View source for Realgar

{{Short description|Arsenic sulfide mineral}}
{{infobox mineral
| name        = Realgar
| category    = [[Sulfide mineral]]
| boxwidth    = 330px
| boxbgcolor  =
| image       = Realgar-229713.jpg
| imagesize   =
| alt         =
| caption     = Realgar crystals, Royal Reward Mine, [[King County, Washington]], US
| formula     = {{chem2|As4S4}} or AsS
| IMAsymbol   = Rlg<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3 |pages=291–320|doi=10.1180/mgm.2021.43 |bibcode=2021MinM...85..291W |s2cid=235729616 |doi-access=free}}</ref>
| molweight   =
| strunz      = 2.FA.15a
| dana        =
| system      = [[Monoclinic]] 
| class       = Prismatic (2/m) <br/><small>(same [[H-M symbol]])</small>
| symmetry    = ''P2<sub>1</sub>/n'' (no. 14)
| unit cell   = a = 9.325(3)&nbsp;[[angstrom|Å]] <br/>b = 13.571(5)&nbsp;Å <br/>c = 6.587(3)&nbsp;Å <br/>β = 106.43°; Z&nbsp;=&nbsp;16
| color       = Red to yellow-orange; in polished section, pale gray, with abundant yellow to red internal reflections
| colour      =
| habit       = Prismatic striated crystals; more commonly massive, coarse to fine granular, or as incrustations
| twinning    = Contact twins on {100}
| cleavage    = Good on {010}; less so on {101}, {100}, {120}, and {110}
| fracture    =
| tenacity    = Sectile, slightly brittle
| mohs        = 1.5–2
| luster      = Resinous to greasy
| streak      = Red-orange to red
| diaphaneity = Transparent
| gravity     = 3.56
| density     =
| polish      =
| opticalprop = Biaxial (−)
| refractive  = n<sub>α</sub> = 2.538<br/> n<sub>β</sub> = 2.684<br/> n<sub>γ</sub> = 2.704
| birefringence = δ = 0.166
| pleochroism = Nearly colorless to pale golden yellow
| 2V          = 40°
| dispersion  = r > v, very strong
| extinction  =
| length fast/slow =
| fluorescence=
| absorption  =
| melt        =
| fusibility  =
| diagnostic  =
| solubility  =
| other       = Toxic and [[carcinogenic]].
Disintegrates on long exposure to light to a powder composed of [[pararealgar]] or [[arsenolite]] and [[orpiment]].
| alteration  =
| references  = <ref name=Handbook>{{cite web |url=http://rruff.info/doclib/hom/realgar.pdf |title=Realgar |website=Handbook of Mineralogy |publisher=RRUFF Project}}</ref><ref name=Mindat>{{Mindat |id=3375 |name=Realgar}}</ref><ref name=Webmin>{{WebMineral |url=http://webmineral.com/data/Realgar.shtml |name=Realgar}}</ref><ref name=Klein>{{cite book |first1=Cornelis |last1=Klein |first2=Cornelius S. |last2=Hurlbut |title=Manual of Mineralogy |publisher=[[Wiley (publisher)|Wiley]] |year=1985 |edition=20th |page=282 |isbn=0-471-80580-7}}</ref><ref>{{cite journal |last1=Hejny |first1=Clivia |last2=Sagl |first2=Raffaela |last3=Többens |first3=Daniel M. |last4=Miletich |first4=Ronald |last5=Wildner |first5=Manfred |last6=Nasdala |first6=Lutz |last7=Ullrich |first7=Angela |last8=Balic-Zunic |first8=Tonci |title=Crystal-structure properties and the molecular nature of hydrostatically compressed realgar |journal=Physics and Chemistry of Minerals |date=May 2012 |volume=39 |issue=5 |pages=399–412 |doi=10.1007/s00269-012-0495-y|bibcode=2012PCM....39..399H |s2cid=96885484 }}</ref>
}}

'''Realgar''' ({{IPAc-en|r|i|ˈ|æ|l|g|ɑr|,_|-|g|ər}} {{respell|ree|AL|gar|,_|-|gər}}), also known as '''[[arsenic blende]]''', '''ruby sulphur''' or '''ruby of arsenic''', is an [[arsenic]] sulfide mineral with the chemical formula {{chem2|α\-As4S4}}. It is a soft, mineral occurring in monoclinic crystals, or in granular, compact, or powdery form, often in association with the related mineral, orpiment ({{chem2|As2S3}}). It is orange-red in color, and burns with a bluish flame releasing fumes of arsenic and sulfur. It is [[Polymorphism (materials science)|trimorphous]] with pararealgar and bonazziite.<ref name=Handbook/>

