Editing Rhyolite

{{short description|Igneous, volcanic rock, of felsic (silica-rich) composition}}
{{other uses}}
{{Infobox rock
|name=Rhyolite
|type=Igneous
|image=Loebejuener porphyr poliert.jpg
|caption=
|composition=[[Quartz]] and [[Feldspar#Alkali feldspars|alkali feldspar]] ([[sanidine]] and sodic [[plagioclase]])
|composition_secondary=[[Biotite]] and [[hornblende]]
|class=[[Felsic]]
|texture=Glassy or [[aphanite|aphanitic]], sometimes [[porphyritic]]
|equivalent=[[Granite]] of intrusive equivalent}}

'''Rhyolite''' ({{IPAc-en|ˈ|r|aɪ|.|ə|l|aɪ|t}} {{respell|RY|ə|lyte}})<ref>{{cite LPD|3}}</ref><ref>{{cite Dictionary.com|rhyolite}}</ref><ref>{{cite Merriam-Webster|rhyolite|access-date=2012-07-10}}</ref><ref>{{cite American Heritage Dictionary|rhyolite}}</ref> is the most [[silica]]-rich of [[volcanic rock]]s. It is generally [[glass]]y or fine-grained ([[aphanitic]]) in [[texture (geology)|texture]], but may be [[porphyritic]], containing larger mineral [[crystal]]s ([[phenocryst]]s) in an otherwise fine-grained [[matrix (geology)|groundmass]]. The [[mineral]] assemblage is predominantly [[quartz]], [[sanidine]], and [[plagioclase]]. It is the [[extrusive]] equivalent of [[granite]].

Its high silica content makes rhyolitic [[magma]] extremely [[viscosity|viscous]]. This favors [[explosive eruption]]s over [[effusive eruption]]s, so this type of magma is more often erupted as [[pyroclastic rock]] than as [[lava flow]]s. Rhyolitic ash-flow [[tuff]]s are among the most voluminous of continental [[igneous rock]] formations.

Rhyolitic tuff has been used extensively for construction. [[Obsidian]], which is rhyolitic [[volcanic glass]], has been used for tools from prehistoric times to the present day because it can be shaped to an extremely sharp edge. Rhyolitic [[pumice]] finds use as an [[abrasive]], in [[concrete]], and as a [[soil amendment]].

== Description ==
[[File: Rhyolite qapf.jpg|thumb|QAPF diagram with rhyolite field highlighted]]
[[File:TAS-Diagramm-rhyolite.png|thumb|TAS diagram with rhyolite field highlighted]]
Rhyolite is an [[Extrusive rock|extrusive]] igneous rock, formed from magma rich in [[Silicate mineral|silica]] that is extruded from a volcanic vent to cool quickly on the surface rather than slowly in the subsurface. It is generally light in color due to its low content of [[mafic]] minerals, and it is typically very fine-grained ([[aphanitic]]) or [[glassy phase|glassy]].<ref name="blatt-tracy-1996-55-74">{{cite book |last1=Blatt |first1=Harvey |last2=Tracy |first2=Robert J. |title=Petrology : igneous, sedimentary, and metamorphic. |date=1996 |publisher=W.H. Freeman |location=New York |isbn=0716724383 |pages=55, 74 |edition=2nd}}</ref>

