Editing Opal (section)

== Sources ==
[[File:Opal from Yowah, Queensland, Australia 2.jpg|thumb|Polished opal from [[Yowah]] (Yowah Nut<ref name="Yowah nut">{{cite web|url=http://www.mindat.org/min-9838.html|title=Yowah Nut: Yowah Nut mineral information and data|website=Mindat.org|date=20 February 2011|access-date=8 March 2011|url-status=live|archive-url=https://web.archive.org/web/20110512015028/http://www.mindat.org/min-9838.html|archive-date=12 May 2011|df=dmy-all}}</ref>), Queensland]]
[[File:Boulder Opal.jpg|thumb|Boulder opal, Carisbrooke Station near [[Winton, Queensland]]]]

The primary sources of opal are Australia and Ethiopia, but because of inconsistent and widely varying accountings of their respective levels of extraction, it is difficult to accurately state what proportion of the global supply of opal comes from either country.
Australian opal has been cited as accounting for 95–97% of the world's supply of precious opal,<ref>{{cite web|url=http://www.itsanhonour.gov.au/symbols/gemstone.cfm|title=Gemstone|website=It's an Honour|publisher=Australian Government|url-status=live|archive-url=https://web.archive.org/web/20110129022445/http://www.itsanhonour.gov.au/symbols/gemstone.cfm|archive-date=29 January 2011|df=dmy-all}}</ref><ref>{{cite web |url=http://www.diamonds.net/Magazine/Article.aspx?ArticleID=46032&RDRIssueID=120 |title=Rapaport Magazine – A Designer Stone |url-status=live |archive-url=https://web.archive.org/web/20141006154330/http://www.diamonds.net/Magazine/Article.aspx?ArticleID=46032&RDRIssueID=120 |archive-date=6 October 2014 |df=dmy-all }}</ref> with the state of [[South Australia]] accounting for 80% of the world's supply.<ref>{{cite web|url=http://www.premcab.sa.gov.au/emblems/opals1.htm|publisher=Government of South Australia|title=Opal – South Australia's Gemstone|access-date=11 July 2012|archive-url=https://web.archive.org/web/20120716230021/http://www.premcab.sa.gov.au/emblems/opals1.htm|archive-date=16 July 2012}}</ref> In 2012, Ethiopian opal production was estimated to be {{convert|14000|kg|abbr=on}} by the United States Geological Survey.<ref>{{citation|last=Yager|first=Thomas R.|contribution=The Mineral Industry of Ethiopia|title=United States Geological Survey, 2012 Minerals Yearbook|pages=17.1–17.5|url=http://minerals.usgs.gov/minerals/pubs/country/2012/myb3-2012-et.pdf|date=1 December 2013|url-status=live|archive-url=https://web.archive.org/web/20141006150924/http://minerals.usgs.gov/minerals/pubs/country/2012/myb3-2012-et.pdf|archive-date=6 October 2014|df=dmy-all}}</ref> [[United States Geological Survey|USGS]] data from the same period (2012), reveals Australian opal production to be $41&nbsp;million.<ref>{{citation |last=Tse |first=Pui-Kwan |contribution=The Mineral Industry of Australia |title=United States Geological Survey, 2012 Minerals Yearbook |pages=3.1–3.27 |date=1 December 2013 |url=http://minerals.usgs.gov/minerals/pubs/country/2012/myb3-2012-as.pdf |access-date=20 September 2014 |url-status=live |archive-url=https://web.archive.org/web/20141006090605/http://minerals.usgs.gov/minerals/pubs/country/2012/myb3-2012-as.pdf |archive-date=6 October 2014 |df=dmy-all }}</ref> Because of the units of measurement, it is not possible to directly compare Australian and Ethiopian opal production, but these data and others suggest that the traditional percentages given for Australian opal production may be overstated.<ref>{{cite web |url=http://www.diamonds.net/Magazine/Article.aspx?ArticleID=38027&RDRIssueID=85 |title=Rapaport Magazine – Ethiopian Opal |url-status=live |archive-url=https://web.archive.org/web/20141006134901/http://www.diamonds.net/Magazine/Article.aspx?ArticleID=38027&RDRIssueID=85 |archive-date=6 October 2014 |df=dmy-all }}</ref> Yet, the validity of data in the USGS report appears to conflict with that of Laurs et al.{{citation needed|date=April 2015}} and Mesfin,{{citation needed|date=April 2015}} who estimated the 2012 Ethiopian opal output (from [[Wegeltena]]) to be only {{convert|750|kg|abbr=on}}.

