Studies on Manganese-Bearing Silicate Minerals from Metamorphosed Manganese Formations of India. II. Blanfordite, Manganoan Diopside, and Brown Manganiferous Pyroxene

Supriya Roy
Department of Geological Sciences, Jadavpur University, Calcutta 32, India

Summary: Three members of the pyroxene group, blanfordite, manganoan diopside, and brown manganiferous pyroxene, form important constituents of the manganese silicate rocks (gondite) of the metamorphosed manganese formations of India. The chemical composition of blanfordite is variable within the diopside-acmite series, that of the manganoan diopside corresponds to the diopside end of this series, and the brown manganiferous pyroxenes are related to aegirine-augites. The majority of the blanfordites studied have a composition within the aegirine-augite field, so that compositionally most of the blanfordites and brown manganiferous pyroxenes are similar in spite of the difference in their pleochroic schemes; The chemical composition of blanfordite varies: in association with calc-magnesian metasediments it has a high percentage of diopside, whereas in gondites and pegmatites its composition approaches more towards the acmite end. The blanfordites are often associated with manganiferous amphiboles such as juddite (manganoan magnesioriebeckite) and winchite (richterite-tremolite with blue and pink pleochroism) but never with tirodite. The brown manganiferous pyroxenes, on the other hand, are associated intimately with tirodite (richterite-tremolite with pleochroism in shades of yellow) but never with winchite and juddite.

Mineralogical Magazine; March 1971 v. 38; no. 293; p. 32-42; DOI: 10.1180/minmag.1971.038.293.04
© 1971, The Mineralogical Society
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