Some of the major uses for Illinois limestone and dolomite are mentioned
below. Not every limestone or dolomite can be used for all purposes
because for each use the stone must fulfill special requirements of a
chemical or physical nature. For example, it must have high purity for
lime, resistance to wear and weather for roads and buildings, and a
pleasing appearance for decorative stone and marble.
_Lime._—When limestone or dolomite is heated to a high temperature, it
undergoes a change and carbon dioxide is liberated. The weight of the
gas set free is equal to somewhat less than half the weight of the rock
if the rock is pure. The solid product remaining after the gas has been
driven off is known as lime. The heating process is called burning.
Besides being used in making mortar and plaster, lime is valuable in
many other ways, especially in various chemical processes of modern
industry. Plants at Chicago and Quincy make lime from Illinois limestone
and dolomite.
[Illustration: Figure 3—An Illinois dolomite quarry.]
_Cement._—Portland cement, sometimes called simply cement, is made at
LaSalle, Oglesby, and Dixon in northern Illinois from limestone and a
smaller, carefully measured amount of clay or shale. Cement also is made
at Joppa in southern Illinois. The blend of materials is thoroughly
ground and mixed, then heated at a high temperature in huge rotating
horizontal furnaces, called kilns, until it forms a clinker. After it
cools, the clinker is ground to a flourlike powder. This is basically
the cement that binds together the mixture of sand and limestone (or
dolomite), or of sand and gravel, to make the concrete from which roads,
bridges, buildings, and other structures are made.
_Aggregate._—The crushed stone used in making concrete is known as
concrete aggregate. This is a major use for Illinois limestones and
dolomites. Large amounts of stone aggregate also are used in bituminous
roads, popularly called “blacktop” roads.
_Agricultural Uses._—Agricultural limestone (agstone) is applied to farm
land to neutralize soil acids and otherwise benefit the soil. Both
limestone and dolomite are so used. Chickens are fed small limestone
chips to provide calcium for the formation of egg shells. Pigs and cows
get calcium from mineral supplements containing powdered pure limestone.
[Illustration: Figure 4—An underground limestone mine.]
_Other Uses._—Illinois limestone or dolomite is used in steel making, as
building stone and marble, as road stone, as ballast for the road beds
of railroad tracks, for making refractory dolomite used in the steel
industry, and for a variety of less common uses.