=== Australia ===
The town of [[Coober Pedy]] in [[South Australia]] is a major source of opal. The world's largest and most valuable gem opal "[[Olympic Australis]]" was found in August 1956 at the "Eight Mile" opal field in Coober Pedy. It weighs {{convert|17000|carat|kg lb}} and is {{convert|11|in|mm}} long, with a height of {{convert|4+3/4|in|mm|abbr=on}} and a width of {{convert|4+1/2|in|mm|abbr=on}}.<ref>{{cite book |last1=Cram |first1=Len |year=2006 |title=A history of South Australian opal, 1840–2005 |location=Lightning Ridge, NSW |publisher=Len Cram |isbn=978-0975721407 |oclc=225050989}}</ref>

The [[Mintabie, South Australia|Mintabie Opal Field]] in South Australia located about {{convert|250|km|abbr=on}} northwest of Coober Pedy has also produced large quantities of crystal opal and the rarer black opal. Over the years, it has been sold overseas incorrectly as Coober Pedy opal. The black opal is said to be some of the best examples found in Australia.

[[Andamooka, South Australia|Andamooka]] in South Australia is also a major producer of matrix opal, crystal opal, and black opal. Another Australian town, [[Lightning Ridge, New South Wales|Lightning Ridge]] in [[New South Wales]], is the main source of black opal, opal containing a predominantly dark background (dark gray to blue-black displaying the play of color), collected from the [[Griman Creek Formation]].<ref>{{cite news |title=The black-opal hunters of outback Australia |last1=Osborne |first1=Zoe |last2=Kitanov |first2=Alex |url=https://www.aljazeera.com/features/longform/2022/7/17/australia-black-opal-miners |newspaper=Al Jazeera |date=17 July 2022 |access-date=8 August 2022}}</ref> Boulder opal consists of [[concretion]]s and fracture fillings in a dark siliceous [[ironstone]] matrix. It is found sporadically in western Queensland, from Kynuna in the north, to [[Yowah]] and [[Koroit opal field|Koroit]] in the south.<ref>{{cite web|url=http://www.nrw.qld.gov.au/mines/fossicking/opal.html|title=Queensland opal|archive-url=https://web.archive.org/web/20071013164838/http://www.nrw.qld.gov.au/mines/fossicking/opal.html |archive-date=13 October 2007 }}</ref> Its largest quantities are found around [[Jundah]] and [[Quilpie]] in [[South West Queensland]]. Australia also has opalized [[fossil]] remains, including dinosaur bones in New South Wales<ref>[https://www.abc.net.au/news/2018-12-05/weewarra-dinosaur/10583990 First dinosaur named in NSW in nearly a century after chance discovery] ''ABC News'', 5 December 2018. Retrieved 5 December 2018.</ref> and South Australia,<ref>[https://www.abc.net.au/news/2018-12-03/rare-dinosaur-fossil-found-in-sa-after-disappearing-for-45-years/10575208 Rare dinosaur fossil discovered on internet after disappearing for decades] ''ABC News'', 3 December 2018. Retrieved 3 December 2018.</ref> and marine creatures in South Australia.<ref name="samuseum.sa.gov.au">{{cite web|url=http://www.samuseum.sa.gov.au/explore/museum-galleries/opal-fossils|publisher=South Australian Museum|title=Opal Fossils|access-date=3 March 2014|url-status=live|archive-url=https://web.archive.org/web/20140213204022/http://www.samuseum.sa.gov.au/explore/museum-galleries/opal-fossils|archive-date=13 February 2014|df=dmy-all}}</ref>

