1.
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
2.
Volcanic rock
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Volcanic rock is a rock formed from magma erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin, for these reasons, in geology, volcanics and shallow hypabyssal rocks are not always treated as distinct. In the context of Precambrian shield geology, the term volcanic is often applied to what are strictly metavolcanic rocks, Volcanic rocks are among the most common rock types on Earths surface, particularly in the oceans. On land, they are common at plate boundaries and in flood basalt provinces. It has been estimated that volcanic rocks cover about 8% of the Earths current land surface, lava Tephra Volcanic bomb Lapilli Volcanic ash Volcanic rocks are usually fine-grained or aphanitic to glass in texture. They often contain clasts of other rocks and phenocrysts, phenocrysts are crystals that are larger than the matrix and are identifiable with the unaided eye. Rhomb porphyry is an example with large rhomb shaped phenocrysts embedded in a fine grained matrix. Volcanic rocks often have a vesicular texture caused by voids left by volatiles trapped in the molten lava, pumice is a highly vesicular rock produced in explosive volcanic eruptions. Most modern petrologists classify igneous rocks, including rocks, by their chemistry when dealing with their origin. The fact that different mineralogies and textures may be developed from the same initial magmas has led petrologists to rely heavily on chemistry to look at a volcanic rocks origin. The chemistry of volcanic rocks is dependent on two things, the composition of the primary magma and the subsequent differentiation. Differentiation of most volcanic rocks tends to increase the silica content, the initial composition of most volcanic rocks is basaltic, albeit small differences in initial compositions may result in multiple differentiation series. The most common of these series are tholeiitic, calc-alkaline, most volcanic rocks share a number of common minerals. Differentiation of volcanic rocks tends to increase the silica content mainly by fractional crystallization, thus, more evolved volcanic rocks tend to be richer in minerals with a higher amount if silica such as phyllo and tectosilicates including the feldspars, quartz polymorphs and muscovite. While still dominated by silicates, more volcanic rocks have mineral assemblages with less silica, such as olivine. Bowens reaction series correctly predicts the order of formation of the most common minerals in volcanic rocks, occasionally, a magma may pick up crystals that crystallized from another magma, these crystals are called xenocrysts. Diamonds found in kimberlites are rare but well-known xenocrysts, the kimberlites do not create the diamonds, Volcanic rocks are named according to both their chemical composition and texture. Basalt is a common volcanic rock with low silica content
3.
Calcium oxide
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Calcium oxide, commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature, the broadly used term lime connotes calcium-containing inorganic materials, in which carbonates, oxides and hydroxides of calcium, silicon, magnesium, aluminium, and iron predominate. By contrast, quicklime specifically applies to the chemical compound calcium oxide. Calcium oxide that survives processing without reacting in building such as cement is called free lime. Both it and a chemical derivative are important commodity chemicals, Calcium oxide is usually made by the thermal decomposition of materials, such as limestone or seashells, that contain calcium carbonate in a lime kiln. This is accomplished by heating the material to above 825 °C, annual worldwide production of quicklime is around 283 million tonnes. China is by far the worlds largest producer, with a total of around 170 million tonnes per year, the United States is the next largest, with around 20 million tonnes per year. Approximately 1.8 t of limestone is required per 1.0 t of quicklime, quicklime has a high affinity for water and is a more efficient desiccant than silica gel. The reaction of quicklime with water is associated with an increase in volume by a factor of at least 2.5, the major use of quicklime is in the Basic oxygen steelmaking process. Its usage varies from about 30–50 kg/t of steel, the quicklime neutralizes the acidic oxides, SiO2, Al2O3, and Fe2O3, to produce a basic molten slag. Ground quicklime is used in the production of aerated concrete blocks, quicklime and hydrated lime can considerably increase the load carrying capacity of clay-containing soils. They do this by reacting with finely divided silica and alumina to produce calcium silicates and aluminates, small quantities of quicklime are used in other processes, e. g. the production of glass, calcium aluminate cement, and organic chemicals. The hydrate can be reconverted to quicklime by removing the water by heating it to redness to reverse the hydration reaction, one litre of water combines with approximately 3.1 kilograms of quicklime to give calcium hydroxide plus 3.54 MJ of energy. This process can be used to provide a convenient portable source of heat, light, When quicklime is heated to 2,400 °C, it emits an intense glow. This form of illumination is known as a limelight, and was used broadly in theatrical productions prior to the invention of electric lighting, cement, Calcium oxide is a key ingredient for the process of making cement. As a cheap and widely available alkali, about 50% of the total quicklime production is converted to calcium hydroxide before use. Both quick- and hydrated lime are used in the treatment of drinking water, petroleum industry, Water detection pastes contain a mix of calcium oxide and phenolphthalein. Should this paste come into contact with water in a storage tank
4.
Aluminium oxide
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Aluminium oxide or aluminum oxide is a chemical compound of aluminium and oxygen with the chemical formula Al2O3. It is the most commonly occurring of several aluminium oxides, and it is commonly called alumina, and may also be called aloxide, aloxite, or alundum depending on particular forms or applications. It occurs naturally in its crystalline polymorphic phase α-Al2O3 as the mineral corundum, varieties of form the precious gemstones ruby. Al2O3 is significant in its use to produce metal, as an abrasive owing to its hardness. Corundum is the most common naturally occurring form of aluminium oxide. Rubies and sapphires are gem-quality forms of corundum, which owe their characteristic colors to trace impurities, rubies are given their characteristic deep red color and their laser qualities by traces of chromium. Sapphires come in different colors given by various other impurities, such as iron, Al2O3 is an electrical insulator but has a relatively high thermal conductivity for a ceramic material. Aluminium oxide is insoluble in water, in its most commonly occurring crystalline form, called corundum or α-aluminium oxide, its hardness makes it suitable for use as an abrasive and as a component in cutting tools. Aluminium oxide is responsible for the resistance of aluminium to weathering. Metallic aluminium is very reactive with oxygen, and a thin passivation layer of aluminium oxide forms on any exposed aluminium surface. This layer protects the metal from further oxidation, the thickness and properties of this oxide layer can be enhanced using a process called anodising. A number of alloys, such as bronzes, exploit this property by including a proportion of aluminium in the alloy to enhance corrosion resistance. Aluminium oxide was taken off the United States Environmental Protection Agencys chemicals lists in 1988, aluminium oxide is on EPAs Toxics Release Inventory list if it is a fibrous form. Al2O3 +6 HF →2 AlF3 +3 H2O Al2O3 +2 NaOH +3 H2O →2 NaAl4 The most common form of aluminium oxide is known as corundum. The oxygen ions form a hexagonal close-packed structure with aluminium ions filling two-thirds of the octahedral interstices. In terms of its crystallography, corundum adopts a trigonal Bravais lattice with a group of R-3c. The primitive cell contains two units of aluminium oxide. Each has a crystal structure and properties
5.
Sodium oxide
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Sodium oxide is a chemical compound with the formula Na2O. It is used in ceramics and glasses, though not in a raw form and it is the base anhydride of sodium hydroxide, so when water is added to sodium oxide NaOH is produced. Na2O + H2O →2 NaOH The alkali metal oxides M2O crystallise in the antifluorite structure, burning sodium in air will produce Na2O and about 20% sodium peroxide Na2O2. 6 Na +2 O2 →2 Na2O + Na2O2 Alternatively, sodium carbonate can be heated to 851 °C, producing carbon dioxide, na2CO3 → Na2O + CO2 At 208 °C, sodium ascorbate will decompose to furan derivatives and sodium oxide. Sodium oxide is a significant component of glasses and windows although it is added in the form of soda, Sodium oxide does not explicitly exist in glasses, since glasses are complex cross-linked polymers. Typically, manufactured glass contains around 15% sodium oxide, 70% silica, the sodium carbonate soda serves as a flux to lower the temperature at which the silica melts. Soda glass has a lower melting temperature than pure silica. These changes arise because the silicon dioxide and soda react to form sodium silicates of the general formula Na2x, na2CO3 → Na2O + CO2 Na2O + SiO2 → Na2SiO3 Sodium oxide information at Webelements
6.
