A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. Earths volcanoes occur because its crust is broken into 17 major, therefore, on Earth, volcanoes are generally found where tectonic plates are diverging or converging. This type of volcanism falls under the umbrella of plate hypothesis volcanism, Volcanism away from plate boundaries has been explained as mantle plumes. These so-called hotspots, for example Hawaii, are postulated to arise from upwelling diapirs with magma from the boundary,3,000 km deep in the Earth. Volcanoes are usually not created where two plates slide past one another. Erupting volcanoes can pose hazards, not only in the immediate vicinity of the eruption. Historically, so-called volcanic winters have caused catastrophic famines, the word volcano is derived from the name of Vulcano, a volcanic island in the Aeolian Islands of Italy whose name in turn comes from Vulcan, the god of fire in Roman mythology.
The study of volcanoes is called volcanology, sometimes spelled vulcanology, at the mid-oceanic ridges, two tectonic plates diverge from one another as new oceanic crust is formed by the cooling and solidifying of hot molten rock. Most divergent plate boundaries are at the bottom of the oceans, most volcanic activity is submarine, black smokers are evidence of this kind of volcanic activity. Where the mid-oceanic ridge is above sea-level, volcanic islands are formed, for example, subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. In this case, the plate subducts, or submerges under the continental plate forming a deep ocean trench just offshore. In a process called flux melting, water released from the subducting plate lowers the temperature of the overlying mantle wedge. This magma tends to be very viscous due to its high content, so it often does not reach the surface. When it does reach the surface, a volcano is formed, typical examples of this kind of volcano are Mount Etna and the volcanoes in the Pacific Ring of Fire.
Because tectonic plates move across them, each volcano becomes dormant and is eventually re-formed as the plate advances over the postulated plume and this theory is currently under criticism, however. The most common perception of a volcano is of a mountain, spewing lava and poisonous gases from a crater at its summit, however. The features of volcanoes are more complicated and their structure. Some volcanoes have rugged peaks formed by lava domes rather than a summit crater while others have features such as massive plateaus
Komatiite is a type of ultramafic mantle-derived volcanic rock. Komatiites have low silicon and aluminium, and high to extremely high magnesium content, komatiite was named for its type locality along the Komati River in South Africa. True komatiites are very rare and essentially restricted to rocks of Archean age and this restriction in age is thought to be due to cooling of the mantle, which may have been up to 500 °C hotter during the early to middle Archaean. The early Earth had much higher heat production, due to the heat from planetary accretion. Geographically, komatiites are restricted in distribution to the Archaean shield areas, Komatiites occur with other ultramafic and high-magnesian mafic volcanic rocks in Archaean greenstone belts. The youngest komatiites are from the island of Gorgona on the Caribbean oceanic plateau off the Pacific coast of Colombia, magmas of komatiitic compositions have a very high melting point, with calculated eruption temperatures in excess of 1600 °C. Basaltic lavas normally have eruption temperatures of about 1100 to 1250 °C, the higher melting temperatures required to produce komatiite have been attributed to the presumed higher geothermal gradients in the Archean Earth.
Komatiitic lava was extremely fluid when it erupted, the major komatiitic sequences preserved in Archaean rocks are thus considered to be lava tubes, ponds of lava etc. where the komatiitic lava accumulated. Komatiite chemistry is different from that of basaltic and other common mantle-produced magmas, Komatiites are considered to have been formed by high degrees of partial melting, usually greater than 50%, and hence have high MgO with low K2O and other incompatible elements. There are two classes of komatiite, aluminium undepleted komatiite and aluminium depleted komatiite, defined by their Al2O3/TiO2 ratios. These two classes of komatiite are often assumed to represent a real petrological source difference between the two related to depth of melt generation. Komatiites probably form in extremely hot mantle plumes, boninite magmatism is similar to komatiite magmatism but is produced by fluid-fluxed melting above a subduction zone. Boninites with 10–18% MgO tend to have higher large-ion lithophile elements than komatiites, the pristine volcanic mineralogy of komatiites is composed of forsteritic olivine and often chromian pyroxene and chromite. A considerable population of komatiite examples show a cumulate texture and morphology, the usual cumulate mineralogy is highly magnesium rich forsterite olivine, though chromian pyroxene cumulates are possible.
