Rhyolite

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For other uses, see Rhyolite (disambiguation).
Rhyolite
Igneous rock
Composition
ClassificationFelsic
PrimaryQuartz and alkali feldspar (sanidine and sodic plagioclase)
SecondaryBiotite and hornblende
TextureGlassy or aphanitic, sometimes porphyritic

Rhyolite (

extrusive equivalent of granite
.

Its high silica content makes rhyolitic

lava flows. Rhyolitic ash-flow tuffs are among the most voluminous of continental igneous rock
formations.

Rhyolitic tuff has been used extensively for construction.

soil amendment
.

Description

QAPF diagram with rhyolite field highlighted
TAS diagram with rhyolite field highlighted

Rhyolite is an

glassy.[5]

An extrusive igneous rock is classified as rhyolite when

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.[6][7][8][9]
: 140–146 

The alkali feldspar in rhyolites is

trydimite are sometimes present along with the quartz. Biotite, augite, fayalite, and hornblende are common accessory minerals.[5]

Geology

Due to their high content of silica and low

lava flows.[10]: 22  Rhyolitic ash flow tuffs are the only volcanic product with volumes rivaling those of flood basalts.[9]: 77  Rhyolites also occur as breccias or in lava domes, volcanic plugs, and dikes.[11][12][9]: 71–72  Rhyolitic lavas erupt at a relatively low temperature of 800 to 1,000 °C (1,470 to 1,830 °F), significantly cooler than basaltic lavas, which typically erupt at temperatures of 1,100 to 1,200 °C (2,010 to 2,190 °F).[9]
: 20 

Rhyolites that cool too quickly to grow

crystals form a natural glass or vitrophyre, also called obsidian.[13] 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.[5]

calc-alkaline rhyolites. As a result of their increased fluidity, they are able to form small-scale flow folds, lava tubes and thin dikes. Peralkaline rhyolites erupt at relatively high temperatures of more than 1,200 °C (2,190 °F). They comprise bimodal shield volcanoes at hotspots and rifts (e.g. Rainbow Range, Ilgachuz Range and Level Mountain in British Columbia, Canada).[15]

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

Cordón Caulle volcanoes in southern Chile.[16][17] The eruption of Novarupta in 1912 was the largest volcanic eruption of the 20th century,[18] and began with explosive volcanism that later transitioned to effusive volcanism and the formation of a rhyolite dome in the vent.[19]

Petrogenesis

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.[10]: 21  Water vapor plays an important role in lowering the melting point of silicic rock,[10]: 43  and some rhyolitic magmas may have a water content as high as 7–8 weight percent.[20][21]: 44 

High-silica rhyolite (HSR), with a silica content of 75 to 77·8% SiO2, forms a distinctive subgroup within the rhyolites. HSRs are the most evolved of all igneous rocks, with a composition very close to the water-saturated granite eutectic and with extreme enrichment in most incompatible elements. 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.[22]

Occurrence

Rhyolite is common along

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.[23]

Rhyolite has been found on islands far from land, but such oceanic occurrences are rare.[24] The 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 magmas of volcanic ocean islands will very occasionally differentiate all the way to peralkaline rhyolites, but differentiation usually ends with trachyte.[25]

Small volumes of rhyolite are sometimes erupted in association with flood basalts, late in their history and where central volcanic complexes develop.[26]

Name

The name rhyolite was introduced into geology in 1860 by the German traveler and geologist Ferdinand von Richthofen[27][28][29] from the Greek word rhýax ("a stream of lava")[30] and the rock name suffix "-lite".[31]

Uses

In 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. Rhyolite was mined there starting 11,500 years ago.[32] Tons of rhyolite were traded across the Delmarva Peninsula,[32] because the rhyolite kept a sharp point when knapped and was used to make spear points and arrowheads.[33]

Obsidian is usually of rhyolitic composition, and it has been used for tools since prehistoric times.

soil amendment.[37] Rhyolitic tuff was used extensively for construction in ancient Rome[38] and has been used in construction in modern Europe.[21]
: 138 

See also

  • List of rock types – List of rock types recognized by geologists
  • Thunderegg – Nodule-like rock, that is formed within rhyolitic volcanic ash layers

References

  1. ISBN 978-1-4058-8118-0
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  2. ^ "rhyolite". Dictionary.com Unabridged (Online). n.d.
  3. ^ "rhyolite". Merriam-Webster.com Dictionary. Retrieved 2012-07-10.
  4. ^ "rhyolite". The American Heritage Dictionary of the English Language (5th ed.). HarperCollins.
  5. ^
    ISBN 0716724383
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  6. S2CID 28548230
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  7. ^ "Rock Classification Scheme - Vol 1 - Igneous" (PDF). British Geological Survey: Rock Classification Scheme. 1: 1–52. 1999.
  8. ^ "Classification of igneous rocks". Archived from the original on 30 September 2011.
  9. ^
    ISBN 9780521880060
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  10. ^
    ISBN 3540127569
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  11. S2CID 128948336
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  12. doi:10.1029/JB094iB08p10379
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  13. ISBN 0697413403
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  14. ISSN 1802-6222
    .
  15. ISBN 0-521-43811-X
    .
  16. Bibcode:2011AGUFM.V42A..01W
    . abstract id. V42A-01. Retrieved 27 October 2020.
  17. S2CID 12887930
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  18. ^ 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.
  19. S2CID 129328343. Archived from the original
    (PDF) on 2020-02-19.
  20. S2CID 129102186
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  21. ^
    ISBN 9783540436508
    .
  22. doi:10.1093/petrology/egt070
    .
  23. ^ Philpotts & Ague 2009, p. 375.
  24. ISBN 1844762696
  25. ^ Philpotts & Ague 2009, pp. 318, 369.
  26. ^ Philpotts & Ague 2009, p. 381.
  27. ^ 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.
  28. ^ Simpson, John A.; Weiner, Edmund S. C., eds. (1989). Oxford English Dictionary. Vol. 13 (2nd ed.). Oxford: Oxford University Press. p. 873.
  29. ISBN 0-691-10279-1
    .
  30. ^ "Definition of RHYOLITE". www.merriam-webster.com. 18 April 2024.
  31. ^ "Definition of LITE". www.merriam-webster.com. 7 May 2023.
  32. ^
    OCLC 47018498
    .
  33. ^ Bricker, Dakota. "Snaggy Ridge Indian Rhyolite Quarries". Mercersburg Historical Society. Retrieved 2019-01-20.
  34. ISBN 978-0-521-42871-2
    . Retrieved 9 September 2011.
  35. PMID 7046256
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  36. ISBN 3-528-02055-5
    . Retrieved 23 March 2019.
  37. ^ Crangle, Robert D. Jr. (January 2012). "Pumice and pumicite – USGS Mineral Resources Program" (PDF). United States Geological Survey. Retrieved 25 November 2018.
  38. doi:10.1111/j.1475-4754.2005.00215.x
    .

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