Oconto County contains very diverse bedrock. The southeastern portion consists of a section of Cambrian and Ordovician sedimentary rocks dipping monoclinally gently to the east, off the Wisconsin Arch. The Cambrian rocks are mostly sandstones, while the Ordovician rocks are carbonate dominated. The northwestern portion contains assorted Proterozoic metamorphic and igneous rocks. Some are granites, meta-volcanic and meta-sedimentary rocks deformed during the 1.80 – 1.85 billion year old Penokean Orogeny. The Penokean orogeny was a continent-continent collision, with the rocks seen in the county being ocean crust and island arc materials caught up in the collision. Excellent examples can be seen in outcrop in the Mountain area. A younger Proterozoic quartzite outcrops at McCaslin Mountain, and can yield nice quartz crystals. Much of the Precambrian in the County is part of the anorogenic 1.4 billion year old Wolf River Batholith. Thick glacial drift, lakes and forests make outcrops scarce, but the drift can yield interesting glacially transported rocks and minerals.
Mineral ListMineral list contains entries from the region specified including sub-localities
28 entries listed. 19 valid minerals.
Localities in this Region
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Dott, Robert H. & J.W. Attig, (2004) Roadside Geology of Wisconsin, Mountain Press, 345 p.