|Felsic: igneous quartz and alkali feldspar (sanidine and sodic plagioclase), biotite and hornblende.|
Rhyolite is an igneous, volcanic rock, of felsic (silica-rich) composition (typically > 69% SiO2 – see the TAS classification). It may have any texture from glassy to aphanitic to porphyritic. The mineral assemblage is usually quartz, sanidine and plagioclase (in a ratio > 2:1 – see the QAPF diagram). Biotite and hornblende are common accessory minerals. It is the extrusive equivalent to granite.
Rhyolite can be considered as the extrusive equivalent to the plutonic granite rock, and consequently, outcrops of rhyolite may bear a resemblance to granite. Due to their high content of silica and low iron and magnesium contents, rhyolite melts are highly polymerized and form highly viscous lavas. They also occur as breccias or in volcanic plugs and dikes. Rhyolites that cool too quickly to grow crystals form a natural glass or vitrophyre, also called obsidian. Slower cooling forms microscopic crystals in the lava and results in textures such as flow foliations, spherulitic, nodular, and lithophysal structures. Some rhyolite is highly vesicular pumice. Many eruptions of rhyolite are highly explosive and the deposits may consist of fallout tephra/tuff or of ignimbrites.
Eruptions of rhyolite are relatively rare compared to eruptions of less felsic lavas. Only three eruptions of rhyolite have been recorded since the start of the 20th century: at the St. Andrew Strait volcano in Papua New Guinea, Novarupta volcano in Alaska, and Chaiten in southern Chile.
Rhyolite has been found on islands far from land, but such oceanic occurrences are rare.
- Etsch Valley Vulcanite Group near Bolzano and the surrounding area
- Gréixer rhyolitic complex at Moixeró range (Catalonia, Spain)
- Iceland: , e.g. Torfajökull, Leirhnjúkur / Krafla, Breiddalur central volcano
- Papa Stour in Shetland
- Copper Coast Geopark in southeast Ireland
- various locations around Snowdonia, Wales
- Massif de l'Esterel, France
- the Thuringian Forest consists mainly of rhyolites, latites and pyroclastic rocks of the Rotliegendes
- Saxony, especially the north west
- Saxony-Anhalt north of Halle
- Saar-Nahe Basin e.g. the Königstuhl (Pfalz) on the Donnersberg mountain
- Black Forest e.g. on the Karlsruher Grat
- Cascade Range
- Cobalt, Ontario
- Rocky Mountains
- Jemez Mountains
- Rhyolite, Nevada was named after a rhyolite deposit that characterised the area.
- Wichita Mountains within the Southern Oklahoma Aulacogen
- St. Francois Mountains
- Mount Jasper, Berlin, New Hampshire
- Crater Lake, Oregon
- the Taupo Volcanic Zone in New Zealand has a large concentration of young rhyolite volcanoes
- the Gondwana Rainforests of Australia World Heritage Area contains rhyolite-restricted flora along the Great Dividing Range
- the Flinders Peak Group in the Teviot Range in the Fassifern Valley is a rhyolite of varying colours.
- The Malani Igneous Suite, Rajasthan, India.
- The Yandang Shan mountain chain, near the town of Wenzhou, Zhejiang province, China
- Tambora, Indonesia
The name rhyolite was introduced into geology in 1860 by the German traveler and geologist Ferdinand von Richthofen from the Greek word rhýax ("a stream of lava") and the rock name suffix "-lite".
In North American pre-historic times, rhyolite was quarried extensively in eastern Pennsylvania in the United States. Among the leading quarries was the Carbaugh Run Rhyolite Quarry Site in Adams County, where as many as fifty small quarry pits are known.
- The Illustrated Encyclopedia of Rocks of the World by John Farndon, page 54.
- J. Martí, G.J. Aguirre-Díaz, A. Geyer. "The Gréixer rhyolitic complex (Catalan Pyrenees): an example of Permian caldera". Workshop on Collapse Calderas – La Réunion 2010. IAVCEI – Commission on Collapse Calderas.
- Cascades Volcano Observatory. "Cascades Volcano Observatory". usgs.gov. Retrieved 19 January 2015.
- ROBERT CINITS. "The Proteus Property" (PDF).
- "Rhyolite Ghost Town". Retrieved 2009-12-22.
- "Yandang Shan". Archived from the original on 2016-02-17. Retrieved 2011-12-22.
- 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. From p. 156: " … ich werde mich daher in den vorliegenden Bemerkungen für alle Gesteine der drei genannten Beudant'schen Gruppen stets des Namens: Rhyolith bedienen, welcher wenigstens ein allgemeines Merkmal der grossen und unendlich reich gegleiderten Gesteingruppe, das eigenthümliche Ansehen geflossener Massen, bezeichnet, … " ( … thus in the present remarks I will always use the name "rhyolite" for all of the rocks of the three aforementioned groups [distinguished by] Beudant [i.e., French geologist François Sulpice Beudant (1787–1850)], which at least designates a general characteristic of the great and infinitely richly divided group of rocks, [having] the specific character of flowed masses, … )
- Simpson, John A.; Weiner, Edmund S. C., eds. (1989). Oxford English Dictionary. 13 (2nd ed.). Oxford: Oxford University Press. p. 873.
- Young, Davis A. (2003). Mind Over Magma: The Story of Igneous Petrology. Princeton University Press. p. 117. ISBN 0-691-10279-1.
- Beckerman, Ira. National Register of Historic Places Inventory/Nomination: Carbaugh Run Rhyolite Quarry Site (36AD30). National Park Service, 1981, 2.
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