Chapter II: Part 2

Many of the early tile plants also made bricks to be used for making foundations, buildings, sidewalks, and other structures. The bricks were made by hand-operated equipment. Some of the old hand-molded bricks may still be seen in older buildings. Now the brick-making process is highly mechanized and even though there are fewer plants they produce more bricks.

Clay and Shale Deposits

Illinois shales are a part of the bedrock—that is, they are associated with indurated rocks such as sandstone and limestone. Most clays are surficial rocks occurring in deposits near the surface, where they lie above the bedrock. Exceptions are certain clays found in extreme southern Illinois and the underclays, also called fireclays, that occur beneath coal seams and are part of the bedrock.

The surficial clays are of two principal kinds—till and loess. Till is a deposit left by glaciers. It is a gray, blue-gray, or brown clay containing varying amounts of sand, pebbles, cobbles, and even boulders. Till is found at many places in the state and is used for brick making, especially in the Chicago area.

Loess is a wind-deposited silty clay or clayey silt and is found in many parts of Illinois. It is thickest on or near the bluffs of the Mississippi, Illinois, and Ohio Rivers. It generally is brown and stands in steep faces in roadcuts and other excavations. It once was widely used for making brick and tile.

Of major importance in making clay products in Illinois are the bedrock shales and the clays associated with the coal-bearing rocks that underlie much of the state. The shales, and the clays to a lesser extent, are dug at many places for making structural clay products such as bricks, structural tile, and drain tile. They also are used to make lightweight aggregate for concrete. The underclays of some of the older coal seams are used to make buff-colored brick, stoneware, and a highly heat-resistant brick (firebrick) that is used in industrial furnaces or in other operations involving high temperatures. Some fireclay, ground as fine as flour, is added to molding sand to make it coherent enough to form into molds for metal casting. Sewer pipe and flue lining also are made from underclays.

Clays unlike those found elsewhere in the state occur in extreme southern Illinois. One of these has the property of removing color from oils and was so used at one time by petroleum refineries. Another, kaolin, was extensively used during World War I for making crucibles.

Clay Minerals

The uses of clay and shale are determined to a large degree by the properties of their clay minerals and to a lesser degree by the impurities present. A clay or shale containing the clay mineral illite, and other similar but less important clay minerals, commonly becomes red when fired and gets hard at a relatively low temperature. It therefore is used to make red bricks, drain tile, building tile, and other structural clay products.

Another clay mineral, kaolinite, generally burns to a light color and is difficult to fuse. Therefore, clays composed wholly or mainly of kaolinite can be used for making buff or light-colored bricks and for the manufacture of highly heat-resistant (refractory) bricks.

The clay mineral in the southern Illinois clay that was used to decolorize oil is montmorillonite. This clay is now used in sweeping compounds, as an oil absorbent, as animal litter, and for other purposes.

Studies of Clay and Shale

In view of the significant relationship between the clay minerals and the utilization of the clays and shales in which they occur, the Illinois Geological Survey has investigated extensively the clay minerals in the clay and shale deposits of Illinois. Many samples were studied by means of powerful microscopes, X-ray, and chemical analysis. Most of the surface clays and shales proved to be composed principally of illite or related minerals. The kaolin clay of extreme southern Illinois contains the mineral kaolinite. The older underclays also contain kaolinite, but many of them also contain smaller amounts of illite.

The Survey also has tested many clays to determine their burning properties and color when fired, and hence their potential uses. The bonding capabilities of other clays have been measured to find out whether they can be used as a bonding material for molding sand. The bloating properties of Illinois clays and shales from many deposits have been studied to determine which are suitable for making lightweight aggregate for the manufacture of concrete.

The object of these studies has been to discover the location, character, and possible uses of the state’s clay and shale resources. Special studies are continuing in several parts of the state. Illinois is well endowed with clays and shales that can be used for a variety of purposes and has resources to fill future as well as present needs.

How Bricks Are Made

Conversion of Illinois clays and shales into useful products is an interesting process and is exemplified by the making of building bricks. Mechanical shovels dig the clay or shale and load it into trucks or small railroad cars that take it to the brick plant. There, machines grind the raw material and mix water with it until it has the consistency of stiff mud.

Next, a machine, which operates somewhat like a meat grinder, extrudes a brick-sized column of clay. As the column moves forward, it is automatically cut into bricks by wires. The bricks are then dried in large heated rooms.

