Rhyolitic tuff has been extensively used 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.
QAPF diagram with rhyolite field highlighted
TAS diagram with rhyolite field highlighted
Rhyolite is an extrusive igneous rock, formed from magma rich in silica that is extruded from a 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.
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) and alkali feldspar makes up 35% to 90% of its total feldspar content. Feldspathoids 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 oxides (K2O plus Na2O). Rhyolite is high in silica and total alkali metal oxides, placing it in the R field of the TAS diagram.:140–146
Due to their high content of silica and low iron and magnesium contents, rhyolitic magmas form highly viscous lavas.:23–26 As a result, many eruptions of rhyolite are highly explosive, and rhyolite occurs more frequently as pyroclastic rock than as lava flows.:22 Rhyolitic ash flow tuffs are the only volcanic product with volumes rivaling those of flood basalts.:77 Rhyolites also occur as breccias or in lava domes, volcanic plugs, and dikes.:71–72 Rhyolitic lavas erupt at a relatively low temperature of 800 °C to 1000 °C, significantly cooler than basaltic lavas, which typically erupt at temperatures of 1100 °C to 1200 °C.:20
Eruptions of rhyolite 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 Chaiten and Cordon Caulle volcanoes in southern Chile. The eruption of Novarupta in 1912 was the largest volcanic eruption of the 20th century, and began with explosive volcanism that later transitioned to effusive volcanism and the formation of a rhyolite dome in the vent.
Rhyolite magmas can be produced by igneous differentiation of a more mafic (silica-poor) magma, through fractional crystallization or by assimilation of melted crustal rock (anatexis). Associations of andesites, dacites, and rhyolites in similar tectonic settings and with similar chemistry suggests that the rhyolite members were formed by differentiation of mantle-derived basaltic magmas at shallow depths. In other cases, the rhyolite appears to be a product of melting of crustal sedimentary rock.:21 Water vapor plays an important role in lowering the melting point of silicic rock,:43 and some rhyolitic magmas may have a water content as high as 7–8 weight percent.:44
Rhyolite has been found on islands far from land, but such oceanic occurrences are rare.
Rhyolite in the Kaldaklofsfjöll, Landmannalaugar, Iceland
Obsidian is usually of rhyolitic composition, and it has been used for tools since prehistoric times. Obsidian scalpels have been investigated for use in delicate surgery. Pumice, also typically of rhyolitic composition, finds important uses as an abrasive, in concrete, and as a soil amendment. Rhyolitic tuff was used extensively for construction in ancient Rome and has been used in construction in modern Europe.:138
Comendite – A hard, peralkaline igneous rock, a type of light blue grey rhyolite
Thunderegg – A nodule-like rock, that is formed within rhyolitic volcanic ash layers
^ abcBlatt, Harvey; Tracy, Robert J. (1996). Petrology : igneous, sedimentary, and metamorphic (2nd ed.). New York: W.H. Freeman. pp. 55, 74. ISBN 0716724383.
^Le Bas, M. J.; Streckeisen, A. L. (1991). "The IUGS systematics of igneous rocks". Journal of the Geological Society. 148 (5): 825–833. Bibcode:1991JGSoc.148..825L. CiteSeerX10.1.1.692.4446. doi:10.1144/gsjgs.148.5.0825. S2CID 28548230.
^"Rock Classification Scheme - Vol 1 - Igneous" (PDF). British Geological Survey: Rock Classification Scheme. 1: 1–52. 1999.
^"CLASSIFICATION OF IGNEOUS ROCKS". Archived from the original on 30 September 2011.
^ abcdePhilpotts, Anthony R.; Ague, Jay J. (2009). Principles of igneous and metamorphic petrology (2nd ed.). Cambridge, UK: Cambridge University Press. ISBN 9780521880060.
^ abcFisher, Richard V.; Schmincke, H.-U. (1984). Pyroclastic rocks. Berlin: Springer-Verlag. ISBN 3540127569.
^Hanson, Richard E.; Schweickert, Richard A. (1 November 1982). "Chilling and Brecciation of a Devonian Rhyolite Sill Intruded into Wet Sediments, Northern Sierra Nevada, California". The Journal of Geology. 90 (6): 717–724. Bibcode:1982JG.....90..717H. doi:10.1086/628726. S2CID 128948336.
^Spell, Terry L.; Kyle, Philip R. (1989). "Petrogenesis of Valle Grande Member rhyolites, Valles Caldera, New Mexico: Implications for evolution of the Jemez Mountains Mgmatic System". Journal of Geophysical Research: Solid Earth. 94 (B8): 10379–10396. Bibcode:1989JGR....9410379S. doi:10.1029/JB094iB08p10379.
^Raymond, Loren A. (1997). Petrology : the study of igneous, sedimentary, metamorphic rocks (Complete customized version ed.). Dubuque, IA: McGraw-Hill Companies, Inc. p. 27. ISBN 0697413403.
^Wilson, C.J. (2011). Insights Into the Workings of Rhyolitic Explosive Eruptions and Their Magmatic Sources. American Geophysical Union Fall Meeting 2011. AGU Fall Meeting Abstracts. 2011. American Geophysical Union. pp. V42A–01. Bibcode:2011AGUFM.V42A..01W. abstract id. V42A-01. Retrieved 27 October 2020.
