Turquoise 3 Polished Nuggets LOT Natural Tumbled Rock Gemstones Kingman Mine USA For Sale

This is a lotof 3 all natural polished nuggets of Kingman mine turquoise from Arizona,United States. These lots weigh 3-5 grams and the pieces measure 10-15 mm each.

I offer ashipping discount for customers who combine their payments for multiplepurchases into one payment! The discount is regular shipping price for thefirst item and just 50 cents for each additional item! To be sure you get yourshipping discount just make sure all the items you want to purchase are in yourcart. sales you win are added to your cart automatically. For any "buyit now" items or second chance offers, be sure to click the "add tocart" button, NOT the "buy it now" button. Once all of youritems are in your cart just pay for them from your cart and the combinedshipping discount should be applied automatically.


I offer amoney back guarantee on every item I sell. If you are not 100% happy with yourpurchase just send me a message to let me know and I will buy back the item foryour full purchase price.

Hi there, Iam selling this really nice lot of 3 Turquoise Mineral Specimen Nuggets. Thesepieces are really nice. They are 100%all natural and practically perfect and ready to go for adding to yourcollection or even wire wrapping and making into jewelry. I purchased thesefrom an old collection and estate of an old time miner. These have probablybeen passed down for generations. These nuggets are from an old miner's oldstock collection. So, I planned to hold onto these for a long time and perhapsmaybe never sell them, but times are tough so we are being forced to sell them.If you have any questions, do not hesitate to ask me.

The followingis information about this from wikipedia:Turquoise

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For otheruses, see Turquoise (disambiguation).

Turquoise

General

Category Phosphate minerals

Formula

(repeatingunit) CuAl6(PO4)4(OH)8·4H2O

Strunz classification 8.DD.15

Crystalsystem Triclinic

Crystal class Pinacoidal (1)

(same H–Msymbol)

Identification

Colour Turquoise, blue, blue-green, green

Crystal habit Massive, nodular

Cleavage Good to perfect_usually N/A

Fracture Conchoidal

Mohs scalehardness 5–6

Luster Waxy to subvitreous

Streak Bluish white

Specificgravity 2.6–2.9

Opticalproperties Biaxial (+)

Refractiveindex nα = 1.610

nβ = 1.615

nγ = 1.650

Birefringence +0.040

Pleochroism Weak

Fusibility Fusible in heated HCl

Solubility Soluble in HCl

References [1][2][3]

Turquoise isan opaque, blue-to-green mineral that is a hydrated phosphate of copper andaluminium, with the chemical formula CuAl6(PO4)4(OH)8·4H2O. It is rare andvaluable in finer grades and has been prized as a gemstone and ornamental stonefor thousands of years owing to its unique hue. In recent times, turquoise hasbeen devalued, like most other opaque gems, by the introduction onto the marketof treatments, imitations and synthetics.

The gemstonehas been known by many names. Pliny the Elder referred to the mineral ascallais (from Ancient Greek κάλαϊς) and the Aztecs knew it as chalchihuitl.[4]The word turquoise dates to the 17th century and is derived from the Frenchturquois for "Turkish" because the mineral was first brought toEurope through Turkey, from mines in the historical Khorasan Province ofPersia.[2][3][4][5]

Contents

1 Properties

2 Formation

3 Occurrence

3.2 Sinai

3.3 United States

3.4 Other sources

4 History of use

5 Cultural associations

6 Imitations

7 Treatments

7.1 Waxing and oiling

7.2 Stabilization

7.3 Dyeing

7.4 Reconstitution

7.5 Backing

8 Valuation and care

9 See also

10 References

11 Further reading

12 External links

Properties

The finest ofturquoise reaches a maximum Mohs hardness of just under 6, or slightly morethan window glass.[2] Characteristically a cryptocrystalline mineral, turquoisealmost never forms single crystals, and all of its properties are highlyvariable. X-ray diffraction testing shows its crystal system to betriclinic.[3][6] With lower hardness comes lower specific gravity(2.60–2.90)[3] and greater porosity; these properties are dependent on grainsize. The lustre of turquoise is typically waxy to subvitreous, and itstransparency is usually opaque, but may be semitranslucent in thin sections.Colour is as variable as the mineral's other properties, ranging from white toa powder blue to a sky blue, and from a blue-green to a yellowish green. Theblue is attributed to idiochromatic copper while the green may be the result ofeither iron impurities (replacing aluminium) or dehydration.

