1.
Igneous rock
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Igneous rock, or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava, the magma can be derived from partial melts of existing rocks in either a planets mantle or crust. Typically, the melting is caused by one or more of three processes, an increase in temperature, a decrease in pressure, or a change in composition, solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive rocks. Igneous rock may form with crystallization to form granular, crystalline rocks, Igneous and metamorphic rocks make up 90–95% of the top 16 km of the Earths crust by volume. Igneous rocks form about 15% of the Earths current land surface, most of the Earths oceanic crust is made of igneous rock. In terms of modes of occurrence, igneous rocks can be either intrusive or extrusive, the mineral grains in such rocks can generally be identified with the naked eye. Intrusive rocks can also be classified according to the shape and size of the intrusive body, typical intrusive formations are batholiths, stocks, laccoliths, sills and dikes. When the magma solidifies within the earths crust, it cools slowly forming coarse textured rocks, such as granite, gabbro, the central cores of major mountain ranges consist of intrusive igneous rocks, usually granite. When exposed by erosion, these cores may occupy huge areas of the Earths surface, intrusive igneous rocks that form at depth within the crust are termed plutonic rocks and are usually coarse-grained. Intrusive igneous rocks that form near the surface are termed subvolcanic or hypabyssal rocks, hypabyssal rocks are less common than plutonic or volcanic rocks and often form dikes, sills, laccoliths, lopoliths, or phacoliths. Extrusive igneous rocks, also known as rocks, are formed at the crusts surface as a result of the partial melting of rocks within the mantle. Extrusive igneous rocks cool and solidify quicker than intrusive igneous rocks and they are formed by the cooling of molten magma on the earths surface. The magma, which is brought to the surface through fissures or volcanic eruptions, hence such rocks are smooth, crystalline and fine-grained. Basalt is an extrusive igneous rock and forms lava flows, lava sheets. Some kinds of basalt solidify to form long polygonal columns, the Giants Causeway in Antrim, Northern Ireland is an example. The molten rock, with or without suspended crystals and gas bubbles, is called magma and it rises because it is less dense than the rock from which it was created. When magma reaches the surface from beneath water or air, it is called lava, eruptions of volcanoes into air are termed subaerial, whereas those occurring underneath the ocean are termed submarine. Black smokers and mid-ocean ridge basalt are examples of volcanic activity
2.
Diamond
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Diamond is a metastable allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the rate from diamond to graphite is negligible at standard conditions. Diamond is renowned as a material with superlative physical qualities, most of which originate from the covalent bonding between its atoms. In particular, diamond has the highest hardness and thermal conductivity of any bulk material and those properties determine the major industrial application of diamond in cutting and polishing tools and the scientific applications in diamond knives and diamond anvil cells. Because of its extremely rigid lattice, it can be contaminated by very few types of impurities, such as boron, small amounts of defects or impurities color diamond blue, yellow, brown, green, purple, pink, orange or red. Diamond also has relatively high optical dispersion, most natural diamonds are formed at high temperature and pressure at depths of 140 to 190 kilometers in the Earths mantle. Carbon-containing minerals provide the source, and the growth occurs over periods from 1 billion to 3.3 billion years. Diamonds are brought close to the Earths surface through deep volcanic eruptions by magma, Diamonds can also be produced synthetically in a HPHT method which approximately simulates the conditions in the Earths mantle. An alternative, and completely different growth technique is chemical vapor deposition, several non-diamond materials, which include cubic zirconia and silicon carbide and are often called diamond simulants, resemble diamond in appearance and many properties. Special gemological techniques have developed to distinguish natural diamonds, synthetic diamonds. The word is from the ancient Greek ἀδάμας – adámas unbreakable, the name diamond is derived from the ancient Greek αδάμας, proper, unalterable, unbreakable, untamed, from ἀ-, un- + δαμάω, I overpower, I tame. Diamonds have been known in India for at least 3,000 years, Diamonds have been treasured as gemstones since their use as religious icons in ancient India. Their usage in engraving tools also dates to early human history, later in 1797, the English chemist Smithson Tennant repeated and expanded that experiment. By demonstrating that burning diamond and graphite releases the same amount of gas, the most familiar uses of diamonds today are as gemstones used for adornment, a use which dates back into antiquity, and as industrial abrasives for cutting hard materials. The dispersion of light into spectral colors is the primary gemological characteristic of gem diamonds. In the 20th century, experts in gemology developed methods of grading diamonds, four characteristics, known informally as the four Cs, are now commonly used as the basic descriptors of diamonds, these are carat, cut, color, and clarity. A large, flawless diamond is known as a paragon and these conditions are met in two places on Earth, in the lithospheric mantle below relatively stable continental plates, and at the site of a meteorite strike. The conditions for diamond formation to happen in the mantle occur at considerable depth corresponding to the requirements of temperature and pressure
3.
Kimberley, Northern Cape
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Kimberley is the largest and capital city of the Northern Cape Province of South Africa. It is located approximately 110 km east of the confluence of the Vaal, the city has considerable historical significance due to its diamond mining past and the siege during the Second Boer War. Notable personalities such as Cecil Rhodes and Barney Barnato made their fortunes here, Kimberley was the first city in the Southern Hemisphere and the second in the world after Philadelphia to integrate electric street lights into its infrastructure on Sept.2,1882. The first Stock Exchange in Africa was also built in Kimberley, in 1866, Erasmus Jacobs found a small brilliant pebble on the banks of the Orange River, on the farm De Kalk leased from local Griquas, near Hopetown, which was his fathers farm. He showed the pebble to his father who sold it, the pebble was purchased from Jacobs by Schalk van Niekerk, who later sold it. It proved to be a 21. 25-carat diamond, and became known as the Eureka, three years later, in 1869, an 83. 5-carat diamond, which became known as the Star of South Africa, was found nearby. This diamond was sold by van Niekerk for £11,200, Henry Richard Giddy recounted how Esau Damoense, the cook for prospector Fleetwood Rawstones Red Cap Party, found diamonds in 1871 on Colesberg Kopje after he was sent there to dig as punishment. Rawstorne took the news to the diggings of the De Beer brothers — his arrival there sparking off the famous New Rush which. Within a month 800 claims were cut into the hillock which were worked frenetically by two to three thousand men, as the land was lowered so the hillock became a mine – in time, the world-renowned Kimberley Mine. The Cape Colony, Transvaal, Orange Free State and the Griqua leader Nikolaas Waterboer all laid claim to the diamond fields, the Free State Boers in particular wanted the area as it lay inside the natural borders created by Orange and Vaal Rivers. Following the mediation that was overseen by the governor of Natal, the Keate Award went in favour of Waterboer, consequently, the territory known as Griqualand West was proclaimed on 27 October 1871. Colonial Commissioners arrived in New Rush on 17 November 1871 to exercise authority over the territory on behalf of the Cape Governor. Digger objections and minor riots led to Governor Barklys visit to New Rush in September the following year, Richard Southey would arrive as Lieutenant-Governor of the intended Crown Colony in January 1873. Months passed however without any sign of the proclamation or of the new constitution and provision for representative government. The delay was in London where Secretary of State for the Colonies, Lord Kimberley, insisted that before electoral divisions could be defined, the places had to receive decent and intelligible names. His Lordship declined to be in any way connected with such a vulgarism as New Rush and as for the Dutch name, the matter was passed to Southey who gave it to his Colonial Secretary J. B. Currey. Roberts writes that when it came to renaming New Rush, proved himself a worthy diplomat and he made quite sure that Lord Kimberley would be able both to spell and pronounce the name of the main electoral division by, as he says, calling it after His Lordship. New Rush became Kimberley, by Proclamation dated 5 July 1873, digger sentiment was expressed in an editorial in the Diamond Field newspaper when it stated we went to sleep in New Rush and waked up in Kimberley, and so our dream was gone
4.
South Africa
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South Africa, officially the Republic of South Africa, is the southernmost country in Africa. South Africa is the 25th-largest country in the world by land area and it is the southernmost country on the mainland of the Old World or the Eastern Hemisphere. About 80 percent of South Africans are of Sub-Saharan African ancestry, divided among a variety of ethnic groups speaking different Bantu languages, the remaining population consists of Africas largest communities of European, Asian, and multiracial ancestry. South Africa is a multiethnic society encompassing a variety of cultures, languages. Its pluralistic makeup is reflected in the recognition of 11 official languages. The country is one of the few in Africa never to have had a coup détat, however, the vast majority of black South Africans were not enfranchised until 1994. During the 20th century, the black majority sought to recover its rights from the dominant white minority, with this struggle playing a role in the countrys recent history. The National Party imposed apartheid in 1948, institutionalising previous racial segregation, since 1994, all ethnic and linguistic groups have held political representation in the countrys democracy, which comprises a parliamentary republic and nine provinces. South Africa is often referred to as the Rainbow Nation to describe the multicultural diversity. The World Bank classifies South Africa as an economy. Its economy is the second-largest in Africa, and the 34th-largest in the world, in terms of purchasing power parity, South Africa has the seventh-highest per capita income in Africa. However, poverty and inequality remain widespread, with about a quarter of the population unemployed, nevertheless, South Africa has been identified as a middle power in international affairs, and maintains significant regional influence. The name South Africa is derived from the geographic location at the southern tip of Africa. Upon formation the country was named the Union of South Africa in English, since 1961 the long form name in English has been the Republic of South Africa. In Dutch the country was named Republiek van Zuid-Afrika, replaced in 1983 by the Afrikaans Republiek van Suid-Afrika, since 1994 the Republic has had an official name in each of its 11 official languages. Mzansi, derived from the Xhosa noun umzantsi meaning south, is a name for South Africa. South Africa contains some of the oldest archaeological and human fossil sites in the world, extensive fossil remains have been recovered from a series of caves in Gauteng Province. The area is a UNESCO World Heritage site and has termed the Cradle of Humankind
5.
Open-pit
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Open-pit, open-cast or open cut mining is a surface mining technique of extracting rock or minerals from the earth by their removal from an open pit or borrow. This form of mining differs from extractive methods that require tunneling into the earth, for minerals that occur deep below the surface—where the overburden is thick or the mineral occurs as veins in hard rock—underground mining methods are used to extract the valued material. Open-pit mines that produce building materials and dimension stone are commonly referred to as quarries, open-pit mines are typically enlarged until either the mineral resource is exhausted, or an increasing ratio of overburden to ore makes further mining uneconomic. When this occurs, the mines are sometimes converted to landfills for disposal of solid wastes. Open-cast mines are dug on benches, which describe vertical levels of the hole and these benches are usually on four to sixty meter intervals, depending on the size of the machinery that is being used. Many quarries do not use benches, as they are usually shallow, most walls of the pit are generally blast mined on an angle less than vertical, to prevent and minimize damage and danger from rock falls. This depends on how weathered the rocks are, and the type of rock, the inclined section of the wall is known as the batter, and the flat part of the step is known as the bench or berm. The steps in the walls help prevent rock falls continuing down the face of the wall. In some instances additional ground support is required and rock bolts, cable bolts, de-watering bores may be used to relieve water pressure by drilling horizontally into the wall, which is often enough to cause failures in the wall by itself. A haul road is situated at the side of the pit, forming a ramp up which trucks can drive, carrying ore. Waste rock is piled up at the surface, near the edge of the open pit and this is known as the waste dump. The waste dump is also tiered and stepped, to minimize degradation, ore which has been processed is known as tailings, and is generally a slurry. This is pumped to a dam or settling pond, where the water evaporates. This toxicity can harm the surrounding environment, after mining finishes, the mine area may undergo land rehabilitation. Waste dumps are contoured to flatten out, to further stabilise them. This is then covered with soil, and vegetation is planted to help consolidate the material. There are no long term studies on the success of these due to the relatively short time in which large scale open pit mining has existed. It may take hundreds to thousands of years for some waste dumps to become acid neutral, the dumps are usually fenced off to prevent livestock denuding them of vegetation
6.
