The pyroxenes of the alkaline igneous complexes of eastern Uganda

Abstract

Summary Chemical analyses, some optical data, and specific gravities are given for 57 pyroxenes from the alkaline rocks of Uganda. They are members of the diopside-hedenbergite-acmite series, the more diopsidic varieties occurring in rocks of the ijolite series and the more acmitic in syenites and carbonatites. TiO 2 is highest in those pyroxenes from rocks that do not contain melanite. The refractive indices and specific gravities are controlled by the Fe 2+ /Mg ratio in the diopsidic pyroxenes and by the Fe 3+ content in the acmitic members. Paragenesis is discussed briefly.