Keywords: 
• East Pacific ocean /
• polymetallic nodule /
• todorokite

Abstract: The reasearch area of polymetallic nodules is located between Clariion Fracture and Clipperton Fracture, where polymetallic nodule resources are most abudant. The authors have investigated in this area for many times, and have obtainted a lot of materials and samples. The todorokite existing in nodules as the most useful manganese mineral is in a close relationship with many metallic elements. To analyse the distribution of todorokite and its relative factors is meaningful for probing into the nodules' formation mechanism. For its poor crystallinity and tiny grain, to identify todorokite is very difficult. By all sorts of analysis methods, the authors tried to prove the existence of todorokite, to study its mineral features and the relationships among its main metallic elements, and then to provide scientific basis for ore dressing and metallurgy.The study result reveals: 1) There exists todorokite in marine nodules that act as the most important manganese mineral phase. Its optic characteristic, x-ray diffraction analysis data and cell parameters are close to those of manganese. Infrared analysis also show typical todorokite spectrums. Electron microscope analysis suggests that the manganese in crystallizing band is mainly todorokite and its Mn, Cu, Ni contents are higher than those in amorphous band. 2)The todorokite content in coarse-surface nodules in deep-sea plain is often richer than that in smooth-surface nodules found in seamount. Todorokite is abundant when the substratum structure is laninar, compact, or taxitic.The paper suggests that the factors causing todorokite distributed in such a way are mainly related with the local geochemical environment. The reduction-oxidation potential value is a direct factor which affects the formation of todorokite. The low reduction-oxidation potential is helpful. The isomorph of some metal elements such as Mn, Ni, Cu, Zn, is positively related to manganese. The slight reduction-oxidation environment and peneliquid substratum are an ideal horizon which is favourable not only to the migration of the Mn ion, but also to the accumulation of Mn. The metal elements engendered by dissolution of the living beings can promote the formation of manganese noudules. Recrystalization also changes a part of amorphous body into todorokite.Based on the study of the nodules' mineralogy, it is suggested that the best mineral resource for ore dressing and metallurgy is rough-surface nodules and semi-rough-surface nodules.