Magnesium oxide
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Magnesium oxide, or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium. It has a formula of MgO and consists of a lattice of Mg2+ ions. Magnesium hydroxide forms in the presence of water, but it can be reversed by heating it to separate moisture, Magnesium oxide was historically known as magnesia alba, to differentiate it from magnesia negra, a black mineral containing what is now known as manganese. While magnesium oxide normally refers to MgO, magnesium peroxide MgO2 is also known as a compound, because of its stability, MgO is used as a model system for investigating vibrational properties of crystals. Magnesium oxide is produced by the calcination of magnesium carbonate or magnesium hydroxide, the latter is obtained by the treatment of magnesium chloride solutions, typically seawater, with lime. Mg2+ + Ca2 → Mg2 + Ca2+ Calcining at different temperatures produces magnesium oxide of different reactivity, high temperatures 1500 -2000 °C diminish the available surface area and produces dead-burned magnesia, an unreactive form used as a refractory. Although some decomposition of the carbonate to oxide occurs at temperatures below 700 °C, MgO is prized as a refractory material, i. e. a solid that is physically and chemically stable at high temperatures. It has two attributes, high thermal conductivity and low electrical conductivity. MgO is used as a refractory material for crucibles. It is a principal fireproofing ingredient in construction materials, as a construction material, magnesium oxide wallboards have several attractive characteristics, fire resistance, termite resistance, moisture resistance, mold and mildew resistance, and strength. MgO is one of the components in Portland cement in dry process plants, many heavy metals species, such as lead and cadmium are most soluble in water at acidic pH as well as high pH. Solubility of metals affects bioavailability of the species and mobility soil, most metal species are toxic to humans at certain concentrations, therefore it is imperative to minimize metal bioavailability and mobility. Metal-hydroxide complexes have a tendency to precipitate out of solution in the pH range of 8-10. Most, if not all products that are marketed as metals stabilization technologies create very high pH conditions in aquifers whereas MgO creates an ideal aquifer condition with a pH of 8-10. Additionally, magnesium, an element to most biological systems, is provided to soil. In medicine, magnesium oxide is used for relief of heartburn and sour stomach, as an antacid, magnesium supplement and it is also used to improve symptoms of indigestion. Side effects of magnesium oxide may include nausea and cramping, in quantities sufficient to obtain a laxative effect, side effects of long-term use include enteroliths resulting in bowel obstruction. It is used as a white color in colorimetry, owing to its good diffusing
7.
Kimberlite
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Kimberlite is an igneous rock best known for sometimes containing diamonds. Kimberlite occurs in the Earths crust in vertical structures known as kimberlite pipes as well as igneous dykes, Kimberlite also occurs as horizontal sills. Kimberlite pipes are the most important source of mined diamonds today, the consensus on kimberlites is that they are formed deep within the mantle. It is this depth of melting and generation which makes kimberlites prone to hosting diamond xenocrysts, despite its relative rarity, kimberlite has attracted attention because it serves as a carrier of diamonds and garnet peridotite mantle xenoliths to the Earths surface. Many kimberlite structures are emplaced as carrot-shaped, vertical intrusions termed pipes, Kimberlite classification is based on the recognition of differing rock facies. These differing facies are associated with a style of magmatic activity, namely crater, diatreme. The morphology of kimberlite pipes, and their classical carrot shape is the result of explosive volcanism from very deep mantle-derived sources. These volcanic explosions produce vertical columns of rock rise from deep magma reservoirs. The morphology of kimberlite pipes is varied but includes a sheeted dyke complex of tabular, within 1. 5–2 km of the surface, the highly pressured magma explodes upwards and expands to form a conical to cylindrical diatreme, which erupts to the surface. The surface expression is rarely preserved but is similar to a maar volcano. The diameter of a pipe at the surface is typically a few hundred meters to a kilometer. Two Jurassic kimberlite dikes exist in Pennsylvania, one, the Gates-Adah Dike, outcrops on the Monongahela River on the border of Fayette and Greene Counties. The other, the Dixonville-Tanoma Dike in central Indiana County, does not outcrop at the surface and was discovered by miners, similarly aged kimberlite is found in several locations in New York Both the location and origin of kimberlitic magmas are subjects of contention. The mechanism of enrichment has also been the topic of interest with models including partial melting, historically, kimberlites have been classified into two distinct varieties termed basaltic and micaceous based primarily on petrographic observations. This was later revised by Smith who renamed these divisions Group I and Group II based on the affinities of these rocks using the Nd, Sr. Mitchell later proposed that these group I and II kimberlites display such distinct differences and he showed that Group II kimberlites show closer affinities to lamproites than they do to Group I kimberlites. Hence, he reclassified Group II kimberlites as orangeites to prevent confusion, olivine lamproites were previously called Group II kimberlite or orangeite in response to the mistaken belief that they only occurred in South Africa. Their occurrence and petrology, however, are identical globally and should not be referred to as kimberlite
8.
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
9.
Proterozoic
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The Proterozoic is a geological eon representing the time just before the proliferation of complex life on Earth. The name Proterozoic comes from Greek and means life, the Greek root protero-, means former, earlier and zoic-, means animal. The Proterozoic Eon extended from 2500 Ma to 541 Ma, and is the most recent part of the Precambrian Supereon and it is subdivided into three geologic eras, the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic. The geologic record of the Proterozoic Eon is more complete than that for the preceding Archean Eon, studies of these rocks have shown that the eon continued the massive continental accretion that had begun late in the Archean Eon. The Proterozoic Eon also featured the first definitive supercontinent cycles and wholly modern mountain building activity, there is evidence that the first known glaciations occurred during the Proterozoic. One of the most important events of the Proterozoic was the accumulation of oxygen in the Earths atmosphere, until roughly 2.3 billion years ago, oxygen was probably only 1% to 2% of its current level. The Banded iron formations, which provide most of the iron ore, are one mark of that mineral sink process. Their accumulation ceased after 1.9 billion years ago, after the iron in the oceans had all been oxidized, red beds, which are colored by hematite, indicate an increase in atmospheric oxygen 2 billion years ago. Such massive iron oxide formations are not found in older rocks, the Proterozoic Eon was a very tectonically active period in the Earth’s history. The late Archean Eon to Early Proterozoic Eon corresponds to a period of increasing crustal recycling, suggesting subduction, evidence for this increased subduction activity comes from the abundance of old granites originating mostly after 2.6 Ga. The appearance of eclogites, which metamorphic rocks created by pressure, are explained using a model that incorporates subduction. As a result of remelting of basaltic oceanic crust due to subduction, the long-term tectonic stability of those cratons is why we find continental crust ranging up to a few billion years in age. It is believed that 43% of modern continental crust was formed in the Proterozoic, 39% formed in the Archean, studies by Condie 2000 and Rino et al.2004 suggest that crust production happened episodically. By isotopically calculating the ages of Proterozoic granitoids it was determined there were several episodes of rapid increase in continental crust production. The reason for these pulses is unknown, but they seemed to have decreased in magnitude after every period, evidence of collision and rifting between continents raises the question as to what exactly were the movements of the Archean cratons composing Proterozoic continents. Paleomagnetic and geochronological dating mechanisms have allowed the deciphering of Precambrian Supereon tectonics and it is known that tectonic processes of the Proterozoic Eon resemble greatly the evidence of tectonic activity, such as orogenic belts or ophiolite complexes, we see today. Hence, most geologists would conclude that the Earth was active at that time and it is also commonly accepted that during the Precambrian, the Earth went through several supercontinent breakup and rebuilding cycles. In the late Proterozoic, the dominant supercontinent was Rodinia and it consisted of a series of continents attached to a central craton that forms the core of the North American Continent called Laurentia
10.
