Volcanic breccias are clastic-textured, extrusive igneous rocks.
They generally appear as multicolored masses of jumbled angular grains.
Volcanic breccias have violent origins. They form from explosive volcanic
eruptions (cf. effusive eruptions - lava flow eruptions). Volcanoes
having felsic or intermediate chemistries typically erupt violently.
Powerful volcanic ash eruptions result in deposits with mixes of large &
small grains. Upon burial & lithification, these deposits become volcanic
The clastic texture of volcanic breccia is often
termed pyroclastic or volcaniclastic.
Volcanic breccia from Mexico with clasts of jelly opal (= dark