Experimental investigation of silicate systems containing two volatile components; Part 2, The effects of NH_3 and HF, in addition to H_2O on the melting temperatures of albite and granite

Abstract

Addition of NH_3 to water-albite and water-granite mixtures at constant pressure raises the melting temperatures of albite and granite, whereas addition of HF to these mixtures causes marked lowering of melting temperatures. Results obtained at 2,750 bars pressure for charges containing 1:1 weight ratio of silicate to total volatiles are presented as perspective TX projections from within isobaric prisms onto the volatile faces of the prisms. In the presence of H_2O alone at 2,750 bars pressure, albite melts between 795°C. and 810°C., and granite begins to melt at 670°C.; in the presence of 8.2 weight percent N_ 3 solution, the melting interval of albite is 805°C. to 825°C., and granite begins to melt at 690°C.; in the presence of 8 weight percent HF solution, the melting interval of albite is 610°C. to 685°C., and granite begins to melt at 595°C. No chemical reaction was detected in systems containing NH_3, but considerable reaction occurs with HF. With increasing HF concentration in the system NaAlSi_3O_8-H_2O-HF, quartz becomes a stable phase and the system is no longer ternary. In the presence of HF solutions, albite crystals grow much larger than in the presence of H_2O alone.