Editing Amethyst (section)

==Hue and tone==
Amethyst occurs in primary [[hue]]s from a light lavender or pale violet to a deep purple. Amethyst may exhibit one or both secondary hues, red and blue.<ref>
{{cite web
 |title=Amethyst: The world's most popular purple gemstone
 |website=geology.com
 |url=http://geology.com/gemstones/amethyst/
 |access-date=29 August 2017
}}
</ref>
High-quality amethyst can be found in [[Siberia]], [[Sri Lanka]], [[Brazil]], [[Uruguay]], and the Far East. The ideal grade, called "Deep Siberian", has a primary purple hue of around 75–80%, with 15–20% blue and (depending on the light source) red secondary hues.<ref name=WiseSecrets1>
{{cite book
 |first = Richard W. |last = Wise
 |year = 2005
 |title = Secrets of the Gem Trade: The connoisseurs' guide to precious gemstones
 |publisher = Brunswick House Press
 |place = Lenox, MA
 |isbn = 0-9728223-8-0
}}
</ref>
"Rose de France" is defined by its markedly light shade of the [[purple]], reminiscent of a [[Lavender (color)|lavender]] / [[Lilac (color)|lilac]] shade. These pale colors were once considered undesirable, but have recently become popular due to intensive marketing.<ref>
{{cite web
 |last1=Arem   |first1=Joel E.
 |last2=Clark  |first2=Donald
 |last3=Smigel |first3=Barbara
 |title=Amethyst: Value, price, and jewelry information
 |website=gemsociety.org
 |publisher = [[International Gem Society]] (IGS)
 |url=https://www.gemsociety.org/article/amethyst-jewelry-and-gemstone-information/
 |access-date=20 April 2021
}}</ref>

Green quartz is sometimes called ''green amethyst''; the scientific name is [[prasiolite]].<ref name=Gemdat>
{{cite web
 |title = Prasiolite gemstone information
 |website = gemdat.org
 |url = http://www.gemdat.org/gem-40112.html
 |access-date = 19 April 2018
}}
</ref>
Other names for green quartz are ''vermarine'' and ''lime citrine''.

Amethyst frequently shows color zoning, with the most intense color typically found at the crystal terminations. One of [[lapidary|gem cutters']] tasks is to make a finished product with even color. Sometimes, only a thin layer of a natural, uncut amethyst is violet colored, or the color is very uneven. The uncut gem may have only a small portion that is suitable for faceting.<ref>
{{cite journal
 |last1 = Lowell  |first1 = J.
 |last2 = Koivula |first2 = J.I.
 |year = 2004
 |title = Amethyst from four peaks, Arizona
 |journal = [[Gems & Gemology]]
 |volume = 40 |number = 3 |pages = 230–238
 |doi = 10.5741/GEMS.40.3.230
 |url = https://www.gia.edu/doc/Amethyst-from-Four-Peaks-Arizona.pdf
 |url-status = live |access-date = 20 April 2021
|archive-url = https://ghostarchive.org/archive/20221009/https://www.gia.edu/doc/Amethyst-from-Four-Peaks-Arizona.pdf
 |archive-date = 9 October 2022
}}
</ref><ref>
{{cite journal
 |last1 = Troilo   |first1 = Fabrizio       |last2 = el Harfi  |first2 = Abdelghani
 |last3 = Mouaddib |first3 = Salahaddine    |last4 = Bitarello |first4 = Erica
 |last5 = Costa    |first5 = Emanuele
 |date = 1 May 2015
|title = Amethyst from Boudi, Morocco
 |journal = Gems & Gemology
 |volume = 51  |issue = 1  |pages = 32–40
 |doi = 10.5741/GEMS.51.1.32
}}
</ref>{{multiple image
| align       = left
| perrow      = 1
| total_width = 250
| image1      = Geode Reference -25.jpg
| caption1    = Natural purple/violet amethyst
| image2      = Citrine améthysée.jpg
| caption2    = Heat-treated amethyst
}}

The color of amethyst has been demonstrated to result from substitution by [[gemstone irradiation|irradiation]] of trivalent iron (Fe<sup>3+</sup>) for silicon in the structure,<ref name=ODongh-2006/><ref>
{{cite book
 |author = Rossman, George R.
 |year = 1994
 |chapter = Chapter&nbsp;13. Colored varieties of the silica minerals
 |pages = 433–468
 |publisher = [[Mineralogical Society of America]] / [[Mineralogical Magazine]]
 |title = Silica: Physical behavior, geochemistry, and materials applications
 |editor1 = Heaney, Peter J.
 |editor2 = Prewitt, Charles T.
 |editor3 = Gibbs, Gerald V.
 |series = Reviews in Mineralogy
 |volume = 29 |issue = 399
 |isbn = 978-0-939950-35-5
 |bibcode = 1996MinM...60..390H
 |doi = 10.1180/minmag.1996.060.399.16
 |s2cid = 201093227
}}
</ref> in the presence of trace elements of large ionic radius,<ref name="scielo.br"/> and to a certain extent, the amethyst color can naturally result from displacement of [[transition metal|transition elements]] even if the iron concentration is low. Natural amethyst is [[dichroism|dichroic]] in reddish violet and bluish violet,<ref name=ODongh-2006/> but when heated, turns yellow-orange, yellow-brown, or dark brownish and may resemble [[Quartz#Citrine|citrine]],<ref>
{{cite web
 |title = Amethyst
 |website = Mindat.org
 |url = http://www.mindat.org/min-198.html
}}
</ref> but loses its dichroism, unlike genuine citrine. When partially heated, amethyst can result in [[ametrine]].

Amethyst can fade in tone if overexposed to light sources, and can be artificially darkened with adequate irradiation.<ref name=ODongh-2006/> It does not [[fluorescence|fluoresce]] under either short-wave or long-wave [[UV light]].