Big Hole
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The first diamonds here were found on Colesberg Kopje by members of the Red Cap Party from Colesberg on the farm Vooruitzigt belonging to the De Beers brothers, in 1871. The ensuing scramble for claims led to the place being called New Rush, from mid-July 1871 to 1914 up to 50,000 miners dug the hole with picks and shovels, yielding 2,720 kilograms of diamonds. The Big Hole has a surface of 17 hectares and is 463 metres wide and it was excavated to a depth of 240 metres, but then partially infilled with debris reducing its depth to about 215 metres. Since then it has accumulated about 40 metres of water, leaving 175 metres of the hole visible. Once above-ground operations became too dangerous and unproductive, the pipe of the Kimberley Mine was also mined underground by Cecil Rhodes De Beers company to a depth of 1,097 metres. There is currently an effort in progress to register the Big Hole as a World Heritage Site, in 1872, one year after digging started, the population of the camp of diggers grew to around 50,000. As digging progressed, many men met their deaths in mining accidents, the unsanitary conditions, scarcity of water and fresh vegetables as well as the intense heat in the summer, also took their toll. This huge company further worked on the Big Hole until it came to the depth of 215 metres, with an area of about 17 hectares. There are other, larger, mine excavations, but these were created using earth-moving equipment rather than manual labour, there was an official opening during the Kimberleys centenary celebrations in 1971. One of the attractions was the Diamond Hall, the Mine Museum went through subsequent further upgrades. Between 2002 and 2005 De Beers invested R50 million in developing the Big Hole into a tourism facility. The new facility, the Big Hole Kimberley, elaborating a theme of Diamonds and Destiny, was expected to double visitor numbers to the Big Hole
7.
Crust (geology)
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In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle. The crust of the Earth is composed of a variety of igneous, metamorphic. The crust is underlain by the mantle, the upper part of the mantle is composed mostly of peridotite, a rock denser than rocks common in the overlying crust. The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity, the crust occupies less than 1% of Earths volume. The crust of the Earth is of two types, oceanic and continental. The oceanic crust is 5 km to 10 km thick and is composed primarily of basalt, diabase, the continental crust is typically from 30 km to 50 km thick and is mostly composed of slightly less dense rocks than those of the oceanic crust. Some of these less dense rocks, such as granite, are common in the continental crust, both the continental and oceanic crust float on the mantle. Because the continental crust is thicker, it both to greater elevations and greater depth than the oceanic crust. The slightly lower density of continental rock compared to basaltic oceanic rock contributes to the higher relative elevation of the top of the continental crust. As the top of the continental crust reaches elevations higher than that of the oceanic, the temperature of the crust increases with depth, reaching values typically in the range from about 200 °C to 400 °C at the boundary with the underlying mantle. The crust and underlying relatively rigid uppermost mantle make up the lithosphere, because of convection in the underlying plastic upper mantle and asthenosphere, the lithosphere is broken into tectonic plates that move. The temperature increases by as much as 30 °C for every kilometer locally in the part of the crust. Earth has probably always had some form of basaltic crust, in contrast, the bulk of the continental crust is much older. The oldest continental crustal rocks on Earth have ages in the range from about 3.7 to 4, some zircon with age as great as 4.3 billion years has been found in the Narryer Gneiss Terrane. The average age of the current Earths continental crust has been estimated to be about 2.0 billion years, most crustal rocks formed before 2.5 billion years ago are located in cratons. Such old continental crust and the underlying mantle asthenosphere are less dense than elsewhere in Earth, formation of new continental crust is linked to periods of intense orogeny, these periods coincide with the formation of the supercontinents such as Rodinia, Pangaea and Gondwana. The continental crust has a composition similar to that of andesite. The most abundant minerals in Earths continental crust are feldspars, which make up about 41% of the crust by weight, followed by quartz at 12%, Continental crust is enriched in incompatible elements compared to the basaltic ocean crust and much enriched compared to the underlying mantle
8.
Volcanic pipe
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Volcanic pipes are subterranean geological structures formed by the violent, supersonic eruption of deep-origin volcanoes. They are considered to be a type of diatreme, volcanic pipes are composed of a deep, narrow cone of solidified magma, and are usually largely composed of one of two characteristic rock types — kimberlite or lamproite. These rocks reflect the composition of the volcanoes deep magma sources and they are well known as the primary source of diamonds, and are mined for this purpose. Volcanic pipes form as the result of violent eruptions of deep-origin volcanoes, as the body of magma rises toward the surface, the volatile compounds transform to gaseous phase as pressure is reduced with decreasing depth. This sudden expansion propels the magma upward at rapid speeds, resulting in a shallow supersonic eruption, a useful analogy to this process is the uncorking of a shaken bottle of Champagne. Over time, the ring may erode back into the bowl. Kimberlite pipes are the source of most of the worlds diamond production, and also contain other precious gemstones and semi-precious stones, such as garnets, spinels. This broad cone is filled with volcanic ash and materials. Finally, the magma is pushed upward, filling the cone. The result is a martini-glass shaped deposit of material which appears mostly flat from the surface. Udachnaya pipe, a mine in Yakutia, Russia Elliott County Kimberlite Lake Ellen Kimberlite American Museum of Natural History. United States Geological Survey, Special Interest Publication
9.
Dike (geology)
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A dike or dyke, in geological usage, is a sheet of rock that formed in a fracture in a pre-existing rock body. Dikes can be either magmatic or sedimentary in origin, magmatic dikes form when magma intrudes into a crack then crystallizes as a sheet intrusion, either cutting across layers of rock or through an unlayered mass of rock. Clastic dikes are formed when sediment fills a pre-existing crack, an intrusive dike is an igneous body with a very high aspect ratio, which means that its thickness is usually much smaller than the other two dimensions. Thickness can vary from sub-centimeter scale to many meters, and the dimensions can extend over many kilometres. A dike is an intrusion into an opening cross-cutting fissure, shouldering aside other pre-existing layers or bodies of rock, near-horizontal, or conformable intrusions, along bedding planes between strata are called intrusive sills. Sometimes dikes appear in swarms, consisting of several to hundreds of dikes emplaced more or less contemporaneously during a single intrusive event, the worlds largest dike swarm is the Mackenzie dike swarm in the Northwest Territories, Canada. Dikes often form as either radial or concentric swarms around plutonic intrusives, the latter are known as ring dikes. Pegmatite dikes comprise extremely coarse crystalline granitic rocks - often associated with granite intrusions or metamorphic segregations. Aplite dikes are fine-grained or sugary-textured intrusives of granitic composition, in contrast to magmatic dikes, a sill is a magmatic sheet intrusion that forms within and parallel to the bedding of layered rock. Sedimentary dikes or clastic dikes are vertical bodies of rock that cut off other rock layers. Driven by the pressure the sediment breaks through overlying layers. When a soil is under permafrost conditions the water is totally frozen. When cracks are formed in rocks, they may fill up with sediments that fall in from above. The result is a body of sediment that cuts through horizontal layers. Batholith Ring dike Fissure vent Laccolith Runamo, formerly interpreted as a runic inscription
10.
Sill (geology)
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In geology, a sill is a tabular sheet intrusion that has intruded between older layers of sedimentary rock, beds of volcanic lava or tuff, or even along the direction of foliation in metamorphic rock. The term sill is synonymous with concordant intrusive sheet and this means that the sill does not cut across preexisting rocks, in contrast to dikes, discordant intrusive sheets which do cut across older rocks. Sills are fed by dikes, except in locations where they form in nearly vertical beds attached directly to a magma source. These planes or weakened areas allow the intrusion of a thin body of magma paralleling the existing bedding planes, concordant fracture zone. Sills parallel beds and foliations in the country rock. They can be emplaced in a horizontal orientation, although tectonic processes may cause subsequent rotation of horizontal sills into near vertical orientations. Sills can be confused with solidified lava flows, however, there are differences between them. Intruded sills will show partial melting and incorporation of the country rock. On both contact surfaces of the rock into which the sill has intruded, evidence of heating will be observed. Lava flows will show this evidence only on the side of the flow. In addition, lava flows will show evidence of vesicles where gases escaped into the atmosphere. Because sills generally form at shallow depths below the surface, the pressure of overlying rock prevents this from happening much, lava flows will also typically show evidence of weathering on their upper surface, whereas sills, if still covered by country rock, typically do not. Certain layered intrusions are a variety of sill that often contain important ore deposits, phanerozoic examples are usually smaller and include the Rùm peridotite complex of Scotland and the Skaergaard igneous complex of east Greenland. These intrusions often contain concentrations of gold, platinum, chromium, despite their concordant nature, many large sills change stratigraphic level within the intruded sequence, with each concordant part of the intrusion linked by relatively short dike-like segments. Such sills are known as transgressive, examples include the Whin Sill, the geometry of large sill complexes in sedimentary basins has become clearer with the availability of 3D seismic reflection data. Such data has shown that many sills have a saucer shape. Sill may also refer to the rise in depth near the mouth of a fjord caused by the moraine of the previous glacier. Sill swarm Batholith Stock Dike Laccolith Sheet intrusion
11.
Mantle (geology)
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The mantle is a layer inside a terrestrial planet and some other rocky planetary bodies. For a mantle to form, the body must be large enough to have undergone the process of planetary differentiation by density. The mantle surrounds the planetary core, the mantle is surrounded by the crust. The terrestrial planets, the Moon, two of Jupiters moons and the asteroid Vesta each have a made of silicate rock. Interpretation of spacecraft data suggests that at least two moons of Jupiter, as well as Titan and Triton each have a mantle made of ice or other solid volatile substances. The interior of Earth, similar to the terrestrial planets, is divided into layers of different composition. The mantle is a layer between the crust and the outer core, Earths mantle is a silicate rocky shell with an average thickness of 2,886 kilometres. The mantle makes up about 84% of Earths volume and it is predominantly solid but in geological time it behaves as a very viscous fluid. The mantle encloses the hot core rich in iron and nickel, past episodes of melting and volcanism at the shallower levels of the mantle have produced a thin crust of crystallized melt products near the surface. A thin crust, the part of the lithosphere, surrounds the mantle and is about 5 to 75 km thick. In some places under the ocean the mantle is exposed on the surface of Earth. The mantle is divided into sections which are based upon results from seismology and these layers are the following, the upper mantle, the transition zone, the lower mantle, and anomalous core–mantle boundary with a variable thickness. The uppermost mantle plus overlying crust are relatively rigid and form the lithosphere, below the lithosphere the upper mantle becomes notably more plastic. In some regions below the lithosphere, the shear velocity is reduced. Inge Lehmann discovered a seismic discontinuity at about 220 km depth, although this discontinuity has been found in other studies, the transition zone is an area of great complexity, it physically separates the upper and lower mantle. Very little is known about the lower mantle apart from that it appears to be relatively seismically homogeneous, the D layer at the core–mantle boundary separates the mantle from the core. A principal source of the heat that drives plate tectonics is the decay of uranium, thorium. The mantle differs substantially from the crust in its properties as the direct consequence of the difference in composition
12.