Therefractive index of turquoise (as measured by sodium light, 589.3 nm) isapproximately 1.61 or 1.62; this is a mean value seen as a single reading on agemological refractometer, owing to the almost invariably polycrystallinenature of turquoise. A reading of 1.61–1.65 (birefringence 0.040, biaxialpositive) has been taken from rare single crystals. An absorption spectrum mayalso be obtained with a hand-held spectroscope, revealing a line at 432 nm anda weak band at 460 nm (this is best seen with strong reflected light). Underlongwave ultraviolet light, turquoise may occasionally fluoresce green, yellowor bright blue; it is inert under shortwave ultraviolet and X-rays.

Turquoise isinsoluble in all but heated hydrochloric acid. Its streak is a pale bluishwhite and its fracture is conchoidal,[3] leaving a waxy lustre. Despite its lowhardness relative to other gems, turquoise takes a good polish. Turquoise mayalso be peppered with flecks of pyrite or interspersed with dark, spiderylimonite veining.

Formation

"BigBlue", a large turquoise specimen from the copper mine at Cananea, Sonora,Mexico

As asecondary mineral, turquoise forms by the action of percolating acidic aqueoussolutions during the weathering and oxidation of pre-existing minerals. Forexample, the copper may come from primary copper sulfides such as chalcopyriteor from the secondary carbonates malachite or azurite; the aluminium may derivefrom feldspar; and the phosphorus from apatite. Climate factors appear to playan important role as turquoise is typically found in arid regions, filling orencrusting cavities and fractures in typically highly altered volcanic rocks,often with associated limonite and other iron oxides. In the SouthwesternUnited States turquoise is almost invariably associated with the weatheringproducts of copper sulfide deposits in or around potassium-feldspar-bearingporphyritic intrusives. In some occurrences alunite, potassium aluminiumsulfate, is a prominent secondary mineral. Typically turquoise mineralizationis restricted to a relatively shallow depth of less than 20 metres (66 feet),although it does occur along deeper fracture zones where secondary solutionshave greater penetration or the depth to the water table is greater.

Turquoise isnearly always cryptocrystalline and massive and assumes no definite externalshape. Crystals, even at the microscopic scale, are exceedingly rare. Typicallythe form is vein or fracture filling, nodular, or botryoidal in habit.Stalactite forms have been reported. Turquoise may also pseudomorphouslyreplace feldspar, apatite, other minerals, or even fossils. Odontolite isfossil bone or ivory that has been traditionally thought to have been alteredby turquoise or similar phosphate minerals such as the iron phosphatevivianite. Intergrowth with other secondary copper minerals such as chrysocollais also common.

Occurrence

MassiveKingman blue turquoise in matrix with quartz from Mineral Park, Arizona, US Turquoisewas among the first gems to be mined, and many historic sites have beendepleted, though some are still worked to this day. These are all small-scaleoperations, often seasonal owing to the limited scope and remoteness of thedeposits. Most are worked by hand with little or no mechanization. However,turquoise is often recovered as a byproduct of large-scale copper miningoperations, especially in the United States.

Sinai

Since atleast the First Dynasty (3000 BCE) in ancient Egypt, and possibly before then,turquoise was used by the Egyptians and was mined by them in the SinaiPeninsula. This region was known as the Country of Turquoise by the nativeMonitu. There are six mines in the peninsula, all on its southwest coast,covering an area of some 650 km2 (250 sq mi). The two most important of thesemines, from a historic perspective, are Serabit el-Khadim and Wadi Maghareh,believed to be among the oldest of known mines. The former mine is situatedabout 4 kilometres from an ancient temple dedicated to the deity Hathor.