Pleistocene
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The Pleistocene is the geological epoch which lasted from about 2,588,000 to 11,700 years ago, spanning the worlds most recent period of repeated glaciations. The end of the Pleistocene corresponds with the end of the last glacial period, the Pleistocene is the first epoch of the Quaternary Period or sixth epoch of the Cenozoic Era. In the ICS timescale, the Pleistocene is divided into four stages or ages, all of these stages were defined in southern Europe. In addition to this subdivision, various regional subdivisions are often used. Charles Lyell introduced the term pleistocene in 1839 to describe strata in Sicily that had at least 70% of their molluscan fauna still living today and this distinguished it from the older Pliocene Epoch, which Lyell had originally thought to be the youngest fossil rock layer. The Pleistocene has been dated from 2.588 million to 11,700 years before present and it covers most of the latest period of repeated glaciation, up to and including the Younger Dryas cold spell. The end of the Younger Dryas has been dated to about 9640 BC, the IUGS has yet to approve a type section, Global Boundary Stratotype Section and Point, for the upper Pleistocene/Holocene boundary. The proposed section is the North Greenland Ice Core Project ice core 75°06 N 42°18 W, the lower boundary of the Pleistocene Series is formally defined magnetostratigraphically as the base of the Matuyama chronozone, isotopic stage 103. Above this point there are notable extinctions of the calcareous nanofossils, Discoaster pentaradiatus, the Pleistocene covers the recent period of repeated glaciations. The name Plio-Pleistocene has, in the past, been used to mean the last ice age. The revised definition of the Quaternary, by pushing back the date of the Pleistocene to 2.58 Ma. Pleistocene climate was marked by repeated glacial cycles in which continental glaciers pushed to the 40th parallel in some places and it is estimated that, at maximum glacial extent, 30% of the Earths surface was covered by ice. In addition, a zone of permafrost stretched southward from the edge of the sheet, a few hundred kilometres in North America. The mean annual temperature at the edge of the ice was −6 °C, during interglacial times, such as at present, drowned coastlines were common, mitigated by isostatic or other emergent motion of some regions. The effects of glaciation were global, antarctica was ice-bound throughout the Pleistocene as well as the preceding Pliocene. The Andes were covered in the south by the Patagonian ice cap, there were glaciers in New Zealand and Tasmania. The current decaying glaciers of Mount Kenya, Mount Kilimanjaro, glaciers existed in the mountains of Ethiopia and to the west in the Atlas mountains. In the northern hemisphere, many glaciers fused into one, the Cordilleran ice sheet covered the North American northwest, the east was covered by the Laurentide
11.
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
12.
Cinder cone
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A cinder cone or scoria cone is a steep conical hill of loose pyroclastic fragments, such as either volcanic clinkers, cinders, volcanic ash, or scoria that has been built around a volcanic vent. They consist of loose pyroclastic debris formed by explosive eruptions or lava fountains from a single, typically cylindrical, most cinder cones have a bowl-shaped crater at the summit. The rock fragments, often called cinders or scoria, are glassy and contain numerous gas bubbles frozen into place as magma exploded into the air, cinder cones range in size from tens to hundreds of meters tall. Cinder cones are made of pyroclastic material, many cinder cones have a bowl-shaped crater at the summit. During the waning stage of an eruption, the magma has lost most of its gas content. This gas-depleted magma does not fountain but oozes quietly into the crater or beneath the base of the cone as lava. Lava rarely issues from the top because the loose, uncemented cinders are too weak to support the pressure exerted by molten rock as it rises toward the surface through the central vent, because it contains so few gas bubbles, the molten lava is denser than the bubble-rich cinders. Thus, it burrows out along the bottom of the cinder cone, lifting the less dense cinders like a cork on water. When the eruption ends, a cone of cinders sits at the center of a surrounding pad of lava. If the crater is breached, the remaining walls form an amphitheatre or horseshoe shape around the vent. Cinder cones are found on the flanks of shield volcanoes, stratovolcanoes. For example, geologists have identified nearly 100 cinder cones on the flanks of Mauna Kea and these cones are also referred to as scoria cones and cinder and spatter cones. The most famous cinder cone, Paricutin, grew out of a field in Mexico in 1943 from a new vent. Eruptions continued for nine years, built the cone to a height of 424 meters, the Earths most historically active cinder cone is Cerro Negro in Nicaragua. It is part of a group of four cinder cones NW of Las Pilas volcano. Since its initial eruption in 1850, it has erupted more than 20 times, based on satellite images it was suggested that cinder cones might occur on other terrestrial bodies in the solar system too. They were reported on the flanks of Pavonis Mons in Tharsis and it is also suggested that domical structures in Marius Hills might represent lunar cinder cones. The size and shape of cinder cones depend on environmental properties as different gravity and/or atmospheric pressure might change the dispersion of ejected scoria particles, some cinder cones are monogenetic – the result of a single, never-to-be-repeated eruption
13.
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
14.
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
15.
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
16.
Eclogite
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Eclogite is a mafic metamorphic rock. Eclogite forms at pressures greater than typical of the crust of the Earth. An unusually dense rock, eclogite can play an important role in driving convection within the solid Earth, the fresh rock can be striking in appearance, with red to pink garnet in a green matrix of sodium-rich pyroxene. Accessory minerals include kyanite, rutile, quartz, lawsonite, coesite, amphibole, phengite, paragonite, zoisite, dolomite, corundum, plagioclase is not stable in eclogite. Eclogite typically results from metamorphism of mafic igneous rock as it plunges into the mantle in a subduction zone. Such eclogites are generally formed from precursor mineral assemblages typical of blueschist-facies or amphibolite-facies metamorphism, eclogite can also form from magmas that crystallize and cool within the mantle or lower crust. Eclogite facies is determined by the temperatures and pressures required to metamorphose basaltic rocks to an eclogite assemblage, the typical eclogite mineral assemblage is garnet plus clinopyroxene. Eclogites record pressures in excess of 1.2 GPa at >400–1000 °C and this is high-pressure, medium- to high-temperature metamorphism. Diamond and coesite occur as trace constituents in some eclogites and record particularly high pressures, in fact, such ultrahigh-pressure metamorphism has been defined as metamorphism within the eclogite facies but at pressures greater than those of the quartz-coesite transition. Some UHP rocks appear to record burial at depths greater than 150 km, the rarity of lawsonite eclogites therefore does not reflect unusual formation conditions but unusual exhumation processes. Lawsonite eclogite is known from the U. S. Guatemala, Corsica, Australia, the Dominican Republic, Canada, eclogite is the highest pressure metamorphic facies and is usually the result of advancement from blueschist metamorphic conditions. Eclogite is a rare and important rock because it is formed only by conditions typically found in the mantle or the lowermost part of thickened crust, eclogite may completely retrogress to amphibolite or granulite during exhumation. Xenoliths of eclogite occur in kimberlite pipes of Africa, Russia, Canada, felsic rocks in these terranes contain sillimanite, kyanite, coesite, orthoclase and pyroxene, and are rare, peculiar rocks formed by an unusual tectonic event. Peridotite is the dominant rock type of the mantle, not eclogite. Likewise, peridotite is a more important source rock of common magmas. Melting of eclogite to produce basalt directly is not supported in modern petrology. Unreasonably high degrees of melting are required to attain basaltic compositions. To get a basalt from melting an eclogite it has to undergo 100% partial melting, instead, basalts can be modelled as having been produced by 1 to 25% partial melting of peridotite, such as harzburgite and lherzolite
17.