=== Ethiopia ===
[[File:Amazing Play of Color - Opal from GemSelect..webm|thumb|right|Opal from Ethiopia]]

It has been reported that Northern African opal was used to make tools as early as 4000 BC.{{Citation needed|date=August 2020}} The first published report of gem opal from [[Ethiopia]] appeared in 1994, with the discovery of precious opal in the Menz Gishe District, North Shewa Province.<ref>{{cite journal |last=Barot |first=N. |date=1994 |title=New precious opal deposit found in Ethiopia |journal=ICA Gazette }}</ref> The opal, found mostly in the form of nodules, was of volcanic origin and was found predominantly within weathered layers of [[rhyolite]].<ref>{{cite journal |title=Opal from Shewa Province, Ethiopia |journal=Gems & Gemology |date=Summer 1996 |last1=Johnson |first1=Mary L. |last2=Kammerling |first2=Robert C. |last3=DeGhionno |first3=Dino G. |last4=Koivula |first4=John I. |volume=32 |issue=2 |pages=112–120 |df=dmy-all |doi=10.5741/GEMS.32.2.112 |doi-access=free }}</ref> This Shewa Province opal was mostly dark brown in color and had a tendency to crack. These qualities made it unpopular in the gem trade. In 2008, a new opal deposit was found approximately 180&nbsp;km north of Shewa Province, near the town of [[Wegeltena]], in Ethiopia's [[Wollo Province]]. The Wollo Province opal was different from the previous Ethiopian opal finds in that it more closely resembled the sedimentary opals of Australia and Brazil, with a light background and often vivid play-of-color.<ref>{{cite journal |last=Rondeau |first=Benjamin |date=Summer 2010 |title=Play-of-color from Wegeltena, Wollo Province, Ethiopia |journal=Gems & Gemology |doi=10.5741/GEMS.46.2.90 |doi-access=free }}</ref> Wollo Province opal, more commonly referred to as "Welo" or "Wello" opal, has become the dominant Ethiopian opal in the gem trade.<ref>{{cite journal |last=Gashaw |first=Yidneka |date=8 April 2012 |title=Opal Trade Transforms North Wollo |url=http://addisfortune.com/Vol_12_No_623_Archive/agenda.htm |journal=Addis Fortune |url-status=usurped |archive-url=https://web.archive.org/web/20140924044930/http://addisfortune.com/Vol_12_No_623_Archive/agenda.htm |archive-date=24 September 2014 |df=dmy-all }}</ref>[[File:Jupiter 20 Opal and Diamond Pendant.jpg|thumb|left|200px|Gem grade Ethiopian Welo precious opal pendant]]

=== Virgin Valley, Nevada ===
[[File:nev opal09.jpg|thumb|Multicolored rough opal specimen from Virgin Valley, Nevada, US]]

