Summary: The occurrence of coexisting paragonite (containing 0·70 % CaO) and muscovite (containing 0·16 % CaO) in a staurolite-grade paragonite-muscovite-hornblende-garnet-biotite schist from Sulitjelma enables an estimate to be made of the temperature of recrystallization, using an extension, based on crystal chemistry considerations and available analyses of muscovites and paragonites from metamorphic rocks, of the experimentally determined solvus in the K-Na white mica system into the Ca-K-Na system. This temperature of recrystallization is approximately 550–70 °C and is consistent with the experimental data on the coexistence of staurolite and quartz in the system Fe-A1-Si-O-H (Richardson, 1968).