Region 3: Mineral Resources of the Inland Basin

Because the Inland Basin is represented in a relatively small area in the Midwest and its rocks are not particularly rich in minerals, this region contains little in the way of exploitable mineral resources. The ancient seas of the Mississippian era, during which the rocks formed, provided some evaporite minerals, but they are commercially viable to mine in only a few places. Rock salt is mined in northeastern Ohio, beginning in Cuyahoga, Lake, Wayne, and Summit Counties, and sometimes going deep under Lake Erie. Farther south, Licking County also produces salt. The only other mineral resource produced in the Inland Basin of the Midwest is in Martin County, Indiana, where gypsum is mined (Figure 5.6).

Figure 5.6: Principal mineral-producing localities in the Inland Basin, associated primarily with Paleozoic deposition of sand, carbonate sediments, and occasionally evaporates in the warm shallow continental seas filling the Appalachian Basin (see Chapter 1: Geologic History and Chapter 2: Rocks).

Figure 5.6: Principal mineral-producing localities in the Inland Basin, associated primarily with Paleozoic deposition of sand, carbonate sediments, and occasionally evaporates in the warm shallow continental seas filling the Appalachian Basin (see Chapter 1: Geologic History and Chapter 2: Rocks).

Mississippian rocks in Illinois host Illinois’ state mineral: fluorite (CaF2). During the Jurassic, more than 100 million years after the limestone bedrock was laid down, geothermally heated water full of dissolved chemicals was forced through existing cracks. Fluorite crystals precipitated onto the walls of these cracks, forming Illinois’ famous deposits. Fluorite is mined primarily to be converted into hydrogen fluoride (HF), a chemical with a wide range of applications. While colorful and translucent, fluorite is too soft to see extensive use as a semiprecious gemstone.