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56-478: The São Francisco Craton is an ancient craton in the eastern part of South America . The craton crops out in the Brazilian states of Minas Gerais and Bahia . It includes a number of blocks of Archean basement , separated by orogenic belts . The belts are characterized by sedimentary basins and passive continental margins containing granite intrusions . The Paleoproterozoic (about 2.5 to 2.0 Ga)

112-489: A half-life of 717,000 years. Excessive quantities of stable Mg have been observed in the Ca-Al-rich inclusions of some carbonaceous chondrite meteorites . This anomalous abundance is attributed to the decay of its parent Al in the inclusions, and researchers conclude that such meteorites were formed in the solar nebula before the Al had decayed. These are among

168-490: A magnesium-based engine . Magnesium also reacts exothermically with most acids such as hydrochloric acid (HCl), producing magnesium chloride and hydrogen gas, similar to the HCl reaction with aluminium, zinc, and many other metals. Although it is difficult to ignite in mass or bulk, magnesium metal will ignite. Magnesium may also be used as an igniter for thermite , a mixture of aluminium and iron oxide powder that ignites only at

224-400: A rising plume of molten material from the deep mantle. This would have built up a thick layer of depleted mantle underneath the cratons. A third model suggests that successive slabs of subducting oceanic lithosphere became lodged beneath a proto-craton, underplating the craton with chemically depleted rock. A fourth theory presented in a 2015 publication suggests that the origin of

280-527: A common reservoir. Magnesium is the eighth-most-abundant element in the Earth's crust by mass and tied in seventh place with iron in molarity . It is found in large deposits of magnesite , dolomite , and other minerals , and in mineral waters, where magnesium ion is soluble. Although magnesium is found in more than 60 minerals , only dolomite , magnesite , brucite , carnallite , talc , and olivine are of commercial importance. The Mg cation

336-506: A high purity product is easily achievable. China is almost completely reliant on the silicothermic Pidgeon process . Besides the Pigeon process, the second most used process for magnesium production is electrolysis . This is a two step process. The first step is to prepare feedstock containing magnesium chloride and the second step is to dissociate the compound in electrolytic cells as magnesium metal and chlorine gas . The basic reaction

392-457: A solid residue very close in composition to Archean lithospheric mantle, but continental shields do not contain enough komatiite to match the expected depletion. Either much of the komatiite never reached the surface, or other processes aided craton root formation. There are many competing hypotheses of how cratons have been formed. Jordan's model suggests that further cratonization was a result of repeated continental collisions. The thickening of

448-429: A solid solution with calcium oxide by calcining the mineral dolomite , which is a solid solution of calcium and magnesium carbonates: Reduction occurs at high temperatures with silicon. A ferrosilicon alloy is used rather than pure silicon as it is more economical. The iron component has no bearing on the reaction, having the simplified equation: The calcium oxide combines with silicon as the oxygen scavenger, yielding

504-1231: A term for mountain or orogenic belts . Later Hans Stille shortened the former term to Kraton , from which craton derives. Examples of cratons are the Dharwar Craton in India, North China Craton , the East European Craton , the Amazonian Craton in South America, the Kaapvaal Craton in South Africa, the North American Craton (also called the Laurentia Craton), and the Gawler Craton in South Australia. Cratons have thick lithospheric roots. Mantle tomography shows that cratons are underlain by anomalously cold mantle corresponding to lithosphere more than twice

560-545: A variety of compounds important to industry and biology, including magnesium carbonate , magnesium chloride , magnesium citrate , magnesium hydroxide (milk of magnesia), magnesium oxide , magnesium sulfate , and magnesium sulfate heptahydrate ( Epsom salts ). As recently as 2020, magnesium hydride was under investigation as a way to store hydrogen. Magnesium has three stable isotopes : Mg , Mg and Mg . All are present in significant amounts in nature (see table of isotopes above). About 79% of Mg

616-408: A very high temperature. Organomagnesium compounds are widespread in organic chemistry . They are commonly found as Grignard reagents , formed by reaction of magnesium with haloalkanes . Examples of Grignard reagents are phenylmagnesium bromide and ethylmagnesium bromide . The Grignard reagents function as a common nucleophile , attacking the electrophilic group such as the carbon atom that

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672-438: Is Mg . The isotope Mg is radioactive and in the 1950s to 1970s was produced by several nuclear power plants for use in scientific experiments. This isotope has a relatively short half-life (21 hours) and its use was limited by shipping times. The nuclide Mg has found application in isotopic geology , similar to that of aluminium. Mg is a radiogenic daughter product of Al , which has