Volcanic rocks rich in magnesium may be produced by accumulation of olivine phenocrysts in basalt melts of normal chemistry, the often rarely preserved flow top breccia and pillow margin zones in some komatiite flows are essentially volcanic glass, quenched in contact with overlying water or air. Because they are cooled, they represent the liquid composition of the komatiites. The spinifex texture is named after an Australian grass that grows in clumps with similar shapes, primary mineral species encountered in komatiites include olivine, the pyroxenes augite and bronzite, chromite and rarely pargasitic amphibole. Secondary minerals include serpentine, amphibole, sodic plagioclase, iron oxides and rarely phlogopite, all known komatites have been metamorphosed, therefore should technically be termed metakomatiite though the prefix meta is inevitably assumed
A dike or dyke, in geological usage, is a sheet of rock that formed in a fracture in a pre-existing rock body. Dikes can be either magmatic or sedimentary in origin, magmatic dikes form when magma intrudes into a crack crystallizes as a sheet intrusion, either cutting across layers of rock or through an unlayered mass of rock. Clastic dikes are formed when sediment fills a pre-existing crack, an intrusive dike is an igneous body with a very high aspect ratio, which means that its thickness is usually much smaller than the other two dimensions. Thickness can vary from sub-centimeter scale to many meters, and the dimensions can extend over many kilometres. A dike is an intrusion into an opening cross-cutting fissure, shouldering aside other pre-existing layers or bodies of rock, near-horizontal, or conformable intrusions, along bedding planes between strata are called intrusive sills. Sometimes dikes appear in swarms, consisting of several to hundreds of dikes emplaced more or less contemporaneously during a single intrusive event, the worlds largest dike swarm is the Mackenzie dike swarm in the Northwest Territories, Canada.
Dikes often form as either radial or concentric swarms around plutonic intrusives, the latter are known as ring dikes. Pegmatite dikes comprise extremely coarse crystalline granitic rocks - often associated with granite intrusions or metamorphic segregations. Aplite dikes are fine-grained or sugary-textured intrusives of granitic composition, in contrast to magmatic dikes, a sill is a magmatic sheet intrusion that forms within and parallel to the bedding of layered rock. Sedimentary dikes or clastic dikes are vertical bodies of rock that cut off other rock layers. Driven by the pressure the sediment breaks through overlying layers. When a soil is under permafrost conditions the water is totally frozen. When cracks are formed in rocks, they may fill up with sediments that fall in from above. The result is a body of sediment that cuts through horizontal layers. Batholith Ring dike Fissure vent Laccolith Runamo, formerly interpreted as a runic inscription
Greenland is an autonomous constituent country within the Danish Realm between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for more than a millennium. The majority of its residents are Inuit, whose ancestors began migrating from the Canadian mainland in the 13th century, Greenland is the worlds largest island. Three-quarters of Greenland is covered by the permanent ice sheet outside Antarctica. With a population of about 56,480, it is the least densely populated country in the world, the Arctic Umiaq Line ferry acts as a lifeline for western Greenland, connecting the various cities and settlements. Greenland has been inhabited off and on for at least the last 4,500 years by Arctic peoples whose forebears migrated there from what is now Canada, Norsemen settled the uninhabited southern part of Greenland beginning in the 10th century, and Inuit peoples arrived in the 13th century.
