BGS Rock Classification Scheme

Pyroclastic-breccia - A type of pyroclastic-rock. In the Rock Classification Scheme, it is a pyroclastic-rock in which more than 75% of the pyroclastic fragments exceed 64 mm in size. Agglomerate and pyroclastic-breccia are separated according to the relative proportion of blocks (angular fragments exceeding 64 mm) and bombs (rounded fragments exceeding 64 mm): if blocks dominate over bombs the rock is pyroclastic-breccia. It is the consolidated equivalent of block-tephra or bomb-block-tephra. British Geological Survey Research Report RR/99/06, section 4.2 and fig. 4.

Code PYRBRC
Description Pyroclastic-breccia - A type of pyroclastic-rock. In the Rock Classification Scheme, it is a pyroclastic-rock in which more than 75% of the pyroclastic fragments exceed 64 mm in size. Agglomerate and pyroclastic-breccia are separated according to the relative proportion of blocks (angular fragments exceeding 64 mm) and bombs (rounded fragments exceeding 64 mm): if blocks dominate over bombs the rock is pyroclastic-breccia. It is the consolidated equivalent of block-tephra or bomb-block-tephra. British Geological Survey Research Report RR/99/06, section 4.2 and fig. 4.
Qualifiers No qualifiers currently exist.
Definition Unimodal well sorted lithic clastic material >10% debris formed by volcanic processes >75vol% pyroclastic fragments, >75% blocks (angular) >64mm composition; lithification not defined
Linked data http://data.bgs.ac.uk/id/EarthMaterialClass/RockName/PYRBRC

CAVEAT

"Thumbnail" definitions attached to some of the table entries are an interim attempt to provide simple short descriptions of the "unqualified" rock types presented within the BGS Rock Classification Scheme. Every effort has been made to ensure accuracy and consistency but minor contradictions or omissions might be present. The BGS welcomes any feedback pointing out such minor imperfections and/or providing constructive comment and suggestions for improvement of the definitions. In the first instance such feedback should be directed to Dr Tim McCormick.