Characteristics of manganese nodules from sub-equatorial Indian Ocean between 4 °30’ S and 10 °30’ S latitudes

17-21Manganese nodules from study area show rough surfaced nodules, occurring in SW part and abundant in greater water depths. They contain todorokite as the dominant mineral phase, have thicker oxide layer and are rich in Mn/Fe and Cu/Ni. In contrast smooth textured nodules, occurring in the NE part, show decrease in abundances with water depth, contain both todorokite and δ -MnO2, record thin oxide layer and are poor in Mn/Fe and Cu/Ni. Possible diagenetic and hydrogenous influence on the formation and metal enrichment of rough and smooth textured nodules respectively have been discussed