State Symbol: Illinois State Mineral — Fluorite

photo of purple fluorite

The name fluorite comes from the Latin fluere which means “to flow.” This name comes from the fact that fluorite melts easily. Fluorite is the natural crystalline form of calcium fluoride (CaF2). It is a transparent to translucent, glassy mineral. When pure fluorite is crystal clear, however flourite can show many different colors depending on tiny amounts of other elements taking the place of the calcium in the molecular structure. Sometimes a single crystal may have bands of several colors. Fluorite often forms beautiful cube-shaped crystals. For a better look at some spectacular fluorite crystals, take a look at this QTVR object movie.

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 (12 m). Because of these deposits, Illinois is the largest producer of fluorite in the United States.

photo of yellow fluorite

The deposits in Illinois were formed as hot water flowed up into the limestone of the area from deeper in the earth. Mineral deposits formed in this manner are called hydrothermal deposits. The hot water flowed up along weak areas in the rocks of this area. These weak areas are associated with the faults of the Wabash and Reelfoot rift zones. These two rift zones are responsible for earthquakes such as the famous series of quakes at New Madrid, Missouri. The southern Illinois flourite deposits probably formed between 100 and 250 million years ago.

Fluorite is an important industrial mineral. The most common use is as a flux in producing steel. Another important use is in making hydrofluoric acid, which is used in pottery, optics, and plastics. Fluorite is also used in making opalescent glass and in enameling cookware.

The Symbol

A bill designating Fluorite as the Official State mineral was passed in 1965 by the General Assembly.


C.W. Chesterman, 1978, The Audubon Society Field Guide to North American Rocks and Minerals, New York: Alfred A. Knopf, Inc., 849pp.
C.S. Hurlbut, Jr. and C. Klein, 1977, Manual of Mineralogy (19th edition), New York: John Wiley & Sons, Inc. 532pp.
M. Prinz, G. Harlow, and J. Peters, 1978, Guide to Rocks and Minerals, New York: Simon and Schuster, 607pp. Fluorite, “The Most Colorful Mineral in the World.” Amethyst Galleries web site. Illinois State Geological Survey site’s page on the state mineral.