Item talk:Q161268

Geoscience Ontology Description

Metamorphic rock characterized by 50 percent or more of combined chlorite, actinolite and epidote. Category for rocks generally named greenschist or greenstone. Rock classified as Greenschist is difficult to categorize in the CGI SimpleLithology scheme. This stems in part from the variation in usage and the general fuzzy definition of the term. The definition of greenschist is generally something along the lines of 'metamorphosed rock with a greenish colour, characterized by the presence of actinolite, chlorite and epidote, and containing a planar or linear fabric. The presence or absence of schistose fabric in rocks called 'greenschist' is problematic. The fabric present in many rocks called greenschist is too weak or variably developed to meet the definition of 'schist' per CGI SimpleLithology. Generally if the rock has achieved metamorphic grade such that the term 'gneiss' is applicable, it would not be called greenschist. Thus, 'greenschist' would correspond most closely to a chlorite + actinolite rich 'Foliated metamorphic rock', but if it actually meets the definition of 'Schist' it would be a chlorite + actinolite 'Schist'.