Volatiles
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In planetary science, volatiles are the group of chemical elements and chemical compounds with low boiling points that are associated with a planets or moons crust or atmosphere. Examples include nitrogen, water, carbon dioxide, ammonia, hydrogen, methane, in astrogeology, these compounds, in their solid state, often comprise large proportions of the crusts of moons and dwarf planets. In contrast with volatiles, elements and compounds with high boiling points are known as refractory substances, the terms gas and ice in this context can apply to compounds that may be solids, liquids or gases. The Moon is very low in volatiles, its crust contains oxygen chemically bound into the rocks, in igneous petrology the term more specifically refers to the volatile components of magma that affect the appearance and explosivity of volcanoes. Volatiles in a magma with a high viscosity, generally felsic with a silica content. Volatiles in a magma with a low viscosity, generally mafic with a silica content, tend to vent. Some volcanic eruptions are explosive because the mixing water and magma reaching the surface, releases energy suddenly. Moreover, in cases, the eruption is caused by volatiles dissolved in the magma. Approaching the surface, pressure decreases and the volatiles evolve creating bubbles that circulate in the liquid, the bubbles are connected together forming a network. This especially increments the fragmentation into small drops or spray or coagulate clots in gas, generally, 95-99% of magma is liquid rock. However, the percentage of gas present, represents a very large volume when it expands on reaching atmospheric pressure. Gas is a preponderant part in a system because it generates explosive eruptions. Magma in the mantle and lower crust have a lot of volatiles within and water, also they leak hydrogen sulfide and sulfur dioxide. Sulfur dioxide is usually possible to find in basaltic and rhyolite rocks, volcanoes also release a high amount of hydrogen chloride and hydrogen fluoride as volatiles. There are three factors that effect the dispersion of volatiles in magma, confining pressure, composition of magma. Pressure and composition are the most important parameters, to understand how the magma behaves rising the surface, the role of solubility within the magma must be known. An empirical law has used for different magma-volatiles combination. For instance, for water in magma the equation is n=0.1078 P where n is the amount of dissolved gas as weight percentage, the value changes for example for water in rhyolite where n=0.4111 P and for the carbon dioxide is n=0.0023 P
13.
Xenocryst
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A xenolith is a rock fragment which becomes enveloped in a larger rock during the latters development and solidification. In geology, the term xenolith is almost exclusively used to describe inclusions in igneous rock during magma emplacement, a xenocryst is an individual foreign crystal included within an igneous body. Examples of xenocrysts are quartz crystals in a silica-deficient lava and diamonds within kimberlite diatremes, although the term xenolith is most commonly associated with igneous inclusions, a broad definition could include rock fragments which have become encased in sedimentary rock. Xenoliths are sometimes found in recovered meteorites, xenoliths and xenocrysts provide important information about the composition of the otherwise inaccessible mantle. Basalts, kimberlites, lamproites and lamprophyres, which have their source in the mantle, often contain fragments. Xenoliths of dunite, peridotite and spinel lherzolite in basaltic lava flows are one example, kimberlites contain, in addition to diamond xenocrysts, fragments of lherzolites of varying composition. The aluminium-bearing minerals of these fragments provide clues to the depth of origin, calcic plagioclase is stable to a depth of 25 km. Between 25 km and about 60 km, spinel is the stable aluminium phase, at depths greater than about 60 km, dense garnet becomes the aluminium-bearing mineral. Some kimberlites contain xenoliths of eclogite, which is considered to be the high-pressure metamorphic product of basaltic oceanic crust, the large-scale inclusion of foreign rock strata at the margins of an igneous intrusion is called a roof pendant. Blatt, Harvey, and Robert J. Tracy
14.
Peridotite
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Peridotite is a dense, coarse-grained igneous rock consisting mostly of the minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica and it is high in magnesium, reflecting the high proportions of magnesium-rich olivine, with appreciable iron. Peridotite is derived from the Earths mantle, either as solid blocks and fragments, the compositions of peridotites from these layered igneous complexes vary widely, reflecting the relative proportions of pyroxenes, chromite, plagioclase, and amphibole. Peridotite is the dominant rock of the part of the Earths mantle. The word peridotite comes from the gemstone peridot, which consists of pale green olivine, classic peridotite is bright green with some specks of black, although most hand samples tend to be darker green. Peridotitic outcrops typically range from bright yellow to dark green in color. While green and yellow are the most common colors, peridotitic rocks may exhibit a range of colors such as blue, brown. Dunite, more than 90% olivine, typically with Mg/Fe ratio of about 9,1, wehrlite, mostly composed of olivine plus clinopyroxene. Harzburgite, mostly composed of olivine plus orthopyroxene, and relatively low proportions of basaltic ingredients, lherzolite, most common form of peridotite, mostly composed of olivine, orthopyroxene, and clinopyroxene, and have relatively high proportions of basaltic ingredients. Partial fusion of lherzolite and extraction of the melt fraction can leave a residue of harzburgite. Magnesium-rich olivine forms a proportion of peridotite, and so magnesium content is high. Layered igneous complexes have more varied compositions, depending on the fractions of pyroxenes, chromite, plagioclase. Minor minerals and mineral groups in peridotite include plagioclase, spinel, garnet, amphibole, in peridotite, plagioclase is stable at relatively low pressures, aluminous spinel at higher pressures, and garnet at yet higher pressures. Peridotite is the dominant rock of the Earths mantle above a depth of about 400 km, below that depth, olivine is converted to the higher-pressure mineral wadsleyite. Oceanic plates consist of up to about 100 km of peridotite covered by a thin crust, the crust, commonly about 6 km thick, consists of basalt, gabbro, and minor sediments. The peridotite below the ocean crust, abyssal peridotite, is found on the walls of rifts in the sea floor. Oceanic plates are usually subducted back into the mantle in subduction zones, peridotites also occur as fragments carried up by magmas from the mantle. Among the rocks that commonly include peridotite xenoliths are basalt and kimberlite, certain volcanic rocks, sometimes called komatiites, are so rich in olivine and pyroxene that they also can be termed peridotite
15.
Xenolith
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A xenolith is a rock fragment which becomes enveloped in a larger rock during the latters development and solidification. In geology, the term xenolith is almost exclusively used to describe inclusions in igneous rock during magma emplacement, a xenocryst is an individual foreign crystal included within an igneous body. Examples of xenocrysts are quartz crystals in a silica-deficient lava and diamonds within kimberlite diatremes, although the term xenolith is most commonly associated with igneous inclusions, a broad definition could include rock fragments which have become encased in sedimentary rock. Xenoliths are sometimes found in recovered meteorites, xenoliths and xenocrysts provide important information about the composition of the otherwise inaccessible mantle. Basalts, kimberlites, lamproites and lamprophyres, which have their source in the mantle, often contain fragments. Xenoliths of dunite, peridotite and spinel lherzolite in basaltic lava flows are one example, kimberlites contain, in addition to diamond xenocrysts, fragments of lherzolites of varying composition. The aluminium-bearing minerals of these fragments provide clues to the depth of origin, calcic plagioclase is stable to a depth of 25 km. Between 25 km and about 60 km, spinel is the stable aluminium phase, at depths greater than about 60 km, dense garnet becomes the aluminium-bearing mineral. Some kimberlites contain xenoliths of eclogite, which is considered to be the high-pressure metamorphic product of basaltic oceanic crust, the large-scale inclusion of foreign rock strata at the margins of an igneous intrusion is called a roof pendant. Blatt, Harvey, and Robert J. Tracy
16.
Magma
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Besides molten rock, magma may also contain suspended crystals, dissolved gas and sometimes gas bubbles. Magma often collects in magma chambers that may feed a volcano or solidify underground to form an intrusion, magma is capable of intruding into adjacent rocks, extrusion onto the surface as lava, and explosive ejection as tephra to form pyroclastic rock. Magma is a complex high-temperature fluid substance, temperatures of most magmas are in the range 700 °C to 1300 °C, but very rare carbonatite magmas may be as cool as 600 °C, and komatiite magmas may have been as hot as 1600 °C. Environments of magma formation and compositions are commonly correlated, environments include subduction zones, continental rift zones, mid-ocean ridges and hotspots. Despite being found in such locales, the bulk of the Earths crust. Except for the outer core, most of the Earth takes the form of a rheid. Magma, as liquid, preferentially forms in high temperature, low pressure environments within several kilometers of the Earths surface, magma compositions may evolve after formation by fractional crystallization, contamination, and magma mixing. By definition rock formed of solidified magma is called igneous rock, melting of solid rocks to form magma is controlled by three physical parameters, temperature, pressure, and composition. Mechanisms are discussed in the entry for igneous rock, as a rock melts, its volume changes. When enough rock is melted, the small globules of melt link up, under pressure within the earth, as little as a fraction of a percent partial melting may be sufficient to cause melt to be squeezed from its source. The degree of melting is critical for determining what type of magma is produced. The degree of partial melting required to form a melt can be estimated by considering the relative enrichment of incompatible elements versus compatible elements, incompatible elements commonly include potassium, barium, cesium, and rubidium. Rock types produced by small degrees of melting in the Earths mantle are typically alkaline. Typically, primitive melts of this composition form lamprophyre, lamproite, kimberlite and sometimes nepheline-bearing mafic rocks such as alkali basalts, pegmatite may be produced by low degrees of partial melting of the crust. Some granite-composition magmas are eutectic melts, and they may be produced by low to high degrees of melting of the crust. At high degrees of melting of the crust, granitoids such as tonalite, granodiorite and monzonite can be produced. Being only the time in recorded history that magma had been reached, IDDP decided to invest in the hole. A cemented steel case was constructed in the hole with a perforation at the close to the magma
17.
