AskDefine | Define rhyolite

Dictionary Definition

rhyolite n : very acid volcanic rock

User Contributed Dictionary



  1. an igneous, volcanic (extrusive) rock, of felsic composition, with aphanitic to porphyritic texture.

Extensive Definition

This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.
Rhyolite is an igneous, volcanic (extrusive) rock, of felsic (silicon-rich) composition (typically >69% SiO2 — see the TAS classification). It may have any texture from aphanitic to porphyritic. The mineral assemblage is usually quartz, alkali feldspar and plagioclase (in a ratio > 1:2 — see the QAPF diagram). Biotite and hornblende are common accessory minerals.
Rhyolite can be considered as the extrusive equivalent to the plutonic granite rock, and consequently, outcroppings of it often 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 can also occur as breccias or in volcanic necks and dykes. 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 or of ignimbrites.


rhyolite in Bulgarian: Риолит
rhyolite in Czech: Ryolit
rhyolite in German: Rhyolith
rhyolite in Estonian: Rüoliit
rhyolite in Spanish: Riolita
rhyolite in French: Rhyolite
rhyolite in Korean: 유문암
rhyolite in Italian: Riolite
rhyolite in Hebrew: ריוליט
rhyolite in Lithuanian: Riolitas
rhyolite in Dutch: Rhyoliet
rhyolite in Japanese: 流紋岩
rhyolite in Polish: Ryolit
rhyolite in Portuguese: Riólito
rhyolite in Romanian: Riolit
rhyolite in Slovak: Ryolit
rhyolite in Finnish: Ryoliitti
rhyolite in Swedish: Ryolit
rhyolite in Chinese: 流紋岩
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