BGS Rock Classification Scheme
Migmatitic rock - A megascopically composite rock consisting of two or more petrographically different parts, one of which is the country rock in a more or less metamorphic stage, the other is of pegmatitic, aplitic, granitic or generally plutonic appearance. Migmatitic rocks contain leucosomes, mesosomes and melanosomes. Leucosomes are defined as being of variable scale and comprising the leucocratic, quartzofeldspathic or feldspathic fraction of the rock. Mesosome is the part of the rock having the appearance of an ordinary metamorphic rock, that is schist or gneiss, and is generally of intermediate colour between the leucosome and melanosome. The melanosome is the melanocratic, mafic-rich fraction of the migmatitic rock, complementary to the leucosome. The neosome comprises both the leucosome and the melanosome. Most migmatitic rocks occur in middle to upper amphibolite facies and granulite facies terrains. They may be produced by partial melting, injection or solid state diffusion processes. British Geological Survey Research Report RR/99/02, section 9.3.
| Code | MIGM |
|---|---|
| Description | Migmatitic rock - A megascopically composite rock consisting of two or more petrographically different parts, one of which is the country rock in a more or less metamorphic stage, the other is of pegmatitic, aplitic, granitic or generally plutonic appearance. Migmatitic rocks contain leucosomes, mesosomes and melanosomes. Leucosomes are defined as being of variable scale and comprising the leucocratic, quartzofeldspathic or feldspathic fraction of the rock. Mesosome is the part of the rock having the appearance of an ordinary metamorphic rock, that is schist or gneiss, and is generally of intermediate colour between the leucosome and melanosome. The melanosome is the melanocratic, mafic-rich fraction of the migmatitic rock, complementary to the leucosome. The neosome comprises both the leucosome and the melanosome. Most migmatitic rocks occur in middle to upper amphibolite facies and granulite facies terrains. They may be produced by partial melting, injection or solid state diffusion processes. British Geological Survey Research Report RR/99/02, section 9.3. |
| Qualifiers | No qualifiers currently exist. |
| Definition | Megascopically composite rock (protolith undefined) of two or more petrographically different layers/parts, including mesosome or palaeosome (apparent metamorphic country rock), leucosome (leucocratic, quartz/feldspar), melanosome (melanocratic) |
| Linked data | http://data.bgs.ac.uk/id/EarthMaterialClass/RockName/MIGM |
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.