Editing Chrysoberyl (section)

==Alexandrite==
The alexandrite variety displays a color change dependent upon the nature of ambient lighting. Alexandrite results from small scale replacement of aluminium by chromium ions in the crystal structure, which causes intense absorption of light over a narrow range of wavelengths in the yellow region (520–620&nbsp;[[nanometre|nm]])<ref name="alexandrite">{{cite web |url=http://www.alexandrite.net/chapters/faq/why-does-alexandrite-appear-to-change-color-in-sunlight-and-artificial-light.html |title=Why does alexandrite appear to change color in sunlight and artificial light? |access-date=6 June 2014 |url-status=live |archive-url=https://web.archive.org/web/20140714222751/http://www.alexandrite.net/chapters/faq/why-does-alexandrite-appear-to-change-color-in-sunlight-and-artificial-light.html |archive-date=14 July 2014 }}</ref><ref>{{cite journal|last1=Xie|first1=Fei|last2=Cao|first2=Yu|first3=Cindy|last3=Ranchon|first4=Alan|last4=Hart|first5=Robin|last5=Hansen|first6=Jeffrey E.|last6=Post|first7=Coralyn W.|last7=Whitney|first8=Emma|last8=Dawson-Tarr|first9=Alan J.|last9=Drew|first10=David J.|last10=Dunstan|date=April 9, 2020|title=Explanation of the Colour Change in Alexandrites|journal=Scientific Reports|volume= 10|issue=1|pages=6130|doi=10.1038/s41598-020-62707-3|pmid=32273534|pmc=7145866|bibcode=2020NatSR..10.6130X|doi-access=free}}</ref> of the visible light spectrum.<ref name="alexandrite" /> Because [[color vision|human vision]] is most sensitive to green light and least sensitive to red light, alexandrite appears greenish in daylight where the full spectrum of visible light is present, and reddish in incandescent light which emits less green and blue light.<ref name="alexandrite" /><ref>{{cite journal|last1=Xie|first1=Fei|last2=Cao|first2=Yu|first3=Cindy|last3=Ranchon|first4=Alan|last4=Hart|first5=Robin|last5=Hansen|first6=Jeffrey E.|last6=Post|first7=Coralyn W.|last7=Whitney|first8=Emma|last8=Dawson-Tarr|first9=Alan J.|last9=Drew|first10=David J.|last10=Dunstan|date=April 9, 2020|title=Explanation of the Colour Change in Alexandrites|journal=Scientific Reports|volume=10|issue=1|pages=6130|doi=10.1038/s41598-020-62707-3|pmid=32273534|pmc=7145866|bibcode=2020NatSR..10.6130X|doi-access=free}}</ref> This color change is independent of any change of hue with viewing direction through the crystal that would arise from [[pleochroism]].<ref name="alexandrite" />

Alexandrite from the [[Ural Mountains]] in Russia can be green by daylight and red by incandescent light. Other varieties of alexandrite may be yellowish or pink in daylight and a [[Aquilegia canadensis|columbine]] or [[raspberry]] red by incandescent light.{{Citation needed|date=May 2024}}

Stones that show a dramatic color change and strong colors (e.g., red-to-green) are rare and sought-after,<ref name="gia.edu" /> but stones that show less distinct colors (e.g. yellowish green changing to brownish yellow) may also be considered "alexandrite" by gem labs such as the Gemological Institute of America.<ref>{{cite web|url=http://www.bonhams.com/auctions/21649/lot/1345|title=Bonhams : Alexandrite and Platinum and Diamond Ring|access-date=20 January 2017|url-status=live|archive-url=https://web.archive.org/web/20160307031508/http://www.bonhams.com/auctions/21649/lot/1345/|archive-date=7 March 2016}}</ref><ref>{{cite web|url=http://www.gia.edu/cs/Satellite?pagename=GST/Dispatcher&childpagename=GIA/Page/ReportCheck&c=Page&cid=1355954554547&reportno=6157619556|title=GIA – Report Check|access-date=20 January 2017|url-status=live|archive-url=https://web.archive.org/web/20161012093416/http://www.gia.edu/cs/Satellite?pagename=GST%2FDispatcher&childpagename=GIA%2FPage%2FReportCheck&c=Page&cid=1355954554547&reportno=6157619556|archive-date=12 October 2016}}</ref>

