Forest Preserve District of Cook County, Illinois
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Nature Bulletin No. 361-A   December 6, 1969
Forest Preserve District of Cook County 
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

Among all the states, Illinois stands at the top or very near the top in its production of corn, hogs, soybeans, oats and chickens. The same is true in industries: meat packing, steel, agricultural machinery, tractors, radios, telephones, paint, candy and many others. It is one of the leading producers of coal. Not commonly known, however, is the fact that the world's largest fluorite mines are located in Pope and Hardin counties along the Ohio River, and few people realize what an important part this mineral plays in our daily lives.

Chlorine, bromine, iodine and fluorine are chemical elements always found in combination with some metal. Common salt is chloride of sodium. Fluorspar, or Fluorite, is fluoride of calcium. Although quite common, occurring in several states and in foreign countries, there are few deposits with veins large enough to be mined commercially. Almost half of what is used in this country comes from southern Illinois and most of the remainder from Kentucky, just across the river. It is mined from veins as much as 800 feet below the surface.

In many respects, fluorspar is one of the most remarkable of minerals, and one of the most useful, but people seldom hear about it because it is mostly used to help make something else, as a "silent partner". Geologists call it "the most versatile servant of industry". Its name comes from a Latin word meaning: "I flow". About 1888, when the open-hearth process of making steel came into use, it was found that the addition of a small quantity of fluorspar as a fluxing agent speeded up the process, saved fuel and produced purer better steel. It enables operation of the furnace at lower temperature, changes the slag from an unmanageable mass to a fluid substance easily drawn off, and removes sulfur or other impurities. Until recent years, the steel industry used most of all fluorspar mined. Formerly, the manufacture of aluminum depended upon the only known deposit of "cryolite" -- sodium aluminum fluoride -- in Greenland. Synthetic cryolite, made from fluorspar, is now the key to our vast production of cheap aluminum.

Forty years ago, hydrofluoric acid was used chiefly for etching glass and in insecticides. Made by treating fluorspar with sulfuric acid, it is one of the most corrosive substances known and had to be kept in lead containers. Today, it is the key material in the manufacture of high-octane gasoline for aviation, an important group of plastics, insecticides, and the refrigerants known as Freons -- ideal for use in homes and public places because they are colorless, odorless, non- poisonous and non-inflammable.

Fluorspar plays an important part in the manufacture of glazed tiles; enamel coatings on steel for stoves, refrigerators, table tops, counters and other equipment for such places as kitchens and bathrooms; opalescent glass for light bulbs, lamp shades and soda fountains; abrasives; and special lenses for the optical industries. The uses for this Jack-of-many-trades are almost endless.

Fluorspar crystals are usually cubes, as in salt, and it is one of the most beautiful of all minerals. None other varies so widely in shades and tints of many colors: white, amethyst (most common), blues from light azure to ultramarine, purple, yellow, red, brown and even black -- depending upon the iron manganese or other impurities present. Some varieties glow in an invisible ultraviolet light, and hence our term "fluorescent". It mars too easily to be used for jewelry, although the Mound Builders carved it into statuettes and ornaments and a big pink slab of fluorspar has long served as the doorstep to the old Kinkaid home on the Ohio River.

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