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.
Fluorite is a widespread and common mineral. It often occurs as a primary mineral in veins or as a mix of lead, zinc and silver ores. Fluorite is also found in sedimentary rocks such as limestones and dolomites as well as in igneous rocks such as granites. Fluorite occurs commonly as cubic, octahedral and dodecahedral crystals in many different colors ranging from colorless and completely transparent to yellow, green, blue, purple, pink or black. Crystals may be large and penetration twins are fairly common. “Hoppered” specimens are in great demand. Fluorite may glow blue or violet in SW or MW ultraviolet light.
