Formula: Mixture of hydrated iron oxides
Limonite is a general term for a mixture of fine-grained iron oxides, generally dominated by goethite, but also possibly containing hematite, lepidochrocite and other minerals. It forms from the weathering of other iron minerals, and may be precipitated by iron rich surface or ground water. It is a useful field term, and has been frequently used in the literature. The localities below have been described as containing limonite, but the sources do not give enough information to determine exactly which minerals are present.
FLORENCE COUNTY: Limonite occurs as a component of the oxidized ore formed on iron formation in a number of small iron mines in T.40N. R.18E., where it occurs with magnetite, grunerite, siderite and stilpnomelane. These mines include the Florence Mine (sec. 20-21), the Ernst Mine (SW SW sec. 27), the Badger Mine (SE SE sec. 34), the Buckeye Mine (SW SE sec. 33, and the Commonwealth Mine (NE SW sec. 34) (Dutton, 1971).
PIERCE COUNTY: Limonite occurs as beds, nodules and concretions with variable intermixtures of clay, sand and chert fragments on top of the Shakopee dolostone at several spots near Spring Valley. These were locally and briefly mined in the early 1900’s at the Gilman Deposit, west of Spring Valley (SW sec. 1 T.27N. R.16W.) and at the Cady Deposit (SW NE SW sec. 14 T.27N. R.15W.) (Allen, 1909, Van Hise and Leith, 1911, Rosenberg, 1991).
RICHLAND COUNTY: North (1913) reported limonite as large pseudomorphs after marcasite and pyrite crystal clusters found on the hilltops north of the Wisconsin River. The pseudomorphs occurred loose on the surface or embedded in clay. The pseudomorphs were sharp and preserved such details as twin boundaries. Clusters were up to 14.5 cm. long with individual crystals up to 4 cm. long.
— Botryoidal to stalactitic limonite was exposed in a shaft dug in the 1800’s in the NE sec. 3 T.12N. R.2E. (Heyl, et al., 1959).
SAUK COUNTY: Limonite was a component of the ore at the old iron mines near North Freedom. These include the Calhoon Mine (NW SW NW sec. 11 T.11N. R.6E), the Illinois Mine ( NE NW SE sec. 16 T.11N. R.6E.) and the Sauk Mine (NW SE SE sec. 10 T.11N. R.5E.) (Gietkowski, 1972).