The turquoiseis found in sandstone that is, or was originally, overlain by basalt. Copperand iron workings are present in the area. Large-scale turquoise mining is notprofitable today, but the deposits are sporadically quarried by Bedouin peoplesusing homemade gunpowder.[citation needed] In the rainy winter months, minersface a risk from flash flooding; even in the dry season, death from thecollapse of the haphazardly exploited sandstone mine walls is not unheard of.The colour of Sinai material is typically greener than Persian material, but isthought to be stable and fairly durable. Often referred to as "Egyptianturquoise", Sinai material is typically the most translucent, and undermagnification its surface structure is revealed to be peppered with dark bluediscs not seen in material from other localities.

A selectionof Ancestral Pueblo (Anasazi) turquoise and orange argillite inlay pieces fromChaco Canyon, New Mexico, US (dated c. 1020–1140) show the typical colour rangeand mottling of American turquoise. Some likely came from Los Cerrillos.

United States

A fineturquoise specimen from Los Cerrillos, New Mexico, US, at the SmithsonianMuseum. Cerrillos turquoise was widely used by Native Americans prior to theSpanish conquest.

Bisbeeturquoise commonly has a hard chocolate brown coloured matrix.

Untreatedturquoise, Nevada, US. Rough nuggets from the McGinness Mine, Austin. Blue andgreen cabochons showing spiderweb, Bunker Hill Mine, Royston

The SouthwestUnited States is a significant source of turquoise; Arizona, California (SanBernardino, Imperial, Inyo counties), Colorado (Conejos, El Paso, Lake,Saguache counties), New Mexico (Eddy, Grant, Otero, Santa Fe counties) andNevada (Clark, Elko, Esmeralda County, Eureka, Lander, Mineral County and Nyecounties) are (or were) especially rich. The deposits of California and NewMexico were mined by pre-Columbian Native Americans using stone tools, somelocal and some from as far away as central Mexico. Cerrillos, New Mexico isthought to be the location of the oldest mines; prior to the 1920s, the statewas the country's largest producer; it is more or less exhausted today. Onlyone mine in California, located at Apache Canyon, operates at a commercialcapacity today.

The turquoiseoccurs as vein or seam fillings, and as compact nuggets; these are mostly smallin size. While quite fine material is sometimes found, rivalling Persianmaterial in both colour and durability, most American turquoise is of a lowgrade (called "chalk turquoise"); high iron levels mean greens andyellows predominate, and a typically friable consistency in the turquoise'suntreated state precludes use in jewellery.

Arizona iscurrently the most important producer of turquoise by value.[5] Several minesexist in the state, two of them famous for their unique colour and quality andconsidered the best in the industry: the Sleeping Beauty Mine in Globe ceasedturquoise mining in August 2012. The mine chose to send all ore to the crusherand to concentrate on copper production due to the rising price of copper onthe world market. The price of natural untreated Sleeping Beauty turquoise hasrisen dramatically since the mine's closing. The Kingman Mine as of 2015 stilloperates alongside a copper mine outside of the city. Other mines include theBlue Bird mine, Castle Dome, and Ithaca Peak, but they are mostly inactive dueto the high cost of operations and federal regulations The Phelps DodgeLavender Pit mine at Bisbee ceased operations in 1974 and never had a turquoisecontractor. All Bisbee turquoise was "lunch pail" mined. It came outof the copper ore mine in miners' lunch pails. Morenci and Turquoise Peak areeither inactive or depleted.

