Rhyolite
From Free net encyclopedia
Rhyolite is an igneous, volcanic (extrusive) rock, of felsic composition, with aphanitic to porphyritic texture. Mineral assembly is usually quartz, alkali feldspar and plagioclase (in a ratio > 1:2). Biotite and pyroxene are common accessory minerals.
Rhyolite can be considered as the extrusive equivalent to the plutonic granite rock. Due to their high content of silica and low iron and magnesium contents, rhyolites polymerize quickly and form highly viscous lavas. They can also occur as breccias or in volcanic necks and dikes. 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. Image:Different rocks at Panum Crater-750px.jpg
See also
de:Rhyolith et:Rüoliit fr:Rhyolite it:Riolite nl:Rhyoliet ja:流紋岩 pl:Ryolit sk:Ryolit sv:Ryolit