The Baltimore Gneiss is a Precambrian geological formation in the Piedmont region of Maryland , Pennsylvania , and Delaware .
31-477: At least 95 percent of the Baltimore Gneiss can be described as quartzo-feldspathic gneiss of granodioritic to granitic composition, with the remaining 5 percent consisting of amphibolite . The age of the Baltimore Gneiss has been constrained to 1.0-1.1 Ga. The Gneiss is homogeneous overall, but is recognized as having four subdivisions. These are the layered gneiss member , the augen gneiss member ,
62-552: A banded texture characterized by alternating darker and lighter colored bands and without a distinct cleavage . Gneisses are common in the ancient crust of continental shields . Some of the oldest rocks on Earth are gneisses, such as the Acasta Gneiss . In traditional English and North American usage, a gneiss is a coarse-grained metamorphic rock showing compositional banding ( gneissic banding ) but poorly developed schistosity and indistinct cleavage . In other words, it
93-572: A broad textural category for medium- to coarse-grained metamorphic rock that shows poorly developed schistosity, with compositional layering over 5 millimeters (0.20 in) thick and tending to split into plates over 1 centimeter (0.39 in) thick. Neither definition depends on composition or origin, though rocks poor in platy minerals are more likely to produce gneissose texture. Gneissose rocks thus are largely recrystallized but do not carry large quantities of micas, chlorite or other platy minerals. Metamorphic rock showing stronger schistosity
124-453: A centimeter to decimeter scale. The augen gneiss member consists of two belts of fine to medium grained gneiss bearing biotite, microcline, quartz, and plagioclase, with abundant large ovoids ( augen ) consisting of microcline and/or quartz. The streaked-augen gneiss member consists of uniform, medium-grained biotite-microcline-quartz-plagioclase gneiss, with augen that have a "stretched" or "streaked" appearance. The hornblende gneiss member
155-640: A refolded nappe system beneath the Towson anticline. The cores of these nappes consist of the Baltimore Gneiss. The Baltimore Gneiss has been affected by three deformation periods: the Grenvillian , known from radiometric age data, for which nearly all resulting structural features where destroyed or obstructed by later tectonic deformation; the Taconic - Acadian , which involved three phases of folding, amphibolite facies metamorphism, local migmatization , and
186-475: Is a gneiss resulting from metamorphism of granite, which contains characteristic elliptic or lenticular shear-bound grains ( porphyroclasts ), normally feldspar , surrounded by finer grained material. The finer grained material deforms around the more resistant feldspar grains to produce this texture. Migmatite is a gneiss consisting of two or more distinct rock types, one of which has the appearance of an ordinary gneiss (the mesosome ), and another of which has
217-488: Is a metamorphic rock composed of mineral grains easily seen with the unaided eye, which form obvious compositional layers, but which has only a weak tendency to fracture along these layers. In Europe, the term has been more widely applied to any coarse, mica -poor, high-grade metamorphic rock. The British Geological Survey (BGS) and the International Union of Geological Sciences (IUGS) both use gneiss as
248-518: Is called gneissic banding. The darker bands have relatively more mafic minerals (those containing more magnesium and iron ). The lighter bands contain relatively more felsic minerals (minerals such as feldspar or quartz , which contain more of the lighter elements, such as aluminium , sodium , and potassium ). The banding is developed at high temperature when the rock is more strongly compressed in one direction than in other directions ( nonhydrostatic stress ). The bands develop perpendicular to
279-449: Is classified as schist, while metamorphic rock devoid of schistosity is called a granofels . Gneisses that are metamorphosed igneous rocks or their equivalent are termed granite gneisses, diorite gneisses, and so forth. Gneiss rocks may also be named after a characteristic component such as garnet gneiss, biotite gneiss, albite gneiss, and so forth. Orthogneiss designates a gneiss derived from an igneous rock , and paragneiss
310-517: Is one from a sedimentary rock . Both the BGS and the IUGS use gneissose to describe rocks with the texture of gneiss, though gneissic also remains in common use. For example, a gneissose metagranite or a gneissic metagranite both mean a granite that has been metamorphosed and thereby acquired gneissose texture. The minerals in gneiss are arranged into layers that appear as bands in cross section. This
