BGS Rock Classification Scheme

Dacite (TAS) - A type of dacitic-rock, classified using the total alkali silica (TAS) classification. The TAS classification may be used if the mineral mode of a normal fine-grained crystalline rock cannot be determined due either to the presence of glass or to the fine-grained nature of the rock. The definition of dacite (TAS) is as shown in British Geological Survey Research Report RR/99/06, section 5.2 and figs. 17b, 20.

Code DAT
Description Dacite (TAS) - A type of dacitic-rock, classified using the total alkali silica (TAS) classification. The TAS classification may be used if the mineral mode of a normal fine-grained crystalline rock cannot be determined due either to the presence of glass or to the fine-grained nature of the rock. The definition of dacite (TAS) is as shown in British Geological Survey Research Report RR/99/06, section 5.2 and figs. 17b, 20.
Qualifiers No qualifiers currently exist.
Definition Fine-grained, av.<0.25mm normal crystalline extrusive/intrusive rock; quartz 20-60% of QAPF, feldspar >65% plagioclase, TAS SiO2 63-77wt%, Na2O+K2O <8wt%
Linked data http://data.bgs.ac.uk/id/EarthMaterialClass/RockName/DAT

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.