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
18.
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
19.
Iron
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Iron is a chemical element with symbol Fe and atomic number 26. It is a metal in the first transition series and it is by mass the most common element on Earth, forming much of Earths outer and inner core. It is the fourth most common element in the Earths crust, like the other group 8 elements, ruthenium and osmium, iron exists in a wide range of oxidation states, −2 to +6, although +2 and +3 are the most common. Elemental iron occurs in meteoroids and other low oxygen environments, but is reactive to oxygen, fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give hydrated iron oxides, commonly known as rust. Unlike the metals that form passivating oxide layers, iron oxides occupy more volume than the metal and thus flake off, Iron metal has been used since ancient times, although copper alloys, which have lower melting temperatures, were used even earlier in human history. Pure iron is soft, but is unobtainable by smelting because it is significantly hardened and strengthened by impurities, in particular carbon. A certain proportion of carbon steel, which may be up to 1000 times harder than pure iron. Crude iron metal is produced in blast furnaces, where ore is reduced by coke to pig iron, further refinement with oxygen reduces the carbon content to the correct proportion to make steel. Steels and iron alloys formed with metals are by far the most common industrial metals because they have a great range of desirable properties. Iron chemical compounds have many uses, Iron oxide mixed with aluminium powder can be ignited to create a thermite reaction, used in welding and purifying ores. Iron forms binary compounds with the halogens and the chalcogens, among its organometallic compounds is ferrocene, the first sandwich compound discovered. Iron plays an important role in biology, forming complexes with oxygen in hemoglobin and myoglobin. Iron is also the metal at the site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants. A human male of average height has about 4 grams of iron in his body and this iron is distributed throughout the body in hemoglobin, tissues, muscles, bone marrow, blood proteins, enzymes, ferritin, hemosiderin, and transport in plasma. The mechanical properties of iron and its alloys can be evaluated using a variety of tests, including the Brinell test, Rockwell test, the data on iron is so consistent that it is often used to calibrate measurements or to compare tests. An increase in the content will cause a significant increase in the hardness. Maximum hardness of 65 Rc is achieved with a 0. 6% carbon content, because of the softness of iron, it is much easier to work with than its heavier congeners ruthenium and osmium. Because of its significance for planetary cores, the properties of iron at high pressures and temperatures have also been studied extensively
20.
Leucite
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Goniometric measurements made by Gerhard vom Rath in 1873 led him to refer the crystals to the tetragonal system. This pseudo-cubic character of leucite is very similar to that of the mineral boracite, the crystals are white or ash-grey in colour, hence the name suggested by A. G. Werner in 1701, from λευκος, white. The Mohs hardness is 5.5, and the specific gravity 2.47, inclusions of other minerals, arranged in concentric zones, are frequently present in the crystals. On account of the color and form of the crystals the mineral was known as white garnet. This article incorporates text from a now in the public domain, Chisholm, Hugh
21.
Titanium
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Titanium is a chemical element with symbol Ti and atomic number 22. It is a transition metal with a silver color, low density. Titanium is resistant to corrosion in sea water, aqua regia, titanium was discovered in Cornwall, Great Britain, by William Gregor in 1791, and it is named by Martin Heinrich Klaproth for the Titans of Greek mythology. The metal is extracted from its principal mineral ores by the Kroll, the most common compound, titanium dioxide, is a popular photocatalyst and is used in the manufacture of white pigments. Other compounds include titanium tetrachloride, a component of smoke screens and catalysts, and titanium trichloride, the two most useful properties of the metal are corrosion resistance and strength-to-density ratio, the highest of any metallic element. In its unalloyed condition, titanium is as strong as some steels, there are two allotropic forms and five naturally occurring isotopes of this element, 46Ti through 50Ti, with 48Ti being the most abundant. Although they have the number of valence electrons and are in the same group in the periodic table. As a metal, titanium is recognized for its high strength-to-weight ratio and it is a strong metal with low density that is quite ductile, lustrous, and metallic-white in color. The relatively high melting point makes it useful as a refractory metal and it is paramagnetic and has fairly low electrical and thermal conductivity. Commercial grades of titanium have ultimate tensile strength of about 434 MPa, equal to that of common, low-grade steel alloys, titanium is 60% denser than aluminium, but more than twice as strong as the most commonly used 6061-T6 aluminium alloy. Certain titanium alloys achieve tensile strengths of over 1400 MPa, however, titanium loses strength when heated above 430 °C. Titanium is not as hard as some grades of heat-treated steel, it is non-magnetic, machining requires precautions, because the material might gall unless sharp tools and proper cooling methods are used. Like steel structures, those made from titanium have a limit that guarantees longevity in some applications. The metal is an allotrope of an hexagonal α form that changes into a body-centered cubic β form at 882 °C. The specific heat of the α form increases dramatically as it is heated to this transition temperature but then falls, similar to zirconium and hafnium, an additional omega phase exists, which is thermodynamically stable at high pressures, but metastable at ambient pressures. This phase is usually hexagonal or trigonal and can be considered to be due to a soft longitudinal acoustic phonon of the β phase causing collapse of planes of atoms, like aluminium and magnesium, titanium metal and its alloys oxidize immediately upon exposure to air. Titanium readily reacts with oxygen at 1,200 °C in air and it is, however, slow to react with water and air at ambient temperatures because it forms a passive oxide coating that protects the bulk metal from further oxidation. When it first forms, this layer is only 1–2 nm thick but continues to grow slowly
22.
Aluminium
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Aluminium or aluminum is a chemical element in the boron group with symbol Al and atomic number 13. It is a silvery-white, soft, nonmagnetic, ductile metal, Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments. Instead, it is combined in over 270 different minerals. The chief ore of aluminium is bauxite, Aluminium is remarkable for the metals low density and its ability to resist corrosion through the phenomenon of passivation. Aluminium and its alloys are vital to the industry and important in transportation and structures, such as building facades. The oxides and sulfates are the most useful compounds of aluminium, despite its prevalence in the environment, no known form of life uses aluminium salts metabolically, but aluminium is well tolerated by plants and animals. Because of these salts abundance, the potential for a role for them is of continuing interest. Aluminium is a soft, durable, lightweight, ductile. It is nonmagnetic and does not easily ignite, a fresh film of aluminium serves as a good reflector of visible light and an excellent reflector of medium and far infrared radiation. The yield strength of aluminium is 7–11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa. Aluminium has about one-third the density and stiffness of steel and it is easily machined, cast, drawn and extruded. Aluminium atoms are arranged in a cubic structure. Aluminium has an energy of approximately 200 mJ/m2. Aluminium is a thermal and electrical conductor, having 59% the conductivity of copper. Aluminium is capable of superconductivity, with a critical temperature of 1.2 kelvin. Aluminium is the most common material for the fabrication of superconducting qubits, the strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper. This corrosion resistance is reduced by aqueous salts, particularly in the presence of dissimilar metals. In highly acidic solutions, aluminium reacts with water to form hydrogen, primarily because it is corroded by dissolved chlorides, such as common sodium chloride, household plumbing is never made from aluminium
23.
