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Steel Jewellery Wholesale Jewellery 40% OFF Wholesale with quantity discounts, Sterling Silver, Fashion Glamour Jewellery. Necklaces, Bracelets, Bangles, Rings, Earrings, Pendants, Body Piercing Jewellery Turquoise is an opaque, blue-to-green mineral that is a hydrous phosphate of copper and aluminium, with the chemical formula CuAl6(PO4)4(OH)8·4H2O. It is rare and valuable in finer grades and has been prized as a gem and ornamental stone for thousands of years owing to its unique hue. In recent times turquoise, like most other opaque gems, has been devalued by the introduction of treatments, imitations, and synthetics onto the market. The substance has been known by many names, but the word turquoise was derived around the 16th century from the French language turquie, for Central Asian[4] material which was early imported through Turkey. Contents * 1 Properties of turquoise * 2 Formation * 3 Occurrence o 3.1 Iran o 3.2 Sinai o 3.3 United States o 3.4 Other sources * 4 History of its use * 5 Imitations * 6 Treatments o 6.1 Waxing and Oiling o 6.2 Stabilization o 6.3 Dyeing o 6.4 Reconstitution o 6.5 Irradiation o 6.6 Backing * 7 Valuation and care * 8 See also * 9 Notes * 10 References [edit] Properties of turquoise Even the finest of turquoise is fracturable, reaching a maximum hardness of just under 6, or slightly more than window glass. Characteristically a cryptocrystalline mineral, turquoise almost never forms single crystals and all of its properties are highly variable. Its crystal system is proven to be triclinic via X-ray diffraction testing. With lower hardness comes lower specific gravity (2.60–2.90) and greater porosity: These properties are dependent on grain size. The lustre of turquoise is typically waxy to subvitreous, and transparency is usually opaque, but may be semitranslucent in thin sections. Colour is as variable as the mineral's other properties, ranging from white to a powder blue to a sky blue, and from a blue-green to a yellowish green. The blue is attributed to idiochromatic copper while the green may be the result of either iron impurities (replacing aluminium) or dehydration. The refractive index (as measured by sodium light, 589.3 nm) of turquoise is approximately 1.61 or 1.62; this is a mean value seen as a single reading on a gemmological refractometer, owing to the almost invariably polycrystalline nature of turquoise. A reading of 1.61–1.65 (birefringence 0.040, biaxial positive) has been taken from rare single crystals. An absorption spectrum may also be obtained with a hand-held spectroscope, revealing a line at 432 nanometres and a weak band at 460 nanometres (this is best seen with strong reflected light). Under longwave ultraviolet light, turquoise may occasionally fluoresce green, yellow or bright blue; it is inert under shortwave ultraviolet and X-rays. Turquoise is insoluble in all but heated hydrochloric acid. Its streak is a pale bluish white and its fracture is conchoidal, leaving a waxy lustre. Despite its low hardness relative to other gems, turquoise takes a good polish. Turquoise may also be peppered with flecks of pyrite or interspersed with dark, spidery limonite veining. [edit] Formation As a secondary mineral, turquoise apparently forms by the action of percolating acidic aqueous solutions during the weathering and oxidation of pre-existing minerals. For example, the copper may come from primary copper sulfides such as chalcopyrite or from the secondary carbonates malachite or azurite; the aluminium may derive from feldspar; and the phosphorus from apatite. Climate factors appear to play an important role as turquoise is typically found in arid regions, filling or encrusting cavities and fractures in typically highly altered volcanic rocks, often with associated limonite and other iron oxides. In the American southwest 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 aluminium sulfate, is a prominent secondary mineral. Typically turquoise mineralization is restricted to a relatively shallow depth of less than 20 metres (66 ft), although it does occur along deeper fracture zones where secondary solutions have greater penetration or the depth to the water table is greater. Although the features of turquoise occurrences are consistent with a secondary or supergene origin, some sources refer to a hypogene origin. The hypogene hypothesis, which holds that the aqueous solutions originate at significant depth, from hydrothermal processes. Initially at high temperature, these solutions rise upward to surface layers, interacting with and leaching essential elements from pre-existing minerals in the process. As the solutions cool, turquoise precipitates, lining cavities and fractures within the surrounding rock. This hypogene process is applicable to the original copper sulfide deposition; however, it is difficult to account for the many features of turquoise occurrences by a hypogene process. That said, there are reports of two phase fluid inclusions within turquoise grains that give elevated homogenization temperatures of 90 to 190 °C that require explanation. Turquoise is nearly always cryptocrystalline and massive and assumes no definite external shape. Crystals, even at the microscopic scale, are exceedingly rare. Typically the form is vein or fracture filling, nodular, or botryoidal in habit. Stalactite forms have been reported. Turquoise may also pseudomorphously replace feldspar, apatite, other minerals, or even fossils. Odontolite is fossil bone or ivory that has been traditionally thought to have been altered by turquoise or similar phosphate minerals such as the iron phosphate vivianite. Intergrowth with other secondary copper minerals such as chrysocolla is also common. Tags: Sterling Silver Fashion Glamour Jewellery Necklaces Bracelets Bangles Rings Earrings Pendants, Body Piercing Jewellery Amber Turquoise Marcasite chain omega cross butterfly angle rose cat flower skull charms beads
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