The Norse colonies disappeared in the late 15th century, soon after their demise, beginning in 1499, the Portuguese briefly explored and claimed the island, naming it Terra do Lavrador. In the early 18th century, Scandinavian explorers reached Greenland again, to strengthen trading and power, Denmark-Norway affirmed sovereignty over the island. Greenland was settled by Vikings more than a thousand years ago, Vikings set sail from Greenland and Iceland, discovering North America nearly 500 years before Columbus reached Caribbean islands. Though under continuous influence of Norway and Norwegians, Greenland was not formally under the Norwegian crown until 1262, the Kingdom of Norway was extensive and a military power until the mid-14th century. Thus, the two kingdoms resources were directed at creating Copenhagen, Norway became the weaker part and lost sovereignty over Greenland in 1814 when the union was dissolved. Greenland became a Danish colony in 1814, and was made a part of the Danish Realm in 1953 under the Constitution of Denmark, in 1973, Greenland joined the European Economic Community with Denmark.
However, in a referendum in 1982, a majority of the population voted for Greenland to withdraw from the EEC which was effected in 1985, Greenland contains the worlds largest and most northernly national park, Northeast Greenland National Park. Greenland is divided into four municipalities - Sermersooq, Qaasuitsup and it retains control of monetary policy, providing an initial annual subsidy of DKK3.4 billion, which is planned to diminish gradually over time. Greenland expects to grow its economy based on increased income from the extraction of natural resources, the capital, held the 2016 Arctic Winter Games. At 70%, Greenland has one of the highest shares of renewable energy in the world, the early Viking settlers named the island as Greenland. In the Icelandic sagas, the Norwegian-born Icelander Erik the Red was said to be exiled from Iceland for manslaughter, along with his extended family and his thralls, he set out in ships to explore an icy land known to lie to the northwest. After finding an area and settling there, he named it Grœnland
Calcium is a chemical element with symbol Ca and atomic number 20. Calcium is a soft grayish-yellow alkaline earth metal, fifth-most-abundant element by mass in the Earths crust, the ion Ca2+ is the fifth-most-abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride and sulfate. Free calcium metal is too reactive to occur in nature, Calcium is produced in supernova nucleosynthesis. Calcium is a trace element in living organisms. It is the most abundant metal by mass in animals, and it is an important constituent of bone, teeth. In cell biology, the movement of the calcium ion into, Calcium carbonate and calcium citrate are often taken as dietary supplements. Calcium is on the World Health Organizations List of Essential Medicines, Calcium has a wide variety of applications, almost all of which are associated with calcium compounds and salts. Calcium metal is used as a deoxidizer and decarbonizer for production of ferrous and nonferrous alloys. In steelmaking and production of iron, Ca reacts with oxygen, Calcium carbonate is used in manufacturing cement and mortar, lime and aids in production in the glass industry.
It has chemical and optical uses as mineral specimens in toothpastes, Calcium hydroxide solution is used to detect the presence of carbon dioxide in a gas sample bubbled through a solution. The solution turns cloudy where CO2 is present, Calcium arsenate is used in insecticides. Calcium carbide is used to make acetylene gas and various plastics, Calcium chloride is used in ice removal and dust control on dirt roads, as a conditioner for concrete, as an additive in canned tomatoes, and to provide body for automobile tires. Calcium citrate is used as a food preservative, Calcium cyclamate is used as a sweetening agent in several countries. In the United States, it has been outlawed as a suspected carcinogen, Calcium gluconate is used as a food additive and in vitamin pills. Calcium hypochlorite is used as a swimming pool disinfectant, as an agent, as an ingredient in deodorant. Calcium permanganate is used in rocket propellant, textile production, as a water sterilizing agent. Calcium phosphate is used as a supplement for animal feed, fertilizer, in production for dough and yeast products, in the manufacture of glass.
