Prehnite-pumpellyite facies metamorphism in Precambrian basement rocks of S Sweden

Very small amounts of prehnite and pumpellyite have been found, often as lenses in biotite crystals, in otherwise quite ordinary quartzo-feldspathic gneisses and granitoid rocks forming common components of the Precambrian basement of S Sweden. It is concluded that both minerals belong to the same metamorphic paragenesis, which also includes quartz, K-feldspar, albite, epidote, colourless mica and chlorite. The presence of this paragenesis, in however slight amounts, signifies that the rocks bear the imprint of a phase of metamorphism belonging to the prehnite-pumpellyite facies.