Editing Turquoise (section)

== Properties ==
The finest of turquoise reaches a maximum [[Mohs scale of mineral hardness|Mohs hardness]] of just under 6, or slightly more than window [[glass]].<ref name="mindat" /> Characteristically a [[cryptocrystalline]] mineral, turquoise almost never forms single [[crystal]]s, and all of its properties are highly variable. [[X-ray diffraction]] testing shows its [[crystal system]] to be [[triclinic]].<ref name="rruff" /><ref>{{cite web |url=http://rruff.info/Turquoise/R050554 |publisher=RRUFF Project |title=Turquoise R050554 |url-status=dead |archive-url=https://web.archive.org/web/20170502182409/http://rruff.info/Turquoise/R050554 |archive-date=2017-05-02 |access-date=2017-10-19 }}</ref> With lower hardness comes greater [[porosity]].<ref  name=Sinkankas1964>{{cite book |last1=Sinkankas |first1=John |title=Mineralogy for amateurs. |date=1964 |publisher=Van Nostrand |location=Princeton, N.J. |isbn=0442276249 |pages=425–426}}</ref> The [[Lustre (mineralogy)|lustre]] of turquoise is typically waxy to subvitreous, and its [[Transparency (optics)|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 [[Minerals#Colour and streak|idiochromatic]] copper<ref name=Rossman1981>{{cite journal|last1=Rossman |first1=G. R. |year=1981 |title=Color in gems: The new technologies |journal=Gems & Gemology |volume=17 |number=2 |pages=60–71 |doi=10.5741/GEMS.17.2.60 |url=https://www.gia.edu/doc/SU81.pdf |access-date=13 August 2022}}</ref> while the green may be the result of [[iron]] impurities (replacing copper.)<ref name="VigierEtal2019">{{cite book |editor1-last=Vigier |editor1-first=Emmanuelle |editor2-last=Querré |editor2-first=Guirec |editor3-last=Cassen |editor3-first=Serge |title=La parure en callaïs du néolithique européen |date=2019 |publisher=Archaeopress Publishing Ltd. |location=Oxford |isbn=9781789692815 |url=https://books.google.com/books?id=-vIYEAAAQBAJ |access-date=13 August 2022}}</ref>{{rp|29}}

The [[refractive index]] of turquoise varies from 1.61 to 1.65 on the three crystal axes, with [[birefringence]] 0.040, biaxial positive, as measured from rare single crystals.<ref name=Hurlbut/>

Crushed turquoise is soluble in hot [[hydrochloric acid]].<ref name=Sinkankas1964/> Its [[Streak (mineralogy)|streak]] is white to greenish to blue, and its [[fracture]] is smooth to [[conchoidal fracture|conchoidal]].<ref name="rruff"/> 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.

Turquoise is nearly always cryptocrystalline and massive and assumes no definite external shape. Crystals, even at the microscopic scale, are rare. Typically the form is a vein or fracture filling, nodular, or [[botryoidal]] in [[crystal habit|habit]].<ref name="Hurlbut"/> [[Stalactite]] forms have been reported. Turquoise may also [[pseudomorph]]ously replace feldspar, apatite, other minerals, or even [[fossil]]s. [[Odontolite]] is fossil bone or [[ivory]] that has historically been 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. Turquoise is distinguished from chrysocolla, the only common mineral with similar properties, by its greater hardness.<ref name="Hurlbut"/>

Turquoise forms a complete [[solid solution]] series with '''chalcosiderite''', {{chem2|CuFe6(PO4)4(OH)8*4H2O}}, in which [[ferric]] iron replaces aluminium.<ref name=Hurlbut/>