Craton
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A craton is an old and stable part of the continental lithosphere, where the lithosphere consists of the Earths two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and rifting of continents, cratons are found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by sedimentary rock. They have a thick crust and deep roots that extend as much as several hundred kilometres into the Earths mantle. The term craton is used to distinguish the stable portion of the continental crust from regions that are geologically active. Cratons can be described as shields, in which the basement rock crops out at the surface, the word craton was first proposed by the Austrian geologist Leopold Kober in 1921 as Kratogen, referring to stable continental platforms, and orogen as a term for mountain or orogenic belts. Later authors shortened the term to kraton and then to craton. Cratons are subdivided geographically into geologic provinces, a geologic province is a spatial entity with common geologic attributes. A province may include a single dominant structural element such as a basin or a fold belt. Adjoining provinces may appear similar in structure but be considered due to differing histories. At that depth, craton roots extend into the asthenosphere, craton lithosphere is distinctly different from oceanic lithosphere because cratons have a neutral or positive buoyancy, and a low intrinsic isopycnic density. This low density offsets density increases due to contraction and prevents the craton from sinking into the deep mantle. Cratonic lithosphere is much older than oceanic lithosphere—up to 4 billion years versus 180 million years, rock fragments carried up from the mantle by magmas containing peridotite have been delivered to the surface as inclusions in subvolcanic pipes called kimberlites. These inclusions have densities consistent with composition and are composed of mantle material residual from high degrees of partial melt. Peridotite is strongly influenced by the inclusion of moisture, craton peridotite moisture content is unusually low, which leads to much greater strength. It also contains high percentages of low-weight magnesium instead of higher-weight calcium, peridotites are important for understanding the deep composition and origin of cratons because peridotite nodules are pieces of mantle rock modified by partial melting. Harzburgite peridotites represent the crystalline residues after extraction of melts of compositions like basalt, an associated class of inclusions called eclogites, consists of rocks corresponding compositionally to oceanic crust that has metamorphosed under deep mantle conditions. Isotopic studies reveal that many eclogite inclusions are samples of ancient oceanic crust subducted billions of years ago to depths exceeding 150 km into the deep kimberlite diamond areas and they remained fixed there within the drifting tectonic plates until carried to the surface by deep-rooted magmatic eruptions
18.
Lithosphere
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A lithosphere is the rigid, outermost shell of a terrestrial-type planet or natural satellite that is defined by its rigid mechanical properties. On Earth, it is composed of the crust and the portion of the mantle that behaves elastically on time scales of thousands of years or greater. The outermost shell of a planet, the crust, is defined on the basis of its chemistry. Earths lithosphere includes the crust and the uppermost mantle, which constitute the hard, the lithosphere is subdivided into tectonic plates. The uppermost part of the lithosphere that chemically reacts to the atmosphere, hydrosphere and biosphere through the forming process is called the pedosphere. The lithosphere is underlain by the asthenosphere which is the weaker, hotter, the study of past and current formations of landscapes is called geomorphology. The concept of the lithosphere as Earth’s strong outer layer was described by A. E. H, love in his 1911 monograph Some problems of Geodynamics and further developed by Joseph Barrell, who wrote a series of papers about the concept and introduced the term lithosphere. The concept was based on the presence of significant gravity anomalies over continental crust and these ideas were expanded by Reginald Aldworth Daly in 1940 with his seminal work Strength and Structure of the Earth and have been broadly accepted by geologists and geophysicists. The temperature at which olivine begins to deform viscously is often used to set this isotherm because olivine is generally the weakest mineral in the upper mantle, the mantle part of the lithosphere consists largely of peridotite. The crust is distinguished from the mantle by the change in chemical composition that takes place at the Moho discontinuity. Oceanic lithosphere consists mainly of mafic crust and ultramafic mantle and is denser than continental lithosphere, oceanic lithosphere thickens as it ages and moves away from the mid-ocean ridge. This thickening occurs by conductive cooling, which converts hot asthenosphere into lithospheric mantle and causes the oceanic lithosphere to become increasingly thick, the thickness of the mantle part of the oceanic lithosphere can be approximated as a thermal boundary layer that thickens as the square root of time. H ∼2 κ t Here, h is the thickness of the mantle lithosphere, κ is the thermal diffusivity for silicate rocks. The age is equal to L/V, where L is the distance from the spreading centre of mid-oceanic ridge. Oceanic lithosphere is less dense than asthenosphere for a few tens of millions of years and this is because the chemically differentiated oceanic crust is lighter than asthenosphere, but thermal contraction of the mantle lithosphere makes it more dense than the asthenosphere. New oceanic lithosphere is constantly being produced at mid-ocean ridges and is recycled back to the mantle at subduction zones, geoscientists can directly study the nature of the subcontinental mantle by examining mantle xenoliths brought up in kimberlite, lamproite, and other volcanic pipes. The histories of these xenoliths have been investigated by many methods, such studies have confirmed that mantle lithospheres below some cratons have persisted for periods in excess of 3 billion years, despite the mantle flow that accompanies plate tectonics. Cryosphere Geosphere Kola Superdeep Borehole Plate tectonics Solid Earth Chernicoff, Stanley, Whitney, earths Crust, Lithosphere and Asthenosphere Crust and Lithosphere
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Asthenosphere
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The asthenosphere is the highly viscous, mechanically weak and ductilely deforming region of the upper mantle of the Earth. It lies below the lithosphere, at depths between approximately 80 and 200 km below the surface, the Lithosphere-Asthenosphere boundary is usually referred to as LAB. The asthenosphere is generally solid, although some of its regions could be melted, the lower boundary of the asthenosphere is not well defined. The thickness of the asthenosphere depends mainly on the temperature, in some regions the asthenosphere could extend as deep as 700 km. It is considered the region of mid-ocean ridge basalt. The asthenosphere is a part of the mantle just below the lithosphere that is involved in plate tectonic movement. The lithosphere-asthenosphere boundary is taken at the 1300 °C isotherm, above which the mantle behaves in a rigid fashion. Seismic waves pass relatively slowly through the asthenosphere compared to the lithospheric mantle, thus it has been called the low-velocity zone. This decreasing in seismic waves velocity from lithosphere to asthenosphere could be caused by the presence of a small percentage of melt in the asthenosphere. The lower boundary of the LVZ lies at a depth of 180–220 km, in the old oceanic mantle the transition from the lithosphere to the asthenosphere, the so-called lithosphere-asthenosphere boundary is shallow with a sharp and large velocity drop. At the mid-ocean ridges the LAB rises to within a few kilometers of the ocean floor, the upper part of the asthenosphere is believed to be the zone upon which the great rigid and brittle lithospheric plates of the Earths crust move about. In this way, it flows like a current, radiating heat outward from the Earths interior. Above the asthenosphere, at the rate of deformation, rock behaves elastically and, being brittle, can break. The rigid lithosphere is thought to float or move about on the slowly flowing asthenosphere, an Introduction to the Solar System. San Diego State University, The Earths internal heat energy and interior structure
20.
Facies
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Ideally, a sedimentary facies is a distinctive rock unit that forms under certain conditions of sedimentation, reflecting a particular process or environment. Sedimentary facies are either descriptive or interpretative, sedimentary facies are bodies of sediment that are recognizably distinct from adjacent sediments that resulted from different depositional environments. Generally, geologists distinguish facies by the aspect of the rock or sediment being studied, Facies based on petrological characters are called lithofacies, whereas facies based on fossil content are called biofacies. A facies is usually further subdivided, for example, one might refer to a tan, the characteristics of the rock unit come from the depositional environment and from the original composition. Sedimentary facies reflect their depositional environment, each facies being a kind of sediment for that area or environment. Since its inception, the concept has been extended to related geological concepts. For example, characteristic associations of organic microfossils, and particulate organic material, discrete seismic units are similarly referred to as seismic facies. Walthers Law of Facies, or simply Walthers Law, named after the geologist Johannes Walther, conversely, it states that when a depositional environment migrates laterally, sediments of one depositional environment come to lie on top of another. In Russia the law is known as Golovkinsky-Walthers Law, honoring also Nikolai A. Golovkinsky, a classic example of this law is the vertical stratigraphic succession that typifies marine transgressions and regressions. The sequence of minerals that develop during progressive metamorphism define a facies series, seismic facies are mappable three-dimensional seismic units composed of reflection units whose parameters differ from adjacent facies units. Lithofacies Metamorphic rock Sequence stratigraphy Stratum
21.
Geomorphology
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Geomorphology is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or near the Earths surface. Geomorphologists work within disciplines such as geography, geology, geodesy, engineering geology, archaeology. This broad base of interests contributes to many styles and interests within the field. Earths surface is modified by a combination of processes that sculpt landscapes, and geologic processes that cause tectonic uplift and subsidence. Many of these factors are strongly mediated by climate, the broad-scale topographies of the Earth illustrate this intersection of surface and subsurface action. Mountain belts are uplifted due to geologic processes, denudation of these high uplifted regions produces sediment that is transported and deposited elsewhere within the landscape or off the coast. On progressively smaller scales, similar ideas apply, where individual landforms evolve in response to the balance of additive processes, often, these processes directly affect each other, ice sheets, water, and sediment are all loads that change topography through flexural isostasy. Topography can modify the climate, for example through orographic precipitation. Many geomorphologists are particularly interested in the potential for feedbacks between climate and tectonics, mediated by geomorphic processes, in addition to these broad-scale questions, geomorphologists address issues that are more specific and/or more local. Fluvial geomorphologists focus on rivers, how they transport sediment, migrate across the landscape, cut into bedrock, respond to environmental and tectonic changes, and interact with humans. Soils geomorphologists investigate soil profiles and chemistry to learn about the history of a landscape and understand how climate, biota. Other geomorphologists study how hillslopes form and change, still others investigate the relationships between ecology and geomorphology. Because geomorphology is defined to comprise everything related to the surface of the Earth and its modification, geomorphologists use a wide range of techniques in their work. These may include fieldwork and field data collection, the interpretation of remotely sensed data, geochemical analyses, geomorphologists may rely on geochronology, using dating methods to measure the rate of changes to the surface. Practical applications of geomorphology include hazard assessment, river control and stream restoration, planetary geomorphology studies landforms on other terrestrial planets such as Mars. Indications of effects of wind, fluvial, glacial, mass wasting, meteor impact, tectonics and this effort not only helps better understand the geologic and atmospheric history of those planets but also extends geomorphological study of the Earth. Planetary geomorphologists often use Earth analogues to aid in their study of surfaces of other planets, other than some notable exceptions in antiquity, geomorphology is a relatively young science, growing along with interest in other aspects of the earth sciences in the mid-19th century. This section provides a brief outline of some of the major figures
22.
