Abstract
The study was carried out in order to characterize and identify oxide and layer silicate minerals present in terrestrial Fe/Mn nodules and their surrounding soils occurring in Okinawa, Japan, with respect to the genesis of these materials. Ferrous-manganese nodules were found in Okinawan soils derived from parent material of Ryukyus limestone. Mineral composition was characterized using the successive selective dissolution procedure (SSDP) by treatments of sodium hydroxide (NaOH), hydroxylamine hydrochloride (HAHC) at 25°C and 60°C and dithionite-citrate-bicarbonate (DCB) in combination with X-ray diffraction and SEM techniques. Detailed micro-morphology of manganese minerals, observed in most of the nodules, showed pseudo-hexagonal platelets for high crystalline lithiophorite while poor crystalline birnessite exhibited globular shape like structure. Goethite and gibbsite as iron and aluminum oxide minerals respectively, were detected in all samples. Lepidocrocite, an iron oxide mineral found in one of the samples, was dissolved by NaOH treatment. Major layer silicate minerals detected in all samples were kaolinite (Kt) and illite (It). In addition, intergraded mineral vermiculite-chlorite (Vt-Ch) was observed in most of the samples. All nodule samples and their surrounding soils used in this work had almost same composition for layer silicate minerals. According to the similarity on mineralogy of layer silicate minerals in both nodule and its correlated surrounding soil, it is suggested that Fe/Mn nodules might be developed in the surrounding soils.
