bayerite

Turquoise (or turquois) is opaque, blue-to-green hydrated copper aluminium phosphate mineral according to the chemical formula CuAl6(PO4)4(OH)8·5H2O. It is rare and valuable in finer grades and has been enjoyed as a gem and ornamental stone for thousands of years owing to its unique hue. In recent times turquoise—like most other opaque gems— ...

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• Turquoise - Properties
• Turquoise - Formation
• Turquoise - Occurrence
• Turquoise - Iran
• Turquoise - Sinai
• Turquoise - United States
• Turquoise - Other sources
• Turquoise - History of use
• Turquoise - Imitations
• Turquoise - Treatments
• Turquoise - Valuation and care

Read more here: » Turquoise: Encyclopedia - Turquoise

Raney nickel - Alloy preparation. Alloys are prepared commercially by melting the active metal (nickel in this case, but iron and copper "Raney-type" catalysts can be prepared as well) and aluminium in a crucible and quenching the resultant melt, which is then crushed into a fine powder.[2] This powder may be screened for a specific particle size range depending on the a ...

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Raney nickel, Raney nickel - Preparation, Raney nickel - Alloy preparation, Raney nickel - Activation, Raney nickel - Properties, Raney nickel - Applications, Raney nickel - Safety, Raney nickel - Development

Read more here: » Raney nickel: Encyclopedia II - Raney nickel - Preparation

Turquoise was among the first gems to be mined, and while many historic sites have been depleted, some are still worked to this day. These are all small-scale, often seasonal operations, owing to the limited scope and remoteness of the deposits. Most are worked by hand with little or no mechanization. However, turquoise is often recovered as a byproduct of large-scale copper mining operations, especially in the United States.

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Turquoise, Turquoise - Properties, Turquoise - Formation, Turquoise - Occurrence, Turquoise - Iran, Turquoise - Sinai, Turquoise - United States, Turquoise - Other sources, Turquoise - History of use, Turquoise - Imitations, Turquoise - Treatments, Turquoise - Valuation and care

Read more here: » Turquoise: Encyclopedia II - Turquoise - Occurrence

Due to its large surface area and high volume of contained hydrogen gas, dry, activated Raney nickel is a pyrophoric material that should be handled under an inert atmosphere. Raney nickel is typically supplied as a 50% slurry in water. Care should be taken never to expose Raney nickel to air. Even after reaction, Raney nickel contains significant amounts of hydrogen gas, and will ignite when exposed to air. Raney nickel will produce hazardous fumes when burning, and therefore the use of a gas mask is recommended when extinguishing fi ...

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Raney nickel, Raney nickel - Preparation, Raney nickel - Alloy preparation, Raney nickel - Activation, Raney nickel - Properties, Raney nickel - Applications, Raney nickel - Safety, Raney nickel - Development

Read more here: » Raney nickel: Encyclopedia II - Raney nickel - Safety

Macroscopically Raney nickel looks like a finely divided gray powder. Microscopically, each particle of this powder looks like a three-dimensional mesh, with pores of irregular size and shape of which the vast majority are created during the leaching process. Raney nickel is notable for being thermally and structurally stable as well has having a large BET surface area. These properties are a direct result of the activation process and contribu ...

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Raney nickel, Raney nickel - Preparation, Raney nickel - Alloy preparation, Raney nickel - Activation, Raney nickel - Properties, Raney nickel - Applications, Raney nickel - Safety, Raney nickel - Development

Read more here: » Raney nickel: Encyclopedia II - Raney nickel - Properties

Raney nickel is used in a large number of industrial processes and in organic synthesis because of its stability and high catalytic activity at room temperature.[2][4] It is typically used in the reduction of compounds that have multiple bonds, such as alkynes, alkenes[5], nitriles[6], dienes, aromatics^{See also:}

Raney nickel, Raney nickel - Preparation, Raney nickel - Alloy preparation, Raney nickel - Activation, Raney nickel - Properties, Raney nickel - Applications, Raney nickel - Safety, Raney nickel - Development

Read more here: » Raney nickel: Encyclopedia II - Raney nickel - Applications

Turquoise is treated to enhance both its colour and durability (i.e., increased hardness and decreased porosity). Historically, light waxing and oiling were the first treatments to be used (since ancient times), providing a wetting effect (thereby enhancing the colour and lustre); this treatment is more or less acceptable by tradition, and because such material is usually of a higher grade to begin with. Conversely, the later development of pressure impregnation of otherwise unsaleable chalky American material by epoxy and plastics (such as ...