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
24.
Potassium
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Potassium is a chemical element with symbol K and atomic number 19. It was first isolated from potash, the ashes of plants, in the periodic table, potassium is one of the alkali metals. Potassium in nature only in ionic salts. It is found dissolved in sea water, and is part of many minerals, naturally occurring potassium is composed of three isotopes, of which 40K is radioactive. Traces of 40K are found in all potassium, and it is the most common radioisotope in the human body, Potassium is chemically very similar to sodium, the previous element in Group 1 of the periodic table. They have a similar energy, which allows for each atom to give up its sole outer electron. That they are different elements combine with the same anions to make similar salts was suspected in 1702. Most industrial applications of potassium exploit the high solubility in water of potassium compounds, heavy crop production rapidly depletes the soil of potassium, and this can be remedied with agricultural fertilizers containing potassium, accounting for 95% of global potassium chemical production. Potassium ions are necessary for the function of all living cells, fresh fruits and vegetables are good dietary sources of potassium. Potassium is the second least dense metal after lithium and it is a soft solid with a low melting point, and can be easily cut with a knife. Freshly cut potassium is silvery in appearance, but it begins to tarnish toward gray immediately on exposure to air, in a flame test, potassium and its compounds emit a lilac color with a peak emission wavelength of 766.5 nanometers. Neutral potassium atoms have 19 electrons, one more than the stable configuration of the noble gas argon. This process requires so little energy that potassium is readily oxidized by atmospheric oxygen, in contrast, the second ionization energy is very high, because removal of two electrons breaks the stable noble gas electronic configuration. Potassium therefore does not readily form compounds with the state of +2 or higher. Potassium is an active metal that reacts violently with oxygen in water. With oxygen it forms potassium peroxide, and with water potassium forms potassium hydroxide, the reaction of potassium with water is dangerous because of its violent exothermic character and the production of hydrogen gas. Hydrogen reacts again with atmospheric oxygen, producing water, which reacts with the remaining potassium and this reaction requires only traces of water, because of this, potassium and the liquid sodium-potassium — NaK — are potent desiccants that can be used to dry solvents prior to distillation. Because of the sensitivity of potassium to water and air, reactions with other elements are only in an inert atmosphere such as argon gas using air-free techniques
25.
Richterite
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Richterite is a sodium calcium magnesium silicate mineral belonging to the amphibole group. If iron replaces the magnesium within the structure of the mineral, it is called ferrorichterite, if fluorine replaces the hydroxyl, richterite crystals are long and prismatic, or prismatic to fibrous aggregate, or rock-bound crystals. Colors of richterite range from brown, grayish-brown, yellow, brownish- to rose-red, richterite occurs in thermally metamorphosed limestones in contact metamorphic zones. It also occurs as a product in mafic igneous rocks. The mineral was named in 1865 for the German mineralogist Hieronymous Theodor Richter, bonewitz,2008, Smithsonian Rock and Gem
26.
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
27.
Sanidine
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Sanidine is the high temperature form of potassium feldspar with a general formula K. Sanidine is found most typically in felsic volcanic rocks such as obsidian, rhyolite and trachyte. Sanidine crystallizes in the crystal system. Orthoclase is a monoclinic polymorph stable at lower temperatures, at yet lower temperatures, microcline, a triclinic polymorph of potassium feldspar, is stable. Due to the temperature and rapid quenching, sanidine can contain more sodium in its structure than the two polymorphs that equilibrated at lower temperatures. Sanidine and high albite constitute a solid solution series with intermediate compositions termed anorthoclase, exsolution of an albite phase does occur, resulting cryptoperthite can best be observed in electron microprobe images. Hurlbut, Cornelius S. Klein, Cornelis,1985, Manual of Mineralogy, 20th ed. Wiley, ISBN 0-471-80580-7
28.
Chromium
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Chromium is a chemical element with symbol Cr and atomic number 24. It is the first element in Group 6 and it is a steely-grey, lustrous, hard and brittle metal which takes a high polish, resists tarnishing, and has a high melting point. The name of the element is derived from the Greek word χρῶμα, chrōma, meaning color, Chromium metal is of high value for its high corrosion resistance and hardness. A major development was the discovery that steel could be highly resistant to corrosion and discoloration by adding metallic chromium to form stainless steel. Stainless steel and chrome plating together comprise 85% of the commercial use, trivalent chromium ion is an essential nutrient in trace amounts in humans for insulin, sugar and lipid metabolism, although the issue is debated. While chromium metal and Cr ions are not considered toxic, hexavalent chromium is toxic and carcinogenic, abandoned chromium production sites often require environmental cleanup. Chromium is remarkable for its properties, it is the only elemental solid which shows antiferromagnetic ordering at room temperature. Above 38 °C, it changes to paramagnetic, Chromium metal left standing in air is passivated by oxidation, forming a thin, protective, surface layer. This layer is a structure only a few molecules thick. It is very dense, and prevents the diffusion of oxygen into the underlying metal and this is different from the oxide that forms on iron and carbon steel, through which elemental oxygen continues to migrate, reaching the underlying material to cause incessant rusting. Passivation can be enhanced by short contact with oxidizing acids like nitric acid, passivated chromium is stable against acids. Passivation can be removed with a reducing agent that destroys the protective oxide layer on the metal. Chromium metal treated in this way readily dissolves in weak acids, Chromium, unlike such metals as iron and nickel, does not suffer from hydrogen embrittlement. However, it suffer from nitrogen embrittlement, reacting with nitrogen from air. Chromium is the 22nd most abundant element in Earths crust with a concentration of 100 ppm. Chromium compounds are found in the environment from the erosion of chromium-containing rocks, Chromium is mined as chromite ore. About two-fifths of the ores and concentrates in the world are produced in South Africa, while Kazakhstan, India, Russia. Untapped chromite deposits are plentiful, but geographically concentrated in Kazakhstan, although rare, deposits of native chromium exist
29.
Nickel
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Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a golden tinge. Nickel belongs to the metals and is hard and ductile. Meteoric nickel is found in combination with iron, a reflection of the origin of elements as major end products of supernova nucleosynthesis. An iron–nickel mixture is thought to compose Earths inner core, use of nickel has been traced as far back as 3500 BCE. Nickel was first isolated and classified as an element in 1751 by Axel Fredrik Cronstedt. The elements name comes from a mischievous sprite of German miner mythology, Nickel, an economically important source of nickel is the iron ore limonite, which often contains 1–2% nickel. Nickels other important ore minerals include garnierite, and pentlandite, major production sites include the Sudbury region in Canada, New Caledonia in the Pacific, and Norilsk in Russia. Nickel is slowly oxidized by air at room temperature and is considered corrosion-resistant, historically, it has been used for plating iron and brass, coating chemistry equipment, and manufacturing certain alloys that retain a high silvery polish, such as German silver. About 6% of world production is still used for corrosion-resistant pure-nickel plating. Nickel-plated objects sometimes provoke nickel allergy, Nickel has been widely used in coins, though its rising price has led to some replacement with cheaper metals in recent years. Nickel is one of four elements that are ferromagnetic around room temperature, alnico permanent magnets based partly on nickel are of intermediate strength between iron-based permanent magnets and rare-earth magnets. The metal is valuable in modern times chiefly in alloys, about 60% of world production is used in nickel-steels, other common alloys and some new superalloys comprise most of the remainder of world nickel use, with chemical uses for nickel compounds consuming less than 3% of production. As a compound, nickel has a number of chemical manufacturing uses. Nickel is a nutrient for some microorganisms and plants that have enzymes with nickel as an active site. Nickel is a metal with a slight golden tinge that takes a high polish. It is one of four elements that are magnetic at or near room temperature. Its Curie temperature is 355 °C, meaning that bulk nickel is non-magnetic above this temperature, the unit cell of nickel is a face-centered cube with the lattice parameter of 0.352 nm, giving an atomic radius of 0.124 nm
30.
