Studies in the Feldspar Group

Abstract

Soda feldspar is believed to crystallize in three different phases having definite relationships with the three crystal phases of potash feldspar; the relations between composition and optic properties in these three series are shown in three diagrams, and those between adularia and celsian in a fourth. Finally, another diagram shows the classifications of plagioclase proposed by various authorities, together with a modification suggested by the writer.