Volcanism
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It includes all phenomena resulting from and causing magma within the crust or mantle of the body, to rise through the crust and form volcanic rocks on the surface. Magma from the mantle or lower crust rises through its crust towards the surface, if magma reaches the surface, its behavior depends on the viscosity of the molten constituent rock. Viscous magma produces volcanoes characterised by explosive eruptions, while non-viscous magma produce volcanoes characterised by effusive eruptions pouring large amounts of lava onto the surface, in some cases, rising magma can cool and solidify without reaching the surface. Instead, the cooled and solidified igneous mass crystallises within the crust to form an igneous intrusion, as magma cools the chemicals in the crystals formed are effectively removed from the main mix of the magma, so the chemical content of the remaining magma evolves as it solidifies slowly. Fresh unevolved magma injections can remobilise more evolved magmas, allowing eruptions from more viscous magmas, movement of molten rock in the mantle, caused by thermal convection currents, coupled with gravitational effects of changes on the earths surface drive plate tectonic motion and ultimately volcanism. Volcanoes are places where magma reaches the earths surface, the type of volcano depends on the location of the eruption and the consistency of the magma. These are formed where magma pushes between existing rock, intrusions can be in the form of batholiths, dikes, sills, earthquakes are generally associated with plate tectonic activity, but some earthquakes are generated as a result of volcanic activity. These are formed where water interacts with volcanism and these include geysers, fumaroles, hotsprings and mudpots, they are often used as a source of geothermal energy. The amount of gas and ash emitted by volcanic eruptions has a significant effect on the Earths climate, large eruptions correlate well with some significant climate change events. When the magma cools it solidifies and forms rocks, the type of rock formed depends on the composition of the magma. Magma that reaches the surface to become lava cools rapidly resulting in rocks with small crystals such as basalt, some of this magma may cool extremely rapidly and will form volcanic glass such as obsidian. Magma that remains trapped below ground in thin intrusions cools slower than magma exposed to the surface, magma that remains trapped in large quantities below ground cools most slowly resulting in rocks with larger crystals - such as granite and gabbro. Existing rocks that come into contact with magma may be melted and assimilated into the magma, other rocks adjacent to the magma may be altered by contact metamorphism or metasomatism as they are affected by the heat and escaping or externally circulating hydrothermal fluids. Volcanism is not confined only to Earth, but is thought to be found on any body having a solid crust, evidence of volcanism should still be found on any body that has had volcanism at some point in its history. It can be surmised that volcanism exists on planets and moons of this type in other systems as well. In 2014, scientists found 70 lava flows which formed on the Moon in the last 100 million years, bimodal volcanism Continental drift Hotspot Volcanic arc Glossary of Volcanic Terms. G. J. Hudak, University of Wisconsin Oshkosh,2001, crumpler, L. S. and Lucas, S. G. Volcanoes of New Mexico, An Abbreviated Guide For Non-Specialists. New Mexico Museum of Natural History and Science Bulletin, archived from the original on 2007-03-21
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Earth's mantle
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The mantle is a layer inside a terrestrial planet and some other rocky planetary bodies. For a mantle to form, the body must be large enough to have undergone the process of planetary differentiation by density. The mantle surrounds the planetary core, the mantle is surrounded by the crust. The terrestrial planets, the Moon, two of Jupiters moons and the asteroid Vesta each have a made of silicate rock. Interpretation of spacecraft data suggests that at least two moons of Jupiter, as well as Titan and Triton each have a mantle made of ice or other solid volatile substances. The interior of Earth, similar to the terrestrial planets, is divided into layers of different composition. The mantle is a layer between the crust and the outer core, Earths mantle is a silicate rocky shell with an average thickness of 2,886 kilometres. The mantle makes up about 84% of Earths volume and it is predominantly solid but in geological time it behaves as a very viscous fluid. The mantle encloses the hot core rich in iron and nickel, past episodes of melting and volcanism at the shallower levels of the mantle have produced a thin crust of crystallized melt products near the surface. A thin crust, the part of the lithosphere, surrounds the mantle and is about 5 to 75 km thick. In some places under the ocean the mantle is exposed on the surface of Earth. The mantle is divided into sections which are based upon results from seismology and these layers are the following, the upper mantle, the transition zone, the lower mantle, and anomalous core–mantle boundary with a variable thickness. The uppermost mantle plus overlying crust are relatively rigid and form the lithosphere, below the lithosphere the upper mantle becomes notably more plastic. In some regions below the lithosphere, the shear velocity is reduced. Inge Lehmann discovered a seismic discontinuity at about 220 km depth, although this discontinuity has been found in other studies, the transition zone is an area of great complexity, it physically separates the upper and lower mantle. Very little is known about the lower mantle apart from that it appears to be relatively seismically homogeneous, the D layer at the core–mantle boundary separates the mantle from the core. A principal source of the heat that drives plate tectonics is the decay of uranium, thorium. The mantle differs substantially from the crust in its properties as the direct consequence of the difference in composition
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Diatreme
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A diatreme, sometimes known as a maar-diatreme volcano, is a volcanic pipe formed by a gaseous explosion. A relatively shallow crater is left and a rock filled fracture in the Earths crust, diatremes breach the Earths surface and produce a steep inverted cone shape. The term diatreme has been applied more generally to any body of broken rock formed by explosive or hydrostatic forces. Maar-diatreme volcanoes are not uncommon, reported as the second most common type of volcanoes on continents, igneous intrusions cause the formation of a diatreme, only in the specific setting where groundwater exists. This means most igneous intrusions do not produce diatremes, diatreme formation is sometimes associated with kimberlite magma, which originates in the upper mantle. When a diatreme is formed due to an intrusion, there is a possibility that diamonds may be brought up. Kimberlite magmas can sometimes include chunks of diamond as xenoliths, making them economically significant, diatremes are sometimes associated with deposition of economically significant mineral deposits. A significant diatreme event was that which formed the giant Sullivan galena orebody in British Columbia, other diatremes in British Columbia include the Blackfoot diatreme and Cross diatreme. 15,2003, pp. 72-83 Definition from blogspot. com
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Maar
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A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption. A maar characteristically fills with water to form a shallow crater lake which may also be called a maar. The name comes from a Moselle Franconian dialect word used for the lakes of the Daun area of Germany. Maars range in size from 60 to 8,000 m across and from 10 to 200 m deep, most maars have low rims composed of a mixture of loose fragments of volcanic rocks and rocks torn from the walls of the diatreme. Maar lakes, also referred to simply as maars, occur when groundwater or precipitation fills the funnel-shaped, examples of these types of maar are the three maars at Daun in the Eifel mountains of Germany. A dry maar results when a maar lake dries out, becomes aggraded or silted up, an example of the latter is the Eckfelder Maar. Near Steffeln is the Eichholzmaar which has dried out during the last century and is being renaturalised into a maar, in some cases the underlying rock is so porous that maar lakes are unable to form. After winters of snow and rainfall many dry maars fill partially and temporarily with water, others contain small bogs or often artificial ponds that, however. The largest known maars are found on the Seward Peninsula in northwest Alaska and these maars range in size from 4,000 to 8,000 m in diameter and a depth up to 300 m. These eruptions occurred in a period of about 100,000 years and their large size is due to the explosive reaction that occurs when magma comes into contact with permafrost. Hydromagmatic eruptions are explosive when the ratio of water to magma is low. Since permafrost melts slowly, it provides a source of water to the eruption while keeping the water to magma ratio low. This produces the prolonged, explosive eruptions that created these large maars, examples of the Seward Peninsula maars include North Killeak Maar, South Killeak Maar, Devil Mountain Maar and Whitefish Maar. Maars occur in western North America, Patagonia in South America, the Eifel region of Germany, elsewhere in Europe, La Vestide du Pal in the Ardèche department of France provides a spectacular example of a maar easily visible from the ground or air. Kilbourne Hole and Hunts Hole, in southern New Mexico near El Paso, the Crocodile Lake in Los Baños in the Philippines was originally thought of as a volcanic crater is also a maar. The notorious, carbon dioxide-saturated Lake Nyos in Africa is another example, an excellent example of a maar is Zuni Salt Lake in New Mexico, a shallow saline lake that occupies a flat-floored crater about 6,500 ft across and 400 ft deep. Its low rim is composed of pieces of basaltic lava and wall rocks of the underlying diatreme. Maars in Canada are found in the Wells Gray-Clearwater volcanic field of east-central British Columbia, a notable field of maars is found in the Pali-Aike Volcanic Field in Patagonia, South America
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Jurassic
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The Jurassic is a geologic period and system that spans 56.3 million years from the end of the Triassic Period 201.3 million years ago to the beginning of the Cretaceous Period 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era, also known as the Age of Reptiles, the start of the period is marked by the major Triassic–Jurassic extinction event. The Jurassic is named after the Jura Mountains within the European Alps, by the beginning of the Jurassic, the supercontinent Pangaea had begun rifting into two landmasses, Laurasia to the north and Gondwana to the south. This created more coastlines and shifted the continental climate from dry to humid, on land, the fauna transitioned from the Triassic fauna, dominated by both dinosauromorph and crocodylomorph archosaurs, to one dominated by dinosaurs alone. The first birds also appeared during the Jurassic, having evolved from a branch of theropod dinosaurs, other major events include the appearance of the earliest lizards, and the evolution of therian mammals, including primitive placentals. Crocodilians made the transition from a terrestrial to a mode of life. The oceans were inhabited by marine reptiles such as ichthyosaurs and plesiosaurs, the chronostratigraphic term Jurassic is directly linked to the Jura Mountains. The name Jura is derived from the Celtic root jor, which was Latinised into juria, the Jurassic period is divided into the Early Jurassic, Middle, and Late Jurassic epochs. The Jurassic System, in stratigraphy, is divided into the Lower Jurassic, Middle, the separation of the term Jurassic into three sections goes back to Leopold von Buch. The Jurassic North Atlantic Ocean was relatively narrow, while the South Atlantic did not open until the following Cretaceous period, the Tethys Sea closed, and the Neotethys basin appeared. Climates were warm, with no evidence of glaciation, as in the Triassic, there was apparently no land over either pole, and no extensive ice caps existed. In contrast, the North American Jurassic record is the poorest of the Mesozoic, the Jurassic was a time of calcite sea geochemistry in which low-magnesium calcite was the primary inorganic marine precipitate of calcium carbonate. Carbonate hardgrounds were thus very common, along with calcitic ooids, calcitic cements, the first of several massive batholiths were emplaced in the northern American cordillera beginning in the mid-Jurassic, marking the Nevadan orogeny. Important Jurassic exposures are found in Russia, India, South America, Japan, Australasia. As the Jurassic proceeded, larger and more groups of dinosaurs like sauropods and ornithopods proliferated in Africa. Middle Jurassic strata are well represented nor well studied in Africa. Late Jurassic strata are also poorly represented apart from the spectacular Tendaguru fauna in Tanzania, the Late Jurassic life of Tendaguru is very similar to that found in western North Americas Morrison Formation. During the Jurassic period, the primary living in the sea were fish
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Pennsylvania
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Pennsylvania /ˌpɛnsᵻlˈveɪnjə/, officially the Commonwealth of Pennsylvania, is a state located in the northeastern and Mid-Atlantic regions of the United States. The Appalachian Mountains run through its middle, Pennsylvania is the 33rd largest, the 5th most populous, and the 9th most densely populated of the 50 United States. The states five most populous cities are Philadelphia, Pittsburgh, Allentown, Erie, the state capital, and its ninth-largest city, is Harrisburg. Pennsylvania has 140 miles of shoreline along Lake Erie and the Delaware Estuary. The state is one of the 13 original founding states of the United States, it came into being in 1681 as a result of a land grant to William Penn. Part of Pennsylvania, together with the present State of Delaware, had earlier been organized as the Colony of New Sweden and it was the second state to ratify the United States Constitution, on December 12,1787. Independence Hall, where the United States Declaration of Independence and United States Constitution were drafted, is located in the states largest city of Philadelphia, during the American Civil War, the Battle of Gettysburg, was fought in the south central region of the state. Valley Forge near Philadelphia was General Washingtons headquarters during the winter of 1777–78. Pennsylvania is 170 miles north to south and 283 miles east to west, of a total 46,055 square miles,44,817 square miles are land,490 square miles are inland waters, and 749 square miles are waters in Lake Erie. It is the 33rd largest state in the United States, Pennsylvania has 51 miles of coastline along Lake Erie and 57 miles of shoreline along the Delaware Estuary. Cities include Philadelphia, Reading, Lebanon and Lancaster in the southeast, Pittsburgh in the southwest, the tri-cities of Allentown, Bethlehem, the northeast includes the former anthracite coal mining communities of Scranton, Wilkes-Barre, Pittston City, and Hazleton. Erie is located in the northwest, the state has 5 regions, namely the Allegheny Plateau, Ridge and Valley, Atlantic Coastal Plain, Piedmont, and the Erie Plain. Straddling two major zones, the majority of the state, with the exception of the corner, has a humid continental climate. The largest city, Philadelphia, has characteristics of the humid subtropical climate that covers much of Delaware. Moving toward the interior of the state, the winter climate becomes colder, the number of cloudy days increase. Western areas of the state, particularly locations near Lake Erie, can receive over 100 inches of snowfall annually, the state may be subject to severe weather from spring through summer into fall. Tornadoes occur annually in the state, sometimes in large numbers, the Tuscarora Nation took up temporary residence in the central portion of Pennsylvania ca. Both the Dutch and the English claimed both sides of the Delaware River as part of their lands in America
28.
