Editing Turquoise (section)

== Imitations ==
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[[File:Chrysocolla USA.jpg|left|frame|Some natural blue to blue-green materials, such as this [[botryoid]]al [[chrysocolla]] with [[Drusy stones|drusy]] [[quartz]], are occasionally confused with or used to imitate turquoise.]]

The Egyptians were the first to produce an artificial imitation of turquoise, in the glazed earthenware product [[Egyptian faience|faience]]. Later glass and [[vitreous enamel|enamel]] were also used, and in modern times more sophisticated [[porcelain]], [[plastic]]s, and various assembled, pressed, bonded, and [[Sintering|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(II) phosphate]]. Most of these products differ markedly from natural turquoise in both physical and chemical properties, but in 1972 [[Pierre Gilson]] introduced one fairly close to a true [[Chemical synthesis|synthetic]] (it does differ in chemical composition owing to a binder used, meaning it is best described as a simulant rather than a synthetic). Gilson turquoise is made in both a uniform colour and with black "spiderweb matrix" veining not unlike the natural Nevada material.

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

These fakes are detected by [[gemology|gemologists]] using a number of tests, relying primarily on non-destructive, close examination of surface structure under magnification; a featureless, pale blue background peppered by flecks or spots of whitish material is the typical surface appearance of natural turquoise, while manufactured imitations will appear radically different in both colour (usually a uniform dark blue) and texture (usually granular or sugary). Glass and plastic will have a much greater translucency, with bubbles or flow lines often visible just below the surface. Staining between grain boundaries may be visible in dyed imitations.

Some destructive tests may be necessary; for example, the application of diluted [[hydrochloric acid]] will cause the [[carbonate]]s odontolite and magnesite to [[effervescence|effervesce]] and howlite to turn green, while a heated probe may give rise to the pungent smell so indicative of plastic. Differences in [[specific gravity]], [[refractive index]], light absorption (as evident in a material's [[absorption spectrum]]), and other physical and optical properties are also considered as means of separation.