The Virgin Valley<ref>{{cite web|url=http://www.mindat.org/loc-5881.html|title=Virgin Valley District, Humboldt Co., Nevada|website=mindat.org|url-status=live|archive-url=https://web.archive.org/web/20120430090041/http://www.mindat.org/loc-5881.html|archive-date=30 April 2012|df=dmy-all}}</ref> opal fields of [[Humboldt County, Nevada|Humboldt County]] in northern [[Nevada]] produce a wide variety of precious black, crystal, white, fire, and lemon opal. The black fire opal is the official gemstone of Nevada. Most of the precious opal is partial wood replacement. The precious opal is hosted and found ''[[In situ#Earth and atmospheric sciences|in situ]]'' within a subsurface horizon or zone of [[bentonite]], which is considered a "lode" deposit. Opals which have weathered out of the ''in situ'' deposits are alluvial and considered [[placer deposit]]s. [[Miocene]]-age opalised teeth, bones, fish, and a snake head have been found. Some of the opal has high water content and may desiccate and crack when dried. The largest producing mines of Virgin Valley have been the famous Rainbow Ridge,<ref>{{cite web|url=http://www.mindat.org/loc-19286.html|title=Rainbow Ridge Mine|website=mindat.org|url-status=live|archive-url=https://web.archive.org/web/20120430115218/http://www.mindat.org/loc-19286.html|archive-date=30 April 2012|df=dmy-all}}</ref> Royal Peacock,<ref>{{cite web|url=http://www.mindat.org/loc-30709.html|title=Royal Peacock Group Mines, Virgin Valley District, Humboldt Co., Nevada|website=mindat.org|url-status=live|archive-url=https://web.archive.org/web/20120430124208/http://www.mindat.org/loc-30709.html|archive-date=30 April 2012|df=dmy-all}}</ref> Bonanza,<ref>{{cite web|url=http://www.mindat.org/loc-8801.html|title=Bonanza Opal Workings (Virgin Opal), Virgin Valley District, Humboldt Co., Nevada|website=mindat.org|url-status=live|archive-url=https://web.archive.org/web/20120430120653/http://www.mindat.org/loc-8801.html|archive-date=30 April 2012|df=dmy-all}}</ref> Opal Queen,<ref>{{cite web|url=http://www.mindat.org/loc-213530.html|title=Opal Queen group, Virgin Valley District, Humboldt Co., Nevada|website=mindat.org|url-status=live|archive-url=https://web.archive.org/web/20120430115233/http://www.mindat.org/loc-213530.html|archive-date=30 April 2012|df=dmy-all}}</ref> and WRT Stonetree/Black Beauty<ref>{{cite web|url=http://www.mindat.org/loc-228982.html|title=Stonetree Opal Mine, WRT Stonetree group, Virgin Valley District, Humboldt Co., Nevada|website=mindat.org|url-status=live|archive-url=https://web.archive.org/web/20120430115929/http://www.mindat.org/loc-228982.html|archive-date=30 April 2012|df=dmy-all}}</ref> mines. The largest unpolished black opal in the Smithsonian Institution, known as the "Roebling opal",<ref>{{cite web|url=http://geogallery.si.edu/index.php/en/1167897/roebling-opal/1|title=Roebling Opal|publisher=National Museum of Natural History|url-status=dead|archive-url=https://web.archive.org/web/20121107052201/http://geogallery.si.edu/index.php/en/1167897/roebling-opal/1|archive-date=7 November 2012|df=dmy-all}}</ref> came out of the tunneled portion of the Rainbow Ridge Mine in 1917, and weighs {{convert|2585|carat|g oz}}. The largest polished black opal in the [[Smithsonian Institution]] comes from the Royal Peacock opal mine in the Virgin Valley, weighing {{convert|160|carat|g oz}}, known as the "Black Peacock".<ref>{{cite journal|journal=Lapidary Journal|title=Opal|date=March 1971|pages=1522, 1542}}</ref>

=== Mexico ===

Fire opal is a transparent to translucent opal with warm body colors of yellow to orange to red. Although fire opals don't usually show any play of color, they occasionally exhibit bright green flashes. The most famous source of fire opals is the state of [[Querétaro]] in Mexico; these opals are commonly called Mexican fire opals.<ref>{{cite journal |last1=Koivula |first1=John |title=Opal from Querétaro, Mexico: Occurrence and Inclusions |journal=Gems & Gemology |date=1983 |volume=19 |issue=2 |pages=87–96|doi=10.5741/GEMS.19.2.87 |doi-access=free }}</ref> Fire opals that do not show a play of color are sometimes referred to as jelly opals. Mexican opals are sometimes cut in their rhyolitic host material if it is hard enough to allow cutting and polishing. This type of Mexican opal is referred to as a Cantera opal. Another type of opal from Mexico, referred to as Mexican water opal, is a colorless opal that exhibits either a bluish or golden internal sheen.<ref name="LetsTalk">{{cite web|first1=James|last1=Swisher|first2=Edna B.|last2=Anthony|url=http://www.attawaygems.com/NMFG/Lets_talk_gemstones_opal.htm|title=Let's Talk Gemstones: Opal|url-status=live|archive-url=https://web.archive.org/web/20111107214533/http://www.attawaygems.com/NMFG/Lets_talk_gemstones_opal.htm|archive-date=7 November 2011|df=dmy-all}}</ref>[[File:Precious Mexican Fire Opal with attached matrix.jpg|thumb |left|alt=A specimen of recently mined Precious Mexican Fire Opal. The background host rock (matrix) has characteristic pink-white coloration.|Precious Mexican Fire Opal has bright green and yellow patches (play of color) with an orange-red background typical of Fire Opal.]]
Opal occurs in significant quantity and variety in central Mexico, where [[mining]] and production first originated in the state of [[Querétaro]]. In this region the opal deposits are located mainly in the mountain ranges of three municipalities: [[Colón, Querétaro|Colón]], [[Tequisquiapan]], and [[Ezequiel Montes]]. During the 1960s through to the mid-1970s, the Querétaro mines were heavily mined. Today's opal miners report that it was much easier to find quality opals with a lot of fire and play of color back then, whereas today the gem-quality opals are very hard to come by and command hundreds of US dollars or more. The orange-red background color is characteristic of all "fire opals," including "Mexican fire opal".

