rhyolite

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rhyolite,

fine-grained light-colored acidic volcanic rockrock,
aggregation of solid matter composed of one or more of the minerals forming the earth's crust. The scientific study of rocks is called petrology. Rocks are commonly divided, according to their origin, into three major classes—igneous, sedimentary, and metamorphic.
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. Rhyolite is chemically the equivalent of granite, and is thus composed primarily of quartz and orthoclase feldspar with subordinate amounts of plagioclase feldspar, biotite mica, amphiboles, and pyroxenes. Rhyolite lava exhibits a typical banded structure produced by its flow pattern. Rhyolite lavas occur in continental and submarine volcanoes, especially island arcs, and in igneous dikes. Rhyolite lavas are typically highly viscous and are explosively ejected from volcanoes. Rhyolites were formed in profusion in the Yellowstone Park area and throughout the southwestern portion of the United States.
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Rhyolite

 

(also liparite), a cenotypal, extrusive rock rich in silica (68-77 percent SiO2). It has a porphyritic texture and contains phenocrysts of quartz, potassium feldspar, plagioclase, and, less commonly, biotite or pyroxene in a glassy groundmass, usually with flow texture. A glassy variety virtually without phenocrysts is called obsidian. Paleotypal analogs are classified according to their alkali composition as keratophyres (sodic) or orthophyres (potassic). Rhyolite is the extrusive equivalent of granitoids.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

rhyolite

[′rī·ə‚līt]
(petrology)
A light-colored, aphanitic volcanic rock composed largely of alkali feldspar and free silica with minor amounts of mafic minerals; the extrusive equivalent of granite.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
* Sheets of sodic alkaline rhyolite occur in the western part of the area.
Five major rhyolite source groups are represented at Linda's Point (Table 4).
This volcanism consists of calc-alkaline/A-type rhyolites similar in age (348-342 Ma) to the granitic clast of the Del Raton conglomerate.
Finally, the parent material that originated these soils are rhyolites for the central part and limestone for the northeastern part: The resulting Vertisols in both areas are soils rich in clay, organic matter, Ca, Mg and K; they also present high cation exchange capacity and base saturation (Tables I and II), which gives them high fertility.
Rhyolite samples are dominated by ash to lapilli crystal tuff; aphanitic to weakly porphyritic flow-banded pyroclastic beds are also present.
For nine months Dr Bevins and Dr Ixer collected and identified samples from Pembrokeshire's rock outcrops to try to find the origins of rhyolite debitage rocks that can be found at Stonehenge.
The nomenclature of geological units of the massif has been updated following the rules of lithodemic units [5], as follows [6]: 1) Metasedimentary rocks: Barbasco Metasedimentary Suite (Canaote Quartzite, Cerrajon Metapelite), Mireles Phyllite (with Cambrian-Ordovician trilobites); 2) Volcanic rocks: Guacamayas Super-Suite: Teresen Rhyolitic Suite (Corcovado Rhyolite, Tirado Rhyolite, La Bandola Rhyolite), El Penon Latitic Suite (El Oso Quartz Latite, Segoviera Rhyolite); and 3) El Baul Granitic Suite (Pinero Granite, Mata Oscura Granite and Mogote Granite).
The pioneer geological works in the Sierra San Miguel correspond to Walther (1927), Caorsi & Goni (1958) and Bossi & Fernandez (1963) and it has been described as a volcanic/sub-volcanic association composed by granophyres and, subordinated rhyolites. These lithologies were later integrated to the Arequita Formation by Bossi (1966).
2) the rocks consist primarily of rhyolites and other volcanic rocks forming five distinct lava flows a few hundred meters thick.
One wonders if Cunnington had also recognised rhyolites and tuffs in the barrow, neither of which are local to Salisbury Plain.
The system was field-tested at Navan Resources' Aguas Tenidas Este deposit in the Iberian Pyrite Belt of southern Spain, a region of pyrite-rich massive sulphide deposits hosted within a sequence of rhyolites, rhyholitic and chloritic tuffs, and black shales.