Coal, the Organic Rock
Every rock has a story. This earth cache is about the story that coal tells.
So what is coal? Coal is fossilized dead plant material that once piled deep on the bottom of ancient swamps. Coal differs from every other kind of rock in that it is made of organic carbon: the actual remains, not just mineralized fossils, of dead plants. Today the vast majority of dead plant matter is consumed by fire and decay, returning its carbon to the atmosphere as the gas carbon dioxide—it is oxidized. The carbon in coal, however, was preserved from oxidation and remains in a chemically reduced form, available for oxidation.
Peat is a deposit of woody dead plant material, the precursor to coal and petroleum. Peat is plant matter that is partially decomposed under conditions of no oxygen. When dug from the ground peat is about 75 percent water by weight; once dried it is about 60 percent carbon and makes a useful fuel in many regions. Peat forms large and widespread deposits in the northern latitudes, where wet ground (peat bogs and fens) and abundant plant growth favor its preservation. Peat turns slowly into coal with burial and pressure as gentle heat drives out light hydrocarbons. These volatile compounds become petroleum
Coal geologists study coal just the way other geologists study other rocks. But instead of talking about the minerals that make up the rock (because there are none, just bits of organic matter), coal geologists refer to the macerals, of which there are three groups: inertinite, liptinite, and vitrinite. To oversimplify a complex subject, inertinite is generally derived from plant tissues, liptinite from pollen and resins, and vitrinite from humus or broken-down plant matter.
Coal in Illinois
Coal has been mined in 73 counties in Illinois and more than 4500 coal mines have been operated since commercial mining began in 1810. The Illinois State Geological Survey (ISGS) has compiled maps of known mines for each of these counties in order for the public to identify mined areas, both underground and surface. Little or no information is available for many of the mines, especially the older ones, because mining activity was not regulated or documented until the late 1800’s. If you ever need additional info, please contact ISGS Coal section at 217-333-7256.
Surface mining is used to produce most of the coal in the U.S. because it is less expensive than underground mining. Surface mining can be used when the coal is buried less than 200 feet underground. In surface mining, giant machines remove the topsoil and layers of rock to expose large beds of coal. Once the mining is finished, the dirt and rock are returned to the pit, the topsoil is replaced, and the area is replanted. The land can then be used for croplands, wildlife habitats, recreation, or offices or stores.
Underground mining sometimes called deep mining, is used when the coal is buried several hundred feet below the surface. Some underground mines are 1,000 feet deep. To remove coal in these underground mines, miners ride elevators down deep mine shafts where they run machines that dig out the coal.
Grades of Coal
Coal comes in three main types, or grades. First the swampy peat is squeezed and heated to form a brown, soft coal called lignite. In the process, the material releases hydrocarbons, which migrate away and eventually becomes petroleum. With more heat and pressure lignite releases more hydrocarbons and becomes the higher-grade bituminous coal. Bituminous coal is black, hard and usually dull to glossy in appearance. Still greater heat and pressure yields anthracite, the highest grade of coal. In the process, the coal releases methane or natural gas. Anthracite, a shiny, hard black stone, is nearly pure carbon and burns with great heat and little smoke.
If coal is subjected to still more heat and pressure, it becomes a metamorphic rock as the macerals finally crystallize into a true mineral, graphite. This slippery mineral still burns, but it is much more useful as a lubricant, an ingredient in pencils and other roles. Still more valuable is the ultimate fate of deeply buried carbon, which at conditions found in the mantle is transformed into a new crystalline form diamond.
The Future of Coal
Three centuries after it was discovered in America, coal is still providing power for the nation. As we begin a new century, coal faces many challenges to its premier status, but its importance can never be questioned. The fuel, coal that enabled the United States to become a wealthiest industrialized nation in the world is still responsible for half the nation’s electrical power. Coal provides 49% of the electricity in this nation.
The coal industry is now required to follow new regulations that require mined land to be returned to its approximate original contour, with the exception of mountaintop removal operations, in accordance with federal Surface Mining Control and Reclamation Act of 1977. According the 1977 law, mountaintops may be reclaimed as flat land, which leaves he land more valuable for development. Reclaimed land must be as useful as the land was before mining.
The Earthcache Site:
ISGS mine map of approximate cache area. No info on this area or the nearby mine listing. The green shows the area was strip mined and now abandoned.
To Claim This Cache:
1. Coal forms primarily from ancient plant material that accumulated in surface environments where the complete decay of organic matter was prevented. The initial stage of the decay of a dead plant is a soft, woody material known as ____.
2. What type of coal would you expect to find at this site?
3. How far from the road is the coal seam at the posted coordinates?
4. Post at picture of yourself/group at the posted coordinates in front of the coal seam.
Send an email with the above information to receive credit for this find. Logs without pictures or answers will be deleted.
