BGS Rock Classification Scheme

Block-bomb-tephra - A type of pyroclastic-sediment. In the Rock Classification Scheme, it is a pyroclastic-sediment in which the average size of more than 75% of the pyroclastic fragments exceeds 64 mm. Block-tephra, bomb-block-tephra, block-bomb-tephra, and bomb-tephra are separated according to the relative proportion of blocks (angular fragments exceeding 64 mm) and bombs (rounded fragments exceeding 64 mm): if between 25% and 50% of all pyroclastic fragments bigger than 64 mm are blocks the sediment is block-bomb-tephra. It is the unconsolidated equivalent of agglomerate. British Geological Survey Research Report RR/99/06, section 4.2 and fig. 4.

Code BLBTPH
Description Block-bomb-tephra - A type of pyroclastic-sediment. In the Rock Classification Scheme, it is a pyroclastic-sediment in which the average size of more than 75% of the pyroclastic fragments exceeds 64 mm. Block-tephra, bomb-block-tephra, block-bomb-tephra, and bomb-tephra are separated according to the relative proportion of blocks (angular fragments exceeding 64 mm) and bombs (rounded fragments exceeding 64 mm): if between 25% and 50% of all pyroclastic fragments bigger than 64 mm are blocks the sediment is block-bomb-tephra. It is the unconsolidated equivalent of agglomerate. British Geological Survey Research Report RR/99/06, section 4.2 and fig. 4.
Qualifiers No qualifiers currently exist.
Definition Unimodal, well sorted, unlithified clastic material >10% debris formed by volcanic processes, >75% pyroclastic fragments, >75vol% >64mm blocks<bombs (rounded), 50-75% bombs; a pyroclastic sediment
Linked data http://data.bgs.ac.uk/id/EarthMaterialClass/RockName/BLBTPH

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.