BGS Rock Classification Scheme
Lapilli-ash - 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 is less than 64 mm. Lapilli-tephra, lapilli-ash, and ash are separated according to the relative proportion of lapilli-grade (2 - 64 mm) and ash-grade (<2 mm) fragments: if between 25% and 75% of the fragments are lapilli the sediment is lapilli-ash. It is the unconsolidated equivalent of lapilli-tuff. British Geological Survey Research Report RR/99/06, section 4.2 and fig. 4.
| Code | LPASH |
|---|---|
| Description | Lapilli-ash - 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 is less than 64 mm. Lapilli-tephra, lapilli-ash, and ash are separated according to the relative proportion of lapilli-grade (2 - 64 mm) and ash-grade (<2 mm) fragments: if between 25% and 75% of the fragments are lapilli the sediment is lapilli-ash. It is the unconsolidated equivalent of lapilli-tuff. British Geological Survey Research Report RR/99/06, section 4.2 and fig. 4. |
| Qualifiers | No qualifiers currently exist. |
| Definition | Unlithified clastic material >10% debris formed by volcanic processes, >75vol% pyroclastic fragments, 25-75% lapilli 2-64mm; a pyroclastic sediment |
| Linked data | http://data.bgs.ac.uk/id/EarthMaterialClass/RockName/LPASH |
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.