728-658: Is a gray-white lightweight metal, two-thirds the density of aluminium. Magnesium has the lowest melting (923 K (650 °C)) and the lowest boiling point (1,363 K (1,090 °C)) of all the alkaline earth metals. Pure polycrystalline magnesium is brittle and easily fractures along shear bands . It becomes much more malleable when alloyed with small amounts of other metals, such as 1% aluminium. The malleability of polycrystalline magnesium can also be significantly improved by reducing its grain size to about 1  μm or less. When finely powdered, magnesium reacts with water to produce hydrogen gas: However, this reaction

784-480: Is a liquid metal. At the YSZ/liquid metal anode O is oxidized. A layer of graphite borders the liquid metal anode, and at this interface carbon and oxygen react to form carbon monoxide. When silver is used as the liquid metal anode, there is no reductant carbon or hydrogen needed, and only oxygen gas is evolved at the anode. It was reported in 2011 that this method provides a 40% reduction in cost per pound over

840-582: Is as follows: The temperatures at which this reaction is operated is between 680 and 750 °C. The magnesium chloride can be obtained using the Dow process , a process that mixes sea water and dolomite in a flocculator or by dehydration of magnesium chloride brines. The electrolytic cells are partially submerged in a molten salt electrolyte to which the produced magnesium chloride is added in concentrations between 6-18%. This process does have its share of disadvantages including production of harmful chlorine gas and

896-425: Is essential to all cells and some 300 enzymes . Magnesium ions interact with polyphosphate compounds such as ATP , DNA , and RNA . Hundreds of enzymes require magnesium ions to function. Magnesium compounds are used medicinally as common laxatives and antacids (such as milk of magnesia ), and to stabilize abnormal nerve excitation or blood vessel spasm in such conditions as eclampsia . Elemental magnesium

952-479: Is first treated with lime (calcium oxide) and the precipitated magnesium hydroxide is collected: The hydroxide is then converted to magnesium chloride by treatment with hydrochloric acid and heating of the product to eliminate water: The salt is then electrolyzed in the molten state. At the cathode , the Mg ion is reduced by two electrons to magnesium metal: At the anode , each pair of Cl ions

1008-426: Is less dense than aluminium and is used primarily as a component in strong and lightweight alloys that contain aluminium. In the cosmos , magnesium is produced in large, aging stars by the sequential addition of three helium nuclei to a carbon nucleus. When such stars explode as supernovas , much of the magnesium is expelled into the interstellar medium where it may recycle into new star systems. Magnesium

1064-441: Is much less dramatic than the reactions of the alkali metals with water, because the magnesium hydroxide builds up on the surface of the magnesium metal and inhibits further reaction. The principal property of magnesium metal is its reducing power. One hint is that it tarnishes slightly when exposed to air, although, unlike the heavier alkaline earth metals , an oxygen-free environment is unnecessary for storage because magnesium

1120-401: Is oxidized to chlorine gas, releasing two electrons to complete the circuit: The carbothermic route to magnesium has been recognized as a low energy, yet high productivity path to magnesium extraction. The chemistry is as follows: C + MgO → CO + Mg A disadvantage of this method is that slow cooling the vapour can cause the reaction to quickly revert. To prevent this from happening,

1176-514: Is present within the polar bond of a carbonyl group. A prominent organomagnesium reagent beyond Grignard reagents is magnesium anthracene , which is used as a source of highly active magnesium. The related butadiene -magnesium adduct serves as a source for the butadiene dianion. Complexes of dimagnesium(I) have been observed. The presence of magnesium ions can be detected by the addition of ammonium chloride , ammonium hydroxide and monosodium phosphate to an aqueous or dilute HCl solution of

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1232-447: Is protected by a thin layer of oxide that is fairly impermeable and difficult to remove. Direct reaction of magnesium with air or oxygen at ambient pressure forms only the "normal" oxide MgO. However, this oxide may be combined with hydrogen peroxide to form magnesium peroxide , MgO 2 , and at low temperature the peroxide may be further reacted with ozone to form magnesium superoxide Mg(O 2 ) 2 . Magnesium reacts with nitrogen in

1288-452: 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 and iron. 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

