Abstract
The bottom sediments sampled from Lake Biwa, in the southwest of Japan, contain sand-size pellet grains which consist of diatom bodies, detrital quartz and small feldspar fragments with cementing material enclosing them. Vivianite grows in the fecal pellets. Vivianite content is loosely related to water depth as a whole, and there is a large fluctuation in it. The authigenic vivianite has a much higher manganese content than any other published vivianite composition, and Mn/(Mn+Fe) ratio in the vivianite reaches nearly 0.5 at its maximum. Manganese content in the vivianite increases with the water depth of sample localities.
