Editing Chatoyancy (section)

{{Short description|Optical reflectance effect in materials}}
{{Redirect|Cat's eye effect|other uses|Cat's eye (disambiguation){{!}}Cat's eye}}
{{lead|date=October 2023}}
[[File:Tigers-Eye.jpg|thumb|right|[[Tiger's eye]]]]
[[File:Tigers eye crystal444.jpg|thumb|right|Tiger's eye]]

In [[gemology]], '''chatoyancy''' ({{IPAc-en|ʃ|ə|ˈ|t|ɔɪ|.|ən|s|i}} {{respell|shə|TOY|ən|see}}), also called '''chatoyance''' or the '''cat's eye effect''',<ref>{{cite book |first1=Walter|last1=Schumann |first2=Daniel|last2=Reinersmann |translator-first=Elizabeth E.|translator-last=Shea |title=Minerals of the World |year=2008 |publisher=[[Sterling Publishing]] |location=New York |isbn=9781402753398 |page=19 |url=https://books.google.com/books?id=VoCM1wgXLAAC&q=chatoyancy&pg=PA19 |edition=2nd}}</ref> is an [[optical phenomenon|optical]] reflectance effect seen in certain [[gemstone]]s. (Historically, the term has applied specifically to gems; in woods and other materials the effect is more broadly known as "figure" or iridescence.) 

Coined from the French {{lang|fr|œil de chat}}, meaning cat's eye, the chatoyant effect is typically characterized by one or more well-defined bands of reflected light, reminiscent of a cat's eye, which appear to glide across a gem's surface as the object is moved, or when the observer moves while viewing it. 

Chatoyancy is caused by the presence of fibrous structures within the material, such as in [[tiger's eye]] quartz, or by fibrous inclusions and cavities, as seen in cat's eye [[chrysoberyl]], in which the effect is caused by the presence of titanium dioxide, which aligns perpendicularly to produce the effect.<ref>{{cite book|last=Mukherjee|first=Swapna|title=Applied mineralogy : applications in industry and environment|year=2011|publisher=Springer|location=Dordrecht|isbn=978-9400711617|url=https://books.google.com/books?id=mllvP7ZmWqkC&q=chatoyancy&pg=PA381}}</ref><ref>{{cite book|title=The Oxford companion to the earth|year=2006|publisher=Oxford Univ. Press|location=Oxford|isbn=9780198540397|edition=1st|editor-first=Paul L.|editor-last=Hancock|editor-first2=Brian J.|editor-last2=Skinner|chapter=gemstones|url-access=registration|url=https://archive.org/details/oxfordcompaniont00hanc}}</ref>