A chemical and mineralogical study of the pyroxenes from some African alkaline complexes

Abstract

The thesis describes a group of pyroxenes belonging to a diopside-hedenbergite-acmite series, which come from the alkaline rocks of East and Southern Africa. The pyroxenes have been analysed chemically; and two refractive indices and the specific gravity have been determined. Values obtained for the A' lambda c angle have been included in the study. The compositions of the pyroxenes depend on the area from which they come and also on the rock types in which they occur; but all the pyroxenes from the African alkaline rocks fall within a well-defined band of composition. It has been found that differences in content of the minor constituents depend both on composition and the area from which they come. The Fe+2/Mg ratio in the more diopsidic pyroxenes, and the Fe+3 content in those nearer acmite control the physical properties.