Monongahela River
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The Monongahela joins the Allegheny River to form the Ohio River at Pittsburgh. The Native American word Monongahela means falling banks, in reference to the instability of the rivers banks. The Lenape Language Project renders the word as Mënaonkihëla, translated where banks cave in or erode, from the verbs mënaonkihële the dirt caves off and mënaonke, it has a loose bank. Monongalia County and the town of Monongah, both in West Virginia, are named for the river, as is Monongahela in Pennsylvania, the river is navigable its entire length with a series of locks and dams that maintain a minimum depth of 9 feet to accommodate coal-laden barges. In Pennsylvania, the Monongahela is met by two tributaries, the Cheat River, which joins at Point Marion, and the Youghiogheny River. The upper drainage area of the basin is renowned for its whitewater kayaking opportunities. The land here is of a rugged plateau type which allows streams to gather sufficient water volume before they fall off the plateau. An ice dam created a vast lake—known as Lake Monongahela—stretching from its outlet at present-day Beaver, Pennsylvania for 200 miles south to at least Weston, West Virginia. It was as much as 100 miles wide at its maximum, hundreds of feet deep in places, its western and southern overflow gradually created the present-day upper Ohio River Valley. The Monongahela River valley was the site of a famous, if small, battle that was one of the first in the French and it resulted in a sharp defeat for British and Colonial forces against those of the French and their Native American allies. Originally planned to run as far south as the Cheat River, the system was extended to Fairmont, in 1897, the federal government took possession of the Monongahela Navigation through condemnation proceedings. Later, the combinations were increased in size and reduced in number. In 2006, the system, operated by the U. S. Army Corps of Engineers, had nine dam-locks along 128.7 miles of waterway. The locks overcame a change in elevation of about 147 feet, briefly linked to the Monongahela Navigation was the Youghiogheny Navigation, a slack water system of 18.5 miles between McKeesport and West Newton. It had two dam-locks overcoming a change in elevation of about 27 feet, opening in 1850, it was destroyed by a flood in 1865. During the 19th century, the Monongahela was heavily used by industry, three ships in the United States Navy have been named Monongahela after the river. In the 1930s, severe drought caused the river to run dry, the river was the site of a famous airplane crash that has become the subject of numerous urban legends and conspiracy theories. All six crewmen survived the crash, but two later succumbed to exposure and drowned, despite the relative shallowness of the water, the aircraft was never recovered
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Fayette County, Pennsylvania
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Fayette County is a county located in the U. S. state of Pennsylvania. Fayette County is located in southwestern Pennsylvania, adjacent to Maryland, as of the 2010 census, the population was 136,606. The county was created on September 26,1783, from part of Westmoreland County, Fayette County is part of the Pittsburgh, PA Metropolitan Statistical Area. The first Europeans in Fayette County were explorers, who had used an ancient American Indian trail that bisected the county on their journey across the Appalachian Mountains. In 1754, when control of the area was still in dispute between France and Great Britain, 22-year-old George Washington fought against the French at Jumonville Glen and Fort Necessity. British forces under Washington and General Edward Braddock improved roads throughout the region, during the American Revolution, Fayette County was plagued by attacks from British-allied Indians and remained isolated as a frontier region. Also retarding settlement was a dispute with Virginia, Virginias District of West Augusta. In 1780 the dispute was settled by the government in favor of Pennsylvania. President George Washington called out the militias to restore order, Fayette County continued to be important to travelers in the early 1800s. The National Road provided a route through the mountains of the county for settlers heading west, the shipyards in Brownsville on the Monongahela River built ships for both the domestic and international trade. As Pittsburgh developed its industries in the century, Fayette County become a center of coal mining. From the 1880s to the early 1900s, the great expansion in steel production became nationally important. Both new European immigrants and African Americans in the Great Migration from the rural South were attracted to the Pittsburgh area for industrial jobs, the historic Scottish and German farming communities established in the earlier 19th century were soon overshadowed by the wave of immigrants from Southern and Eastern Europe. By World War II, Fayette County had a new unionized working class that enjoyed increased prosperity, in the 1950s, however, the coal industry fell into decline. In the 1970s, the restructuring and collapse of American steel resulted in a loss of industrial jobs. The population has declined since the peak in 1940, as residents have had to move elsewhere for work, the loss of union jobs caused many working families to drop out of the middle class. Only a few mines are being worked in the 21st century, the region is slowly transitioning toward the service sector, with an increase in jobs in fields such as telemarketing. According to the U. S. Census Bureau, the county has an area of 798 square miles
30.
Greene County, Pennsylvania
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Greene County is a county located in the U. S. state of Pennsylvania. As of the 2010 census, the population was 38,686, Greene County was created on February 9,1796, from part of Washington County and named for General Nathanael Greene. Greene County is part of the Pittsburgh DMA and it is located in the area of southwestern Pennsylvania that was formerly claimed by Virginia, the District of West Augusta. According to the U. S. Census Bureau, the county has an area of 578 square miles. The population density was 67 people per square mile, there were 16,678 housing units at an average density of 29 per square mile. 1.2 percent of the population were Hispanic or Latino of any race,27.0 percent of all households were made up of individuals and 11.7 percent had someone living alone who was 65 years of age or older. The average household size was 2.42 and the family size was 2.91. The median age was 41.1 years, for every 100 females there were 106.2 males. For every 100 females age 18 and over, there were 105.6 males, as of November 2010, there are 50,640 registered voters in Greene County. The Meadow Ridge office park has served the county since the early 2000s, waynesburg University Greene County is divided into five public school districts. There are 15 public schools that serve Greene County, Pennsylvania. S, under Pennsylvania law, there are four types of incorporated municipalities, cities, boroughs, townships, and, in at most two cases, towns. S. Census Bureau for the purposes of compiling demographic data and they are not actual jurisdictions under Pennsylvania law. Other unincorporated communities, such as villages, may be listed here as well, the population ranking of the following table is based on the 2010 census of Greene County. † county seat National Register of Historic Places listings in Greene County, Pennsylvania Official website
31.
Indiana County, Pennsylvania
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Indiana County is a county located in the U. S. state of Pennsylvania. As of the 2010 census, the population was 88,880, the county was created on March 30,1803, from parts of Westmoreland and Clearfield counties and later organized in 1806. Indiana County derives its name from the Iroquois Six Nations so-called Indiana Grant of 1768, the proposed colony or part thereof was variously labelled on maps of the late 1700s as Indiana, Vandalia, Pittsylvania, or Westsylvania. This area was unrelated to and physically separated from the later named, Indiana County comprises the Indiana, PA Micropolitan Statistical Area, which is also included in the Pittsburgh-New Castle-Weirton, PA-WV-OH Combined Statistical Area. It is in the region of the Pittsburgh media market. Indiana County is served by three different area codes,724,814, and 582, the county proclaims itself the Christmas Tree Capital of the World, shipping over one million trees annually. According to the U. S. Census Bureau, the county has an area of 834 square miles. The population density was 108 people per square mile, there were 37,250 housing units at an average density of 45 per square mile. The racial makeup of the county was 96. 87% White,1. 57% Black or African American,0. 08% Native American,0. 74% Asian,0. 01% Pacific Islander,0. 16% from other races, and 0. 58% from two or more races. 0. 51% of the population were Hispanic or Latino of any race,25. 9% were of German,11. 6% Italian,10. 7% Irish,8. 6% American,7. 1% English and 6. 8% Polish ancestry according to Census 2000. 26. 50% of all households were made up of individuals and 11. 80% had someone living alone who was 65 years of age or older, the average household size was 2.47 and the average family size was 2.99. In the county, the population was out with 21. 10% under the age of 18,16. 60% from 18 to 24,24. 80% from 25 to 44,22. 70% from 45 to 64. The median age was 36 years, for every 100 females there were 94.00 males. For every 100 females age 18 and over, there were 90.60 males, the United States Office of Management and Budget has designated Indiana County as the Indiana, PA Micropolitan Statistical Area. As of the 2010 U. S. Census the micropolitan area ranked 4th most populous in the State of Pennsylvania, in West Virginia the counties included are Brooke and Hancock. The Combined Statistical Area ranked 4th in the State of Pennsylvania and 20th most populous in the United States with a population of 2,660,727. As of the 2016 primary election held April 26,2016, there were 48,710 registered voters across Indiana Countys 69 precincts,20,089 Democrats,22,134 Republicans, and 6,487 Independents. This represents a slight demographic shift since November 2008, when a total of 58,077 registered voters were 45. 89% Democrat,41. 60% Republican, the county is also the site of the Homer City Generating Station, a coal-burning power plant
32.
Lamproite
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Lamproites are ultrapotassic mantle-derived volcanic and subvolcanic rocks. They have low CaO, Al2O3, Na2O, high K2O/Al2O3, Lamproites are geographically widespread yet are volumetrically insignificant. They also vary widely in age, from Proterozoic to Pleistocene, lamproite volcanology is varied, with both diatreme styles and cinder cone or cone edifices known. Lamproites form from partially melted mantle at depths exceeding 150 km and this observation also reconciles the depth of melting with the peculiar geochemistry, which is most easily explained by melting of already felsic material under deep mantle conditions. The mineralogy of lamproites is controlled by their peculiar geochemistry, with a predominance of rare silica-deficient mineral species and rare, a variety of rare trace minerals occur. The rocks are high in potassium with 6 to 8% potassium oxide, high chromium and nickel content is typical. The rocks commonly are altered to talc with carbonate or serpentine, chlorite, zeolites and quartz may also occur. The presence of all the phases is not required in order to classify a rock as a lamproite. Any one mineral may be dominant, and this, together with the two or three other minerals present, suffices to determine the petrographic name. The economic significance of lamproite became known with the 1979 discovery of the Argyle diamond pipe in Western Australia and this discovery led to the intense study and re-evaluation of other known lamproite occurrences worldwide, previously only kimberlite pipes were considered economically viable sources of diamonds. The Argyle diamond mine remains the only economically viable source of lamproite diamonds and this deposit differs markedly by having a high content of diamonds but low quality of most stones. Research at Argyle diamond have shown that most stones are of E-type, the Argyle diamond mine is the main source of rare pink diamonds. Olivine lamproite pyroclastic rocks and dikes are sometimes hosts for diamonds, the diamonds occur as xenocrysts that have been carried to the surface or to shallow depths by the lamproite diapiric intrusions. The diamonds of Crater of Diamonds State Park near Murfreesboro, Arkansas are found in a lamproite host, modern terminology classes all as lamproites but modifies this term with the mineral abundances as per the standard IUGS rules. Kimberlite Lamprophyre Ultrapotassic igneous rocks Bergman, S. C,1987, Lamproites and other potassium-rich igneous rocks, a review of their occurrences, mineralogy and geochemistry. In, Alkaline Igneous rocks, Fitton, J. G. and Upton, B. G. J, Mitchell, R. H. Bergman, S. C. Murphy, D. T. Collerson, K. D. Kamber, B. S. Lamproites from Gaussberg, Antarctica, edgar, A. D, Le Bas, M. J. Mitchell, R. H. Rock, N. M. S. Classification of lamprophyres, lamproites, kimberlites, and the kalsilitic, melilitic, the Canadian Mineralogist, Vol 34, Part 2
33.