From the driers, the bricks go to huge ovens (kilns) and are heated until they are hard and have attained the desired color. This is known as firing or burning the bricks. Temperatures employed are rarely lower than 1800° F.

Three kinds of kilns are used in Illinois for burning bricks—beehive, tunnel, and scove. A beehive kiln (fig. 21) has a round base and a dome-shaped top and somewhat resembles an oversized beehive. Unfired bricks are stacked in the kiln and the doors are sealed with burned bricks and clay. Fires are started in hearths or fire boxes in the wall of the kiln and the heat is circulated into and through the kiln. It usually takes several days to fire the bricks adequately and let the kiln cool so that the bricks can be removed.

Tunnel kilns, made from heat-resistant bricks, are actually tunnels big enough for a man to stand in. The unburned bricks are loaded on flat steel cars on top of a layer of refractory blocks that protect the steel from the heat. The cars enter the kiln and heating begins. As they move through the kiln, they carry the bricks through a firing area, then through a cooling zone, and finally out into the air.

In some brickyards in the Chicago area, dried unburned bricks are carefully stacked by machines into piles about 17 feet high, 35 feet wide, and 115 feet long, which are known as scoves or scove kilns. A layer of burned bricks that is plastered with clay covers the sides of the scove. A jet of flame is directed through small tunnels at the base of the scove, and the heat fires the bricks.

During 1963, more than 325,000,000 bricks were produced by Illinois brick plants. In the same year, the value of all the clay and clay products produced in Illinois was nearly $54,000,000. Besides brick and drain tile, the products of the clay and shale industry of Illinois include refractory brick, building block and tile, fire-proofing, sewer pipe, flue liners, stoneware, lightweight bloated burned clay aggregate for concrete, and a variety of unburned clays for special purposes, including bonding clay, refractory fireclays, absorbent for use on garage floors, and litter for animal cages.

PEAT

After the retreat of the last of the great ice sheets from Illinois, numerous ponds and lakes were left in northern Illinois, especially in the eastern section. Some of them were soon drained by natural processes, but others remained. In the shallow water along their shores grew various plants, chiefly reeds and sedges and, locally, a variety of moss. As the plants died, their partially decomposed remains were preserved beneath the water. Ultimately, the ponds and lakes were overgrown and more or less completely filled by the plants and their remains, giving rise to peat (fig. 22) bogs.

Some peat bogs have been drained and are now used as farm land. Others remain and a few of them are the source of peat or humus for horticultural purposes. Producing operations are located in northeastern Illinois and in Whiteside County in northwestern Illinois.

OTHER MINERAL RESOURCES

In the future, new uses will be made of the Illinois industrial minerals already discussed. In addition, other mineral resources of the state that are not now being used may be the bases of new mineral industries. Some of these minerals are at present too costly to mine because the deposits are deeply buried or are not sufficiently rich to be worked at a profit. Others are not convenient to markets, and still others have no present commercial use. In years to come, however, changes may occur that will make it practical to mine, process, and use some of these resources. Furthermore, some other mineral deposits that are now being utilized in a limited way may have greater future use. The Illinois Geological Survey continues to study the location, character, and composition of many such mineral materials and is alert for the development of new uses. Some of the materials are discussed briefly below.

Gypsum and Anhydrite

Gypsum is a mineral that consists of calcium sulfate plus two molecules of water (CaSO₄·2H₂O). By suitably heating it, the amount of water can be reduced, and a product called calcined gypsum (plaster of paris) results. This material changes back to gypsum if mixed with an appropriate quantity of water. The ability of calcined gypsum to “set” when water is added makes it important in the manufacture of a variety of plasters and related products, especially building materials. Gypsum also is used in cement making and in agriculture.

Anhydrite (CaSO₄) is like gypsum except that it contains no water and hence cannot be made into plaster of paris. Its uses are limited in the United States.

Wells that were drilled for oil, water, or coal have encountered gypsum and/or anhydrite in some parts of south-central Illinois, but the gypsum and anhydrite are not known to crop out at the surface. A study of diamond drill cores and well cuttings on file at the Survey showed that the shallowest gypsum and anhydrite reported occurred at a depth of 470 feet in Madison County. The greatest continuous thickness of gypsum found was 2 feet; but in one well, over 6 feet of strata was penetrated that averaged almost 75 percent gypsum. It is possible that thicker deposits of gypsum might be found if drilling were done especially in search of it.

