AskDefine | Define rhyolitic

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.

References

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