341-950: Is probably derived from the Middle High German noun gneist "spark" (so called because the rock glitters). Gneiss is used as a building material, such as the Facoidal gneiss. It's used extensively in Rio de Janeiro . Gneiss has also been used as construction aggregate for asphalt pavement . Herring Run The Herring Run is an 11.1-mile-long (17.9 km) tributary of the Back River located in Baltimore , Maryland . The 31-square-mile (80 km ) watershed has its headwaters in Towson, Maryland , and flows through Baltimore County and Baltimore City and back into
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#1732798394784372-489: Is similar to the layered gneiss member, but with hornblende -bearing dark gneiss accounting for about half of the outcrop area. The Slaughterhouse Gneiss weathers to a pinkish to orange color, and consists of relatively uniform, medium-grained microcline-quartz-plagioclase gneiss with muscovite, biotite, or both. The Phoenix, Texas, Chattalolanee, and Towson gneiss anticlines in the Baltimore, Maryland area are all part of
403-510: Is subjected to extreme temperature and pressure and is composed of alternating layers of sandstone (lighter) and shale (darker), which is metamorphosed into bands of quartzite and mica. Another cause of banding is "metamorphic differentiation", which separates different materials into different layers through chemical reactions, a process not fully understood. Augen gneiss , from the German : Augen [ˈaʊɡən] , meaning "eyes",
434-526: The streaked-augen gneiss member , and the hornblende gneiss member . Additionally, the Baltimore Gneiss outcrops into three discrete masses of uniform, well-foliated to massive granitic gneiss referred to as the Slaughterhouse Gneiss . The layered gneiss member consists of dark and light layers of gneiss bearing biotite , microcline , quartz , and plagioclase , varying from biotite schist to quartzo-feldspathic granofels interlayered on
465-459: The 1700s were constructed of gneiss quarried from Jones Falls. In addition to use in buildings, gneiss from Jones Falls and Gwynn Falls quarries was used for foundations, roads, and curbstones in Baltimore. Some quarrymen referred to the gneiss as "blue stone" due to the blue-gray color of its fresh surface. The last building stone quarry in Baltimore closed in 1958. The type locality of the Baltimore Gneiss as described by William Patrick Crowley of
496-710: The Dulaney Valley Road bridge. The type locality of the hornblende gneiss member includes outcrops along an unnamed stream between Malvern Avenue and Boyce Avenue. The type locality of the Slaughterhouse Gneiss outcrops along the Slaughterhouse Branch southeast of the Baltimore Beltway (I-695). Some notable exposures of the Baltimore Gneiss in addition to the type localities mentioned above include outcrops along
527-593: The Maryland Geological Survey in 1976 is defined as outcrops along Towson Run from Bellona Avenue to Towsontown Boulevard. Formerly, the type locality was considered as referring to layered gneisses which outcrop along Jones Falls and Gwynns Falls in Baltimore City, however, chemical and textural analysis followed by zircon age measurements determined that these gneisses represent a distinct younger geologic unit. The type locality of
558-739: The Rapids Trail in the McKeldin Area of Patapsco Valley State Park and along roads around the Loch Raven Reservoir . Gneiss Gneiss ( / n aɪ s / nice ) is a common and widely distributed type of metamorphic rock . It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks . This rock is formed under pressures anywhere from 2 to 15 kbar, sometimes even more, and temperatures over 300 °C (572 °F). Gneiss nearly always shows
589-458: The amphibolite or granulite facies. These form most of the exposed rock in Archean cratons . Gneiss domes are common in orogenic belts (regions of mountain formation). They consist of a dome of gneiss intruded by younger granite and migmatite and mantled with sedimentary rock. These have been interpreted as a geologic record of two distinct mountain-forming events, with the first producing
620-538: The appearance of an intrusive rock such pegmatite , aplite , or granite the ( leucosome ). The rock may also contain a melanosome of mafic rock complementary to the leucosome. Migmatites are often interpreted as rock that has been partially melted, with the leucosome representing the silica-rich melt, the melanosome the residual solid rock left after partial melting, and the mesosome the original rock that has not yet experienced partial melting. Gneisses are characteristic of areas of regional metamorphism that reaches
651-416: The bottom of the deck in the other direction. These forces stretch out the rock like a plastic , and the original material is spread out into sheets. Per the polar decomposition theorem , the deformation produced by such shearing force is equivalent to rotation of the rock combined with shortening in one direction and extension in another. Some banding is formed from original rock material (protolith) that