^Magnall, N.; James, M.R.; Tuffen, H.; Vye-Brown, C. (2017). "Emplacing a Cooling-Limited Rhyolite Lava Flow: Similarities with Basaltic Lava Flows". Frontiers in Earth Science. 5: 44. Bibcode:2017FrEaS...5...44M. doi:10.3389/feart.2017.00044. S2CID 12887930.
^Fierstein, Judy; Hildreth, Wes; Hendley, James W. II; Stauffer, Peter H. (1998). "Can Another Great Volcanic Eruption Happen in Alaska? – U.S. Geological Survey Fact Sheet 075-98". Version 1.0. United States Geological Survey. Retrieved September 10, 2008. Cite journal requires |journal= (help)
^Nguyen, Chinh T.; Gonnermann, Helge M.; Houghton, Bruce F. (August 2014). "Explosive to effusive transition during the largest volcanic eruption of the 20th century (Novarupta 1912, Alaska)". Geology. 42 (8): 703–706. Bibcode:2014Geo....42..703N. doi:10.1130/G35593.1.
^Ewart, A.; Hildreth, W.; Carmichael, I. S. E. (1 March 1975). "Quaternary acid magma in New Zealand". Contributions to Mineralogy and Petrology. 51 (1): 1–27. Bibcode:1975CoMP...51....1E. doi:10.1007/BF00403509. S2CID 129102186.
^ abSchmincke, Hans-Ulrich (2003). Volcanism. Berlin: Springer. ISBN 9783540436508.
^ abcdFarndon, John (2007) The Illustrated Encyclopedia of Rocks of the World. Southwater. p. 54. ISBN 1844762696
^Martí, J.; Aguirre-Díaz, G.J. and Geyer, A. (2010). "The Gréixer rhyolitic complex (Catalan Pyrenees): an example of Permian caldera". Workshop on Collapse Calderas – La Réunion. IAVCEI – Commission on Collapse Calderas.
^Berg, Sylvia E.; Troll, Valentin R.; Harris, Chris; Deegan, Frances M.; Riishuus, Morten S.; Burchardt, Steffi; Krumbholz, Michael (October 2018). "Exceptionally high whole-rock δ18O values in intra-caldera rhyolites from Northeast Iceland". Mineralogical Magazine. 82 (5): 1147–1168. Bibcode:2018MinM...82.1147B. doi:10.1180/mgm.2018.114. ISSN 0026-461X.
^Poitrasson, F.; Pin, C. (1998). "Extreme Nd isotope homogeneity in a large rhyolitic province: the Estérel massif, southeast France". Bulletin of Volcanology. 60 (3): 213–223. Bibcode:1998BVol...60..213P. doi:10.1007/s004450050228. S2CID 129024115.
^Mortazavi, M.; Sparks, R.S.J. (2004). "Origin of rhyolite and rhyodacite lavas and associated mafic inclusions of Cape Akrotiri, Santorini: the role of wet basalt in generating calcalkaline silicic magmas". Contributions to Mineralogy and Petrology. 146 (4): 397–413. Bibcode:2004CoMP..146..397M. doi:10.1007/s00410-003-0508-4. S2CID 129739700.
^"Yandang Shan". Archived from the original on 2016-02-17. Retrieved 2011-12-22.
^LeMasurier, W.E.; Futa, K.; Hole, M.; Kawachi, Y. (2003). "Polybaric Evolution of Phonolite, Trachyte, and Rhyolite Volcanoes in Eastern Marie Byrd Land, Antarctica: Controls on Peralkalinity and Silica Saturation". International Geology Review. 45 (12): 1055–1099. Bibcode:2003IGRv...45.1055L. doi:10.2747/0020-6822.214.171.1245. S2CID 130450918.
^Richthofen, Ferdinand Freiherrn von (1860). "Studien aus den ungarisch-siebenbürgischen Trachytgebirgen" [Studies of the trachyte mountains of Hungarian Transylvania]. Jahrbuch der Kaiserlich-Königlichen Geologischen Reichsanstalt (Wein) [Annals of the Imperial-Royal Geological Institute of Vienna] (in German). 11: 153–273.
^Simpson, John A.; Weiner, Edmund S. C., eds. (1989). Oxford English Dictionary. 13 (2nd ed.). Oxford: Oxford University Press. p. 873.
^Cotterell, Brian; Kamminga, Johan (1992). Mechanics of pre-industrial technology: an introduction to the mechanics of ancient and traditional material culture. Cambridge University Press. pp. 127–. ISBN 978-0-521-42871-2. Retrieved 9 September 2011.
^Buck, BA (March 1982). "Ancient Technology in Contemporary Surgery". The Western Journal of Medicine. 136 (3): 265–269. PMC1273673. PMID7046256.
^Grasser, Klaus (1990). Building with Pumice(PDF). Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ). p. 64. ISBN 3-528-02055-5. Retrieved 23 March 2019.
^Crangle, Robert D. Jr. (January 2012). "Pumice and pumicite – USGS Mineral Resources Program" (PDF). United States Geological Survey. Retrieved 25 November 2018.
^Jackson, M. D.; Marra, F.; Hay, R. L.; Cawood, C.; Winkler, E. M. (2005). "The Judicious Selection and Preservation of Tuff and Travertine Building Stone in Ancient Rome*". Archaeometry. 47 (3): 485–510. doi:10.1111/j.1475-4754.2005.00215.x.