1344-454: Is the eighth most abundant element in the Earth's crust and the fourth most common element in the Earth (after iron , oxygen and silicon ), making up 13% of the planet's mass and a large fraction of the planet's mantle . It is the third most abundant element dissolved in seawater, after sodium and chlorine . This element is the eleventh most abundant element by mass in the human body and

1400-541: Is the second-most-abundant cation in seawater (about 1 ⁄ 8 the mass of sodium ions in a given sample), which makes seawater and sea salt attractive commercial sources for Mg. To extract the magnesium, calcium hydroxide is added to the seawater to precipitate magnesium hydroxide . Magnesium hydroxide ( brucite ) is poorly soluble in water and can be collected by filtration. It reacts with hydrochloric acid to magnesium chloride . From magnesium chloride, electrolysis produces magnesium. World production

1456-524: The Baltic Shield had been eroded into a subdued terrain already during the Late Mesoproterozoic when the rapakivi granites intruded. Magnesium Magnesium is a chemical element ; it has symbol   Mg and atomic number  12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of

1512-694: The Congo Craton and the São Francisco block in South America. The ancient Paleoproterozoic orogenic belts of the São Francisco Craton contain many economically important minerals, particularly those containing iron (as in the Iron Quadrangle ) and gold , and are a major source of income for the mining industry in Brazil. Craton The term craton is used to distinguish the stable portion of

1568-503: The continental crust from regions that are more geologically active and unstable. Cratons are composed of two layers: a continental shield , in which the basement rock crops out at the surface, and a platform which overlays the shield in some areas with sedimentary rock . The word craton was first proposed by the Austrian geologist Leopold Kober in 1921 as Kratogen , referring to stable continental platforms, and orogen as

1624-407: The periodic table ) it occurs naturally only in combination with other elements and almost always has an oxidation state of +2. It reacts readily with air to form a thin passivation coating of magnesium oxide that inhibits further corrosion of the metal. The free metal burns with a brilliant-white light. The metal is obtained mainly by electrolysis of magnesium salts obtained from brine . It

1680-406: The "cratonic regime". It involves processes of pediplanation and etchplanation that lead to the formation of flattish surfaces known as peneplains . While the process of etchplanation is associated to humid climate and pediplanation with arid and semi-arid climate, shifting climate over geological time leads to the formation of so-called polygenetic peneplains of mixed origin. Another result of

1736-573: The corrosion rate of magnesium in a salt solution by a factor of nearly ten. Magnesium's tendency to creep (gradually deform) at high temperatures is greatly reduced by alloying with zinc and rare-earth elements . Flammability is significantly reduced by a small amount of calcium in the alloy. By using rare-earth elements, it may be possible to manufacture magnesium alloys that are able to not catch fire at higher temperatures compared to magnesium's liquidus and in some cases potentially pushing it close to magnesium's boiling point. Magnesium forms

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1792-502: 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 ( xenoliths ) 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 craton composition and are composed of mantle material residual from high degrees of partial melt. Peridotite

1848-413: The cratons is similar to crustal plateaus observed on Venus, which may have been created by large asteroid impacts. In this model, large impacts on the Earth's early lithosphere penetrated deep into the mantle and created enormous lava ponds. The paper suggests these lava ponds cooled to form the craton's root. The chemistry of xenoliths and seismic tomography both favor the two accretional models over

1904-399: The crust associated with these collisions may have been balanced by craton root thickening according to the principle of isostacy . Jordan likens this model to "kneading" of the cratons, allowing low density material to move up and higher density to move down, creating stable cratonic roots as deep as 400 km (250 mi). A second model suggests that the surface crust was thickened by

1960-476: The crystalline residues after extraction of melts of compositions like basalt and komatiite . The process by which cratons were formed is called cratonization . There is much about this process that remains uncertain, with very little consensus in the scientific community. However, the first cratonic landmasses likely formed during the Archean eon. This is indicated by the age of diamonds , which originate in

2016-426: The depleted "lid" formed by the first layer. The impact origin model does not require plumes or accretion; this model is, however, not incompatible with either. All these proposed mechanisms rely on buoyant, viscous material separating from a denser residue due to mantle flow, and it is possible that more than one mechanism contributed to craton root formation. The long-term erosion of cratons has been labelled

2072-471: The late Archean, accompanied by voluminous mafic magmatism. However, melt extraction alone cannot explain all the properties of craton roots. Jordan notes in his paper that this mechanism could be effective for constructing craton roots only down to a depth of 200 kilometers (120 mi). The great depths of craton roots required further explanation. The 30 to 40 percent partial melting of mantle rock at 4 to 10 GPa pressure produces komatiite magma and

