Phase-equilibrium studies in the system NaAlSiO₄ (nepheline)–KAlSiO₄ (kalsilite)–SiO₂-H₂O

Abstract

Summary Phase-equilibrium relations have been determined at 1000 kg/cm 2 water pressure for compositions within the system NaAlSi 3 O 8 -KalSi 3 O 8 -NaAlSiO 4 -KAlSiO 4 in the area adjacent to the temperature minimum. The composition and temperature of the minimum are Ne 50 Ks 19 Qz 31 and 750° ± 7° C respectively. The compositions of 102 plutonic rocks and 122 extrusive rocks, from Washington's tables, that carry 80% or more of normative Ab + Or + Ne have been plotted; the areas of high density show a marked similarity to the positions of the low-temperature regions of the synthetic system and suggest that many undersaturated rocks are derived by fractional crystallization from a trachytic magma.