==Etymology==
Its name comes from the Arabic ''rahj al-ġār'' ({{lang|ar|رهج الغار}} {{IPA|ar|rahdʒælɣaːr|}} {{pronunciation|Q109746-ar.ogg|listen|help=no}}, "powder of the mine"), via Medieval Latin, and its earliest record in English is in the 1390s.<ref name="Websters-Third">{{cite book|title=Webster's Third New International Dictionary|publisher=Merriam-Webster, inc.|year=1993|editor=Philip Babcock Grove|isbn=3-8290-5292-8}}</ref><ref>{{Cite web|url=https://www.mindat.org/min-46093.html|title = Bonazziite}}</ref><ref>{{Cite web|url=https://www.ima-mineralogy.org/Minlist.htm|title=List of Minerals|date=21 March 2011}}</ref>

==Uses==
Realgar is a minor ore of arsenic extracted in China, Peru, and the Philippines.<ref>{{cite web |title=Arsenic |date=January 2021 |website=Mineral commodity summaries |publisher=United States Geological Survey |url=https://pubs.usgs.gov/periodicals/mcs2021/mcs2021-arsenic.pdf |access-date=28 February 2021}}</ref>

===Historical uses===
Realgar was used by firework manufacturers in white flame and star compositions and to produce yellow smoke in daytime fireworks.<ref>{{cite book |last1=Weingart |first1=George Washington |title=Pyrotechnics |date=1947 |publisher=G.W. Weingart |location=USA |page=9 |edition=2nd: Revised, Enlarged, and Corrected |chapter-url=https://archive.org/details/Pyrotechnics_by_G._Weingart_2nd_ed._Corrected/page/n22/mode/1up |access-date=26 September 2025 |language=en |chapter=I |quote=Red Arsenic... They are very useful in making white stars, especially as they  take fire far more easily than those made from antimony.}}</ref><ref>{{cite book |last1=Izzo |first1=Colonello Dott. Attilio |editor1-last=Hoepli |editor1-first=Ulrico |title=Pirotecnia e Fuochi Artificiali |publisher=A. Izzo |date=1950 |location=Milano |pages=216,218 |language=it |chapter=5-1: Ricettario di Composizioni Pirotecniche |trans-title=Pyrotechnics and Fireworks |url=http://www.fuochidifraia.it/linked/pirotecnica%20e%20%20%20fuochi%20artificiali%20%20%201.pdf}}</ref>

Realgar has been used to kill weeds, insects, and rodents,<ref>{{cite report |title=Realgar |date=April 2008 |series=Hazardous Substance Factsheet |publisher=State of New Jersey |department=N.J. Department of Environmental Protection |url=http://nj.gov/health/eoh/rtkweb/documents/fs/0156.pdf}}</ref> even though more effective arsenic-based anti-pest agents are available such as [[cacodylic acid]], {{chem2|(CH3)2As(O)OH}}, an [[Organoarsenic chemistry|organoarsenic compound]] used as an herbicide.{{cn|date=September 2025}}

Realgar was also used by Ancient Greek apothecaries to make a medicine known as "bull's blood".<ref name=Arnould>{{cite journal |last=Arnould |first=Dominique |year=1993 |title=Boire le sang de taureau: La mort de Thémistocle |trans-title=Drinking bull's blood: The death of Themistocles |journal=Revue de philologie, de littérature et d'histoire anciennes |volume=LXVII |issue=2 |pages=229–235 |language=fr}}</ref> The Greek physician [[Nicander]] described a death by "bull's blood", which matches the known effects of arsenic poisoning.<ref name=Arnould/> Bull's blood is the poison that is said to have been used by [[Themistocles]] and [[Midas]] for suicide.<ref name=Arnould/>

The Chinese name for realgar is {{lang|zh|[[wikt:雄黃|雄黃]]}} ([[Standard Chinese|Mandarin]] {{Transliteration|zh|xiónghuáng}}), literally 'masculine yellow', as opposed to orpiment which is 'feminine yellow'.<ref>{{cite journal |author=Jie Liu |author2=Yuanfu Lu |author3=Qin Wu |author4=Robert A. Goyer |author5=Michael P. Waalkes |date=August 2008 |title=Mineral arsenicals in traditional medicines: Orpiment, realgar, and arsenolite |journal=Journal of Pharmacology and Experimental Therapeutics |volume=326 |issue=2 |pages=363–368 |doi=10.1124/jpet.108.139543 |pmid=18463319 |url=https://jpet.aspetjournals.org/content/jpet/early/2008/05/07/jpet.108.139543.full.pdf |access-date=2021-06-05 |pmc=2693900 |archive-date=2022-07-06 |archive-url=https://web.archive.org/web/20220706070124/https://jpet.aspetjournals.org/content/jpet/early/2008/05/07/jpet.108.139543.full.pdf |url-status=dead }}</ref>