Talc
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Talc is a clay mineral composed of hydrated magnesium silicate with the chemical formula H2Mg34 or Mg3Si4O102. In loose form, it, along with starch, was one of the most widely used substances known as baby powder It occurs as foliated to fibrous masses. It has a perfect cleavage, and the folia are not elastic. Mohs scale of hardness, based on scratch hardness comparison. As such, talc can easily be scratched by a fingernail, talc has a specific gravity of 2. 5–2.8, a clear or dusty luster, and is translucent to opaque. Talc is not soluble in water, but is soluble in dilute mineral acids. Its color ranges from white to grey or green and it has a greasy feel. Soapstone is a rock composed predominantly of talc. The word talc derives from Medieval Latin talcus, which in turn originates from Arabic, طلق ṭalq which in turn was derived from Persian, in the ancient times, the word was used for various related minerals, including talc, mica, and selenite. Talc is a mineral that results from the metamorphism of magnesian minerals such as serpentine, pyroxene, amphibole. This is known as talc carbonation or steatization and produces a suite of known as talc carbonates. This is typically associated with high-pressure, low-temperature minerals such as phengite, garnet, such rocks are typically white, friable, and fibrous, and are known as whiteschist. Talc is a trioctahedral layered mineral, its structure is similar to pyrophyllite, talc is a common metamorphic mineral in metamorphic belts that contain ultramafic rocks, such as soapstone, and within whiteschist and blueschist metamorphic terranes. Talc carbonate ultramafics are typical of areas of the Archaean cratons. Talc-carbonate ultramafics are also known from the Lachlan Fold Belt, eastern Australia, from Brazil, the Guiana Shield, and from the belts of Turkey, Oman. Notable economic talc occurrences include the Mount Seabrook talc mine, Western Australia, the France-based Luzenac Group is the worlds largest supplier of mined talc. Its largest talc mine at Trimouns near Luzenac in southern France produces 400,000 tonnes of talc per year, talc is used in many industries, including paper making, plastic, paint and coatings, rubber, food, electric cable, pharmaceuticals, cosmetics, and ceramics. A coarse grayish-green high-talc rock is soapstone or steatite, used for stoves, sinks, electrical switchboards, crayons, soap and it is often used for surfaces of laboratory table tops and electrical switchboards because of its resistance to heat, electricity and acids
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Carbonate minerals
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IMA-CNMNC proposes a new hierarchical scheme. This list uses the Classification of Nickel–Strunz
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Serpentine subgroup
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The serpentine subgroup are greenish, brownish, or spotted minerals commonly found in serpentinite rocks. They are used as a source of magnesium and asbestos, the name is thought to come from the greenish color being that of a serpent. In mineralogy and gemology, serpentine may refer to any of 20 varieties belonging to the serpentine group, owing to admixture, these varieties are not always easy to individualize, and distinctions are not usually made. There are three important mineral polymorphs of serpentine, antigorite, chrysotile and lizardite, the serpentine group of minerals are polymorphous, meaning that they have the same chemical formulae, but the atoms are arranged into different structures, or crystal lattices. Chrysotile, which has a habit, is one polymorph of serpentine and is an important component of asbestos. Other polymorphs in the group may have a platy habit. Antigorite and lizardite are the polymorphs with platy habit, many types of serpentine have been used for jewellery and hardstone carving, sometimes under the name false jade or Teton jade. Their olive green colour and smooth or scaly appearance is the basis of the name from the Latin serpentinus, meaning serpent rock and they have their origins in metamorphic alterations of peridotite and pyroxene. Serpentines may also pseudomorphously replace other magnesium silicates, alterations may be incomplete, causing physical properties of serpentines to vary widely. Where they form a significant part of the surface, the soil is unusually high in clay. Antigorite is the polymorph of serpentine that most commonly forms during metamorphism of wet ultramafic rocks and is stable at the highest temperatures—to over 600 °C at depths of 60 km or so. In contrast, lizardite and chrysotile typically form near the Earths surface and break down at low temperatures. It has been suggested that chrysotile is never stable relative to either of the other two serpentine polymorphs, samples of the oceanic crust and uppermost mantle from ocean basins document that ultramafic rocks there commonly contain abundant serpentine. Antigorite contains water in its structure, about 13 percent by weight, the flora is generally very distinctive, with specialised, slow-growing species. Areas of serpentine-derived soil will show as strips of shrubland and open, scattered small trees within otherwise forested areas, most serpentines are opaque to translucent, light, soft, infusible and susceptible to acids. All are microcrystalline and massive in habit, never being found as single crystals, lustre may be vitreous, greasy or silky. Colours range from white to grey, yellow to green, and brown to black, many are intergrown with other minerals, such as calcite and dolomite. Occurrence is worldwide, New Caledonia, Canada, US, Afghanistan, Britain, Greece, China, Ural Mountains, France, Korea, Austria, India, Myanmar, New Zealand, Norway and Italy are notable localities
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Chlorite group
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The chlorites are a group of phyllosilicate minerals. Chlorites can be described by the following four endmembers based on their chemistry via substitution of the four elements in the silicate lattice, Mg, Fe, Ni. Clinochlore, O108 Chamosite, O108 Nimite, O108 Pennantite, 64O108 In addition, zinc, lithium, the great range in composition results in considerable variation in physical, optical, and X-ray properties. Similarly, the range of chemical composition allows chlorite group minerals to exist over a range of temperature and pressure conditions. For this reason chlorite minerals are ubiquitous minerals within low and medium temperature metamorphic rocks, some rocks, hydrothermal rocks. The name chlorite is from the Greek chloros, meaning green, the typical general formula is, 34O102·36. This formula emphasizes the structure of the group, chlorites have a 2,1 sandwich structure, this is often referred to as a talc layer. Unlike other 2,1 clay minerals, a chlorites interlayer space is composed of 6 and this 6 unit is more commonly referred to as the brucite-like layer, due to its closer resemblance to the mineral brucite. Therefore, chlorites structure appears as follows, -t-o-t-brucite-t-o-t-brucite, thats why they are also called 2,1,1 minerals. An older classification divided the chlorites into two subgroups, the orthochlorites and leptochlorites, the terms are seldom used and the ortho prefix is somewhat misleading as the chlorite crystal system is monoclinic and not orthorhombic. Chlorite is commonly found in rocks as an alteration product of mafic minerals such as pyroxene, amphibole. Chlorite is a common mineral associated with ore deposits and commonly occurs with epidote, sericite, adularia. Chlorite is also a metamorphic mineral, usually indicative of low-grade metamorphism. It is the species of the zeolite facies and of lower greenschist facies. It occurs in the quartz, albite, sericite, chlorite, within ultramafic rocks, metamorphism can also produce predominantly clinochlore chlorite in association with talc. Chlorite occurs naturally in a variety of locations and forms, for example, chlorite is found naturally in certain parts of Wales in mineral schists. Chlorite is found in large boulders scattered on the surface on Ring Mountain in Marin County. Clinoclore, pennantite, and chamosite are the most common varieties, several other sub-varieties have been described
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Magnetite
