Chemical compositions of the coexisting amphiboles, clinopyroxenes and pyroxenoids in manganese ore deposits from Japan and India

The chemical compositions of the coexisting manganoan amphiboles (mainly the Na-Ca- and alkali-amphibole series) manganoan clinopyroxenes (the aegirine-diopside-johannsenite series) and pyroxenoids were analyzed by means of an EPMA method. As the number of diopside molecule in manganoan clinopyroxenes coexisting with pyroxenoids increases, the num- ber of johannsenite molecule in them also tends to increase. Although the oxidation conditions during the ore formation do not have much effect on the Mn content of clinopyroxenes, they strongly affect the ferrous iron content in pyroxenoids. The calcium content in the M2 site of clinopyroxene is larger than that in the M4 site of amphibole. The M1 site of clinopyroxene can accommodate much more Mn ions than the M1, M2 and M3 sites of the coexisting amphibole. On the other hand, Mg ions can occupy much more easily in the M1, M2 and M3 sites of amphibole than the M1 site of clinopyroxene. This study shows that among the coexisting amphiboles, manganoan clinopyroxenes and pyroxenoids, almost all the rhodonites and pyroxmangites can accommodate the smallest amounts of Mg, Ca and Fe2+ in their structures