Studies on different‐sized polymetallic nodules from the Central Indian Ocean Basin reveal that chemical composition is largely related to the nodule diameter which show systematic decrease in Mn, Cu, and Ni content with increase in nodule size. S and I type nodules are more abundant than B, L, and V types. Nodules grouped according to their size have common morphological, mineralogical, and geochemical characteristics and all six groups have distinguishing properties. There is evidence which suggests that the smaller (M and I) nodules are diagenetic and the larger (S, B, L, and V) are hydrogenetic, exhibiting variations in todorokite abundance and in chemical composition. There is also substantial evidence that the nodules of high economic value (Cu + Ni + Co%) can be sorted out on the basis of simple morphological parameters.