Gator Girl Rocks

Rockhounding Illinois

Illinois is a good state for rockhounders.  The Mazon Creek fossil sites are well known throughout the world.  Illinois also is famous for its fluorite deposits.  At least nine meteorites have been found in the state including the Benld Meteorite that, in 1938, hit and penetrated a garage and ended up embedded in the seat of an automobile.  In addition, the Field Museum is one of the finest museums in the world for rockhounders.

State Rocks, Gemstones, Minerals, Fossils, & Dinosaurs

Rockhounding Tip:  Knowing state rocks, gemstones, minerals, fossils, and dinosaurs often can be very useful information for rockhounders.  Ordinarily, states with significant mineral deposits, valuable gemstones, fossils, or unusual or significant rock occurrences will designate an official state mineral, rock/stone, gemstone, fossil, or dinosaur to promote interest in the state’s natural resources, history, tourism, etc.  Accordingly, such state symbols often are a valuable clue as to potential worthwhile rockhounding opportunities.

State Mineral:  Fluorite (1965)

Illinois designated fluorite as its official state mineral in 1965.  Fluorite is the natural crystalline form of calcium fluoride.  It is a transparent to translucent, glassy mineral.  When pure,                                                        fluorite is crystal clear.  Fluorite, however, can show many different colors depending on tiny amounts of other elements taking the place of the calcium in the molecular structure (colors include deep purple, amethyst, sky blue, sea green, sunny yellow, & crystal clear).  Sometimes a single crystal may have bands of several colors.  Fluorite often forms beautiful cube-shaped crystals.  The name comes from the Latin word fluere meaning ‘to flow’ because fluorite melts easily at high temperatures.  The fluorite from the Weardale district of England fluoresces brightly in short wave black light, but the fluorite from Illinois does not fluoresce at all.  The term fluorescence is derived from fluorite, as it was the first mineral discovered to exhibit this property.
  The most important fluorite deposits in the United States are found at Rosiclare and Cave-in-Rock in southern Illinois.  At Rosiclare, fluorite occurs in veins in the limestone bedrock.  Some of these veins are as much as 40 feet wide.  Because of these deposits, Illinois has been the largest producer of fluorite in the United States.  Fluorite is used in making steel (it helps molten steel flow more easily and removes impurities), enamels, hydrofluoric acid, aluminum, glass, and many chemicals. 

State Fossil:  Tully Monster [Tullimonstrum gregarium] (1989)
Illinois designated the Tully Monster as its official state fossil in 1989.  The Tully monster was a soft-bodied, invertebrate, marine animal – an animal that has no shell and no backbone, and lived in the ocean.  It had an elongate, segmented body that tapered at both ends and usually was less than six inches long.  At the front was a long snout ending in a "jaw" with eight tiny "teeth."  At the other end there was a tail and two fins.  Two eyes on stalks projected out sideways near the front of the body.  The Tully monster lived 340 to 280 million years ago during the Pennsylvanian Period.  At that time, the land that is now Illinois was located near the Earth's equator and dense swamps, forested with primitive plants, covered much of western and central Illinois.  Francis Tully first found the ‘Tully Monster’ fossils in 1958.  He took the specimens to the Field Museum of Natural History in Chicago.  The specimens defied identification and became known as the ‘Tully Monster.’  The name stuck.  When Dr. Eugene Richardson formally described the new animal, he gave it the name Tullimonstrum gregarium.  The species name gregarium means common.  This refers to the fact that Tully Monsters are fairly common fossils in the Mazon Creek deposits.  More recently they also have been found in open-pit coalmines in central Illinois.  More than 100 Tully Monster fossils have been found in Illinois.

Rockhounding Resources

Illinois State Geological Survey
The Illinois State Geological Survey publishes The Guide for Beginning Fossil Hunters

 

• Raymond Wiggers, Geology Underfoot in Illinois (1996).
• June Culp Zeitner, Midwest Gem, Fossil, & Mineral Trails: Great Lakes States (Rev. ed., June 1999 - first published in 1955). 
• June Culp Zeitner, Midwest Gem Trails: Field Guide for the Gem Hunter, the Mineral Collector, and the Tourist (3d. Rev. ed., 1964 – originally published in 1956). 
• Allan W. Eckert, Earth Treasures Vol. 1 - Northeastern Quadrant (1985; reprint in 2000).
• James Martin Monaco & Jeannette Hathway Monaco, Fee Mining & Mineral Adventures in the Eastern U.S. (2d ed. 2010).
• Kathy J. Rygle & Stephen F. Pedersen, Northeast Treasure Hunter's Gem & Mineral Guide (4th ed. 2008).

Museums of Interest to Rockhounders

Field Museum
Chicago, Illinois
The museum’s exhibits include Sue, the largest most complete T. Rex dinosaur in the world.  The museum’s permanent exhibits include the Grainger Hall of Gems and the Hall of Jades.  This museum is amazing.  It has a fabulous collection of rocks, minerals, gemstones, and fossils.  Definitely worth a visit.

 

Illinois State Museum
Springfield, Illinois
The museum exhibits rocks, minerals, and fossils.

