Limestone and dolomite are the most abundant rocks quarried in Illinois. Small amounts of marble, limestone, and sandstone for building stone are also produced. In addition, some glacial boulders and cobbles are used for rock gardens and in home construction. The crushed limestone industry is Illinois’ most important rock products industry.
WHAT ARE LIMESTONE AND DOLOMITE?
Limestone is a sedimentary rock that consists chiefly of calcite, which is composed of calcium, carbon, and oxygen. Dolomite is a variety of limestone that contains considerable magnesium in addition to the other elements. Limestones were deposited on the floors of ancient seas that repeatedly covered most parts of Illinois. Shelled creatures, corals, and coral reefs helped build up the thick limestone deposits (figs. [13] and [14]).
Figure 13—Piece of limestone largely made up of fossil brachiopod shells.
WHERE ARE LIMESTONE AND DOLOMITE QUARRIES LOCATED IN ILLINOIS?
Limestone and dolomite quarries are located along the southern, western, and northern margins of the state where the thick deposits of these rocks crop out at the surface. Although bedrock was deposited in horizontal layers, it has since been downfolded into the Illinois Basin whose center is in southeastern Illinois. Thus, the thick limestones and dolomites that are quarried along the margins of the state are too deeply buried to be quarried in the central part of this basin ([fig. 15]).
Figure 14—Fossils commonly found in Illinois rocks.
Strophomena 1× Paleoneilo 1× Ctenodonta ⅔× Dolmanites ½× Archimedes 1× Hormotoma Polygyra 1× Mucrospirifer 1½× Atrypa ⅔× Crinoid Columnais 1× Halysites ⅔× Hexagonaria 1× Microcylus 1× Streptelasma ⅔× Lithostrationella ½× Lophophyllum 1×