Formula: Ca(Fe,Mg,Mn)(CO3)2 Hexagonal
Ankerite is formed as a sedimentary precipitate, a groundwater and hydrothermal precipitate and by metamorphic recrystallization of iron-rich sedimentary rocks.
ASHLAND COUNTY: Ankerite is a component of the Ironwood iron formation in the Penokean Range of Northern Wisconsin. It may be found, among other sites, at the old Berkshire Mine in the SW SE Sec. 9 T.44N. R.2W. (Mudrey, 1970).
LAFAYETTE COUNTY: Ankerite is reported from the mines of the Upper Mississippi Valley zinc-lead district in the Calamine and Belmont Quadrangles (Klemic and West, 1964).
SAUK COUNTY: Ankerite is a component of the Freedom Formation in the old iron mines of Baraboo District. Here it is interbedded with chert and associated with calcite, dolomite, kaolin and siderite (Van Hise and Leith, 1911).
WOOD COUNTY: Cream colored rhombic microcrystals of ankerite occur in veins in red granite at the Fredrick Schill Quarry northeast of Vesper on the east side of Hwy. 186 (Buchholz, 1999).