Calcium phosphide is used in fireworks, torpedoes, Calcium sulfate is used as common blackboard chalk, as well as, in its hemihydrate form, Plaster of Paris
Bushveld Igneous Complex
Located in South Africa, the BIC contains some of the richest ore deposits on Earth. Gabbro or norite is quarried from parts of the Complex, the site was discovered around 1897 by Gustaaf Molengraaff. The Bushveld Igneous Complex covers an area in the central Transvaal. It is divided into an eastern and western lobe, with a northern extension. All three sections of the system were formed around the same time—about 2 billion years ago—and are remarkably similar and these intrusions are thought to predate the nearby Vredefort impact to the south, by some 30 million years. Large portions of the area are covered by younger rocks. The extrusions were emplaced over an early diabasic sill, outcrops of which are visible on the side of the Complex. These are typically greenish in colour and composed of clinopyroxene, altered to hornblende and plagioclase, the Complex includes layered mafic intrusions and a felsic phase. The complex has its centre located north of Pretoria in South Africa at about 25° S.
It covers over 66,000 km2, an area the size of Ireland, the complex varies in thickness, in places reaching 9 kilometres thick. The orebodies within the complex include the UG2 reef containing up to 43. 5% chromite, the Merensky Reef varies from 30 to 90 cm in thickness. It is a norite with extensive chromitite and sulfide layers or zones containing the ore, the Reef contains an average of 10 ppm platinum group metals in pyrrhotite and pyrite as well as in rare platinum group minerals and alloys. The Merensky and UG-2 reefs contain approximately 90% of the worlds known PGM reserves, about 80% of the platinum and 20% of the palladium mined each year are produced from these horizons. Richardson, Stephen H. Shirey, Steven B, continental mantle signature of Bushveld magmas and coeval diamonds. Viljoen, M. J. Schürmann, L. W. Platinum-group metals, council for Geoscience Handbook 16, Mineral Resources of South Africa
Gabbro refers to a large group of dark, often phaneritic, mafic intrusive igneous rocks chemically equivalent to basalt. It forms when magma is trapped beneath the Earths surface. Much of the Earths oceanic crust is made of gabbro, formed at mid-ocean ridges, Gabbro is found as plutons associated with continental volcanism. Due to its variant nature, the term gabbro may be applied loosely to a range of intrusive rocks. The term gabbro was used in the 1760s to name a set of types that were found in the ophiolites of the Apennine Mountains in Italy. Then, in 1809, the German geologist Christian Leopold von Buch used the term more restrictively in his description of these Italian ophiolitic rocks and he assigned the name gabbro to rocks that geologists nowadays would more strictly call metagabbro. Von Buch named gabbro after Gabbro, a village in Rosignano Marittimo municipality of Tuscany, Gabbro is dense, greenish or dark-colored and contains pyroxene and minor amounts of amphibole and olivine.
The pyroxene content is mostly clinopyroxene, generally augite, but small amounts of orthopyroxene may be present, if the amount of orthopyroxene is more than 95% of the total pyroxene content, the rock is termed norite. On the other hand, gabbro has more than 95% of its pyroxenes in the form of the monoclinic clinopyroxene/s, the calcium rich plagioclase feldspar and pyroxene content vary between 10% - 90% in gabbro. If more than 90% plagioclase is present, the rock is an anorthosite, if on the other hand, the rock contains more than 90% pyroxenes, it is termed pyroxenite. Gabbro may contain amounts of olivine and biotite. The quartz content in gabbro is less than 5% of total volume, quartz gabbros or monzogabbros are known to occur, for example the cizlakite at Pohorje in northeastern Slovenia, and are probably derived from magma that was over-saturated with silica. Gabbros contain minor amounts, typically a few percent, of iron-titanium oxides such as magnetite, Gabbro is generally coarse grained, with crystals in the size range of 1 mm or greater.