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Turquoise, Turquoise - Properties, Turquoise - Formation, Turquoise - Occurrence, Turquoise - Iran, Turquoise - Sinai, Turquoise - United States, Turquoise - Other sources, Turquoise - History of use, Turquoise - Imitations, Turquoise - Treatments, Turquoise - Valuation and care

Read more here: » Turquoise: Encyclopedia II - Turquoise - Treatments

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 altere ...

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Turquoise, Turquoise - Properties, Turquoise - Formation, Turquoise - Occurrence, Turquoise - Iran, Turquoise - Sinai, Turquoise - United States, Turquoise - Other sources, Turquoise - History of use, Turquoise - Imitations, Turquoise - Treatments, Turquoise - Valuation and care

Read more here: » Turquoise: Encyclopedia II - Turquoise - Formation

The pastel shades of turquoise have endeared it to many great cultures of antiquity: it has adorned the rulers of Ancient Egypt, the Aztecs (and possibly other Pre-Columbian Mesoamericans), Persia, Mesopotamia, the Indus Valley, and to some extent in ancient China since at least the Shang Dynasty [2]. Despite being one of the oldest gems, probably first introduced to Europe (through Turkey) with other Silk Road novelties, turquoise did not become important as an ornamental stone in the West until the 14th century, following a decline in the ...

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Turquoise, Turquoise - Properties, Turquoise - Formation, Turquoise - Occurrence, Turquoise - Iran, Turquoise - Sinai, Turquoise - United States, Turquoise - Other sources, Turquoise - History of use, Turquoise - Imitations, Turquoise - Treatments, Turquoise - Valuation and care

Read more here: » Turquoise: Encyclopedia II - Turquoise - History of use

The Egyptians were apparently the first to produce an artificial imitation of turquoise, in the glazed earthenware product faience. Later glass and enamel were also used, and in modern times more sophisticated ceramics, porcelain, plastics, and various assembled, pressed, bonded, and sintered products (composed of various copper and aluminium compounds) have been developed: examples of the latter include "Viennese turquoise", made from precipitated aluminium phosphate coloured by copper oleate; and "neolith", a mixture of bayerite and copper ...

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Turquoise, Turquoise - Properties, Turquoise - Formation, Turquoise - Occurrence, Turquoise - Iran, Turquoise - Sinai, Turquoise - United States, Turquoise - Other sources, Turquoise - History of use, Turquoise - Imitations, Turquoise - Treatments, Turquoise - Valuation and care

Read more here: » Turquoise: Encyclopedia II - Turquoise - Imitations

Even the finest of turquoise is fracturable, reaching a maximum hardness of just under 6, or slightly less 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 (high 2.90, low 2.60) and greater porosity: These properties are dependent on grain size. The lustre of turquoise is typically waxy to subvitreous, and tran ...

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Turquoise, Turquoise - Properties, Turquoise - Formation, Turquoise - Occurrence, Turquoise - Iran, Turquoise - Sinai, Turquoise - United States, Turquoise - Other sources, Turquoise - History of use, Turquoise - Imitations, Turquoise - Treatments, Turquoise - Valuation and care

Read more here: » Turquoise: Encyclopedia II - Turquoise - Properties

Richness of colour is the chief determiner of value in turquoise; generally speaking, the most desirable is a strong sky to "robin's egg" blue (in reference to the eggs of the American Robin); value decreases with the increase of green hue, lightening of colour, and mottling. In Tibet, however, a greener blue is said to be preferred. Whatever the colour, turquoise should not be excessively soft or chalky; even if treated, such lesser material (to which most turquoise belongs) is liable to fade or discolour over time ...

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Turquoise, Turquoise - Properties, Turquoise - Formation, Turquoise - Occurrence, Turquoise - Iran, Turquoise - Sinai, Turquoise - United States, Turquoise - Other sources, Turquoise - History of use, Turquoise - Imitations, Turquoise - Treatments, Turquoise - Valuation and care

Read more here: » Turquoise: Encyclopedia II - Turquoise - Valuation and care