Nevada is thecountry's other major producer, with more than 120 mines which have yieldedsignificant quantities of turquoise. Unlike elsewhere in the US, most Nevadamines have been worked primarily for their gem turquoise and very little hasbeen recovered as a byproduct of other mining operations. Nevada turquoise isfound as nuggets, fracture fillings and in breccias as the cement fillinginterstices between fragments. Because of the geology of the Nevada deposits, amajority of the material produced is hard and dense, being of sufficientquality that no treatment or enhancement is required. While nearly every countyin the state has yielded some turquoise, the chief producers are in Lander andEsmeralda counties. Most of the turquoise deposits in Nevada occur along a widebelt of tectonic activity that coincides with the state's zone of thrustfaulting. It strikes about N15°E and extends from the northern part of ElkoCounty, southward down to the California border southwest of Tonopah. Nevadahas produced a wide diversity of colours and mixes of different matrixpatterns, with turquoise from Nevada coming in various shades of blue, blue-green,and green. Some of this unusually coloured turquoise may contain significantzinc and iron, which is the cause of the beautiful bright green to yellow-greenshades. Some of the green to green yellow shades may actually be variscite orfaustite, which are secondary phosphate minerals similar in appearance toturquoise. A significant portion of the Nevada material is also noted for itsoften attractive brown or black limonite veining, producing what is called"spiderweb matrix". While a number of the Nevada deposits were firstworked by Native Americans, the total Nevada turquoise production since the1870s has been estimated at more than 600 tons, including nearly 400 tons fromthe Carico Lake mine. In spite of increased costs, small scale mining operationscontinue at a number of turquoise properties in Nevada, including the Godber,Orvil Jack and Carico Lake mines in Lander County, the Pilot Mountain Mine inMineral County, and several properties in the Royston and Candelaria areas ofEsmerelda County.[7]

In 1912, thefirst deposit of distinct, single-crystal turquoise was discovered in LynchStation, Campbell County, Virginia. The crystals, forming a druse over themother rock, are very small; 1 mm (0.04 in) is considered large. Until the1980s Virginia was widely thought to be the only source of distinct crystals;there are now at least 27 other localities.[citation needed]

In an attemptto recoup profits and meet demand, some American turquoise is treated orenhanced to a certain degree. These treatments include innocuous waxing andmore controversial procedures, such as dyeing and impregnation (seeTreatments). There are however, some American mines which produce materials ofhigh enough quality that no treatment or alterations are required. Any suchtreatments which have been performed should be disclosed to the buyer on saleof the material.

Other sources

Turquoiseprehistoric artefacts (beads) are known since the fifth millennium BCE fromsites in the Eastern Rhodopes in Bulgaria - the source for the raw material ispossibly related to the nearby Spahievo Ph-Zn ore field.[8]

China hasbeen a minor source of turquoise for 3,000 years or more. Gem-quality material,in the form of compact nodules, is found in the fractured, silicified limestoneof Yunxian and Zhushan, Hubei province. Additionally, Marco Polo reportedturquoise found in present-day Sichuan. Most Chinese material is exported, buta few carvings worked in a manner similar to jade exist. In Tibet, gem-qualitydeposits purportedly exist in the mountains of Derge and Nagari-Khorsum in theeast and west of the region respectively.[9]

Other notablelocalities include: Afghanistan; Australia (Victoria and Queensland); northIndia; northern Chile (Chuquicamata); Cornwall; Saxony; Silesia; and Turkestan.

History ofuse

Trade inturquoise crafts, such as this freeform pendant dating from 1000–1040, isbelieved to have brought the Ancestral Puebloans of the Chaco Canyon greatwealth.

The pastelshades of turquoise have endeared it to many great cultures of antiquity: ithas adorned the rulers of Ancient Egypt, the Aztecs (and possibly otherPre-Columbian Mesoamericans), Persia, Mesopotamia, the Indus Valley, and tosome extent in ancient China since at least the Shang Dynasty.[10] Despitebeing one of the oldest gems, probably first introduced to Europe (throughTurkey) with other Silk Road novelties, turquoise did not become important asan ornamental stone in the West until the 14th century, following a decline inthe Roman Catholic Church's influence which allowed the use of turquoise insecular jewellery. It was apparently unknown in India until the Mughal period,and unknown in Japan until the 18th century. A common belief shared by many ofthese civilizations held that turquoise possessed certain prophylacticqualities; it was thought to change colour with the wearer's health and protecthim or her from untoward forces.

