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 breccias.


The clastic texture of volcanic breccia is often termed pyroclastic or volcaniclastic.


Volcanic breccia



Volcanic breccia from Mexico with clasts of jelly opal (= dark orangish-red pieces).



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