Metamorphism and Mineral Identification by Gamma Ray Methods

Abstract

IT is usually from the investigations of mineralogy that an estimation of the grade of metamorphism is made, since the appearance of some minerals and disappearance of others—or the change of composition in a solid solution series—is often symptomatic of the intensity of metamorphism. “For example, biotite is a common mineral of metamorphic rocks; however, it does not occur in very low grade rocks, its composition then being represented by mixtures of muscovite and chlorite. Minerals of the epidote group are characteristic of low grade rocks. At higher grades of metamorphism these minerals are largely converted to anorthite which enters into plagioclase. In lowest grade rocks the plagioclase is nearly pure albite and it increases in calcium content as the grade of metamorphism increases”¹.