Realgar was, along with orpiment, traded in the [[Roman Empire]] and was used as a red paint pigment. Early occurrences of realgar as a red paint pigment are known for works of art from China, India, Central Asia, and Egypt. It was used in Venetian fine-art painting during the [[Renaissance]] era, though rarely elsewhere in Europe, a use which died out by the 18th century.<ref>{{cite web |url=http://cameo.mfa.org/wiki/Realgar |title=Realgar |publisher=Museum of Fine Arts |place=Boston, MA}}</ref> It was also used as medicine. Other traditional uses include manufacturing lead shot, printing, and dyeing{{how?|reason=It's a pigment, not a dye.|date=September 2025}} [[Calico (textile)|calico]] cloth. It was used to poison rats in medieval Spain and in 16th century England.<ref>{{cite book |title=Remarques sur les mots français dérivés de l'arabe |trans-title=Notes on French words derived from Arabic |author=Henri Lammens S.J. |year=1890 |publisher=Beyrouth Impr. Catholique |url=https://archive.org/stream/remarquessurlesm00lammuoft#page/201/mode/1up |via=archive.org |language=fr}}</ref>

== Occurrence ==
Realgar most commonly occurs as a low-temperature [[hydrothermal]] [[Vein (geology)|vein]] mineral associated with other arsenic and antimony minerals. It also occurs as [[Volcanic sublimate|volcanic sublimations]] and in hot spring deposits. It occurs in association with orpiment, [[arsenolite]], [[calcite]] and [[barite]].<ref name=Handbook/>

It is found with lead, silver and gold ores in Hungary, Bohemia and Saxony. In the US it occurs notably in Mercur, Utah; Manhattan, Nevada; and in the geyser deposits of Yellowstone National Park.<ref name=Klein/>

After a long period of exposure to light, realgar changes form to a yellow powder known as pararealgar ({{chem2|β\-As4S4}}). It was once thought that this powder was the yellow sulfide (orpiment), but is a distinct chemical compound.<ref name=AM77>{{cite journal|last1=Douglass|first1=D. L.|last2=Shing|first2=Chichang|last3=Wang|first3=Ge|title=The light-induced alteration of realgar to pararealgar|journal=American Mineralogist|date=1992|volume=77|pages=1266–1274|url=http://www.minsocam.org/ammin/AM77/AM77_1266.pdf|accessdate=11 August 2014}}</ref>

==Gallery ==
<gallery widths="130px" heights="130px">
Image:Realgar-unit-cell-3D-balls.png|The [[Crystal structure#Unit cell|unit cell]] of realgar, showing clearly the {{chem2|As4S4}} molecules it contains
File:Realgar-md56a.jpg|Cluster of realgar crystals from Getchell Mine, Adam Peak, Potosi District, Humboldt County, Nevada, United States
File:Realgar-Picropharmacolite-117490.jpg|Cherry-red realgar crystals atop a matrix, and a sharp acicular spray of the rare species picropharmacolite (white needles) below
File:Réalgar, quartz, chalcopyrite, galène 90.3.9834.jpg|Crystals of realgar, quartz, chalcopyrite and galena, from Quiruvilca Mine, La Libertad, Peru
</gallery>

==See also==
{{Portal|Earth sciences}}
* [[Classification of minerals (disambiguation)|Classification of minerals]]
* [[List of inorganic pigments]]
* [[List of minerals]]
*[[Realgar wine]] or Xionghuang wine is a Chinese alcoholic drink that is made from Chinese liquor dosed with powdered realgar.<ref name="China Daily Dragon Boat Festival activities expanded">{{cite news |title=Dragon Boat Festival activities expanded |work=www.chinadaily.com.cn |url=http://www.chinadaily.com.cn/english/doc/2004-06/22/content_341276.htm |access-date=11 March 2023}}</ref>

==References==
{{Reflist}}

==Further reading==
*{{cite book |title=A New English Dictionary on Historical Principles |last1=Craigie |first1=W.A. |last2=Bradley |first2=H. |editor=Sir James, A.H. Murray |year=1914 |publisher=Clarendon Press at Oxford |page=202 |chapter=Realgar |chapter-url=https://archive.org/stream/oed8aarch#page/n215/mode/1up |via=archive.org |language=en}}
* {{cite book |author=William Mesny |title=Mesny's Chinese Miscellany. A Text Book of Notes on China and the Chinese. |publisher=Shanghai |volume=III |year=1899 |page=251}}
* {{cite book |author=William Mesny |title=Mesny's Chinese Miscellany. A Text Book of Notes on China and the Chinese. |publisher=Shanghai |volume=IV |year=1905 |pages=425–426}}

==External links==
{{Commons category|Realgar}}
* [http://www.mindat.org/min-3107.html Mindat.org: Pararealgar]

{{Arsenic compounds}}
{{Sulfur compounds}}

[[Category:Arsenic minerals]]
[[Category:Sulfide minerals]]
[[Category:Alchemical substances]]
[[Category:Monoclinic minerals]]
[[Category:Minerals in space group 14]]
[[Category:Inorganic pigments]]
[[Category:Blendes]]