Weathering of Pyrite Pyrite in rock outcrops along the Ocoee River. Pyrite is iron sulfide and has the chemical formula FeS 2 . You can see gold-colored cubes of pyrite scattered through many of the rocks along the Ocoee River. Weathering of pyrite has made the rusty-colored stains on some of the outcrops. When pyrite is exposed to air and water, it can become chemically unstable and change to other minerals, releasing acid in the process.
Acidic conditions can develop in streams and be harmful to fish and plants.
Limestone was one of the types of rocks used to modify the river channel at the Ocoee Whitewater Center because limestone counteracts the acid contained in storm runoff. This publication is one of a series of general interest publications prepared by the U.S. Geological Survey to provide information about the earth sciences, natural resources, and the environment.