Fragmental/volcaniclastic igneous rock and sediment

Clastic rocks and sediments with mostly volcanic-derived clasts, containing at least 25% by volume of pyroclastic fragments. Volcaniclastic rocks and sediments were defined by Fisher (1961) and redefined in Fisher and Smith (1991) to include any natural materials composed in part or entirely of volcanic fragments, formed by any particle-forming mechanism (e.g. pyroclastic, hydroclastic, epiclastic, autoclastic, transported by any mechanism, deposited in any physiogeographic environment or mixed with any other volcaniclastic type or with any nonvolcanic fragment types in any proportion’. The term volcanogenic is used by other authors and has a broadly similar meaning. To be classified as ‘volcaniclastic’, Gillespie and Styles (1999) suggest that a volcaniclastic rock or sediment must have more than 10% by volume of volcanic debris. Volcanic debris is defined as fragments originating by volcanic processes, either primary or after redeposition. Many volcaniclastic rocks and sediments can also be classified within the scheme for ‘Sedimentary rocks and sediments’.