How Are Chemical Sedimentary Rocks Formed?
Chemical sedimentary rocks are formed by natural chemical reactions in nature. These reactions take place mainly through the process of chemical precipitation. Precipitation is the process in which dissolved minerals separate from a body of water and accumulate as a solid on the sea or lake bottom. To better visualize this process, dissolve some table salt in a pan of water. After the water has evaporated (this may take a few days), salt crystals will reappear as it precipitates from the water. Gypsum is a very common type of chemical sedimentary rock in South Dakota. It is a soft rock that is used as a soil additive and to make plaster of Paris. Some of the gypsum in South Dakota formed from the evaporation of shallow seas millions of years ago. Gypsum exists as white beds within the red rocks near Spearfish and in the eastern rolling hills in Custer State Park. Other types of gypsum are found in parts of eastern South Dakota. Clear gypsum crystals up to 3 inches (7.6 cm) long can be
