These dominate the outcrops in a band reaching from the lower St. Croix River to the west, south along the Mississippi to the Illinois border, west across southern quarter of the state, and continuing north along the entire Lake Michigan shoreline. The dolomite is believed to be a secondary replacement of original limestone while the sediment was undergoing lithification. Dolomite also forms as later drusy crystals lining vugs in dolostones. Dolomite may form as a hydrothermal replacement mineral and, as such, is especially abundant as a gangue minral in the ore deposits of the Upper Mississippi Valley zinc-lead district in southwestern Wisconsin.
Ferroan dolomite appears in several of the state's Precambrian iron formations.
Finally, dolomite locally occurs in the state in marbles. Only some of the most typical or important localities for dolomite are mentioned below. Dolomite is a common rock-forming mineral in the Bad River dolostone found throughout the Penokee Range area. It is associated with calcite, tremolite, chlorite, quartz, sericite, pyrite and magnetite. 15 T.44N R.5W, and at Penokee Gap in the SE NW sec.