Constraints on some phase relations in the system CaO-MnO-MgO-K2O-Al2O3-SiO2-H2O inferred from mineral data from Buritirama, Brazil - Schultz-Güttler, Rainer Aloys; Peters, Tj.; Valarelli, José Vicente (Schweizerische mineralogische und petrographische mitteilungen, 1986)