An extrusive igneous rock is classified as rhyolite when [[quartz]] constitutes 20% to 60% by volume of its total content of quartz, [[alkali feldspar]], and [[plagioclase]] ([[QAPF diagram|QAPF]]) and alkali feldspar makes up 35% to 90% of its total feldspar content. [[Feldspathoid]]s are not present. This makes rhyolite the extrusive equivalent of granite. However, while the [[IUGS]] recommends classifying volcanic rocks on the basis of their mineral composition whenever possible, volcanic rocks are often glassy or so fine-grained that mineral identification is impractical. The rock must then be classified chemically based on its content of silica and [[alkali metal oxide]]s ([[Potassium oxide|K<sub>2</sub>O]] plus [[Sodium oxide|Na<sub>2</sub>O]]). Rhyolite is high in silica and total alkali metal oxides, placing it in the R field of the [[TAS classification|TAS diagram]].<ref>{{Cite journal|last1=Le Bas|first1=M. J.|last2=Streckeisen|first2=A. L.|title=The IUGS systematics of igneous rocks|journal=Journal of the Geological Society|volume=148|issue=5|pages=825–833|doi=10.1144/gsjgs.148.5.0825|bibcode=1991JGSoc.148..825L|year=1991|citeseerx=10.1.1.692.4446|s2cid=28548230}}</ref><ref>{{Cite journal|date=1999|title=Rock Classification Scheme - Vol 1 - Igneous|url=http://nora.nerc.ac.uk/id/eprint/3223/1/RR99006.pdf|journal=British Geological Survey: Rock Classification Scheme|volume=1|pages=1–52}}</ref><ref>{{Cite web|url=http://geology.csupomona.edu/alert/igneous/igclass.htm|title=Classification of igneous rocks|archive-url=https://web.archive.org/web/20110930102012/http://geology.csupomona.edu/alert/igneous/igclass.htm|archive-date=30 September 2011|url-status=dead}}</ref><ref name="philpotts-ague-2009">{{cite book |last1=Philpotts |first1=Anthony R. |last2=Ague |first2=Jay J. |title=Principles of igneous and metamorphic petrology |date=2009 |publisher=Cambridge University Press |location=Cambridge, UK |isbn=9780521880060 |edition=2nd}}</ref>{{rp|140–146}}

The alkali feldspar in rhyolites is [[sanidine]] or, less commonly, [[orthoclase]]. It is rarely [[anorthoclase]]. These feldspar minerals sometimes are present as phenocrysts. The plagioclase is usually [[sodium]]-rich ([[oligoclase]] or [[andesine]]). [[Cristobalite]] and [[trydimite]] are sometimes present along with the quartz. [[Biotite]], [[augite]], [[fayalite]], and [[hornblende]] are common accessory minerals.<ref name="blatt-tracy-1996-55-74"/>

==Geology==
Due to their high content of silica and low [[iron]] and [[magnesium]] contents, rhyolitic [[magmas]] form highly viscous [[lava]]s.<ref name="philpotts-ague-2009"/>{{rp|23–26}} As a result, many eruptions of rhyolite are highly explosive, and rhyolite occurs more frequently as [[pyroclastic rock]] than as [[lava flow]]s.<ref name="fisher-schmincke-1984">{{cite book |last1=Fisher |first1=Richard V. |last2=Schmincke |first2=H.-U. |title=Pyroclastic rocks |date=1984 |publisher=Springer-Verlag |location=Berlin |isbn=3540127569}}</ref>{{rp|22}} Rhyolitic ash flow [[tuff]]s are the only volcanic product with volumes rivaling those of [[flood basalt]]s.<ref name="philpotts-ague-2009"/>{{rp|77}} Rhyolites also occur as [[breccia]]s or in [[lava dome]]s, [[volcanic plug]]s, and [[dike (geology)|dikes]].<ref>{{cite journal |last1=Hanson |first1=Richard E. |last2=Schweickert |first2=Richard A. |title=Chilling and Brecciation of a Devonian Rhyolite Sill Intruded into Wet Sediments, Northern Sierra Nevada, California |journal=The Journal of Geology |date=1 November 1982 |volume=90 |issue=6 |pages=717–724 |doi=10.1086/628726|bibcode=1982JG.....90..717H |s2cid=128948336 }}</ref><ref>{{cite journal |last1=Spell |first1=Terry L. |last2=Kyle |first2=Philip R. |title=Petrogenesis of Valle Grande Member rhyolites, Valles Caldera, New Mexico: Implications for evolution of the Jemez Mountains Mgmatic System |journal=Journal of Geophysical Research: Solid Earth |date=1989 |volume=94 |issue=B8 |pages=10379–10396 |doi=10.1029/JB094iB08p10379|bibcode=1989JGR....9410379S }}</ref><ref name="philpotts-ague-2009"/>{{rp|71–72}} Rhyolitic lavas erupt at a relatively low temperature of {{convert|800|to|1000|°C|abbr=on}}, significantly cooler than basaltic lavas, which typically erupt at temperatures of {{convert|1100|to|1200|°C|abbr=on}}.<ref name="philpotts-ague-2009"/>{{rp|20}}