Feldspar-Bearing Sands

Feldspar is the name applied to a group of minerals that are mainly silicates of potassium, sodium, and calcium. Various kinds of feldspar are used industrially in making glass, enamels, pottery, and other products. All the feldspar now used in Illinois is shipped into the state. The discovery by the Illinois Survey that some Illinois sands contain considerable feldspar led Survey geologists and chemists to find where deposits highest in feldspar occur, what kinds of feldspar they contain, and whether it could be separated from the sand in which it occurs. Beach sands, river sands, dune sands, and sands from other kinds of deposits were studied.

It was found that many sands contain more than 15 percent feldspar and some as much as 25 percent. Means of separating the feldspar from the sand are believed to exist, but problems relating to the purity of the separated spar remain to be solved.

Brines

No salt is now produced in Illinois, but at one time the state was a major salt producer. Salt works were in operation near Equality, Central City, Murphysboro, St. John, Danville, and possibly other places. The salt was obtained by evaporating salt water (brine) that came from natural springs or from wells. The Equality area was a particularly important producer of salt in the 1800’s. Discovery elsewhere in the Middle West of deposits of rock salt and brines that contained more salt than those of Illinois is said to have been responsible for the discontinuance of salt making in the state.

No salt beds crop out in Illinois, nor are any known to have been encountered in the many wells that have been drilled for coal, oil, or water. However, most oil well drilling encounters brines containing various amounts and kinds of salts, including the common table salt, sodium chloride.

For reasons relating to the production of oil, Survey geologists and chemists have collected and analyzed many samples of Illinois oil field brines, and data are therefore available on their salt content. No commercial use is being made of the brines as sources of salt.

Oil Shale

Illinois has a large oil-producing industry that obtains oil from wells. The state also contains beds of shale that yield oil when the shale is heated.

In order to estimate the present and future importance of the oil shale resources, the Survey collected and tested more than 100 shale samples from 41 Illinois counties. A few samples contained more than 25 gallons of oil per ton of shale, but most contained less than 15 gallons per ton. A study of the crude oil distilled from selected shale samples showed it to be somewhat different from the oil that comes from wells. It could, nevertheless, be made to yield gasoline, fuel oil, and other products if suitably processed.

The shale strata generally the richest in oil are found above coal seams, are black, and are sometimes called slate by coal miners. They are rarely more than 3 feet thick, but they extend over large areas.

Sandstone

Sandstone has a long history of use in Illinois. Pioneers built foundations for their houses and barns and curbs around their wells from it. Slabs of sandstone were once a popular material for sidewalks, some of which are still in use. Churches and other sizable buildings have been constructed from it, and at one time an Illinois sandstone was used to make grindstones. Except for the St. Peter Sandstone, which was discussed under “Silica Sand,” the use of sandstone has decreased, although comparatively small quantities are still used as building stone.

Most Illinois sandstones may be thought of as a mass of sand whose grains are more or less firmly cemented together by clay, iron oxide, and quartz, either singly or in combination, or, less commonly, by calcite. The grains are particles of various minerals, but most of them are quartz.

Sandstones are especially common in the hill country of extreme southern Illinois. The Survey’s investigations in this area revealed that if they are suitably processed some of the sandstones may have possibilities for commercial use. Sandstones in other parts of the state also have been studied, with similar conclusions.

Barite

Barite (barium sulfate, BaSO₄) is a deceptive mineral—it is much heavier than it looks. Barite found in Illinois is generally white or light colored, and, although some of it looks rather like white limestone, it is more than half again as heavy as limestone. Barite’s unusual weight is responsible for one of its major uses—as a constituent of drilling muds for the oil industry. These muds are a mixture of clay, water, and a weighting material such as barite. They are used in various ways in the drilling of oil wells by rotary drills. Barite also is an important raw material for the manufacture of chemicals.

Barite is found in Hardin and Pope Counties, the site of the fluorspar industry. According to studies made by Survey geologists, the barite occurs both as veins and beds associated with fluorspar, but its distribution is irregular and the deposits are of limited size. A barite mine is said to have been worked years ago, and more recently comparatively small tonnages have been taken from open pits. Future exploration in southern Illinois may reveal deposits of barite that will be profitable to mine.

Greensand

In some parts of Illinois occur sands or sandstone that contain numerous grains of the green mineral glauconite. If the sands are not discolored by iron compounds or other substances, they too have a greenish color and, therefore, are called greensands. Glauconite varies in composition but contains potassium, magnesium, iron, aluminum, silicon, and water. Greensand is said to be used in relatively small amounts as a soil conditioner and as a water-softening agent.

