Extrusive rock
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Extrusive rock refers to the mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out onto the surface as lava or explodes violently into the atmosphere to fall back
A volcanic rock from Italy with a relatively large six-sided phenocryst (diameter about 1 mm) surrounded by a fine-grained groundmass, as seen in thin section under a petrographic microscope
Rhyolite
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Rhyolite is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained in texture, but may be porphyritic, containing larger mineral crystals in an otherwise fine-grained groundmas
Extrusive rock
…may cool with large or small vesicles (bubble-shaped cavities) such as in pumice, scoria, or vesicular basalt. Other examples of extrusive rocks are rhyolite and andesite. The texture of extrusive rocks is characterized by fine-grained crystals indistinguishable to the human eye, described as aphantic…
Loebejuener porphyr poliert
QAPF diagram with rhyolite field highlighted
Rhyolite beach on Lake Superior
Aphanitic rhyolite