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. [Illustration: Figure 22—Peat from Kane County showing its fibrous nature and remains of plants.] 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