Illinois Rocks and Minerals

Illinois is not known for producing many gemstones or minerals.

But Illinois was the leading producer of fluorite in the United States for many years, and the mineral was named the official state mineral in 1965. The last Illinois fluorite mine closed in 1995 because of Chinese competition.

Also Illinois was the leading state in lead production during the mid-1800s. In Hardin and Pope counties, both zinc and lead were mined in the 1770-1800’s. Small amounts of silver have also been recovered from the galena found in Hardin County.

Illinois is rich in geological history and rock formations. Most of the state consist of prairie over sedimentary rocks. During the Precambrian era igneous rock was deeply buried by 2000–13000 feet of sediments carried by glaciers. Over 90% of Illinois was formerly covered by glaciers. This sedimentary level is known as the Illinois Basin. The Illinois Basin contains coal, oil, gas, and metals. The Ozark plateau and coastal plain of the southeastern part of Illinois and the very northwesternmost corner of the state that lies in the “Driftless Area”, so named because it was never covered by glaciers, contain fluorite, lead and zinc mines.

You can find geodes in the western and southern regions. The Keokuk Geode Beds near Hamilton and Warsaw are world-famous for their size and variety, containing calcite, quartz, aragonite, and pyrite. You may be allowed to dig in this area with a permit. Research online revels several people and rock shops in Hamilton, Illinois that can help you obtain a permit.

Fossils have been found in the northeastern part of the state, including corals, brachiopods, crinoids, stromatoporoids, and bryozoans, and some rarer finds have included trilobites, gastropods, and trace fossils of worms.  

The Mazon Creek fossil deposits are located in Will and Grundy Counties. They are some of the most important fossil deposits in North America because the soft parts of many organisms are preserved. Mazon Creek is famous for carboniferous fossils and is home to the Illinois's State Fossil, Tullimonstrum gregarium, or the Tully Monster. The Tully Monster was a soft-bodied animal that has been found preserved as outlines and flattened forms in nodules of ironstone from several areas in Illinois. It lived in the ocean that covered much of Illinois during the Pennsylvanian Period (about 300 million years ago). The Tully Monster was first found by Mr. Francis Tully in 1958. Tully Monsters are fairly common fossils in the Mazon Creek and more recently they have also been found in open-pit coal mines in central Illin.

Before venturing out-do some research on where and what you can collect. Remember you must have permission to collect on private property.

See my page on Rockhounding Rules for general information on the rules of collecting rocks on various lands.