sed to create chlorofluorocarbons, known as CFC’s. CFC’s were once widely used as the cooling fluid of refrigerators and air-conditioners, as well as the propellant for aerosol cans of paint and hairspray. They are inert compounds that do not react with other substances, are non-toxic and initially appeared to pose little risk to human populations. Consequently they were widely used before researchers realized that CFC’s released into the atmosphere pose a serious threat to the atmospheric ozone layer that protects the Earth’s land life from harmful ultraviolet radiation that can cause cancer and mutations. As ozone naturally forms and breaks apart, it absorbs ultraviolet radiation from the sun, thus shielding the Earth’s surface (and much of its life) from this harmful radiation. However, CFC’s in the high atmosphere help to speed up the process of ozone breaking down, so that much less ultraviolet radiation is absorbed. The radiation that is no longer absorbed can reach the Earth’s surface and poses a particular threat to populations living in high latitude areas, where this process of ‘ozone depletion’ is the most effective. International agreements have now banned the manufacture and use of CFC’s in many nations, but unfortunately this ban is not global so CFC’s still pose a potent, long-term environmental risk.
Fluorite in the Upper Midwest:
Thick widespread carbonate rock units of the Upper Mississippi River Valley once hosted large amounts of fluorite. These deposits formed as hydrothermal fluids moved along fractures in the carbonate rock, altering or dissolving the carbonate minerals and precipitating a wide variety of metallic ores and pore-filling minerals, including fluorite. Most of the richest fluorite deposits have now been mined out, but some fluorite can still be found, especially in Illinois’ Hardin and Pope Counties.