This study was carried out to characterize clay minerals and elemental compositions between Fe/Mn nodules and their surrounding soils in Okinawa and Kume Islands, Japan, and find out reliable sources of their origin. Mineralogical composition of Fe/Mn nodules and surrounding soils was analyzed by the successive selective dissolution procedure (SSDP) combined with XRD technique. Their total elemental composition was carried out using the acid digestion system. Total elemental analysis of extracts were performed by inductively coupled plasma atomic emission spectrometry (ICP-AES). Results explained that Mn minerals of lithiophorite (Lp) and birnessite (Bs) were concentrated only in nodules, while Fe and Al oxides and layer silicate minerals were contained in nodules as well as soils. Secondary mineral of smectite was observed in only one nodule sample and its corresponding soil sample. Concentrations of Ca, P, Mn, Ba, V, Co, Ni, Zn, Cu and Fe in many samples were higher in the nodules than in the surrounding soils, while Ba concentration was unexpectedly higher in nodule samples. Concentrations of Mg, Al, Cr and K were higher in the surrounding soils. Although some nodules had higher concentration of Sr and Na than the surrounding soils, there was no discernible trend towards higher concentration in the nodules. The results suggested that there was a tendency for Mn nodules to concentrate most of Mn minerals and trace elements together with Mn and Ba. Moreover, Fe/Mn nodules in Okinawa and Kume Islands have a close relationship with sea floor activities and "Shimajiri mahji" in the surrounding environment of nodules which could be formulated after upheaval of marine sediments.
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