Geography of Illinois before the dinosaurs. Galena, a lead ore, has been mined in the northwest corner of the state. The ore was processed around Peru, Illinois, where river transport was available to bring the ore to a source of coal. About six tons of coal are needed for each ton of ore. Fluorite, calcium fluoride, is the state mineral. It is mined in the southeastern portion of the state, around Metropolis. Fluorine gas is produced from fluorite. This is used in the production of uranium hexafluoride in Metropolis, Illinois for use at the gaseous diffusion plant in Paducah, Kentucky. Geodes can be
Stephanite tetrahedrite, galena, sphalerite and pyrite. Localities which have yielded good crystallized specimens are Freiberg and Gersdorf near Rosswein in Saxony, Chañarcillo in Chile, and exceptionally Cornwall. In the Comstock lode in Nevada massive stephanite and argentite are important ores of silver. Stephanite Stephanite is a silver antimony sulfosalt mineral with formula: AgSbS It is composed of 68.8% silver, and sometimes is of importance as an ore of this metal. Under the name Schwarzerz it was mentioned by Georgius Agricola in 1546, and it has been variously known as "black silver ore" (German "Schwarzgultigerz"), brittle silver-ore ("Sprödglanzerz"), etc. The name stephanite