Abstract
During alkali metasomatism of the country-rock associated with ijolite-carbonatite complexes the development of sodic amphibole and/or pyroxene is characteristic. In this paper, some new chemical analyses of these minerals, together with published analyses from fenites of Kenya, Uganda and Tanzania, include those of co-existing pairs of amphibole and pyroxene. The common amphiboles of the fenites are magnesioarfvedsonites with 100 Mg: Mg+Fe+Mn ranging from 67 to 36. They co-exist with aegirines having 0.75 to 0.89 ions Fe+3. Most of these minerals are poor in Ca; co-existing pairs tend to show corresponding increases in Ca and in Fe+2. In the syenitic fenites of Tororo and Budeda, considered to have formed at higher temperatures, the stable mineral is aegirine-augite. New analyses of richterite, magnesioarfvedsonite and aegirine from carbonate-rich rocks are also presented, and the relation between fenites and carbonatites is discussed.
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Sutherland, D.S. Sodic amphiboles and pyroxenes from fenites in East Africa. Contr. Mineral. and Petrol. 24, 114–135 (1969). https://doi.org/10.1007/BF00376886
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DOI: https://doi.org/10.1007/BF00376886