Rhyolites that cool too quickly to grow [[crystals]] form a natural glass or vitrophyre, also called [[obsidian]].<ref>{{cite book |last1=Raymond |first1=Loren A. |title=Petrology : the study of igneous, sedimentary, metamorphic rocks |date=1997 |publisher=McGraw-Hill Companies, Inc |location=Dubuque, IA |isbn=0697413403 |page=27 |edition=Complete customized version}}</ref> Slower cooling forms microscopic crystals in the lava and results in textures such as flow [[foliation (geology)|foliations]], [[spherulite|spherulitic]], [[Nodule (geology)|nodular]], and [[lithophysa]]l structures. Some rhyolite is highly [[Vesicular texture|vesicular]] [[pumice]].<ref name="blatt-tracy-1996-55-74"/>

[[Peralkaline rock|Peralkaline]] rhyolites (rhyolites unusually rich in alkali metals) include [[comendite]] and [[pantellerite]].<ref>{{cite journal |last1=Mbowou|first1=Gbambie Isaac Bertrand|last2=Lagmet|first2=Claudial|last3=Nomade|first3=Sébastien|last4=Ngounoun|first4=Ismaïla|last5=Déruelle|first5=Bernard|last6=Ohnenstetter|first6=Daniel|title=Petrology of the Late Cretaceous peralkaline rhyolites (pantellerite and comendite) from Lake Chad, Central Africa|journal=[[Journal of Geosciences]]|year=2012|volume=57|page=127|doi=10.3190/jgeosci.118|issn=1802-6222|doi-access=free}}</ref> Peralkalinity has significant effects on [[lava morphology|lava flow morphology]] and [[mineralogy]], such that peralkaline rhyolites can be 10–30 times more fluid than typical [[calc-alkaline]] rhyolites. As a result of their increased fluidity, they are able to form small-scale flow folds, [[lava tube]]s and thin dikes. Peralkaline rhyolites erupt at relatively high temperatures of more than {{convert|1200|°C|abbr=on}}. They comprise [[bimodal volcanism|bimodal]] [[shield volcano]]es at [[hotspot (geology)|hotspot]]s and [[rift]]s (e.g. [[Rainbow Range (Chilcotin Plateau)|Rainbow Range]], [[Ilgachuz Range]] and [[Level Mountain]] in [[British Columbia]], Canada).<ref>{{cite book|last=Wood|first=Charles A.|author2=Kienle, Jürgen |pages=123. 131, 132, 133 |url=https://books.google.com/books?id=eyDRib-FJh4C|title=Volcanoes of North America: United States and Canada|year=1990|publisher=[[Cambridge University Press]]|location=[[Cambridge]], England|isbn=0-521-43811-X}}</ref>