Greensand is known to occur in the general vicinity of Olmsted in southern Illinois. Near Oregon in northern Illinois an old quarry exposed 10 feet of greenish brown sandstone that contains glauconite. Samples from southern Illinois and from the sandstone at Oregon contained more than 6 percent potassium oxide.

Marl

In some of the lakes and ponds left by the glaciers lived numerous small mollusks with calcium carbonate shells. As the animals died, their shells formed a deposit on the bottom of the lakes and ponds. Certain plants, especially algae, may have added a mudlike precipitate of calcium carbonate to the deposits, and varying amounts of clay washed from the shores mixed with both these materials. The resultant deposit is called marl. Some marl deposits have peat mixed with them, and peat also overlies some marl deposits.

Only comparatively small amounts of marl are known to have been dug in Illinois. One deposit containing many shells and shell fragments, some of it associated with peat, was worked in southeastern Livingston County as a source of agricultural liming material. Other deposits have been reported at other places in northeastern Illinois. The available information indicates that the marl deposits are likely to be principally of local importance.

Tufa and Travertine

The tufa (fig. 23) and travertine occurring as surficial deposits in Illinois were formed by springs. The deposits usually occur at or near the outcrop of a layer of porous water-bearing earth material, such as gravel, sandstone, or fissured limestone, that is underlain by a nonporous clay or shale formation. Water moving down through the porous layer cannot sink through the clay or shale and so is forced to move laterally. Where valleys have cut into the layers of gravel or rock, the water emerges as springs.

If the material through which the water has passed is limestone, or gravel containing limestone as most Illinois gravels do, some of the limestone is likely to have dissolved in the water. When the water issues as a spring, conditions may be such as to cause precipitation of the dissolved limestone as tufa or, more rarely, travertine.

Tufa is generally highly porous and more or less impure, whereas travertine is harder and less porous.

The middle or lower slopes of bluffs are common sites for spring-deposited tufa or travertine. Deposits have been seen in various parts of Illinois, but are not known to have been worked, except in Calhoun County where small quantities of tufa were produced for use as agricultural limestone. It is thought that the tufa and travertine deposits of Illinois are relatively small, but they may be of local importance.

Pyrite and Marcasite

The mineral pyrite consists of iron and sulfur as the compound iron sulfide (FeS₂) and, because of its shiny, brassy yellow color, is sometimes called fool’s gold. Marcasite has the same composition as pyrite, but its crystals have a different shape and it is often lighter colored. Both minerals occur in various parts of the state; they are particularly prevalent in some coal seams, and when so occurring are in some cases called coal brasses or “sulfur.”

Pyrite and marcasite are used commercially as raw materials for making sulfuric acid, although sulfur itself is more extensively used for that purpose. At one time coal brasses recovered during coal-cleaning operations at a northwestern Illinois coal mine were sold for acid making. A large quantity of coal brasses probably could be recovered from such operations at Illinois coal mines.

Uranium

Uranium has been sought in Illinois by many people in recent years. The Geological Survey also carried out a wide search for uranium and particular attention was paid to certain clays and other rocks in Hardin County and certain black shales in other parts of the state.

About 200 samples from Hardin County and 175 samples of the shales were tested by the Survey. No deposits were found that are known to be of the required richness and quantity.

Iron Ore

About the middle of the 19th century two furnaces in Hardin County in extreme southern Illinois for a time produced iron from local limonite ores. The ore is said to have occurred as pellets, chunks, and masses scattered through soil and clay and apparently was of irregular distribution. Little can be seen of the deposits today. Their extent is not known, but they are believed to be of limited size.

The Illinois State Geological Survey carries on a continuous program of research on the industrial minerals and metals of Illinois and their uses.

In addition to the investigations mentioned in this booklet, many others have been made or are in progress. Such studies are necessarily a continuing activity if the full potentialities of Illinois mineral resources are to be realized, for industry continually demands new raw materials and changes its requirements for those now used.

The Survey has issued numerous reports that deal with the resources discussed here and mimeographed lists of these are available upon request.

If reproduction is made of the material herein, acknowledgment of the Illinois State Geological Survey is requested.

Transcriber’s Notes

—Silently corrected a few typos.

—Retained publication information from the printed edition: this eBook
is public-domain in the country of publication.

—In the text versions only, text in italics is delimited by
_underscores_.