Manganese micronodule distribution, size, internal features and chemical composition as well as the composition of associated sediments have been determined in eight sediment cores taken from the siliceous ooze area of the Central Indian Basin (CIB). Micronodule abundance expressed as the number of micronodules per gram of dried sediment (0-375 n/g) and size (75-1000 mu m) show considerable variation with core depth and are directly related to each other. The morphology, surface texture and internal features of the micronodules are similar to those of surface macronodules from the same basin. Micronodules have high contents of Mn (35.02%), Cu (1.6%), Ni (1.4%) and Zn (0.37%), high Mn/Fe ratios (5-101) and very low Fe (1.8%), Al sub(2)O sub(3) (1.3%), TiO sub(2) (0.30%), SiO sub(2) (2.7%) and rare earth element (Sigma 522 ppm) contents compared to surface and buried macronodules. Micronodule abundance, size and composition depend on the redox characteristics of the sedimentary environment and can therefore be used as indicators of the sedimentary environment