BGS Rock Classification Scheme
Eclogite - A type of metamorphic rock with unknown protolith based on modal composition. In the Rock Classification Scheme, it is defined as a rock composed of more than 70% garnet and jadeitic clinopyroxene (omphacite). Eclogites do not contain plagioclase. They may contain other anhydrous minerals such as quartz, kyanite, orthopyroxene and rutile, together forming no more than 30% of the rock. Eclogites result from metamorphism of basaltic or gabbroic igneous rocks under very low P.H20 producing anhydrous mineral assemblages. They define a unique eclogite facies metamorphism, typically reflecting very high pressures although their local occurrence within amphibolite facies rocks suggests they may be formed over a significant range of pressure. British Geological Survey Research Report RR/99/02, section 6.2.
| Code | ECLOG |
|---|---|
| Description | Eclogite - A type of metamorphic rock with unknown protolith based on modal composition. In the Rock Classification Scheme, it is defined as a rock composed of more than 70% garnet and jadeitic clinopyroxene (omphacite). Eclogites do not contain plagioclase. They may contain other anhydrous minerals such as quartz, kyanite, orthopyroxene and rutile, together forming no more than 30% of the rock. Eclogites result from metamorphism of basaltic or gabbroic igneous rocks under very low P.H20 producing anhydrous mineral assemblages. They define a unique eclogite facies metamorphism, typically reflecting very high pressures although their local occurrence within amphibolite facies rocks suggests they may be formed over a significant range of pressure. British Geological Survey Research Report RR/99/02, section 6.2. |
| Qualifiers | No qualifiers currently exist. |
| Definition | Red & green crystalloblastic metamorphic rock (protolith undefined); >70% Mg-rich garnet & jadeitic clinopyroxene (omphacite), <30% anhydrous minerals, quartz/kyanite/orthopyroxene/rutile, no plagioclase |
| Linked data | http://data.bgs.ac.uk/id/EarthMaterialClass/RockName/ECLOG |
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.