View source for Tiger's eye

{{Short description|Chatoyant gemstone from the quartz family}}
{{about|the gemstone|the horse eye color|Tiger eye|the short story|The Tiger's Eye|the characters in the Sailor Moon series|Amazon Trio}}
{{distinguish|Tiger Eyes}}
{{distinguish|Eye of the Tiger}}
{{pp-pc}}
{{Infobox mineral
| name        = Tiger's eye
| image       = Tiger's eye.jpg
| imagesize   = 260px
| alt         = A polished reddish brown stone which is bisected by a band containing golden fibers
| caption     =
| formula     = Silica ({{chem2|SiO2|link=Silicon dioxide}})
| colour       = golden to red-brown
| habit       =
| system      =
| twinning    =
| cleavage    =
| fracture    =
| mohs        = 6.5–7
| luster      = Silky
| refractive  =
| opticalprop =
| birefringence =
| fluorescence =
| pleochroism =
| streak      =
| gravity     = 2.64–2.71
}}

'''Tiger's eye''' (also called '''tiger eye''') is a
[[Chatoyancy|chatoyant]] [[gemstone]] that is usually a [[metamorphic rock]] with a golden to red-brown colour and a [[Lustre (mineralogy)#Silky lustre|silky lustre]]. As members of the [[quartz]] group, tiger's eye and the related blue-coloured mineral hawk's eye gain their silky, lustrous appearance from the parallel intergrowth of quartz crystals and altered [[amphibole]] fibres that have mostly turned into [[limonite]].<ref>{{cite web|title=Tiger's Eye|url=http://www.mindat.org/min-3960.html|website=mindat.org|access-date=16 May 2016}}</ref><ref>{{cite journal|last1=Heaney|first1=Peter|last2=Fisher|first2=Donald|title=New interpretation of the origin of tiger's-eye|journal=Geology|date=April 2003|volume=31|issue=4|pages=323–326|doi=10.1130/0091-7613(2003)031<0323:NIOTOO>2.0.CO;2|bibcode=2003Geo....31..323H}}</ref>

==Other forms of tiger's eye==
''Tiger iron'' is an altered [[rock (geology)|rock]] composed chiefly of tiger's eye, red [[jasper]] and black [[hematite]]. The undulating, contrasting bands of colour and lustre make for an attractive motif and it is mainly used for jewellery-making and ornamentation. Tiger iron is a popular ornamental material used in a variety of applications, from beads to knife [[hilt]]s.

Tiger iron is mined primarily in South Africa and Western Australia. Tiger's eye is composed chiefly of [[silicon dioxide]] ({{chem2|SiO2}}) and is coloured mainly by iron oxide. The [[specific gravity]] ranges from 2.64 to 2.71.<ref>[http://ist-socrates.berkeley.edu/~eps2/wisc/sg.html Listing of SG of gems and gem simulants] {{Webarchive|url=https://web.archive.org/web/20060904000158/http://ist-socrates.berkeley.edu/~eps2/wisc/sg.html |date=2006-09-04 }}, Berkeley.edu</ref> It is formed by the alteration of [[Riebeckite#Crocidolite (fibrous  riebeckite)|crocidolite]].

[[Serpentine group|Serpentine]] deposits in the US states of Arizona and California can have [[Chatoyancy|chatoyant]] bands of [[chrysotile]], a form of [[asbestos]], fibres. These have been cut and sold as "Arizona tiger-eye" and "California tiger's eye" gemstones.<ref>{{cite book|last=Flagg|first=Arthur Leonard|title=Mineralogical Journeys in Arizona|year=1958|publisher=F.H. Bitner|location=Scottsdale|pages=92–93}}</ref><ref>{{cite journal|last=USGS|title=Cat's Eye or Tiger-Eye|journal=Mineral Resources of the United States / Department of the Interior, United States Geological Survey|year=1908–1909|volume=2|page=802|publisher=US Government Printing Office|location=Washington, D.C. |url=https://books.google.com/books?id=afI4AAAAIAAJ}}</ref> The trade name 'pietersite' is used for a [[fracture (geology)|fractured]] or [[breccia]]ted [[chalcedony]] containing [[amphibole]] fibers and promoted as tiger's eye from Namibia and China.<ref>[http://www.mindat.org/min-27262.html Pietersite on Mindat.org]</ref>

==Sources==
[[File:Quartz - Tigers-Eye - raw stone from Southafrica.jpg|thumb|alt="Photograph of a chunk of rock containing horizontal bands which contain golden fibers which are positioned vertically within the bands"|Unpolished tiger's eye from South Africa]]
Common sources of tiger's eye include Australia, Burma, India, Namibia, South Africa, the United States,<ref>{{cite book|last=Schumann|first=Walter|title=Gemstones of the World|year=2009|publisher=Sterling Publishing|location=New York, New York|isbn=978-1-4027-6829-3|edition=Fourth|page=140}}</ref> Brazil, Canada, China, Korea  and Spain.{{Citation needed|date=August 2011}}

==Cultural associations==
In some parts of the world, the stone is believed to ward off the [[evil eye]].<ref>The Encyclopedia of Superstitions
By Richard Webster, p.257</ref>

Roman soldiers wore engraved tigers eye to protect them in battle.

==Cut, treatment and imitation==
[[File:Tigers eye egg shape.jpg|thumb|alt="Photograph of a polished ovoid stone with bands containing shimmering golden fibers"|Oval shape tiger's eye with iron stripes]]
[[File:Blue tiger eye - falcon eye.jpg|thumb|Blue tiger's eye]]

Gems are usually given a [[cabochon]] cut to best display their [[chatoyance]]. Red stones are developed by gentle heat treatments. Dark stones are artificially lightened to improve colour using a [[nitric acid]] treatment.<ref>{{cite book|last=O'Donoghue|first=Michael|title=Synthetic, Imitation, and Treated Gemstones|year=1997|publisher=Butterworth-Heinemann|location=Boston, Massachusetts|isbn=0-7506-3173-2|pages=125–127}}</ref>

Honey-coloured stones have been used to imitate the more valued cat's eye [[chrysoberyl]], cymophane, but the overall effect is often unconvincing. Artificial [[optical fiber|fibre optic]] glass is a common imitation of tiger's eye, and is produced in a wide range of colours.

==References==
{{reflist}}

== External links ==
{{Commons category|Tiger's eye}}
* [http://geology.gsapubs.org/content/32/1/e45.full "New interpretation of the origin of tiger's-eye: Comment and Reply"]. {{doi|10.1130/0091-7613-32.1.e45}}.

{{Jewellery}}
{{Silica minerals}}

[[Category:Quartz gemstones]]