Finer grained equivalents of gabbro are called diabase, although the term microgabbro is often used when extra descriptiveness is desired, Gabbro may be extremely coarse grained to pegmatitic, and some pyroxene-plagioclase cumulates are essentially coarse grained gabbro, some may exhibit acicular crystal habits. Gabbro is usually equigranular in texture, although it may be porphyritic at times, cumulate gabbros are more properly termed pyroxene-plagioclase adcumulate. Gabbro is an part of the oceanic crust, and can be found in many ophiolite complexes as parts of zones III. Long belts of gabbroic intrusions are typically formed at proto-rift zones and around ancient rift zone margins, mantle plume hypotheses may rely on identifying mafic and ultramafic intrusions and coeval basalt volcanism. It is better to base a rock definition on descriptive characteristics of the rather than how or where it was formed
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 and evolution of igneous rocks. Plagioclase is 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, 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 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
Cosmetics, known as make-up, are substances or products used to enhance or alter the appearance or fragrance of the body. Many cosmetics are designed for use of applying to the face and they are generally mixtures of chemical compounds, some being derived from natural sources, and some being synthetics. Common cosmetics include lipstick, eye shadow, rouge, skin cleansers and skin lotions, hairstyling products and this broad definition includes any material intended for use as a component of a cosmetic product. The FDA specifically excludes soap from this category, Egyptian women and men used makeup. They were very fond of eyeliner and eyeshadows in dark colors including blue, Ancient Sumerian men and women were possibly the first to invent and wear lipstick, about 5,000 years ago. They crushed gemstones and used them to decorate their faces, mainly on the lips, around 3000 BC to 1500 BC, women in the ancient Indus Valley Civilization applied red tinted lipstick to their lips for face decoration.
Ancient Egyptians extracted red dye from fucus-algin,0. 01% iodine, and some bromine mannite, lipsticks with shimmering effects were initially made using a pearlescent substance found in fish scales. Six thousand year old relics of the hollowed out tombs of the Ancient Egyptian pharaohs are discovered, according to one source, early major developments include, Kohl used by ancient Egypt as a protective of the eye kohl Castor oil used by ancient Egypt as a protective balm. Skin creams made of beeswax, olive oil, and rose water and lanolin in the nineteenth century. The Ancient Greeks used cosmetics as the Ancient Romans did, Cosmetics are mentioned in the Old Testament, such as in 2 Kings 9,30, where Jezebel painted her eyelids—approximately 840 BC—and in the book of Esther, where beauty treatments are described. One of the most popular traditional Chinese medicines is the fungus Tremella fuciformis, used as a beauty product by women in China, the fungus reportedly increases moisture retention in the skin and prevents senile degradation of micro-blood vessels in the skin, reducing wrinkles and smoothing fine lines.
Cosmetic use was frowned upon at many points in Western history, for example, in the 19th century, Queen Victoria publicly declared make-up improper and acceptable only for use by actors. During the sixteenth century, the attributes of the women who used make-up created a demand for the product among the upper class. As of 2016, the worlds largest cosmetics company is LOréal, the market was developed in the US during the 1910s by Elizabeth Arden, Helena Rubinstein, and Max Factor. These firms were joined by Revlon just before World War II, during the 18th century, there was a high number of incidences of lead-poisoning because of the fashion for red and white lead makeup and powder. This led to swelling and inflammation of the eyes, attacked tooth enamel, heavy use was known to lead to death. Concealer is commonly used by men, Cosmetics brands release products especially tailored for men, and men are increasingly using them. Cosmetics are intended to be applied externally, a subset of cosmetics is called make-up, refers primarily to products containing color pigments that are intended to alter the users appearance
Spinel is the magnesium aluminium member of the larger spinel group of minerals. It has the formula MgAl2O4 in the crystal system. Its name comes from Latin spina, balas ruby is an old name for a rose-tinted variety of spinel. Spinel crystallizes in the system, common crystal forms are octahedra. It has an imperfect cleavage and a conchoidal fracture. Its hardness is 8, its gravity is 3. 5–4.1. It may be colorless, but is usually shades of red, green, brown, black. There is a natural white spinel, now lost, that surfaced briefly in what is now Sri Lanka. The Samarian Spinel is the largest known spinel in the world, the transparent red spinels were called spinel-rubies or balas rubies. In the past, before the arrival of modern science, after the 18th century the word ruby was only used for the red gem variety of the mineral corundum and the word spinel came to be used. Balas is derived from Balascia, the ancient name for Badakhshan, mines in the Gorno Badakhshan region of Tajikistan was for centuries the main source for red and pink spinels.
