VHP Photo Glossary: Andesite
Close view of andesite lava flow Brokeoff Volcano, California
Andesite is a gray to black volcanic rock with between about
52 and 63 weight percent silica (SiO2
contain crystals composed primarily of plagioclase feldspar and
one or more of the minerals pyroxene (clinopyroxene and
orthopyroxene) and lesser amounts of hornblende. At the lower
end of the silica range, andesite lava may also contain olivine.
Andesite magma commonly erupts from stratovolcanoes as thick lava
flows, some reaching several km in length. Andesite magma can also
generate strong explosive eruptions to form pyroclastic flows
and surges and enormous eruption columns. Andesites erupt at
temperatures between 900 and 1100° C.
More about volcanic and plutonic rocks.
Did you know?
The word andesite is derived from the Andes Mountains, located along
the western edge of South America, where andesite rock is common.
Andesite was the main rock type erupted during the great Krakatau
eruption of 1883.