The Aztecsinlaid turquoise, together with gold, quartz, malachite, jet, jade, coral, andshells, into provocative (and presumably ceremonial) mosaic objects such asmasks (some with a human skull as their base), knives, and shields. Naturalresins, bitumen and wax were used to bond the turquoise to the objects' basematerial; this was usually wood, but bone and shell were also used. Like theAztecs, the Pueblo, Navajo and Apache tribes cherished turquoise for itsamuletic use; the latter tribe believe the stone to afford the archer dead aim.Among these peoples turquoise was used in mosaic inlay, in sculptural works,and was fashioned into toroidal beads and freeform pendants. The AncestralPuebloans (Anasazi) of the Chaco Canyon and surrounding region are believed tohave prospered greatly from their production and trading of turquoise objects.The distinctive silver jewellery produced by the Navajo and other SouthwesternNative American tribes today is a rather modern development, thought to datefrom circa 1880 as a result of European influences.

In Persia,turquoise was the de facto national stone for millennia, extensively used todecorate objects (from turbans to bridles), mosques, and other importantbuildings both inside and out,[citation needed] such as the Medresseh-I ShahHusein Mosque of Isfahan. The Persian style and use of turquoise was laterbrought to India following the establishment of the Mughal Empire there, itsinfluence seen in high purity gold jewellery (together with ruby and diamond)and in such buildings as the Taj Mahal. Persian turquoise was often engravedwith devotional words in Arabic script which was then inlaid with gold.

Cabochons ofimported turquoise, along with coral, was (and still is) used extensively inthe silver and gold jewellery of Tibet and Mongolia, where a greener hue issaid to be preferred. Most of the pieces made today, with turquoise usuallyroughly polished into irregular cabochons set simply in silver, are meant forinexpensive export to Western markets and are probably not accuraterepresentations of the original style.

The Egyptianuse of turquoise stretches back as far as the First Dynasty and possiblyearlier; however, probably the most well-known pieces incorporating the gem arethose recovered from Tutankhamun's tomb, most notably the Pharaoh's iconicburial mask which was liberally inlaid with the stone. It also adorned ringsand great sweeping necklaces called pectorals. Set in gold, the gem wasfashioned into beads, used as inlay, and often carved in a scarab motif,accompanied by carnelian, lapis lazuli, and in later pieces, coloured glass.Turquoise, associated with the goddess Hathor, was so liked by the AncientEgyptians that it became (arguably) the first gemstone to be imitated, the fairstructure created by an artificial glazed ceramic product known as faience.

The Frenchconducted archaeological excavations of Egypt from the mid-19th century throughthe early 20th. These excavations, including that of Tutankhamun's tomb,created great public interest in the western world, subsequently influencingjewellery, architecture, and art of the time. Turquoise, already favoured forits pastel shades since around 1810, was a staple of Egyptian Revival pieces.In contemporary Western use, turquoise is most often encountered cut encabochon in silver rings, bracelets, often in the Native American style, or astumbled or roughly hewn beads in chunky necklaces. Lesser material may becarved into fetishes, such as those crafted by the Zuni. While strong sky bluesremain superior in value, mottled green and yellowish material is popular withartisans.

Culturalassociations

In manycultures of the Old and New Worlds, this gemstone has been esteemed forthousands of years as a holy stone, a bringer of good fortune or a talisman.The oldest evidence for this claim was found in Ancient Egypt, where gravefurnishings with turquoise inlay were discovered, dating from approximately3000 BCE. In the ancient Persian Empire, the sky-blue gemstones were earlierworn round the neck or wrist as protection against unnatural death. If theychanged colour, the wearer was thought to have reason to fear the approach ofdoom. Meanwhile, it has been discovered that the turquoise certainly can changecolour, but that this is not necessarily a sign of impending danger. The changecan be caused by the light, or by a chemical reaction brought about bycosmetics, dust or the acidity of the skin.[11]

The goddessHathor was associated with turquoise, as she was the patroness of Serabitel-Khadim, where it was mined. Her titles included "Lady ofTurquoise", "Mistress of Turquoise", and "Lady of TurquoiseCountry".[12]

In Westernculture, turquoise is also the traditional birthstone for those born in themonth of December. The turquoise is also a stone in the Jewish High Priest'sbreastplate, described in Exodus 28. The stone is also considered sacred to theindigenous peoples of the Southwestern United States[13] Zuni and Pueblopeoples of the American Southwest,[14] The pre-Columbian Aztec and Maya alsoconsidered it to be a valuable and culturally important stone.[15]

Imitations

Some naturalblue to blue-green materials, such as this botryoidal chrysocolla with drusyquartz, are occasionally confused with or used to imitate turquoise.