Ultramafic
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Ultramafic are igneous and meta-igneous rocks with a very low silica content, generally >18% MgO, high FeO, low potassium, and are composed of usually greater than 90% mafic minerals. The Earths mantle is composed of ultramafic rocks, ultrabasic is a more inclusive term that includes igneous rocks with low silica content that may not be extremely enriched in Fe and Mg, such as carbonatites and ultrapotassic igneous rocks. Intrusive ultramafic rocks are found in large, layered ultramafic intrusions where differentiated rock types often occur in layers. Such cumulate rock types do not represent the chemistry of the magma from which they crystallized, the ultramafic intrusives include the dunites, peridotites and pyroxenites. Other rare varieties include troctolite which has a percentage of calcic plagioclase. Gabbro and norite often occur in the portions of the layered ultramafic sequences. Hornblendite and, rarely phlogopite, are also found, subvolcanic ultramafic rocks and dykes persist longer, but are also rare. Many of the lavas being produced on Io may be ultramafic, mercury also appears to have ultramafic volcanic rock. Examples include komatiite and picritic basalt, komatiites can be host to ore deposits of nickel. Ultrapotassic, ultramafic rocks such as lamprophyre, lamproite and kimberlite are known to have reached the surface of the Earth. Although no modern eruptions have been observed, analogues are preserved, most of these rocks occur as dikes, diatremes, lopoliths or laccoliths, and very rarely, intrusions. Most kimberlite and lampproite occurrences occur as volcanic and subvolcanic diatremes and maars, vents of Proterozoic lamproite, and Cenozoic lamproite are known, as are vents of Devonian lamprophyre. Kimberlite pipes in Canada, Russia and South Africa have incompletely preserved tephra and these are generally diatreme events and as such are not lava flows although tephra and ash deposits are partially preserved. These represent low-volume volatile melts and attain their ultramafic chemistry via a different process to typical ultramafic rocks, metamorphism of ultramafic rocks in the presence of water and/or carbon dioxide results in two main classes of metamorphic ultramafic rock, talc carbonate and serpentinite. When such metamorphic fluids have less than 10% molar proportion of CO2, reactions favor serpentinisation, the majority of ultramafic rocks are exposed in orogenic belts, and predominate in Archaean and Proterozoic terranes. Ultramafic magmas in the Phanerozoic are rarer, and there are very few recognised true ultramafic lavas in the Phanerozoic, many surface exposures of ultramafic rocks occur in ophiolite complexes where deep mantle-derived rocks have been obducted onto continental crust along and above subduction zones. Serpentine soil is a rich, calcium, potassium and phosphorus poor soil that develops on the regolith derived from ultramafic rocks. Ultramafic rocks also contain elevated amounts of chromium and nickel which may be toxic to plants, as a result, a distinctive type of vegetation develops on these soils
34.
Forsterite
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Forsterite is the magnesium-rich end-member of the olivine solid solution series. It is isomorphous with the iron-rich end-member, fayalite, forsterite crystallizes in the orthorhombic system with cell parameters a 4.75 Å, b 10.20 Å and c 5.98 Å. Forsterite is associated with igneous and metamorphic rocks and has also found in meteorites. In 2005 it was found in cometary dust returned by the Stardust probe. In 2011 it was observed as tiny crystals in the dusty clouds of gas around a forming star, two polymorphs of forsterite are known, wadsleyite and ringwoodite. Both are mainly known from meteorites, peridot is the gemstone variety of forsterite olivine. Forsterite reacts with quartz to form the orthopyroxene mineral enstatite in the following reaction, pure forsterite is composed of magnesium, oxygen and silicon. Other minerals such as monticellite, an uncommon mineral, share the olivine structure. Monticellite is found in contact metamorphosed dolomites, forsterite-rich olivine is the most abundant mineral in the mantle above a depth of about 400 km, pyroxenes are also important minerals in this upper part of the mantle. Due to its melting point, olivine crystals are the first minerals to precipitate from a magmatic melt in a cumulate process. Forsterite-rich olivine is a common product of mantle-derived magma. Olivine in mafic and ultramafic rocks typically is rich in the forsterite end-member, forsterite also occurs in dolomitic marble which results from the metamorphism of high magnesium limestones and dolostones. Nearly pure forsterite occurs in some metamorphosed serpentinites, fayalite-rich olivine is much less common. Nearly pure fayalite is a constituent in some granite-like rocks. Forsterite is mainly composed of the anion SiO44− and the cation Mg2+ in a molar ratio 1,2, silicon is the central atom in the SiO44− anion. Each oxygen atom is bonded to the silicon by a covalent bond. The four oxygen atoms have a negative charge because of the covalent bond with silicon. Therefore, oxygen atoms need to stay far from other in order to reduce the repulsive force between them
35.
Ilmenite
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Ilmenite is the titanium-iron oxide mineral with the idealized formula FeTiO3. It is a weakly magnetic black or steel-gray solid, from the commercial perspective, ilmenite is the most important ore of titanium. Ilmenite is the source of titanium dioxide, which is used in paints, fabrics, plastics, paper, sunscreen, food. Ilmenite crystallizes in the trigonal system, containing high spin ferrous centers, ilmenite is paramagnetic. Ilmenite is commonly recognized in altered igneous rocks by the presence of an alteration product. Often ilmenites are rimmed with leucoxene, which allows ilmenite to be distinguished from magnetite, the example shown in the image at right is typical of leucoxene-rimmed ilmenite. In reflected light it may be distinguished from magnetite by more pronounced reflection pleochroism, samples of ilmenite exhibit a weak response to a hand magnet. Ilmenite most often contains appreciable quantities of magnesium and manganese and the chemical formula can be expressed as O3. Ilmenite forms a solution with geikielite and pyrophanite which are magnesian. At higher temperatures it has been demonstrated there is a solid solution between ilmenite and hematite. There is a miscibility gap at lower temperatures, resulting in a coexistence of two minerals in rocks but no solid solution. This coexistence may result in exsolution lamellae in cooled ilmenites with more iron in the system than can be accommodated in the crystal lattice. Altered ilmenite forms the mineral leucoxene, an important source of titanium in heavy mineral sands ore deposits, leucoxene is a typical component of altered gabbro and diorite and is generally indicative of ilmenite in the unaltered rock. Ilmenite is an accessory mineral found in metamorphic and igneous rocks. It is found in large concentrations in layered intrusions where it forms as part of a layer within the silicate stratigraphy of the intrusion. Ilmenite generally occurs within the portion of such intrusions. Magnesian ilmenite is indicative of kimberlitic paragenesis and forms part of the MARID association of minerals assemblage of glimmerite xenoliths, manganiferous ilmenite is found in granitic rocks and also in carbonatite intrusions where it may also contain anomalous niobium. Many mafic igneous rocks contain grains of magnetite and ilmenite
36.
Pyrope
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The mineral pyrope is a member of the garnet group. Pyrope is the member of the garnet family to always display red colouration in natural samples. Despite being less common than most garnets, it is a widely used gemstone with numerous alternative names, chrome pyrope, and Bohemian garnet are two alternative names, the usage of the latter being discouraged by the Gemological Institute of America. Misnomers include Colorado ruby, Arizona ruby, California ruby, Rocky Mountain ruby, Elie Ruby, Bohemian carbuncle, the composition of pure pyrope is Mg3Al23, although typically other elements are present in at least minor proportions—these other elements include Ca, Cr, Fe and Mn. Pyrope forms a solid solution series with almandine and spessartine, which are known as the pyralspite garnets. Iron and manganese substitute for the magnesium in the pyrope structure, the resultant, mixed composition garnets are defined according to their pyrope-almandine ratio. The semi-precious stone rhodolite is a garnet of ~70% pyrope composition, the origin of most pyrope is in ultramafic rocks, typically peridotite from the Earths mantle, these mantle-derived peridotites can be attributed both to igneous and metamorphic processes. Pyrope also occurs in metamorphic rocks, as in the Dora-Maira massif in the western Alps. In that massif, nearly pure pyrope occurs in crystals to almost 12 cm in diameter, some of that pyrope has inclusions of coesite, pyrope is common in peridotite xenoliths from kimberlite pipes, some of which are diamond-bearing. These varieties are known as chrome-pyrope, or G9/G10 garnets, in hand specimen, pyrope is very tricky to distinguish from almandine, however it is likely to display fewer flaws and inclusions. Other distinguishing criteria are listed in the adjacent table, care should be taken when using these properties as many of those listed have been determined from synthetically grown, pure-composition pyrope. Others, such as pyropes high specific gravity, may be of use when studying a small crystal embedded in a matrix of other silicate minerals. In these cases, mineral association with other mafic and ultramafic minerals may be the best indication that the garnet you are studying is pyrope, in petrographic thin section, the most distinguishing features of pyrope are those shared with the other common garnets, high relief and isotropy. Garnets tend to be less strongly coloured than other silicate minerals in thin section, the lack of cleavage, commonly euhedral crystal morphology, and mineral associations should also be used in identification of pyrope under the microscope. STEHLÍKOVÁ, Dana, The Bohemian Garnet,1
37.
Almandine
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Almandine /ˈælməndɪn/, also known incorrectly as almandite, is a species of mineral belonging to the garnet group. The name is a corruption of alabandicus, which is the name applied by Pliny the Elder to a stone found or worked at Alabanda, Almandine is an iron alumina garnet, of deep red color, inclining to purple. It is frequently cut with a face, or en cabochon. Viewed through the spectroscope in a light, it generally shows three characteristic absorption bands. Almandine is one end-member of a solid solution series, with the other end member being the garnet pyrope. The almandine crystal formula is, Fe3Al23, magnesium substitutes for the iron with increasingly pyrope-rich composition. Almandine crystallizes in the space group Ia3d, with unit-cell parameter a ≈11.512 Å at 100 K. Almandine is antiferromagnetic with the Néel temperature of 7.5 K. It contains two equivalent magnetic sublattices, Almandine occurs rather abundantly in the gem-gravels of Sri Lanka, whence it has sometimes been called Ceylon-ruby. When the color inclines to a violet tint, the stone is often called Syriam garnet, a said to be taken from Syriam. Fine rhombic dodecahedra occur in the rocks of the Zillertal, in Tyrol. An almandine in which the oxide is replaced partly by magnesia is found at Luisenfeld in German East Africa. In the United States there are many localities which yield almandine, fine crystals of almandine embedded in mica-schist occur near Wrangell in Alaska. The coarse varieties of almandine are often crushed for use as an abrasive agent
38.
