Everything about Rhyolite totally explained
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% SiO
2 — 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.
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