BGS Rock Classification Scheme
Anorthosite - A type of anorthositic-rock. In the Rock Classification Scheme, it is a coarse-grained crystalline igneous rock whose mineral mode plots in field 10 of the quartz - alkali feldspar - plagioclase - feldspathoid (QAPF) diagram. Diorite, gabbro and anorthosite are separated according to the average composition of their plagioclase and the proportion of mafic minerals (M): if M is less than 10% the rock is anorthosite. British Geological Survey Research Report RR/99/06, section 5.1 and figs. 9, 11, 12.
| Code | ANO |
|---|---|
| Description | Anorthosite - A type of anorthositic-rock. In the Rock Classification Scheme, it is a coarse-grained crystalline igneous rock whose mineral mode plots in field 10 of the quartz - alkali feldspar - plagioclase - feldspathoid (QAPF) diagram. Diorite, gabbro and anorthosite are separated according to the average composition of their plagioclase and the proportion of mafic minerals (M): if M is less than 10% the rock is anorthosite. British Geological Survey Research Report RR/99/06, section 5.1 and figs. 9, 11, 12. |
| Qualifiers | No qualifiers currently exist. |
| Definition | Coarse-grained, av. between 2-16mm normal crystalline intrusive rock; CI M<10%; quartz <5% of QAPF, feldspar dominant & >90% plagioclase, +/- mica/pyroxene/amphibole/olivine |
| Linked data | http://data.bgs.ac.uk/id/EarthMaterialClass/RockName/ANO |
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.