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Illinois State Geological Symbols
Year Est.
State Mineral
State Fossil
Tully Monster


State Mineral: Fluorite


Fluorite crystal from Chicago. Crystal is displayed at Chicago's Field Museum

Fluorite (sometimes called Fluorspar) is a mineral that is part of the halide family and is composed of calcium and fluorine (CaF2). Named after the Latin word fluere, meaning "to flow", fluorite was frequently used as a flux, due to its ability to easily melt. Fluorite has a couple of diagnostic properties that make it very easy to identify. It is translucent or transparent, and is the only common mineral to have four directions of cleavage. The cleavage, which is the ability to break along specific planes of weakness, causes it to produce an octahedron shaped crystal (i.e. two pyramids attached to each other at the base, as seen in the image). In addition to a low melting point, it is also a fairly soft mineral, being used to denote the hardness of 4 on Mohs Hardness Scale. Fluorite can be found in a wide variety of colors including purple, green, yellow, blue, pink, and brown, however fluorite has a special property in that it fluoresces under a black (UV) light. This means that it glows, a process that, when discovered, was named after the mineral fluorite. Fluorite is formed when hydrothermal fluids flow through limestones, dolostones, and other rocks depositing not only fluorite minerals but also frequently metallic ores including tin, silver, lead, zinc, and copper. Fluorite has a lot uses, making it a valuable ore, the primary use of which is as a source for the element fluorine. From its namesake, Fluorite has been used as a flux for steel production, helping to remove impurities from the melt. In chemical applications it is used to manufactue hydrofluoric acid (HF), which then can be used to create fluorocarbon chemicals, foam blowing agents, refrigerants, and a variety of fluoride chemicals. It is also used to manufacture specialty glass, ceramics, enamelware, the Teflon coating, optical lenses, or even just as a gemstone. Most of the fluorite in the US has been mined out but there are still active deposits within the US, specifically in Illinois. Otherwise, most of the fluorite used in the US is imported from China, Mexico, Mongolia, and South Africa.



Fluorescing of Fluorite crystals at Chicago's Field Museum













State Fossil: Tully Monster



Geology of Illinois's National Parks

Through Pictures

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