1. State Mineral Fluorite Fluorite, or calcium fluoride, CaF 2, became Illinois’ state mineral in 1965.

2. Uses for fluorite Native Americans carved fluorspar ( the rock form of fluorite) to make artifacts. The first recorded use of Illinois' fluorite was in 1823, it was used to manufacture hydrofluoric acid.

3. Fluorite is most valuable as an ingredient of hydrofluoric acid. This acid is used in the manufacture of aerosols, refrigerants, and Teflon.

4. Fluorite is in rocket fuels and an ingredient of insecticides..

5. But most people associate fluorite with a more personal use. It’s in toothpaste and drinking water used to fight tooth decay!

6. Deep purple, amethyst, sky blue, sea green, sunny yellow, and crystal clear—the mineral fluorite comes in many colors.

7. Many types of fluorite even glow under ultraviolet light. They're "fluorescent."

8. Pure fluorite (CaF2), made of the elements calcium (Ca) and fluorine (F), is colorless. The various colors result from tiny amounts of other elements substituting for the calcium in the crystalline structure.

9. As the photos show, fluorite also forms clusters of beautiful cubic crystals.

10. Light reflects strongly from fluorite's crystal faces and cleavage surfaces, which can be polished to a high luster. Lovely as a gemstone, fluorite is brittle and relatively soft (4 on Moh's hardness scale), so it's unsuitable for ring settings.

11. How did Illinois' fluorite deposits form? Hot water containing fluorine and other dissolved chemicals rose from deep in the earth and cooled to form solid crystals. The water flowed through cracks in the limestone rock.

12. Galena Facts Galena, lead sulfide (PbS).

13. In the peak year of 1845, the mining district, with Galena as its hub, produced almost 85% of the nation's lead. Ulysses S. Grant, Galena's most famous citizen, moved to town in 1860, one year before the outbreak of the Civil War.