BGS Rock Classification Scheme

Quartz-alkali-feldspar-trachyte - A type of trachytic-rock. In the Rock Classification Scheme, this name is used for a fine-grained crystalline igneous rock when the modal mineralogy is available, and the mineral mode plots in field 6* of the quartz - alkali feldspar - plagioclase - feldspathoid (QAPF) diagram. British Geological Survey Research Report RR/99/06, section 5.2 and figs. 17a, 19.

Code QAFTR
Description Quartz-alkali-feldspar-trachyte - A type of trachytic-rock. In the Rock Classification Scheme, this name is used for a fine-grained crystalline igneous rock when the modal mineralogy is available, and the mineral mode plots in field 6* of the quartz - alkali feldspar - plagioclase - feldspathoid (QAPF) diagram. British Geological Survey Research Report RR/99/06, section 5.2 and figs. 17a, 19.
Qualifiers No qualifiers currently exist.
Definition Fine-grained, av. <0.25mm normal crystalline extrusive/intrusive rock; quartz 5-20% of QAPF, feldspar >90% alkali feldspar
Linked data http://data.bgs.ac.uk/id/EarthMaterialClass/RockName/QAFTR

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.