Rhyolite is a felsic, extrusive igneous rock.  It has the same chemistry & mineralogy as granite, but is very finely crystalline (aphanitic texture; crystals <1 mm in size) due to cooling of high-viscosity lava.  Rhyolites are often light gray to pinkish to somewhat reddish in color.  Rhyolite lavas are highly viscous (thick & slow-moving) when erupted and often appear as if they have flowed like oozing toothpaste.  Sometimes the term felsite is applied to rhyolites.  There does not seem to be a consistent definition of felsite, cf. rhyolite.  However, felsite appears to be the broader term, applicable to all light-colored volcanic rocks.





Rhyolite (felsite)



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