The Potash-Soda Feldspars

Abstract

Both potash- and soda-feldspar end-members are believed to be trimorphous. The Millard-Michel Lévy theory of submicroscopic twinning and the theory of polymorphism are considered to be independent. The former is not competent to explain the results of thermal analysis or the cusps in the thermal expansion curves. The consequences of trimorphism, including perthites of two generations, are discussed.