Eruptions of rhyolite lava are relatively rare compared to eruptions of less felsic lavas. Only four eruptions of rhyolite have been recorded since the start of the 20th century: at the [[St. Andrew Strait]] volcano in [[Papua New Guinea]] and [[Novarupta]] volcano in [[Alaska]] as well as at [[Chaitén]] and [[Cordón Caulle]] volcanoes in southern [[Chile]].<ref name="Wilson_2011">{{cite conference | url=https://ui.adsabs.harvard.edu/abs/2011AGUFM.V42A..01W/abstract | title=Insights Into the Workings of Rhyolitic Explosive Eruptions and Their Magmatic Sources | publisher=[[American Geophysical Union]] | access-date=27 October 2020 | last=Wilson | first=C.J. | journal=AGU Fall Meeting Abstracts | year=2011 | volume=2011 | pages=V42A–01 | bibcode=2011AGUFM.V42A..01W | conference=American Geophysical Union Fall Meeting 2011 | id=abstract id. V42A-01}}</ref><ref name="Magnall_etal_2017">{{cite journal | title=Emplacing a Cooling-Limited Rhyolite Lava Flow: Similarities with Basaltic Lava Flows | first1=N. | last1=Magnall | first2=M.R. | last2=James | first3=H. | last3=Tuffen | first4=C. | last4=Vye-Brown | journal=Frontiers in Earth Science | year=2017 | volume=5 | page=44 | doi=10.3389/feart.2017.00044| bibcode=2017FrEaS...5...44M | s2cid=12887930 | doi-access=free }}</ref> The eruption of Novarupta in 1912 was the largest volcanic eruption of the 20th century,<ref name="Fierstein1998">{{cite journal |author=Fierstein, Judy |author-link=Judy Fierstein |last2=Hildreth |first2=Wes |author-link2=Wes Hildreth |author3=Hendley, James W. II |author4=Stauffer, Peter H. |year=1998 |title=Can Another Great Volcanic Eruption Happen in Alaska? |url=http://pubs.usgs.gov/fs/fs075-98/ |journal=U.S. Geological Survey Fact Sheet 075-98 |version=Version 1.0 |publisher=[[United States Geological Survey]] |access-date=September 10, 2008}}</ref> and began with explosive volcanism that later transitioned to effusive volcanism and the formation of a rhyolite dome in the vent.<ref name="nguyen-etal-2014">{{cite journal |last1=Nguyen |first1=Chinh T. |last2=Gonnermann |first2=Helge M. |last3=Houghton |first3=Bruce F. |title=Explosive to effusive transition during the largest volcanic eruption of the 20th century (Novarupta 1912, Alaska) |journal=Geology |date=August 2014 |volume=42 |issue=8 |pages=703–706 |doi=10.1130/G35593.1|bibcode=2014Geo....42..703N |s2cid=129328343 |url=https://pdfs.semanticscholar.org/94f8/c9017db99bb31c3d11edd42de0d5e04be424.pdf |archive-url=https://web.archive.org/web/20200219110722/https://pdfs.semanticscholar.org/94f8/c9017db99bb31c3d11edd42de0d5e04be424.pdf |url-status=dead |archive-date=2020-02-19 }}</ref>

==Petrogenesis==
[[File:PinkRhyolite.tif|thumb|Aphanitic rhyolite]]
Rhyolite magmas can be produced by [[igneous differentiation]] of a more mafic (silica-poor) magma, through [[Fractional crystallization (geology)|fractional crystallization]] or by assimilation of melted crustal rock ([[anatexis]]). Associations of [[andesite]]s, [[dacite]]s, and rhyolites in similar tectonic settings and with similar chemistry suggests that the rhyolite members were formed by differentiation of mantle-derived [[basalt]]ic magmas at shallow depths. In other cases, the rhyolite appears to be a product of melting of crustal sedimentary rock.<ref name="fisher-schmincke-1984"/>{{rp|21}} Water vapor plays an important role in lowering the melting point of silicic rock,<ref name="fisher-schmincke-1984"/>{{rp|43}} and some rhyolitic magmas may have a water content as high as 7–8 weight percent.<ref>{{cite journal |last1=Ewart |first1=A. |last2=Hildreth |first2=W. |author-link2=Wes Hildreth |last3=Carmichael |first3=I. S. E. |author-link3=Ian S. E. Carmichael |date=1 March 1975 |title=Quaternary acid magma in New Zealand |journal=Contributions to Mineralogy and Petrology |volume=51 |issue=1 |pages=1–27 |bibcode=1975CoMP...51....1E |doi=10.1007/BF00403509 |s2cid=129102186}}</ref><ref name="schmincke-2003">{{cite book |last1=Schmincke |first1=Hans-Ulrich |title=Volcanism |date=2003 |publisher=Springer |location=Berlin |isbn=9783540436508}}</ref>{{rp|44}}