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Magnetite is a mineral and one of the main iron ores. With the chemical formula Fe3O4, it is one of the oxides of iron, Magnetite is ferrimagnetic, it is attracted to a magnet and can be magnetized to become a permanent magnet itself. It is the most magnetic of all the minerals on Earth. Naturally-magnetized pieces of magnetite, called lodestone, will attract small pieces of iron, today it is mined as iron ore. Small grains of magnetite occur in almost all igneous and metamorphic rocks, Magnetite is black or brownish-black with a metallic luster, has a Mohs hardness of 5–6 and leaves a black streak. The chemical IUPAC name is iron oxide and the chemical name is ferrous-ferric oxide. In addition to rocks, magnetite also occurs in sedimentary rocks, including banded iron formations and in lake. Magnetite nanoparticles are also thought to form in soils, where they probably oxidize rapidly to maghemite, Magnetite has an inverse spinel crystal structure. As a member of the group, it can form solid solutions with similarly structured minerals, including ulvospinel. Titanomagnetite, also known as titaniferous magnetite, is a solution between magnetite and ulvospinel that crystallizes in many mafic igneous rocks. Titanomagnetite may undergo oxyexsolution during cooling, resulting in ingrowths of magnetite and ilmenite, Magnetite has been important in understanding the conditions under which rocks form. Magnetite reacts with oxygen to produce hematite, and the pair forms a buffer that can control oxygen fugacity. Commonly, igneous rocks contain solid solutions of both titanomagnetite and hemoilmenite or titanohematite, Magnetite also is produced from peridotites and dunites by serpentinization. Lodestones were used as a form of magnetic compass. At low temperatures, magnetite undergoes a crystal structure phase transition from a structure to a cubic structure known as the Verwey transition. The Verwey transition occurs around 121 K and is dependent on size, domain state. An isotropic point also occurs near the Verwey transition around 130 K, the Curie temperature of magnetite is 858 K. Magnetite is sometimes found in large quantities in beach sand. Such black sands are found in places, such as Lung Kwu Tan of Hong Kong, California of the United States
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Zeolite
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Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents and catalysts. Based on this, he called the material zeolite, from the Greek ζέω, meaning to boil and λίθος, the classic reference for the field has been Zeolite molecular sieves, structure, chemistry, and use by Donald W. Breck. Zeolites occur naturally but are produced industrially on a large scale. As of September 2016,232 unique zeolite frameworks have been identified, every new zeolite structure that is obtained has to be approved by the International Zeolite Association Structure Commission and receives a three letter designation. Zeolites have a structure that can accommodate a wide variety of cations, such as Na+, K+, Ca2+, Mg2+. These positive ions are rather loosely held and can readily be exchanged for others in a contact solution, some of the more common mineral zeolites are analcime, chabazite, clinoptilolite, heulandite, natrolite, phillipsite, and stilbite. An example of the formula of a zeolite is, Na2Al2Si3O10·2H2O. Natural zeolites form where volcanic rocks and ash layers react with alkaline groundwater, Zeolites also crystallize in post-depositional environments over periods ranging from thousands to millions of years in shallow marine basins. Naturally occurring zeolites are rarely pure and are contaminated to varying degrees by other minerals, metals, quartz, for this reason, naturally occurring zeolites are excluded from many important commercial applications where uniformity and purity are essential. Zeolites are the members of the family of microporous solids known as molecular sieves mainly consisting of Si, Al, O, and metals including Ti, Sn, Zn. The term molecular sieve refers to a property of these materials. This is due to a very regular structure of molecular dimensions. The maximum size of the molecular or ionic species that can enter the pores of a zeolite is controlled by the dimensions of the channels, therefore, the pores in many zeolites are not cylindrical. Zeolites transform to other minerals under weathering, hydrothermal alteration or metamorphic conditions, the sequence of silica-poor volcanic rocks commonly progresses from, Cowlesite → levyne–offretite → analcime → thomsonite–mesolite-scolecite → chabazite → calcite. Industrially important zeolites are produced synthetically, typical procedures entail heating aqueous solutions of alumina and silica with sodium hydroxide. Equivalent reagents include sodium aluminate and sodium silicate, further variations include changes in the cations to include quaternary ammonium cations. Synthetic zeolites hold some key advantages over their natural analogues, the synthetic materials are manufactured in a uniform, phase-pure state. It is also possible to produce zeolite structures that do not appear in nature, Zeolite A is a well-known example
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Quartz
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Quartz is the second most abundant mineral in Earths continental crust, behind feldspar. There are many different varieties of quartz, several of which are semi-precious gemstones, since antiquity, varieties of quartz have been the most commonly used minerals in the making of jewelry and hardstone carvings, especially in Eurasia. The word quartz is derived from the German word Quarz and its Middle High German ancestor twarc, the Ancient Greeks referred to quartz as κρύσταλλος derived from the Ancient Greek κρύος meaning icy cold, because some philosophers apparently believed the mineral to be a form of supercooled ice. Today, the rock crystal is sometimes used as an alternative name for the purest form of quartz. Quartz belongs to the crystal system. The ideal crystal shape is a six-sided prism terminating with six-sided pyramids at each end, well-formed crystals typically form in a bed that has unconstrained growth into a void, usually the crystals are attached at the other end to a matrix and only one termination pyramid is present. However, doubly terminated crystals do occur where they develop freely without attachment, a quartz geode is such a situation where the void is approximately spherical in shape, lined with a bed of crystals pointing inward. α-quartz crystallizes in the crystal system, space group P3121 and P3221 respectively. β-quartz belongs to the system, space group P6222 and P6422. These space groups are truly chiral, both α-quartz and β-quartz are examples of chiral crystal structures composed of achiral building blocks. The transformation between α- and β-quartz only involves a comparatively minor rotation of the tetrahedra with respect to one another, although many of the varietal names historically arose from the color of the mineral, current scientific naming schemes refer primarily to the microstructure of the mineral. Color is an identifier for the cryptocrystalline minerals, although it is a primary identifier for the macrocrystalline varieties. Pure quartz, traditionally called rock crystal or clear quartz, is colorless and transparent or translucent, common colored varieties include citrine, rose quartz, amethyst, smoky quartz, milky quartz, and others. The most important distinction between types of quartz is that of macrocrystalline and the microcrystalline or cryptocrystalline varieties, the cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline. Chalcedony is a form of silica consisting of fine intergrowths of both quartz, and its monoclinic polymorph moganite. Other opaque gemstone varieties of quartz, or mixed rocks including quartz, often including contrasting bands or patterns of color, are agate, carnelian or sard, onyx, heliotrope, amethyst is a form of quartz that ranges from a bright to dark or dull purple color. The worlds largest deposits of amethysts can be found in Brazil, Mexico, Uruguay, Russia, France, Namibia, sometimes amethyst and citrine are found growing in the same crystal. It is then referred to as ametrine, an amethyst is formed when there is iron in the area where it was formed
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Petrography
