The evolution of fleck gneiss and veined gneisses in the Västervik area is treated in view of ion activities and vapour fugacity. It seems probable that the latest recrystallization in the fleck gneiss depends on an increase inaK+causing a breakdown of porphyroblastic cordierite. The formation of some migmatites, on the other hand, may be due to a diastic rise in fH2O.