The Egyptianswere the first to produce an artificial imitation of turquoise, in the glazedearthenware product faience. Later glass and enamel were also used, and inmodern times more sophisticated porcelain, plastics, and various assembled,pressed, bonded, and sintered products (composed of various copper andaluminium compounds) have been developed: examples of the latter include"Viennese turquoise", made from precipitated aluminium phosphatecoloured by copper oleate; and "neolith", a mixture of bayerite andcopper phosphate. Most of these products differ markedly from natural turquoisein both physical and chemical properties, but in 1972 Pierre Gilson introducedone fairly close to a true synthetic (it does differ in chemical compositionowing to a binder used, meaning it is best described as a simulant rather thana synthetic). Gilson turquoise is made in both a uniform colour and with black"spiderweb matrix" veining not unlike the natural Nevada material.

The mostcommon imitation of turquoise encountered today is dyed howlite and magnesite,both white in their natural states, and the former also having natural (andconvincing) black veining similar to that of turquoise. Dyed chalcedony,jasper, and marble is less common, and much less convincing. Other naturalmaterials occasionally confused with or used in lieu of turquoise include:variscite and faustite;[5] chrysocolla (especially when impregnating quartz);lazulite; smithsonite; hemimorphite; wardite; and a fossil bone or tooth calledodontolite or "bone turquoise", coloured blue naturally by themineral vivianite. While rarely encountered today, odontolite was once mined inlarge quantities—specifically for its use as a substitute for turquoise—insouthern France.

These fakesare detected by gemologists using a number of tests, relying primarily onnon-destructive, close examination of surface structure under magnification; afeatureless, pale blue background peppered by flecks or spots of whitishmaterial is the typical surface appearance of natural turquoise, whilemanufactured imitations will appear radically different in both colour (usuallya uniform dark blue) and texture (usually granular or sugary). Glass andplastic will have a much greater translucency, with bubbles or flow lines oftenvisible just below the surface. Staining between grain boundaries may bevisible in dyed imitations.

Somedestructive tests may, however, be necessary; for example, the application ofdiluted hydrochloric acid will cause the carbonates odontolite and magnesite toeffervesce and howlite to turn green, while a heated probe may give rise to thepungent smell so indicative of plastic. Differences in specific gravity,refractive index, light absorption (as evident in a material's absorptionspectrum), and other physical and optical properties are also considered asmeans of separation.

Treatments

Turquoise istreated to enhance both its colour and durability (i.e., increased hardness anddecreased porosity). As is so often the case with any precious stones, fulldisclosure about treatment is frequently not given. Gemologists can detectthese treatments using a variety of testing methods, some of which are destructive,such as the use of a heated probe applied to an inconspicuous spot, which willreveal oil, wax or plastic treatment.

Waxing andoiling

Historically,light waxing and oiling were the first treatments used in ancient times,providing a wetting effect, thereby enhancing the colour and lustre. Thistreatment is more or less acceptable by tradition, especially because treatedturquoise is usually of a higher grade to begin with. Oiled and waxed stonesare prone to "sweating" under even gentle heat or if exposed to toomuch sun, and they may develop a white surface film or bloom over time. (Withsome skill, oil and wax treatments can be restored.)

Stabilization

Materialtreated with plastic or water glass is termed "bonded" or"stabilized" turquoise. This process consists of pressureimpregnation of otherwise unsaleable chalky American material by epoxy andplastics (such as polystyrene) and water glass (sodium silicate) to produce awetting effect and improve durability. Plastic and water glass treatments arefar more permanent and stable than waxing and oiling, and can be applied tomaterial too chemically or physically unstable for oil or wax to providesufficient improvement. Conversely, stabilization and bonding are rejected bysome as too radical an alteration.[16]

The epoxybinding technique was first developed in the 1950s and has been attributed toColbaugh Processing of Arizona, a company that still operates today. Themajority of American material is now treated in this manner although it is acostly process requiring many months to complete.[citation needed]

Dyeing

The use ofPrussian blue and other dyes (often in conjunction with bonding treatments) to"enhance” its appearance, make uniform or completely change the colour, isregarded as fraudulent by some purists,[16] especially since some dyes may fadeor rub off on the wearer. Dyes have also been used to darken the veins ofturquoise.