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Petrography is a branch of petrology that focuses on detailed descriptions of rocks. Someone who studies petrography is called a petrographer, the mineral content and the textural relationships within the rock are described in detail. The classification of rocks is based on the information acquired during the petrographic analysis, petrographic descriptions start with the field notes at the outcrop and include macroscopic description of hand specimens. However, the most important tool for the petrographer is the petrographic microscope, the detailed analysis of minerals by optical mineralogy in thin section and the micro-texture and structure are critical to understanding the origin of the rock. Individual mineral grains from a sample may also be analyzed by X-ray diffraction when optical means are insufficient. The addition of two such prisms to the ordinary microscope converted the instrument into a polarizing, or petrographic microscope, using transmitted light and Nicol prisms, it was possible to determine the internal crystallographic character of very tiny mineral grains, greatly advancing the knowledge of a rocks constituents. During the 1840s, a development by Henry C, sorby and others firmly laid the foundation of petrography. This was a technique to study very thin slices of rock, a slice of rock was affixed to a microscope slide and then ground so thin that light could be transmitted through mineral grains that otherwise appeared opaque. The position of adjoining grains was not disturbed, thus permitting analysis of rock texture, thin section petrography became the standard method of rock study. It was in Europe, principally in Germany, that advanced in the last half of the nineteenth century. The macroscopic characters of rocks, those visible in hand-specimens without the aid of the microscope, are very varied and difficult to describe accurately and fully. The geologist in the field depends principally on them and on a few chemical and physical tests. Although frequently insufficient in themselves to determine the nature of a rock, they usually serve for a preliminary classification. The fine grained species are often indeterminable in this way, shales and clay rocks generally are soft, fine grained, often laminated and not infrequently contain minute organisms or fragments of plants. Limestones are easily marked with a knife-blade, effervesce readily with weak cold acid, other simple tools include the blowpipe, the goniometer, the magnet, the magnifying glass and the specific gravity balance. When dealing with unfamiliar types or with rocks so fine grained that their component minerals cannot be determined with the aid of a hand lens, a microscope is used. Characteristics observed under the microscope include colour, colour variation under plane polarised light, fracture characteristics of the grains, refractive index, in toto, these characteristics are sufficient to identify the mineral, and often to quite tightly estimate its major element composition. The process of identifying minerals under the microscope is fairly subtle, the more difficult and skilful part of optical petrography is identifying the interrelationships between grains and relating them to features seen in hand specimen, at outcrop, or in mapping
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Plagioclase
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Plagioclase is a series of tectosilicate minerals within the feldspar group. Rather than referring to a mineral with a specific chemical composition, plagioclase is a continuous solid solution series. This was first shown by the German mineralogist Johann Friedrich Christian Hessel in 1826, the series ranges from albite to anorthite endmembers, where sodium and calcium atoms can substitute for each other in the minerals crystal lattice structure. Plagioclase in hand samples is often identified by its polysynthetic crystal twinning or record-groove effect, plagioclase is a major constituent mineral in the Earths crust, and is consequently an important diagnostic tool in petrology for identifying the composition, origin and evolution of igneous rocks. Plagioclase is also a constituent of rock in the highlands of the Earths moon. Analysis of thermal emission spectra from the surface of Mars suggests that plagioclase is the most abundant mineral in the crust of Mars, the extinction angle is an optical characteristic and varies with the albite fraction. There are several named plagioclase feldspars that fall between albite and anorthite in the series, the following table shows their compositions in terms of constituent anorthite and albite percentages. Anorthite was named by Gustav Rose in 1823 from the Ancient Greek meaning oblique, anorthite is a comparatively rare mineral but occurs in the basic plutonic rocks of some orogenic calc-alkaline suites. Albite is named from the Latin albus, in reference to its pure white color. It is a common and important rock-making mineral associated with the more acid rock types and in pegmatite dikes, often with rarer minerals like tourmaline. The intermediate members of the group are very similar to each other. Bytownite, named after the name for Ottawa, Canada, is a rare mineral occasionally found in more basic rocks. Labradorite is the characteristic feldspar of the basic rock types such as diorite, gabbro, andesite. Labradorite frequently shows an iridescent display of colors due to light refracting within the lamellae of the crystal and it is named after Labrador, where it is a constituent of the intrusive igneous rock anorthosite which is composed almost entirely of plagioclase. A variety of known as spectrolite is found in Finland. Andesine is a mineral of rocks such as diorite which contain a moderate amount of silica. Oligoclase is common in granite, syenite, diorite, and gneiss and it is a frequent associate of orthoclase. The name oligoclase is derived from the Greek for little and fracture, sunstone is mainly oligoclase with flakes of hematite
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Melilite
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Melilite refers to a mineral of the melilite group. Minerals of the group are solid solutions of several endmembers, the most important of which are gehlenite and åkermanite, a generalized formula for common melilite is 2. Discovered in 1793 near Rome, it has a yellowish, greenish-brown color, the name derives from the Greek words meli honey and lithos stone. Minerals of the group are sorosilicates. They have the basic structure, of general formula A2B. The melilite structure consist of pairs of fused TO4, where T may be Si, Al, B, sharing one corner, the formula of the pair is T2O7. These bow-ties are linked together into sheets by the B cations, the sheets are held together by the A cations, most commonly calcium and sodium. Aluminium may sit on either the T or the B site, minerals with the melilite structure may show a cleavage parallel to the crystallographic directions and may show weaker cleavage perpendicular to this, in the directions. The important endmembers of common melilite are åkermanite Ca2Mg and gehlenite Ca2Al, many melilites also contain appreciable iron and sodium. Some other compositions with the structure include, alumoåkermanite 2, okayamalite Ca2B, gugiaite Ca2Be, hardystonite Ca2Zn, barylite BaBe2. E. they simultaneously show ferroelectric and magnetic ordering at low temperatures and this gives rise to peculiar optical properties, for example Ba2Co shows giant directional dichroism and hosts magnetically switchable chirality. Melilite with compositions dominated by the endmembers akermanite and gehlenite is widely distributed and it occurs in metamorphic and igneous rocks and in meteorites. Typical metamorphic occurrences are in high-temperature metamorphosed impure limestones, for instance, melilite occurs in some high-temperature skarns. Melilite also occurs in unusual silica-undersaturated igneous rocks, some of these rocks appear to have formed by reaction of magmas with limestone. Other igneous rocks containing melilite crystallize from magma derived from the Earths mantle, the presence of melilite is an essential constituent in some rare igneous rocks, such as olivine melilitite. Extremely rare igneous rocks contain as much as 70% melilite, together with such as pyroxene. Melilite is a constituent of some calcium- and aluminium-rich inclusions in chondritic meteorites, isotope ratios of magnesium and some other elements in these inclusions are of great importance in deducing processes that formed our solar system. Classification of minerals List of minerals Deer, W. A. Howie, R. A. and Zussman, J. Disilicates and Ring Silicates, Rock-forming minerals 1B, new York, John Wiley & Sons, ISBN 0-582-46521-4 Zinner, E
40.
Monticellite
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Monticellite and kirschsteinite are gray silicate minerals of the olivine group with compositions CaMgSiO4 and CaFeSiO4, respectively. Most monticellites have the pure magnesium end-member composition but rare ferroan monticellites, pure kirschsteinite is only found in synthetic systems. Monticellite is named after Teodoro Monticelli Italian mineralogist, like other members of the group monticellite and kirschsteinite have orthorhombic unit cells shown in Figure 1. Iron and magnesium ions are located on the M1 inversion sites, deer, W. A. Howie, R. A. and Zussman, J. An introduction to the rock-forming minerals, harlow, Longman ISBN 0-582-30094-0 Mindat. org Webmineral. com Handbook of Mineralogy