Diopside
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Diopside is a monoclinic pyroxene mineral with composition MgCaSi2O6. It forms complete solid solution series with hedenbergite and augite, and partial solid solutions with orthopyroxene and it forms variably colored, but typically dull green crystals in the monoclinic prismatic class. It has two distinct prismatic cleavages at 87 and 93° typical of the pyroxene series. It has a Mohs hardness of six, a Vickers hardness of 7.7 GPa at a load of 0.98 N, and a specific gravity of 3.25 to 3.55. It is transparent to translucent with indices of refraction of nα=1. 663–1.699, nβ=1. 671–1.705, the optic angle is 58° to 63°. Diopside is found in igneous rocks, and diopside-rich augite is common in mafic rocks, such as olivine basalt. Diopside is also found in a variety of rocks, such as in contact metamorphosed skarns developed from high silica dolomites. It is an important mineral in the Earths mantle and is common in peridotite xenoliths erupted in kimberlite, some vermiculite deposits, most notably those in Libby, Montana, are contaminated with chrysotile that formed from diopside. At relatively high temperatures, there is a miscibility gap between diopside and pigeonite, and at lower temperatures, between diopside and orthopyroxene. Chrome diopside is a constituent of peridotite xenoliths, and dispersed grains are found near kimberlite pipes. Occurrences are reported in Canada, South Africa, Russia, Brazil, much chromian diopside from the Green River Basin localities and several of the State Line Kimberlites have been gem in character. Gemstone quality diopside is found in two forms, the black star diopside and the chrome diopside, at 5. 5–6.5 on the Mohs scale, chrome diopside is relatively soft to scratch. Violane is a variety of diopside, violet to light blue in color. Diopside derives its name from the Greek dis, twice, and òpsè, Diopside was discovered and first described about 1800, by Brazilian naturalist Jose Bonifacio de Andrada e Silva. Diopside based ceramics and glass-ceramics have potential applications in various technological areas, a diopside based glass-ceramic named silceram was produced by scientists from Imperial College, UK during the 1980s from blast furnace slag and other waste products. The as produced glass-ceramic is a structural material. Similarly, diopside based ceramics and glass-ceramics have potential applications in the field of biomaterials, nuclear waste immobilization, S. Carter, C. B. Ponton, R. D. Rawlings, P. S. Rogers, Microstructure, chemistry, elastic properties and internal-friction of silceram glass-ceramics, T. Nonami, S. Tsutsumi, Study of diopside ceramics for biomaterials, Journal of Materials Science, Materials in Medicine 10 475-479
39.
Phlogopite
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Phlogopite is a yellow, greenish, or reddish-brown member of the mica family of phyllosilicates. It is also known as magnesium mica, phlogopite is the magnesium endmember of the biotite solid solution series, with the chemical formula KMg3AlSi3O102. Iron substitutes for magnesium in variable amounts leading to the more common biotite with higher iron content, for physical and optical identification, it shares most of the characteristic properties of biotite. Phlogopite is an important and relatively common end-member composition of biotite, several igneous associations are noted, high-alumina basalts, ultrapotassic igneous rocks, and ultramafic rocks. The basaltic occurrence of phlogopite is in association with picrite basalts, phlogopite is stable in basaltic compositions at high pressures and is often present as partially resorbed phenocrysts or an accessory phase in basalts generated at depth. Phlogopite in this association is a primary igneous mineral present because of the depth of melting, phlogopite is often found in association with ultramafic intrusions as a secondary alteration phase within metasomatic margins of large layered intrusions. In some cases the phlogopite is considered to be produced by autogenic alteration during cooling, in other instances, metasomatism has resulted in phlogopite formation within large volumes, as in the ultramafic massif at Finero, Italy, within the Ivrea zone. Phlogopite is encountered as a primary igneous phenocryst within lamproites and lamprophyres, the largest documented single crystal of phlogopite was found in Lacey mine, Ontario, Canada, it measured 10x4. 3x4.3 m3 and weighed about 330 tonnes. Similar-sized crystals were found in Karelia, Russia. Howie, and J. Zussman, Rock-forming minerals, v.3, sheet silicates, p. 42–54 Spencer, Leonard James
40.
Enstatite
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Enstatite is a mineral, the magnesium endmember of the pyroxene silicate mineral series enstatite - ferrosilite. The magnesium rich members of the solid solution series are common rock-forming minerals found in igneous, the intermediate composition, SiO3, has historically been known as hypersthene, although this name has been formally abandoned and replaced by orthopyroxene. When determined petrographically or chemically the composition is given as relative proportions of enstatite and ferrosilite, most natural crystals are orthorhombic although three polymorphs are known. The high temperature, low pressure polymorphs are protoenstatite and protoferrosilite while the low temperature forms, weathered enstatite with a small amount of iron takes on a submetallic luster and a bronze-like color. This material is termed bronzite, although it is correctly called altered enstatite. Bronzite and hypersthene were known long before enstatite, which was first described by G. A. Kenngott in 1855, an emerald-green variety of enstatite is called chrome-enstatite and is cut as a gemstone. The green color is caused by traces of chromium, hence the varietal name, in addition, bronzite is also sometimes used as a gemstone. They also have a prismatic cleavage that is perfect in two directions at 90 degrees, Enstatite is white, gray, greenish, or brown in color, its hardness is 5–6 on the Mohs scale, and its specific gravity is 3. 2–3.3. Isolated crystals are rare, but orthopyroxene is a constituent of various types of igneous rocks. Magnesian orthopyroxene occurs in rocks such as gabbro and diorite. It may form small idiomorphic phenocrysts and also groundmass grains in volcanic rocks such as basalt, andesite, Enstatite, close to En90Fs10 in composition, is an essential mineral in typical peridotite and pyroxenite of the Earths mantle. Xenoliths of peridotite are common in kimberlite and in some basalt, orthopyroxene is an important constituent of some metamorphic rocks such as granulite. Orthopyroxene near pure enstatite in composition occurs in some metamorphosed serpentines, Enstatite is a common mineral in meteorites. Crystals have been found in stony and iron meteorites, including one that fell at Breitenbach in the Ore Mountains, Bohemia. In some meteorites, together with olivine it forms the bulk of the material, it can occur in small masses, or chondrules. Enstatite is one of the few minerals that have been observed in crystalline form outside the Solar System, particularly around evolved stars. Enstatite is thought to be a component of the E-type asteroids, in the Solar System. Deer, W. A. Howie, R. A. and Zussman, an introduction to the rock-forming minerals
41.
Chromite
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Chromite is an iron chromium oxide, FeCr2O4. It is a mineral belonging to the spinel group. Magnesium can substitute for iron in variable amounts as it forms a solution with magnesiochromite. It is by far the most industrially important mineral for the production of chromium, used as an alloying ingredient in stainless. Chromite is found as orthocumulate lenses of chromitite in peridotite from the Earths mantle and it also occurs in layered ultramafic intrusive rocks. In addition, it is found in rocks such as some serpentinites. Ore deposits of chromite form as early magmatic differentiates and it is commonly associated with olivine, magnetite, serpentine, and corundum. The vast Bushveld igneous complex of South Africa is a layered mafic to ultramafic igneous body with some layers consisting of 90% chromite making the rare rock type. The Stillwater igneous complex in Montana also contains significant chromite, the only ores of chromium are the minerals chromite and magnesiochromite. Most of the time, economic geology names chromite the whole chromite-magnesiochromite series, the two main products of chromite refining are ferrochromium and metallic chromium, for those products the ore smelter process differs considerably. Chromite is also used as a material, because it has a high heat stability. The chromium extracted from chromite is used in plating and alloying for production of corrosion resistant superalloys, nichrome. Chromium is used as a pigment for glass, glazes, and paint and it is also sometimes used as a gemstone. In 200214,600,000 metric tons of chromite were mined, the largest producers were South Africa, India, Kazakhstan, Zimbabwe, Finland, Iran, and Brazil with several other countries producing the rest of less than 10% of the world production. Afghanistan has significant deposits of high grade ore, which is mined illegally in Khost Province. In Pakistan, chromite is mined from the rocks in mainly the Muslimbagh killa Saifullah District. Most of the chromite is of metallurgical grade with Cr2O3 averaging 54%, recently, the biggest user of chromite ore has been China, importing large quantities from South Africa, Pakistan, and other countries. The concentrate is used to make ferrochrome, which is in used to make stainless steel
42.
Spinel
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Spinel is the magnesium aluminium member of the larger spinel group of minerals. It has the formula MgAl2O4 in the crystal system. Its name comes from Latin spina, balas ruby is an old name for a rose-tinted variety of spinel. Spinel crystallizes in the system, common crystal forms are octahedra. It has an imperfect cleavage and a conchoidal fracture. Its hardness is 8, its gravity is 3. 5–4.1. It may be colorless, but is usually shades of red, blue, green, yellow, brown, black. There is a natural white spinel, now lost, that surfaced briefly in what is now Sri Lanka. The Samarian Spinel is the largest known spinel in the world, the transparent red spinels were called spinel-rubies or balas rubies. In the past, before the arrival of modern science, spinels, after the 18th century the word ruby was only used for the red gem variety of the mineral corundum and the word spinel came to be used. Balas is derived from Balascia, the ancient name for Badakhshan, mines in the Gorno Badakhshan region of Tajikistan was for centuries the main source for red and pink spinels. Spinel has long been found in the gravel of Sri Lanka and in limestones of the Badakshan Province in modern-day Afghanistan and Tajikistan. Recently gem quality spinels also found in the marbles of Luc Yen, Mahenge and Matombo, Tsavo and in the gravels of Tunduru and this is why spinel and ruby are often found together. Spinel, 2O4, is common in peridotite in the uppermost Earths mantle, Spinel, Al2O4, is a common mineral in the Ca-Al-rich inclusions in some chondritic meteorites. Synthetic spinel, accidentally produced in the middle of the 18th century, has described more recently in scientific publications in 2000 and 2004. By 2015, transparent spinel was being made in sheets and other shapes through sintering, synthetic spinel which looks like glass but has notably higher strength against pressure, can also have applications in military and commercial use. Spinel group Ceylonite The Samarian Spinel, the largest known spinel in the world, part of the Iranian Crown Jewels Black Princes Ruby Deer, Howie, an Introduction to the Rock-Forming Minerals, Longman, pp. 424–433, ISBN 0-582-44210-9. Gemstones of the World 3rd edition, Sterling, pp. 116–117, Spinel structure at the University of Wisconsin - Green Bay Spinel structure at the Institut for materials science of the University of Kiel Value of Spinel
