Description: Ferromanganese nodules similar to those found on the deep sea floor occur in several lakes in Wisconsin, including Lake Michigan. They consist of a mixture of manganese oxides, iron oxides, sand and clay. They are small and not of economic value, but are likely more widespread than reported. (Emanual, 1978, suggests a possible economic use as fume scrubbers in autos and factories.)
The nodules form by precipitation from lake and ground water in areas where the influx of other sediment is low. The Lake Michigan nodules, with up to 22% manganese, were first found in five localities within Green Bay and another in Lake Michigan off the coast of Kewaunee County (Rossman and Callender, 1968). Rossman et. al (1972) noted that the nodules were 0.5 to 5 mm in diameter and contain layers of todorokite, birnessite and “psilomelane” interspersed with layers of iron oxides. The nodules generally form concentrically around a nucleus of rock, clay, quartz, or feldspar.
ONEIDA COUNTY: Bowser et al (1970) described manganiferous crusts and nodules of birnessite and goethite found in Tomahawk, Whitefish, and Green Lakes in Oneida County.