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.
Location of Limestone Deposits
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.
The Geological Survey locates and maps limestone and dolomite deposits and analyzes and tests samples to determine the best possible uses for the stone. Many reports have been published about the character and general use of the deposits in various parts of the state. Other reports deal with the use of limestone and dolomite for specific purposes such as cement making, building and decorative stone, rock wool, terrazzo chips, and lime.
METALLIC ORES AND FLUORSPAR
Lead and Zinc
Lead mining was one of the earliest industries of Illinois. The early settlers’ need for bullets for procuring food and for defense of their lives and property made lead an important commodity, and the deposits of lead ore in the northwestern corner of Illinois were quickly exploited. The ore was the mineral galena ([fig. 5]), for which the city of Galena in Jo Daviess County is believed to have been named.
Figure 5—Galena with cubic cleavage blocks in foreground.