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#1732798394784682-845: The county before discharging into the Back River, which empties into the Chesapeake Bay . The principal tributaries of Herring Run are the Western Branch, Chinquapin Run, Tiffany Run, Armistead Run, Biddison Run, Moores Run and Redhouse Run. The total length of the Herring Run main stem and tributaries is over 41 miles (66 km). Herring Run Park is a 375 acres (152 ha) wooded parkland in northeast Baltimore through which Herring Run flows for 2.3 miles (3.7 km). The politician William Smith lived on land now included in
713-556: The development of the gneiss's pervasive structural elements; and the Alleghanian - Palisades , which resulted in predominantly brittle faulting and open folding. The cause of the Grenvillian deformation is uncertain. The Taconic-Acadian deformation was caused by the collision of an ocean floor/island arc terrane with a continental margin or fringing microcontinent in the early Paleozoic . The Alleghanian-Pallisades deformation
744-402: The direction of greatest compression, also called the shortening direction, as platy minerals are rotated or recrystallized into parallel layers. A common cause of nonhydrodynamic stress is the subjection of the protolith (the original rock material that undergoes metamorphism) to extreme shearing force, a sliding force similar to the pushing of the top of a deck of cards in one direction, and
775-595: The granite basement and the second deforming and melting this basement to produce the domes. However, some gneiss domes may actually be the cores of metamorphic core complexes , regions of the deep crust brought to the surface and exposed during extension of the Earth's crust . The word gneiss has been used in English since at least 1757. It is borrowed from the German word Gneis , formerly also spelled Gneiss , which
806-413: The layered gneiss member includes stream cuts along Herring Run for 255 meters on either side of Arlington Avenue bridge near Morgan State University . The type locality of the augen gneiss member includes outcrops along Long Green Creek 385 meters southeast of Glenarm Road bridge. The type locality of the streaked-augen gneiss member includes outcrops along Merryman Branch 125 meters upstream from
837-521: The middle amphibolite to granulite metamorphic facies . In other words, the rock was metamorphosed at a temperature in excess of 600 °C (1,112 °F) at pressures between about 2 to 24 kbar . Many different varieties of rock can be metamorphosed to gneiss, so geologists are careful to add descriptions of the color and mineral composition to the name of any gneiss, such as garnet-biotite paragneiss or grayish-pink orthogneiss . Continental shields are regions of exposed ancient rock that make up
868-551: The park, which he purchased in 1770. The land for Herring Run Park was donated to the City of Baltimore by the real estate developer Frank Novak . The Maryland Department of the Environment has listed the Herring Run as an impaired tributary, due to the elevated amounts of fecal coliform bacteria found in it. Nonetheless, efforts continue to improve the stream's water quality . The Herring Run Watershed Association (HRWA)
899-596: The stable cores of continents. The rock exposed in the oldest regions of shields, which is of Archean age (over 2500 million years old), mostly belong to granite-greenstone belts. The greenstone belts contain metavolcanic and metasedimentary rock that has undergone a relatively mild grade of metamorphism, at temperatures of 350–500 °C (662–932 °F) and pressures of 200–500 MPa (2,000–5,000 bar). The greenstone belts are surrounded by high-grade gneiss terrains showing highly deformed low-pressure, high-temperature (over 500 °C (932 °F)) metamorphism to
930-433: Was caused by continental rifting in the early Mesozoic, and possibly late-Paleozoic trans-current plate motions. The name Baltimore Gneiss was first used by George Huntington Williams in 1892 to describe the variety of widely distributed gneisses in the Baltimore area. The Baltimore Gneiss has been used in the past as building stone in the Baltimore area. It is thought that some of the first buildings built in Baltimore in
961-569: Was founded in 1978 (originally as the Friends of Northeast Parks and Streams) and is now a fully staffed 501(c)(3) nonprofit organization dedicated to stewarding the watershed. Its efforts include stream cleanups; stream plantings; rain barrel distribution; resident education; green jobs creation; advocacy , and running a native plant nursery. In 2008, HRWA completed construction on the Herring Run Watershed Center,