Rhyolite (/ -/, RY-ə-lyte, RY-oh-) 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.
|Felsic: igneous quartz and alkali feldspar (sanidine and sodic plagioclase), biotite and hornblende|
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, rhyolitic magmas 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.
- 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
- Cascade Range
- Cobalt, Ontario
- Sheep Creek, Idaho
- 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
- Palisade Head, a formation found at Tettegouche State Park, Minnesota
- Mount Kineo, a volcanic plug; an iconic mountain feature located in Moosehead Lake, Rockwood, Maine, United States
- The Taupo Volcanic Zone in New Zealand has a large concentration of young rhyolite volcanoes.
- Glass House Mountains National Park, Queensland, Australia
- 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.
Quarrying by Native Americans
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. Rhyolite was mined there starting 11,500 years ago. Tons of rhyolite were traded across the Delmarva Peninsula, because the rhyolite kept a sharp point when knapped and was used to make spear points and arrowheads.
- 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.
- 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.
- "Definition of RHYOLITE". www.merriam-webster.com.
- "Definition of LITE". www.merriam-webster.com.
- Fergus, Charles (2001). Natural Pennsylvania: Exploring the State Forest Natural Areas. Stackpole Books. p. 30. OCLC 47018498.
- Bricker, Dakota. "Snaggy Ridge Indian Rhyolite Quarries". Mercersburg Historical Society. Retrieved 2019-01-20.
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