Non-Mineral Resources of the Appalachian/Piedmont
The Appalachian/Piedmont region has a diverse assortment of non-mineral resources because of the diverse rocks in the region (Figure 7.8). The sedimentary rock non-mineral resources include the brownstone of the Triassic Rift Basins, as well as clay, lime, crushed stone and industrial sand. Diabase is an igneous rock resource. Metamorphic rocks, such as marble, the serpentinite of the Ultramafic Belt, and slate, are important to the regional economy. Additionally, the Appalachian Piedmont has the fossil fuel anthracite, a form of coal.
Figure 7.8: Principal non-mineral resource-producing localities of the Appalachian/Piedmont. Figure adapted from 1998 United States Geological Survey State Mineral Information.
Sedimentary Rocks
The most distinctive sedimentary rock of the Appalachian/Piedmont region is brownstone, a red to brown sandstone found in the Triassic rift basins of southeastern New York, New Jersey, Pennsylvania and Maryland. As the united continents of Pangea began to break apart during the Triassic and Jurassic, the crust rifted and cracked. Blocks of crust slid downward to produce the rift basins that gradually filled in with sediment. Because of the position of North America with respect to the equator, the Northeast climate was warm and dry. The arid climate and the oxidation of iron in the sediments produced red to brown sedimentary rocks locally known as "brownstone." The fine polish of brownstone made it a popular building and decorative stone that has been used throughout the Northeast, especially in New York City.
Clay, lime, and crushed stone of various rock types are also used in production of cement. Lime, originating from limestone, dolostone or marble, has a variety of uses in construction, the chemical industry and manufacturing of concrete and cement. Lime is very important to agriculture, where it is regularly applied to make the soils "sweeter" or less acidic. Additionally, industrial sand is mined from crushed sandstone and quartzite, as in the Inland Basin Region.
Igneous Rocks
The igneous rock non-mineral resources in the Appalachian/Piedmont region are limited to diabase, formed from magma close to the surface pushing its way through the sediments of the Triassic rift basins. Locally known as "traprock", diabase has the same composition as basalt. Diabase, however, cooled somewhat more slowly beneath the surface, allowing time for formation of visible crystals. Diabase is commercially called "black granite," and thus is listed in Figure 7.8 as dimension-granite in Pennsylvania. It is used as a building stone and facing.
Metamorphic Rocks
There is a wide array of metamorphic rocks in the Appalachian/Piedmont region that are important as non-mineral resources, including marble, serpentinite, slate, and emery. The Marble Valley, stretching from Vermont into western Massachusetts and Connecticut, is the focus of marble quarrying today in the Northeast. Proctor, Vermont, home of the now defunct Vermont Marble Company, was the center of Vermont marble production. Quarrying of marble has significantly declined in the last few decades, as synthetic materials have begun to replace it for many purposes.
The formation of the Marble Valley dates back to the Taconic mountain-building event. As limestone was deposited along the continental shelf in the Iapetus Ocean during the Cambrian, the Taconic volcanic islands and Baltica were approaching from the east. As the approaching volcanic islands compressed the limestone, it was metamorphosed to become marble. The earliest "marbles" quarried were at Isle LaMotte in the Champlain Islands of Vermont because it was easy to transport the marble down Lake Champlain. The islands were a natural place for the development of the marble industry in the Northeast. Technically, though, the Lake Champlain Islanders were quarrying limestone, as the rock had not been metamorphosed enough to be considered a true marble. It is quarried today under the name "Champlain Black," which signifies the black color of the Chazy Limestone.
The slate belt of Vermont and New York is immediately west of the Marble Valley. Slate, which is mildly metamorphosed shale, is used for roofing, flagstones, floor tiles, blackboards and pool tables. In a process similar to the formation of marble in the Marble Valley, the slate formed from Cambrian and Ordovician sediment (in this case, shale) deposited on the seafloor was metamorphosed to slate during the subsequent mountain-building events. More extreme metamorphism than seen in slate resulted in the "emery rock" found in New York in the Manhattan Schist. Emery, an intensely metamorphosed rock made of magnetite, corundum, sillimanite, sapphirine and cordierite, is used as an abrasive for grinding and polishing. Emery is no longer mined in the Appalachian/Piedmont, because synthetic abrasives, less expensive to produce, have replaced it. At one time, though, emery was an important natural resource of the region.
Marble?
Not everything commercially called a marble is a true marble, which lacks fossils and is recrystallized from limestone. The limestone in northwestern Vermont was only very weakly metamorphosed, if at all. Actual marble is found between Manchester and Middlebury Vermont, and parts of western Massachusetts and Connecticut. Green serpentinite rock from the Ultramafic Belt is also quarried and sold as a marble under the name Verde Antique. Serpentinite is hardly a marble. It was formed from the metamorphism of slices of oceanic crust and upper mantle that were scraped off of the oceanic plate being subducted beneath the North American continent during the Ordovician. The Ultramafic Belt, stretching the length of the Appalachian Mountains along the Taconic volcanic island suture zone, also has concentrations of the soft rock soapstone, made primarily from the mineral talc (Figure 7.9).
Fossil Fuels
Figure 7.10: Anthracite coal fields of the Appalachian/Piedmont. Figure adapted from Isachsen, Y.W., et al, 2000, Geology of New York, A Simplified Account; Shultz, C., 1999, The Geology of Pennsylvania; and Schmidt, Martin F., Jr., 1993, Maryland's Geology.
The Appalachian/Piedmont rocks are similar to those in the Inland Basin, with one important difference: the Appalachian/Piedmont rocks have been deformed and metamorphosed, with layers of rock squeezed up into tight folds by the Acadian and Alleghanian mountain-building events. The bituminous coal beds of the Inland Basin were altered a step further in the Appalachian/Piedmont region, squeezed by the mountain-building compression to become anthracite (Figure 7.10). Anthracite is 95% carbon and considerably harder than bituminous coal. The high percentage of carbon in anthracite is due to the release of impurities as gases during compression. Though it is more difficult to ignite, the higher percentage of carbon in anthracite makes it a very clean-burning fuel. However, despite its clean-burning properties, the mining of anthracite has suffered a serious decline due to the expense and difficulty of extraction. Because the anthracite layers are in severely deformed rock and high relief topography, it is difficult and dangerous to follow and mine along a continuous layer.
There are also two bituminous coal fields in the southwestern corner of the Appalachian/Piedmont region where deformation was less severe. In addition to the coal deposits, small natural gas reservoirs are found in Maryland and Pennsylvania’s Appalachian/Piedmont region.
