Figure 9—Active coal mines are scattered around the margin of the basin where the coals are at relatively shallow depths.
KEY SHIPPING MINES Underground Strip Slope LOCAL MINES OVER 25,000 TONS Underground Strip
Coal
Illinois ranks fourth in the nation among states that produce bituminous coal, the type of coal most widely mined in the United States. Coal is used by many manufacturing industries, by public utilities companies that burn coal to generate electricity, and by individuals for heating homes.
All Illinois coal deposits are found in the Pennsylvanian System. Of the many coals, only a few are thick enough to be mined profitably. The coal is of bituminous rank, but it varies in quality. Illinois coal reserves in strata more than 28 inches thick are estimated at 137 billion tons and are larger than those of any other state.
Around the edge of the coal basin where the coal lies at shallow depths, it is commonly mined in open pits (strip mines). However, in the past, most coal has been mined underground, and more than half of Illinois coal is still produced from such mines.
Limestone and Dolomite
There are two types of carbonate rocks in Illinois, limestone and dolomite. In appearance they are almost indistinguishable, although they are different chemically. Limestone is composed mainly of calcium carbonate (the mineral calcite), whereas dolomite is calcium magnesium carbonate (the mineral dolomite).
Limestone deposits are found at many places in the western, southwestern, and southern marginal portions of the state. They are largely of Mississippian and Ordovician age. Lesser deposits of Pennsylvanian limestone are found in the central portion of the state. In the northern fifth of the state, dolomites of Silurian and Ordovician age are exposed at many places.
Limestone and dolomite are quarried for a variety of uses, including aggregate for concrete, agricultural limestone, railroad ballast, chips for bituminous roads, and for use in metallurgical and chemical processes. They also are quarried for building stone at some places, and marble is produced in southern Illinois.