According to a popular but controversial story, alexandrite was discovered by the Finnish mineralogist [[Nils Gustaf Nordenskiöld]] (1792–1866), and named alexandrite in honor of the future [[Emperor of All Russia]] [[Alexander II Romanov]]. Nordenskiöld's initial discovery occurred as a result of an examination of a newly found mineral sample he had received from Perovskii, which he identified as emerald at first.<ref>{{cite web |url=http://www.alexandrite.net/chapters/chapter2/index.html |title="Alexandrite or Diaphanite?". In Alexandrite Tsarstone Collectors Guide. |year=2006 |access-date=2007-07-09 |url-status=live |archive-url=https://web.archive.org/web/20071012002934/http://alexandrite.net/chapters/chapter2/index.html |archive-date=2007-10-12}}</ref><ref>''Nordenskiöld N.'' Alexandrit oder Ural Chrysoberyll // Schriften der St.-Petersburg geschrifteten Russisch-Kaiserlichen Gesellschaft fuer die gesammte Mineralogie. 1842. Bd 1. S. 116–127.</ref> The first emerald mine had been opened in 1831. However, recent research suggests that the stone was discovered by Yakov Kokovin.<ref>{{cite book |last1=Wise |first1=Richard W. |title=Secrets Of the Gem trade |date=2016 |publisher=Brunswick House Press |isbn=9780972822329 |page=93 |edition=Second}}</ref>

Alexandrite {{convert|5|carat|mg}} and larger were traditionally thought to be found only in the Ural Mountains, but have since been found in larger sizes in Brazil.  Other deposits are located in [[India]] ([[Andhra Pradesh]]), [[Madagascar]], Tanzania and Sri Lanka. Alexandrite in sizes over three carats are very rare. Today, several labs can produce [[Synthetic alexandrite|synthetic]] lab-grown stones with the same chemical and physical properties as natural alexandrite. Several methods can produce flux-grown alexandrite, Czochralski (or pulled) alexandrite, and hydrothermally-produced alexandrite. Flux-grown gems are fairly difficult to distinguish from natural alexandrite as they contain inclusions that seem natural. Czochralski or pulled alexandrite is easier to identify because it is very clean and contains curved striations visible under magnification.  Although the color change in pulled stones can be from blue to red, the color change does not truly resemble that of natural alexandrite from any deposit. Hydrothermal lab-grown alexandrite has identical physical and chemical properties to real alexandrite.<ref>{{cite web |url=https://www.gemsociety.org/article/is-synthetic-alexandrite-real-alexandrite/ |title=Is Synthetic Alexandrite Real Alexandrite? |last1=Clark |first1=Donald |website=International Gem Society |access-date=2016-09-21 |url-status=live |archive-url=https://web.archive.org/web/20160707193611/https://www.gemsociety.org/article/is-synthetic-alexandrite-real-alexandrite/ |archive-date=2016-07-07}}</ref>

Some gemstones falsely described as lab-grown [[synthetic alexandrite]] are actually [[corundum]] laced with trace elements (e.g., [[vanadium]]) or color-change [[spinel]] and are not actually chrysoberyl. As a result, they would be more accurately described as ''simulated alexandrite'' rather than "synthetic". This alexandrite-like [[sapphire]] material has been around for almost 100&nbsp;years and shows a characteristic purple-mauve colour change, which does not really look like alexandrite because there is never any green.<ref>{{cite web |url=http://www.alexandrite.net/chapters/chapter7/index.html |title=Alexandrite Synthetics and Imitations, In Alexandrite Tsarstone Collectors Guide. |year=2006 |access-date=2007-07-09 |url-status=live |archive-url=https://web.archive.org/web/20080530143859/http://www.alexandrite.net/chapters/chapter7/index.html |archive-date=2008-05-30}}</ref>

Alexandrite is also known as one of three official [[birthstone]]s for the month of June.

<gallery caption=Alexandrite mode=packed>
Chrysoberyl 1.jpg|Rough alexandrite from Brazil
Chrysobéryl var. alexandrite sous UV (Brésil).jpg|Rough alexandrite under [[Ultraviolet|UV light]]
Alexandrite 26.75cts.jpg|Alexandrite step cut cushion, 26.75 cts. This stone is bluish green in daylight and purple red under incandescent light
Alexandrite ring.jpg|An alexandrite ring with diamonds
</gallery>