Illinois' Industrial Minerals

Industrial minerals have played a critical role in the development of Illinois since the beginning of pioneer settlement in the eighteenth century. Illinois industrial minerals include rocks such as limestone, dolomite, and shale and nonmetallic minerals such as silica sand, clay, and fluorite. Major industrial minerals produced in Illinois today are crushed stone (limestone and dolomite), sand and gravel, clay, silica sand, tripoli (microcrystalline quartz), and peat. Portland cement, lime, and brick are also manufactured. Portland cement is produced from low-magnesium limestone, lime from limestone and dolomite, and brick from clay and shale. Production and use of industrial minerals have been and will continue to be a key component of the state's economy.

Limestone and dolomite are the most widely quarried rocks in Illinois, and crushed stone is the state's most important rock product. Millions of tons of stone are crushed annually for use as construction aggregates, road surfacing material, agricultural limestone, and lime. High calcium limestones are also used as a scrubbing agent for pollution control in power plants and incinerators and as a major ingredient of cement, the binding agent used in concrete pavements and foundations. Limestone and dolomite quarries are located where thick stone deposits occur near the surface, mainly in the northern quarter of the state, the western side of the state, and near the state's southern tip. These deposits are also mined underground in some areas. Underground mining is becoming a desirable method for extracting crushed stone, especially in populated areas and where stone is deeply burried.

Building stone, primarily quarried in Lemont, Joliet, and Grafton, was used extensively during the late nineteenth century in Chicago, St. Louis, and many other midwestern cities. The current Illinois State Capitol building in Springfield is an outstanding example of the use of this rock.

Sand and gravel deposits are widely distributed in select locations across the state; they are most abundant and of highest quality in northeastern Illinois, but less abundant and lower quality elsewhere. Sand and gravel in much of Illinois was deposited by water from the melting glaciers. The huge ice lobes of continental ice sheets that moved into Illinois from Canada carried enormous amounts of rock debris, much of which was washed and sorted by meltwaters into various sand and gravel deposits. Sand deposits of more recent origin are found in larger streams and rivers, where they are recovered by dredging. Many deposits of sand and gravel are used as construction aggregate in asphalt and in concrete pavements and commercial and residential structures, especially in the northern half of the state.

Clay is a very fine-grained material made up of a group of minerals produced by weathering of different kinds of rocks. In Illinois, clay deposits are either unconsolidated surficial clays or consolidated bedrock clays and shales. Clay is used in the manufacture of brick, tile, plaster, and cement and for other uses. Clays make excellent barriers to fluid transport and are used as pond liners, landfill covers, and liners for waste disposal or isolation.

Silica sand consists of fine grains of the mineral quartz. Commercial silica sand is produced from sandstone bedrock and some glacial deposits. Silica sand from northern Illinois is famous for its high purity and is widely used in making high-quality glass. Silica sand is also used as molding sand because it can withstand the high temperatures used in casting steel and other metals. It is also used in fracture-treating wells to help increase oil production. In ground or fine powder, silica sand is used as an ingredient in paint fillers, pottery glazes, and enamel.

Tripoli is a highly porous rock that consists of tiny particles of quartz. Deposits in Illinois are found in the extreme southern portion of the state. Tripoli is used in the ceramic industry, in polishing optical lenses, as paint filler, and as a fine abrasive.

Peat deposits are scattered across northern Illinois and are used mainly as a soil conditioner. This material is debris from the rich growth of plants that accumulated in low bog areas on the land surface after the glaciers melted away.

Fluorite, lead, and zinc production were historically important in Illinois. Fluorite, the official state mineral, metallic lead, and zinc ores are no longer mined in the state.

Beginning in the 1840s, mines were opened in the southeastern tip of the state in Hardin and Pope Counties to initially obtain galena (lead ore) and later fluorite. Illinois fluorite comprised more than 90 percent of the total U.S. production in the early 1980s, but competition from lower priced imports resulted in the last mine closing in 1996.

Lead and zinc ores were mined in northwestern Illinois, primarily around Galena in Jo Daviess County. Native Americans first mined lead ore in the late 1600s to trade with the French. With pioneer settlement in the early 1800s, a major mining industry began to develop. The Galena region became a major source of the nation's lead and zinc for over a century. Today, lead and zinc are no longer mined, the last mine closing in 1972.