BGS Rock Classification Scheme
Basalt, alkali - A type of basalt (TAS). In the Rock Classification Scheme, the root name basalt (TAS) may be divided into alkali basalt and subalkali basalt according to the state of silica saturation. If the analysis contains normative nepheline the rock may be called an alkali basalt. British Geological Survey Research Report RR/99/06, section 5.2.
| Code | BAALK |
|---|---|
| Description | Basalt, alkali - A type of basalt (TAS). In the Rock Classification Scheme, the root name basalt (TAS) may be divided into alkali basalt and subalkali basalt according to the state of silica saturation. If the analysis contains normative nepheline the rock may be called an alkali basalt. British Geological Survey Research Report RR/99/06, section 5.2. |
| Qualifiers | alkali |
| Definition | Fine-grained, av. <0.25mm normal crystalline extrusive/intrusive rock; CI >35 vol% >40 wt%; quartz <20% or feldspathoid <10% of QAPF, feldspar >65% plagioclase; TAS SiO2 45-52wt%, (97% have <48.5), Na2O+K2O 1.4-5wt%, (97%>2.2). CIPW norm with nepheline. |
| Linked data | http://data.bgs.ac.uk/id/EarthMaterialClass/RockName/BAALK |
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.