The oldest mine in Querétaro is Santa Maria del Iris. This mine was opened around 1870 and has been reopened at least 28 times since. At the moment there are about 100 mines in the regions around Querétaro, but most of them are now closed. The best quality of opals came from the mine Santa Maria del Iris, followed by La Hacienda la Esperanza, Fuentezuelas, La Carbonera, and La Trinidad. Important deposits in the state of [[Jalisco]] were not discovered until the late 1950s.

In 1957, Alfonso Ramirez (of Querétaro) accidentally discovered the first opal mine in Jalisco: La Unica, located on the outer area of the volcano of Tequila, near the Huitzicilapan farm in [[Magdalena, Jalisco|Magdalena]]. By 1960 there were around 500 known opal mines in this region alone. Other regions of the country that also produce opals (of lesser quality) are [[Guerrero]], which produces an opaque opal similar to the opals from Australia (some of these opals are carefully treated with heat to improve their colors so high-quality opals from this area may be suspect). There are also some small opal mines in [[Morelos]], [[Durango]], [[Chihuahua (state)|Chihuahua]], [[Baja California]], [[Guanajuato]], [[Puebla]], [[Michoacán]], and [[Estado de México]].

=== Other locations ===
[[File:62cts Brazilian Crystal Opal.JPG|thumb|Brazilian opal]]

Another source of white base opal or creamy opal in the United States is [[Spencer, Idaho]].<ref>{{Cite news|url=https://www.eastidahonews.com/2015/08/future-of-spencer-opal-mining-uncertain/|title=If you've ever wanted an opal – it's time to visit Spencer {{!}} East Idaho News|date=2015-08-06|work=East Idaho News|access-date=2018-02-14}}</ref> A high percentage of the opal found there occurs in thin layers.

Other significant deposits of precious opal around the world can be found in the Czech Republic, Canada, Slovakia, Hungary, Turkey, Indonesia, Brazil (in [[Pedro II, Piauí]]<ref>{{cite web |url=http://www.mindat.org/gallery.php?loc=8782 |title=Boi Morto Mine, Pedro II, Piauí, Brazil |website=Mindat.org |access-date=8 October 2011 |url-status=live |archive-url=https://web.archive.org/web/20110512015022/http://www.mindat.org/gallery.php?loc=8782 |archive-date=12 May 2011 |df=dmy-all }}</ref>), Honduras (more precisely in [[Erandique]]), Guatemala, and Nicaragua.

In late 2008, [[NASA]] announced the discovery of opal deposits on [[Mars]].<ref>{{cite web|url=http://www.jpl.nasa.gov/news/news.cfm?release=2008-198|title=NASA probe finds opals in Martian crevices|website=[[Jet Propulsion Laboratory]]|access-date=29 October 2008|url-status=live|archive-url=https://web.archive.org/web/20090119103930/http://www.jpl.nasa.gov/news/news.cfm?release=2008-198|archive-date=19 January 2009|df=dmy-all}}</ref>