Reconstitution

Perhaps themost extreme of treatments is "reconstitution", wherein fragments offine turquoise material, too small to be used individually, are powdered andthen bonded with resin to form a solid mass. Very often the material sold as"reconstituted" turquoise is artificial, with little or no naturalstone, made entirely from resins and dyes. In the trade "reconstituted"turquoise is often called "block" turquoise or simply"block."

Backing

Since finerturquoise is often found as thin seams, it may be glued to a base of strongerforeign material for reinforcement. These stones are termed "backed,"and it is standard practice that all thinly cut turquoise in the SouthwesternUnited States is backed. Native indigenous peoples of this region, because oftheir considerable use and wearing of turquoise, have found that backingincreases the durability of thinly cut slabs and cabochons of turquoise. Theyobserve that if the stone is not backed it will often crack. Early backingmaterials included the casings of old model T batteries, old phonographrecords, and more recently epoxy steel resins. Backing of turquoise is notwidely known outside of the Native American and Southwestern United Statesjewellery trade. Backing does not diminish the value of high quality turquoise,and indeed the process is expected for most thinly cut American commercialgemstones.[citation needed]

Valuation andcare

Slab ofturquoise in matrix showing a large variety of different colouration

Hardness andrichness of colour are two of the major factors in determining the value ofturquoise; while colour is a matter of individual taste, generally speaking,the most desirable is a strong sky to robin egg blue (in reference to the eggsof the American robin).[9] Whatever the colour, for many applications,turquoise should not be soft or chalky; even if treated, such lesser material(to which most turquoise belongs) is liable to fade or discolour over time andwill not hold up to normal use in jewellery.

The motherrock or matrix in which turquoise is found can often be seen as splotches or anetwork of brown or black veins running through the stone in a netted pattern;this veining may add value to the stone if the result is complementary, but sucha result is uncommon. Such material is sometimes described as "spiderwebmatrix"; it is most valued in the Southwest United States and Far East,but is not highly appreciated in the Near East where unblemished and vein-freematerial is ideal (regardless of how complementary the veining may be).Uniformity of colour is desired, and in finished pieces the quality ofworkmanship is also a factor; this includes the quality of the polish and thesymmetry of the stone. Calibrated stones—that is, stones adhering to standardjewellery setting measurements—may also be more sought after. Like coral andother opaque gems, turquoise is commonly sold at a price according to itsphysical size in millimetres rather than weight.

Turquoise istreated in many different ways, some more permanent and radical than others.Controversy exists as to whether some of these treatments should be acceptable,but one can be more or less forgiven universally: This is the light waxing oroiling applied to most gem turquoise to improve its colour and lustre; if thematerial is of high quality to begin with, very little of the wax or oil isabsorbed and the turquoise therefore does not "rely" on thisimpermanent treatment for its beauty. All other factors being equal, untreatedturquoise will always command a higher price. Bonded and"reconstituted" material is worth considerably less.

Being aphosphate mineral, turquoise is inherently fragile and sensitive to solvents;perfume and other cosmetics will attack the finish and may alter the colour ofturquoise gems, as will skin oils, as will most commercial jewellery cleaningfluids. Prolonged exposure to direct sunlight may also discolour or dehydrateturquoise. Care should therefore be taken when wearing such jewels: cosmetics,including sunscreen and hair spray, should be applied before putting onturquoise jewellery, and they should not be worn to a beach or other sun-bathedenvironment. After use, turquoise should be gently cleaned with a soft cloth toavoid a buildup of residue, and should be stored in its own container to avoidscratching by harder gems. Turquoise can also be adversely affected if storedin an airtight container.

See also

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List ofminerals

Bisbee Blue