Experimental investigation of silicate systems containing two volatile components; Part 2, The effects of NH 3 and HF, in addition to H 2 O on the melting temperatures of albite and granite
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 2 O alone at 2,750 bars pressure, albite melts between 795 degrees C. and 810 degrees C., and granite begins to melt at 670 degrees C.; in the presence of 8.2 weight percent NH 3 solution, the melting interval of albite is 805 degrees C. to 825 degrees C., and granite begins to melt at 690 degrees C.; in the presence of 8 weight percent HF solution, the melting interval of albite is 610 degrees C. to 685 degrees C., and granite begins to melt at 595 degrees 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 3 O 8 -H 2 O-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 2 O alone.