For many years Illinois has led the nation in the production of
fluorspar, accounting annually for about half the total United States
output. The industry is centered in Hardin and Pope Counties where the
deposits occur in veins and beds in rocks of the Mississippian System.
Reserves of fluorspar are adequate to supply the industry for many
years.
[Illustration: Figure 12—Sand and gravel is produced at many places
in the state. Silica sand is produced only from a sandstone in
northern Illinois. Tripoli is found only in southern Illinois.]
KEY
Sand and Gravel
Silica Sand
Molding Sand
Tripoli
Fluorspar is used in the manufacture of hydrofluoric acid, as a flux in
the manufacture of steel, in the refining of aluminum, for the
manufacture of fluorine compounds used in a variety of products, in
ceramic glazes, and for other special purposes.