Pennsylvania State Rock
Anthracite is a hard, lustrous, high-carbon variety of coal. Coal, a brittle, combustible, black or dark brown sedimentary rock, forms from decomposed plant matter that has been subjected to high temperatures. Coal is composed primarily of carbon, with traces of sulfur, hydrogen, and nitrogen.
It is grouped into four ranks according to its carbon content. Anthracite, the highest rank, is over 95 percent carbon and has been partially metamorphosed. In descending rank, the other coals are bituminous (at least 90 percent carbon), sub-bituminous (at least 85 percent), and lignite, which grades into peat. The density of anthracite is 1.3–1.4, higher than other ranks of coal (but only about half as dense as granite or basalt).
A STATE SYMBOL
While Pennsylvania has never designated an official state rock, anthracite coal is an obvious choice because of its economic and historical importance to the state and the nation.
Coal was known to exist in Pennsylvania as early as 1752 near what is now the town of Saltsburg. However, this coal was never mined commercially. By 1761, the phenomenal Pittsburgh coal bed had been discovered. Coal from this bed, underlying large parts of Pennsylvania, West Virginia, Ohio, and Maryland, was a major fuel of the region’s Industrial Revolution and continues to be mined today in 21 counties.
The state’s anthracite deposits, in the eastern part of the state, are smaller in extent but larger in significance. Only about 1.5 percent of coal is anthracite, and Pennsylvania has more anthracite than any other place in the world.
Coal formation began about 350 million years ago in the Carboniferous Period, a time of mild climate and prevalent swamplands. Throughout millions of years, swamp plants that died built up in layers of peat, which was initially about 90 percent water. Aerobic decay in the upper layers of the swamp began the decomposition process, reducing the volume of the organic matter.
Beneath these upper layers, where oxygen did not penetrate, anaerobic bacteria further broke down the plant remains. These bacteria gave off acids, which, at still deeper levels, became too concentrated for bacteria to live. The acidic, anaerobic plant matter had by this time been transformed into a black gel known as gytta, and it no longer underwent decomposition.
The next step in the development of coal was bituminization, which occurred over millions of years as a sedimentary blanket thousands of feet thick buried the ancient swamps, trapping heat rising from deep in the earth. The high temperatures caused the water content to be cooked out of the peat until it formed lignite. If the process continued long enough, the water and organic matter in the peat continued to be forced out, creating purer coal.
Pennsylvania’s anthracite formed in the Pennsylvanian Epoch, which is the term used for the latter half of the Carboniferous Period. Successive generations of swamps in river floodplains and along the coast laid down deposits of peat, which were covered by larger deposits of sediment over many cycles. The sand and silt layers became sandstone, shale, and limestone, while the peat layers evolved into coal. Later mountain-building events would uplift, fold, and deform these sedimentary beds.
Worldwide, recoverable coal exists in about 70 countries. The U.S, Russia, China, and India have by far the largest proven reserves of coal. The two principal anthracite beds of Pennsylvania stretch in northeast-to-southwest oriented bands in the eastern part of the state. The counties with the richest sources are Lackawanda, Luzerne, Carbon, Schuylkill, and Northumberland. In addition, the vast field of bituminous coal underlies Pennsylvania’s southwestern quadrant. In all, 266 mines in 28 counties produce coal.
Coal has been burned in stoves for centuries as a direct source of heat. In modern times, the greatest demand for coal is industrial. Electricity generation from "steam coal" is the most significant of these uses; worldwide, 41.5 percent of electricity is produced in coal-fired power plants.
Coal has other uses besides generating energy. The manufacture of steel requires carbon, most often obtained from metallurgical (hard) coal. Thirteen percent of the world’s hard coal is used to make steel. A surprising array of products is made using coal or its by-products, including paper, creosote, benzene, ammonia, pharmaceuticals, fibers (rayon, nylon), dyes, and solvents.
In 2008, Pennsylvania mined 65.4 million tons of coal, of which 1.7 million tons were anthracite from 66 mines. Pennsylvania was the only U.S. state to produce any anthracite. Total U.S. production of all ranks of coal in 2008 was 1.2 billion tons. World production of all ranks of coal in 2008 was 6.8 billion tons.
Chemical Formula: C
|Author: World Trade Press|