autobrecciated lava

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autobrecciated lava A viscous, commonly silica-rich, lava flow with a congealed crust which has been broken up and fragmented by the continued movement of molten lava within the flow interior. Stressed and deformed by the movement, the crust may fracture in a brittle manner, producing angular, smooth-faced blocks able to weld together if they are hot enough but which otherwise become incorporated into the moving interior of the flow.