Spinel has long been found in the gravel of Sri Lanka and in limestones of the Badakshan Province in modern-day Afghanistan and Tajikistan. Recently gem quality spinels found in the marbles of Luc Yen and Matombo, Tsavo and in the gravels of Tunduru and this is why spinel and ruby are often found together. Spinel, 2O4, is common in peridotite in the uppermost Earths mantle, Spinel, Al2O4, is a common mineral in the Ca-Al-rich inclusions in some chondritic meteorites. Synthetic spinel, accidentally produced in the middle of the 18th century, has described more recently in scientific publications in 2000 and 2004. By 2015, transparent spinel was being made in sheets and other shapes through sintering, synthetic spinel which looks like glass but has notably higher strength against pressure, can have applications in military and commercial use. Spinel group Ceylonite The Samarian Spinel, the largest known spinel in the world, part of the Iranian Crown Jewels Black Princes Ruby Deer, Howie, an Introduction to the Rock-Forming Minerals, Longman, pp. 424–433, ISBN 0-582-44210-9.
Gemstones of the World 3rd edition, Sterling, pp. 116–117, Spinel structure at the University of Wisconsin - Green Bay Spinel structure at the Institut for materials science of the University of Kiel Value of Spinel
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. Thus it is a type of nesosilicate or orthosilicate and it is a common mineral in the Earths subsurface but weathers quickly on the surface. The ratio of magnesium and iron varies between the two endmembers of the solid solution series and fayalite, compositions of olivine are commonly expressed as molar percentages of forsterite and fayalite. Forsterite has a high melting temperature at atmospheric pressure, almost 1,900 °C. The melting temperature varies smoothly between the two endmembers, as do other properties, olivine incorporates only minor amounts of elements other than oxygen, silicon and iron. Manganese and nickel commonly are the elements present in highest concentrations. Olivine gives its name to the group of minerals with a structure which includes tephroite and kirschsteinite. It has a structure similar to magnetite but uses one quadravalent. Olivine gemstones are called peridot and chrysolite, olivine is named for its typically olive-green color, though it may alter to a reddish color from the oxidation of iron.
Translucent olivine is sometimes used as a gemstone called peridot, some of the finest gem-quality olivine has been obtained from a body of mantle rocks on Zabargad island in the Red Sea. Olivine occurs in mafic and ultramafic igneous rocks and as a primary mineral in certain metamorphic rocks. Mg-rich olivine crystallizes from magma that is rich in magnesium and low in silica and that magma crystallizes to mafic rocks such as gabbro and basalt. Ultramafic rocks such as peridotite and dunite can be left after extraction of magmas. Olivine and high pressure structural variants constitute over 50% of the Earths upper mantle, the metamorphism of impure dolomite or other sedimentary rocks with high magnesium and low silica content produces Mg-rich olivine, or forsterite. In contrast, Mg-rich olivine does not occur stably with silica minerals, Mg-rich olivine is stable to pressures equivalent to a depth of about 410 km within Earth. Mg-rich olivine has discovered in meteorites, on the Moon and Mars, falling into infant stars.
Such meteorites include chondrites, collections of debris from the early Solar System, the spectral signature of olivine has been seen in the dust disks around young stars. The tails of comets often have the signature of olivine
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 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 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, 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, 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, Russia. Untapped chromite deposits are plentiful, but geographically concentrated in Kazakhstan, although rare, deposits of native chromium exist