise is nearly always cryptocrystalline and massive and assumes no definite external shape. Crystals, even at the microscopic scale, are exceedingly rare. Typically the skin is veined or fracture filling, nodular, or botryoidal in habit. Stalactite forms have been reported. Turquoise may also pseudormorphously replace feldspar, apatite, or other minerals, or even fossils. Odontolite is fossil bone and ivory that has been traditionally thought to have been altered by turquoise or similar phosphate minerals such as iron phosphate vivianite. Intergrowth with other secondary copper minerals such as chrysocolla is also common.
Turquoise is generally treated so as to enhance its durability and its color. Treatments consists of waxing and oiling, stabilization, dyeing, reconstitution, and backing.
Waxing: light waxing or oiling were the first treatments to be used. It provided the wet look, thereby enhancing the color and luster of the stone. Over time, the s stone could show a white surface film or bloom. It can, with some skill be restored when this happens.
Stabilization: Material is treated with plastic or water glass is commonly referred to as bonded or stabilized turquoise. This process consists of pressure impregnation of otherwise unsaleable chalky American material by epoxy and plastics (polystyrene) and water glass (sodium silicate) to produce a wetting effect and improve durability. The epoxy technique was developed in the 1950s and has been attributed to Colburgh Processing of Arizona, a company still in operation today.
Dyeing: The use of Prussian blue and other dyes, often in conjunction with bonding treatments, to enhance and make the colors more uniform or to completely change the color. This is considered fraudulent by most purists, especially since the dyes may fade out or rub off. Dyes have been known to shrink the veins of the turquoise.
Reconstitution: One of the most extreme treatments is the reconstitution. This is where fragments of material considered too small to be of use is bonded with a resin to form a solid mass. It is commonly referred to as block turquoise.
Backing: Since the finer turquoise is found in the seams, which are thin, it may be glued to a base of stronger material for reinforcement. The Native American indigenous people have found that this increases the durability of the stones they put in their jewelry. They have noticed that stones NOT backed tend to crack easily. Early materials used for backing included old phonograph records, model T batteries but more recently they have started using epoxy steel resins. This does not diminish the value of the turquoise as so many other treatments do.
The different turquoise is known by the name of the mine that produces it. Some of it is solid in color while others may have veins of black which is caused by the presence of iron pyrite, veins of brown which is usually from one of sixteen types of iron oxides- most common being hematite. Spider webbing is a term used to describe the thin lines of matrix that looks like a spider’s web.
Sleeping beauty turquoise comes from the Sleeping Beauty Mine in Globe, Arizona. It however, closed in August 2012. The mining operations are now focused on mining the copper, which is more profitable. It has been rumored that the tailings from the mine are taken to a dump where a third party contracts to go through it. The sleeping beauty turquoise is robin egg blue with little to no veins in it.
Number 8 turquoise come from the Lynn Mining District in Eureka County, Nevada, just north of Carlin, Nevada. It opened in 1929. In 1950, it was bought by two brothers, T.G. Edgar and J.W.Edgar where they found 1600 pounds of this very high grade turquoise. It is known for its spider webbing and light blue to dark blue with green shading. The matrix is usually reddish brown and even black. The mine was closed in 1976.
Bisbee Blue turquoise comes from the area of Bisbee, Arizona. It can be found in different shades of color and quality from soft, low quality pale blue to quality hard brilliant blue and almost every shade in between. Some has a reddish brown spiderweb matrix. The mine is located in the Lavender Pit mine.
Kingman turquoise comes from Kingman, Arizona and predates the statehood of Arizona. The mine has been in operation since the 1880’s. The Native American Indians have been mining the area as far back as 600A.D. They believe the Indians first used charcoal to heat the rocks upon where they would douse them with water from animal skins to fracture the stone exposing the new material underneath. This is where the stabilization process was first created. It is one of the oldest working mines of gem grade turquoise in the United States.
Morenci turquoise came from southern Arizona. The Morenci turquoise mine produced a turquoise that is light to bright blue in hue. This stone has an unusual matrix of irregular quartz and pyrite that, when polished, often resembles silver. Also, a small amount of Morenci turquoise had some brownish matrix called “Morenci red matrix”. One of the first American turquoises to come to the market, Morenci is highly valued and difficult to obtain.The Morenci mine is in southeastern Arizona and is now closed and buried under tons of rock. The land was leeched with chemicals that would destroy any trace of turquoise, which means that there is never a chance to re-open this mine. The former miners of Morenci still have quite a stash of rough stone, enough to release a small amount every year to keep it available.
There are hundreds of mines in the United States and thousands around world so we are unable to list them all. Here is a map of just the southeastern United States.