Trachytes and their feldspar phenocrysts

Abstract

SummaryThe compositions of the groundmass and of the plagioclase and sanidine phenocrysts of a series of over- and under-saturated trachytes indicate that plagioclase will precipitate at some stage in the crystallization interval of all calcium-bearing potassic trachytes. Using this data obtained from natural salic liquids, a concept of crystallization within the system CaA2Si2O8-NaAlSiO4-KAlSiO4-SiO2 may be obtained.