High-silica rhyolite (HSR), with a silica content of 75 to 77·8% {{chem2|SiO2}}, forms a distinctive subgroup within the rhyolites. HSRs are the most [[Igneous differentiation|evolved]] of all igneous rocks, with a composition very close to the water-saturated granite [[Eutectic system|eutectic]] and with extreme enrichment in most [[incompatible element]]s. However, they are highly depleted in [[strontium]], [[barium]], and [[europium]]. They are interpreted as products of repeated melting and freezing of granite in the subsurface. HSRs typically erupt in large [[caldera]] eruptions.<ref>{{cite journal |last1=Wolff |first1=J. A. |last2=Ramos |first2=F. C. |title=Processes in Caldera-Forming High-Silica Rhyolite Magma: Rb-Sr and Pb Isotope Systematics of the Otowi Member of the Bandelier Tuff, Valles Caldera, New Mexico, USA |journal=Journal of Petrology |date=1 February 2014 |volume=55 |issue=2 |pages=345–375 |doi=10.1093/petrology/egt070|doi-access= }}</ref>

== Occurrence ==
[[File:Rhyolite beach on Lake Superior.jpg|thumb|Rhyolite beach on Lake Superior]]
Rhyolite is common along [[convergent plate boundaries]], where a slab of [[oceanic lithosphere]] is being [[Subduction|subducted]] into the [[Earth's mantle]] beneath overriding oceanic or [[continental lithosphere]]. It can sometimes be the predominant igneous rock type in these settings. Rhyolite is more common when the overriding [[lithosphere]] is continental rather than oceanic. The thicker continental crust gives the rising magma more opportunity to differentiate and assimilate crustal rock.{{sfn|Philpotts|Ague|2009|p=375}}

Rhyolite has been found on islands far from land, but such oceanic occurrences are rare.<ref name=Farndon>Farndon, John (2007) ''The Illustrated Encyclopedia of Rocks of the World''. Southwater. p. 54. {{ISBN|1844762696}}</ref> The [[tholeiitic magma series|tholeiitic magmas]] erupted at volcanic ocean islands, such as [[Iceland]], can sometimes differentiate all the way to rhyolite, and about 8% of the volcanic rock in Iceland is rhyolite. However, this is unusual, and the [[Hawaiian Islands]] (for example) have no known occurrences of rhyolite. The [[alkaline magma series|alkaline magmas]] of volcanic ocean islands will very occasionally differentiate all the way to peralkaline rhyolites, but differentiation usually ends with [[trachyte]].{{sfn|Philpotts|Ague|2009|pp=318, 369}}

Small volumes of rhyolite are sometimes erupted in association with [[flood basalt]]s, late in their history and where central volcanic complexes develop.{{sfn|Philpotts|Ague|2009|p=381}}

==Name==
The name rhyolite was introduced into [[geology]] in 1860 by the German traveler and geologist [[Ferdinand von Richthofen]]<ref>{{cite journal|last1=Richthofen|first1=Ferdinand Freiherrn von|title=Studien aus den ungarisch-siebenbürgischen Trachytgebirgen|journal=Jahrbuch der Kaiserlich-Königlichen Geologischen Reichsanstalt (Wein) [Annals of the Imperial-Royal Geological Institute of Vienna]|date=1860|volume=11|pages=153–273|url=https://babel.hathitrust.org/cgi/pt?id=uc1.c2537786;view=1up;seq=277|trans-title=Studies of the [[trachyte]] mountains of Hungarian Transylvania|language=de}}</ref><ref name="OED1">{{cite book | title=Oxford English Dictionary | year=1989 | edition=2nd | volume=13 | page=873 | publisher=[[Oxford University Press]] | location=Oxford | editor1-last=Simpson | editor1-first=John A.  | editor2-last=Weiner | editor2-first=Edmund S. C.}}</ref><ref name="MindMagma">{{cite book | title=Mind Over Magma: The Story of Igneous Petrology | publisher=[[Princeton University Press]] | author=Young, Davis A. | year=2003 | pages=117 | isbn=0-691-10279-1}}</ref> from the Greek word ''rhýax'' ("a stream of lava")<ref>{{cite web|url=https://www.merriam-webster.com/dictionary/rhyolite|title=Definition of RHYOLITE|website=www.merriam-webster.com|date=18 April 2024 }}</ref> and the rock name suffix "-lite".<ref>{{cite web|url=https://www.merriam-webster.com/dictionary/lite|title=Definition of LITE|website=www.merriam-webster.com|date=7 May 2023 }}</ref>

