ABSTRACT
During a survey of northwestern Lake Victoria in the 1970s vivianite-rich nodules were encountered in the lake-bottom sediments of Kome Channel. The deposit is located at the lakeward end of the channel at water depths of 45–50 m. The nodules, which are spherical to discoidal in shape and range from 0.3 to 1.5 mm in diameter, form less than 5 percent of the silty clay sediments of the lake-bottom. The nodules were identified as vivianite (Fe3P2O8 · 8H2O) by X-ray diffractometry and their chemical composition was checked by atomic absorption and X-ray fluorescence methods. Thin section photomicrographs show the nodules to have the typical divergent fibrous structure of vivianite. The vivianite nodules appear to have been formed as a result of solubilization/redeposition in an ionic diffusion gradient process within the sediments.
