Rhyolite is a fine-grained or glassy igneous rock chemically and mineralogically the volcanic equivalent of granite. The name was originally applied to such rocks by von Richthofen (1860, see Johannsen, 1932) on account of the frequently displayed flow banding (prefix rhyo-, from Greek rhyox, stream of lava). Liparite (Roth, 1861 see Johannsen, 1932) is synonymous with rhyolite but the term is now little used.
Varieties
Rhyolites have high SiO2 (usually 68–77%), low normative color indexes (normative ol + opx + cpx + mt + il + hm ≤ 20) and normative plagioclase compositions <An20 (Irvine and Baragar, 1971). They represent the evolved compositions of the subalkaline basalt- andesite–dacite–rhyolite magma series of either tholeiitic or calc-alkaline affinity. Peralkaline magmas can differentiate to either sodic or potassic alkali rhyolites such as comendite or pantellerite. Comendite can be chemically distinguished from pantellerite because it is less peralkaline and...
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Notes
- 1.
*Includes earlier references.
Bibliography
Cameron, M., W. C. Bagby, and K. L. Cameron, 1980, Petrogenesis of voluminous mid-Tertiary ignimbrites of the Sierra Madre Occidental, Mexico, Contrib. Mineral. Petrol. 74, 271–284.
Carmichael, I. S. E., F. J. Turner, and J. Verhoogen, 1974, Igeneous Petrology. New York: McGraw-Hill.
Cole, J. W., 1979, Structure, petrology and genesis of Cenozoic volcanism; Taupo Volcanic Zone, New Zealand—a review, N. Zld J. Geol. Geophys. 22, 631–657.
Irvine, T. N. and W. R. A. Baragar, 1971, A guide to the chemical classification of common volcanic rocks, Can. J. Earth Sci. 8, 523–548.
Johannsen, A., 1932, A Descriptive Petrography of the Igneous Rocks, Vol. II. The Quartz-Bearing Rocks. University of Chicago Press.
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© 1989 Van Nostrand Reinhold
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Durant, G.P. (1989). Rhyolite . In: Petrology. Encyclopedia of Earth Science. Springer, Boston, MA. https://doi.org/10.1007/0-387-30845-8_216
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