==Uses==
In [[Pre-Columbian era|North American pre-historic times]], rhyolite was quarried extensively in what is now eastern [[Pennsylvania]].  Among the leading quarries was the [[Carbaugh Run Rhyolite Quarry Site]] in [[Adams County, Pennsylvania|Adams County]]. Rhyolite was mined there starting 11,500 years ago.<ref name=Fergus>{{cite book|title=Natural Pennsylvania: Exploring the State Forest Natural Areas|first=Charles|last=Fergus|publisher=Stackpole Books|year=2001|page=30|oclc=47018498}}</ref> Tons of rhyolite were traded across the [[Delmarva Peninsula]],<ref name=Fergus/> because the rhyolite kept a sharp point when [[knapping|knapped]] and was used to make spear points and arrowheads.<ref>{{cite web|title=Snaggy Ridge Indian Rhyolite Quarries|first=Dakota|last=Bricker|publisher=Mercersburg Historical Society|url=http://mhs.mercersburg.org/blog/7/|access-date=2019-01-20}}</ref>

Obsidian is usually of rhyolitic composition, and it has been used for tools since prehistoric times.<ref>{{cite book|author1=Cotterell, Brian |author2=Kamminga, Johan |title=Mechanics of pre-industrial technology: an introduction to the mechanics of ancient and traditional material culture|url=https://books.google.com/books?id=0-xOM8y6Uc8C&pg=PA127|access-date=9 September 2011|year=1992|publisher=Cambridge University Press|isbn=978-0-521-42871-2|pages=127–}}</ref> Obsidian scalpels have been investigated for use in delicate surgery.<ref name=obsidian1>{{cite journal |last = Buck |first = BA|date=March 1982|title = Ancient Technology in Contemporary Surgery|journal = The Western Journal of Medicine|volume = 136|issue = 3|pages = 265–269|pmid= 7046256|pmc = 1273673}}</ref> Pumice, also typically of rhyolitic composition, finds important uses as an [[abrasive]], in [[concrete]],<ref>{{cite book |last1=Grasser |first1=Klaus |title=Building with Pumice |pages=64|isbn= 3-528-02055-5 |date=1990|publisher= Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) |url=https://www.humanitarianlibrary.org/sites/default/files/2014/02/GATE_buildingWithPumice.pdf |access-date=23 March 2019}}</ref> and as a [[soil amendment]].<ref name="usgs pumice">{{cite web |last1=Crangle |first1=Robert D. Jr. |title=Pumice and pumicite – USGS Mineral Resources Program |url=https://minerals.usgs.gov/minerals/pubs/commodity/pumice/mcs-2012-pumic.pdf |publisher=United States Geological Survey |access-date=25 November 2018 |date=January 2012}}</ref> Rhyolitic tuff was used extensively for construction in ancient Rome<ref name="jackson-etal-2005">{{cite journal |last1=Jackson |first1=M. D. |last2=Marra |first2=F. |last3=Hay |first3=R. L. |last4=Cawood |first4=C. |last5=Winkler |first5=E. M. |title=The Judicious Selection and Preservation of Tuff and Travertine Building Stone in Ancient Rome* |journal=Archaeometry |date=2005 |volume=47 |issue=3 |pages=485–510 |doi=10.1111/j.1475-4754.2005.00215.x|doi-access=free |bibcode=2005Archa..47..485J }}</ref> and has been used in construction in modern Europe.<ref name="schmincke-2003"/>{{rp|138}}

==See also==
* {{annotated link|List of rock types}}
* {{annotated link|Thunderegg}}

==References==
{{reflist}}

==External links==
{{commons and category|Rhyolite}}
* [https://geology.com/rocks/rhyolite.shtml Geology.com - Rhyolite]
* [https://www.gemstones.com/gemopedia/rhyolite Gemstones.com - guide and properties chart - Rhyolite]

{{igneous rocks}}
{{Rock type}}
{{Volcanoes}}

[[Category:Rhyolite| ]]