Comparison of internal features and microchemistry of ferromanganese crusts from the Central Indian Basin

SEM/probe analyses of two ferromanganese crusts from the Central Indian Basin, formed on basalt substrate, reveal botryoids and cusps. The botryoids composed of δ-MnO₂, are enriched in Co, and the cusps and laminations with todorokite are enriched in Ni and Cu. Microstructural and elemental variations, from the ferromanganese crust outer surface to the basalt substrate, probably reflect changes in the accretion or in the source of metals. The major source of the crust metals is the seawater, as indicated by the Mn/Fe ratio of unity and by the microstructures.