Editing Breccia (section)

====Volcanic====
Volcanic pyroclastic rocks are formed by explosive eruption of lava and any rocks which are entrained within the eruptive column. This may include rocks plucked off the wall of the [[magma]] conduit, or physically picked up by the ensuing [[pyroclastic surge]].<ref name="fisher-schmincke-1984-89-92"/> Lavas, especially [[rhyolite]] and [[dacite]] flows, tend to form clastic volcanic rocks by a process known as ''autobrecciation''. This occurs when the thick, nearly solid lava breaks up into blocks and these blocks are then reincorporated into the lava flow again and mixed in with the remaining liquid magma. The resulting breccia is uniform in rock type and chemical composition.{{sfn|Allaby|2013|loc="Autobrecciated lava"}}

[[Caldera]] collapse leads to the formation of megabreccias, which are sometimes mistaken for outcrops of the caldera floor.{{sfn|Jackson|1997|loc="megabreccia"}} These are instead blocks of precaldera rock, often coming from the unstable oversteepened rim of the caldera.<ref name="goff-etal-2011"/> They are distinguished from ''mesobreccias'' whose clasts are less than a meter in size and which form layers in the caldera floor.{{sfn|Jackson|1997|loc="mesobreccia"}} Some clasts of caldera megabreccias can be over a kilometer in length.<ref name="goff-etal-2011"/>

Within the volcanic conduits of explosive volcanoes the volcanic breccia environment merges into the intrusive breccia environment. There the upwelling lava tends to solidify during quiescent intervals only to be shattered by ensuing eruptions. This produces an ''alloclastic'' volcanic breccia.{{sfn|Fisher|Schmincke|1984|p=89}}{{sfn|Allaby|2013|loc="Alloclast"}}