There are about 200 stone quarries in Illinois. Most of the larger quarries (fig. 3) are in the Chicago, Joliet, Kankakee, and East St. Louis areas, but one or more limestone or dolomite quarry occurs in many counties.
If all the stone taken from Illinois quarries in 1963 were removed from a hole 100 feet square, the hole would penetrate into the earth about 8 miles. It would take more than 350,000 railroad cars holding 100 tons each to haul away the stone. Limestone, dolomite, and their products added over 80 million dollars to the economy of the state in 1963, approximately 8 dollars for each person in Illinois.
Most Illinois limestone and dolomite is quarried from open pits, but in some places, as in the rocky bluffs along the Mississippi River, the stone is taken from underground mines (fig. 4). There is also a dolomite mine in Chicago. At the quarries the first step is the removal of the earth overlying the stone. Next, in both pit and mine, the stone is blasted to free it from the parent deposit and break it into pieces. Mechanical shovels (fig. 3) load the stone into trucks that take it to the crushing plant where powerful crushers further break the stone into pieces. The pieces are sorted into various sizes by large screens. At some of the plants, the stone is ground into powder.
The geologic map of Illinois prepared by the Illinois State Geological survey shows, with reasonable exactness, what bedrock formations would crop out at the surface if the overlying clay, sand, gravel, and earth were removed. Thick dolomite formations would be exposed in much of the northern fifth of the state, but would be rare elsewhere. Thick limestone formations would occur in an almost continuous zone, varying in width from 3 to 25 miles, along the Mississippi River from Rock Island to southern Illinois and then eastward across the extreme southern tip of the state. Limestone also would be seen along the Illinois River from Havana southward.
In the central area of the state, limestones are present, but they are rarely over 25 and often less than 15 feet thick. Consequently, most of the larger quarries are in the northern, western, and southern parts of Illinois. The thinner limestones, nonetheless, are of much importance and are quarried at many places, chiefly to provide agricultural limestone, road stone, and limestone for making cement.