 

Burpee Museum of Natural History
Rockford, Illinois
The museum’s Geoscience exhibit features rocks, minerals, fluorescent minerals, and regional geology.  In addition, the museum’s paleontology exhibits include a variety of fossils.

 

Fryxell Geology Museum
Augustana College - Rock Island, Illinois
The museum, named after Dr. Fritiof Fryxell, has become one of the largest and finest collections of rocks, minerals, and fossils in the Midwest.  Begun in the late 1880s with a modest natural history collection, the museum now boasts over 1,500 rock, mineral, and fossil specimens.  On display are complete skeletons of a Tylosaurus "sea serpent", skulls of Parasaurolophus, Ankylosaurus, Apatosaurus, Allosaurus, and Tyrannosaurus rex as well as a two-billion-year-old fossil!  Of particular interest is a state-of-the-art fluorescent mineral display and an exhibit of the complete 22-foot long skeleton of Cryolophosaurus, a large crested carnivorous dinosaur discovered in Antarctica in 1991 by Augustana paleontologist Dr. William Hammer.

Funk Gem & Mineral Museum
Funk’s Grove, McLean County, Illinois
Located next to the historic 1864 residence of Illinois State Senator and co-founder and director of Chicago's Union Stockyards Lafayette Funk, the Funk Gem and Mineral Museum is certainly the largest single-person display of rare gems, minerals, fossils, petrified wood, and lapidary art in Illinois.  And it bills itself as the largest one-man mineral collection in the world.

Lizzadro Museum of Lapidary Art
Elmhurst, Illinois
The Lizzadro Museum displays more than 200 pieces of jade and other hard stone carvings from around the world, featuring several internationally famous pieces.  Other prime examples of lapidary art are exhibited in the form of snuff bottles, modern and antique vases and bowls, and many other decorative and functional items.  The Rock and Mineral Experience on the lower level presents a variety of exhibits; earth science phenomena, lapidary materials, mineral specimens, and fossils.

 

American Fluorite Museum
Rosiclare, Illinois
The American Fluorite Museum is located in the former office building of the Rosiclare Lead and Fluorspar Mining Company in downtown Rosiclare, Illinois, in the heart of the Southern Illinois - Western Kentucky Fluorite District, once the largest fluorspar mining area in the United States.  Hardin County, Illinois was the largest fluorspar-producing area in the United States.  The Museum features numerous items representing the fluorspar mining industry.

Places to Visit - Interesting Sites To See

Cave-In-Rock State Park
Hardin County, Illinois
Sitting atop the high bluffs overlooking the Ohio River, the heavily wooded park is named for the 55-foot-wide cave that was carved out of the limestone rock by wind and water erosion thousands of years ago.  Historically, the cave was used as a hideout for outlaws, bandits, and river pirates.

 

'Pyrite Sun'

Sparta (Randolph County), Illinois

The pyrite discs are found about 300 feet below the surface in coalmines.  The discs are located in narrow seams of slate (about 320 million years old), between seams of coal in the mines near Sparta, Illinois.  There are several theories about the origin of these formations.  One is that they are pyritized replacements of an earlier fossil creature.  Another is that they are the flattened result of a pyrite crystal spread out under heat and pressure in the seams of slate.

 

Rockhounding Sites for Children & Families

Fossils - Mazon Creek Fossils
Northeast Illinois
Mazon Creek fossils are named for the collecting area in northeastern Illinois where may of the best specimens are found.  Mazon Creek fossils occur within ironstone concretions.  These animal and plant fossils belong to the Pennsylvanian Period that also is called the 'coal age' (approximately 300 million years ago) as extensive coastal swamps during this age developed and peat deposits formed that later turned into coal.  Do to their rapid burial, many organisms were buried alive creating incredibly well preserved specimens.  The concretions occur in layers of shale that were stripped away during coal mining.  Most of the concretions ended up in spoil piles.

 

Fossils - Mazon Creek Fossils:  Mazonia State Fish & Wildlife Area
Mazonia State Fish & Wildlife Area
The Mazonia State Fish and Wildlife Area consists of 1,017 acres and is located in Grundy County three miles southeast of Braidwood on Illinois Route 53 and Huston Road.  Mazonia is well known for Pennsylvanian age fossils.  A day permit is required to collect fossils and may be obtained from the park office or website.  A reporting form also is available for reporting what was found.  Excavations and collecting for commercial purposes are prohibited.  In addition, fossil collecting is restricted to March 1st to September 30th.

 

Geodes
Western Illinois Near Keokuk, Iowa
Although geodes are known from many localities around the world, one of the most productive and famous collecting regions is encompassed within a 50-mile radius of Keokuk, Iowa.  Geodes from this region commonly are referred to as "Keokuk geodes."  Most geodes are derived from strata of the lower Warsaw Formation, a widespread rock unit of Mississippian age.  Muds deposited in a shallow sea about 340 million years ago were primarily calcium carbonate and clay, and were subsequently lithified to form the shales, shaley dolomites, and limestones that we see today.  Fresh geodes can be dug out of exposures of the lower Warsaw Formation, where they are concentrated in certain layers.  Where water and streamflow have eroded these strata, concentrations of geodes may accumulate in stream channels.