Feldspar-liquid equilibria in pantellerites; an experimental study

Abstract

Liquidus surfaces of two planes, one with 4.5 percent acmite and 4.5 percent sodium metasilicate and the other with 8.3 percent acmite and 8.3 percent sodium metasilicate in the system NaAlSi 3 O 8 -KAlSi 3 O 8 -SiO 2 -H 2 O (P H 2 O = 1000 kg/cm 2 ) were determined. The minima on the two liquidus surfaces, when projected on to the NaAlSi 3 O 8 - KAlSi 3 O 8 -SiO 2 plane, shift to the KAlSi 3 O 8 -SiO 2 join with the higher amounts of acmite and sodium metasilicate. The experiments support the hypothesis that pantellerites are derived by fractional crystallization from a parent liquid of trachytic composition.