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.