2128-461: The longevity of cratons is that they may alternate between periods of high and low relative sea levels . High relative sea level leads to increased oceanicity, while the opposite leads to increased inland conditions . Many cratons have had subdued topographies since Precambrian times. For example, the Yilgarn Craton of Western Australia was flattish already by Middle Proterozoic times and

2184-424: The magnesium can be dissolved directly in a suitable metal solvent before reversion starts happening. Rapid quenching of the vapour can also be performed to prevent reversion. A newer process, solid oxide membrane technology, involves the electrolytic reduction of MgO. At the cathode, Mg ion is reduced by two electrons to magnesium metal. The electrolyte is yttria-stabilized zirconia (YSZ). The anode

2240-530: The oldest objects in the Solar System and contain preserved information about its early history. It is conventional to plot Mg / Mg against an Al/Mg ratio. In an isochron dating plot, the Al/Mg ratio plotted is Al / Mg . The slope of the isochron has no age significance, but indicates the initial Al / Al ratio in the sample at the time when the systems were separated from

2296-664: The overall reaction being very energy intensive, creating environmental risks. The Pidgeon process is more advantageous regarding its simplicity, shorter construction period, low power consumption and overall good magnesium quality compared to the electrolysis method. In the United States, magnesium was once obtained principally with the Dow process in Corpus Christi TX , by electrolysis of fused magnesium chloride from brine and sea water . A saline solution containing Mg ions

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2352-420: The plume model. However, other geochemical evidence favors mantle plumes. Tomography shows two layers in the craton roots beneath North America. One is found at depths shallower than 150 km (93 mi) and may be Archean, while the second is found at depths from 180 to 240 km (110 to 150 mi) and may be younger. The second layer may be a less depleted thermal boundary layer that stagnated against

2408-443: The quantity of these metals improves corrosion resistance. Sufficient manganese overcomes the corrosive effects of iron. This requires precise control over composition, increasing costs. Adding a cathodic poison captures atomic hydrogen within the structure of a metal. This prevents the formation of free hydrogen gas, an essential factor of corrosive chemical processes. The addition of about one in three hundred parts arsenic reduces

2464-539: The roots of cratons, and which are almost always over 2 billion years and often over 3 billion years in age. Rock of Archean age makes up only 7% of the world's current cratons; even allowing for erosion and destruction of past formations, this suggests that only 5 to 40 percent of the present continental crust formed during the Archean. Cratonization likely was completed during the Proterozoic . Subsequent growth of continents

2520-455: The salt. The formation of a white precipitate indicates the presence of magnesium ions. Azo violet dye can also be used, turning deep blue in the presence of an alkaline solution of magnesium salt. The color is due to the adsorption of azo violet by Mg(OH) 2 . As of 2013, magnesium alloys consumption was less than one million tonnes per year, compared with 50 million tonnes of aluminium alloys . Their use has been historically limited by

2576-518: The shores of the Great Salt Lake . In September 2021, China took steps to reduce production of magnesium as a result of a government initiative to reduce energy availability for manufacturing industries, leading to a significant price increase. The Pidgeon process and the Bolzano process are similar. In both, magnesium oxide is the precursor to magnesium metal. The magnesium oxide is produced as

2632-573: The solid state if it is powdered and heated to just below the melting point, forming Magnesium nitride Mg 3 N 2 . Magnesium reacts with water at room temperature, though it reacts much more slowly than calcium, a similar group 2 metal. When submerged in water, hydrogen bubbles form slowly on the surface of the metal; this reaction happens much more rapidly with powdered magnesium. The reaction also occurs faster with higher temperatures (see § Safety precautions ). Magnesium's reversible reaction with water can be harnessed to store energy and run

2688-515: The surrounding hotter, but more chemically dense, mantle. In addition to cooling the craton roots and lowering their chemical density, the extraction of magma also increased the viscosity and melting temperature of the craton roots and prevented mixing with the surrounding undepleted mantle. The resulting mantle roots have remained stable for billions of years. Jordan suggests that depletion occurred primarily in subduction zones and secondarily as flood basalts . This model of melt extraction from

2744-403: The tendency of Mg alloys to corrode, creep at high temperatures, and combust. In magnesium alloys, the presence of iron , nickel , copper , or cobalt strongly activates corrosion . In more than trace amounts, these metals precipitate as intermetallic compounds , and the precipitate locales function as active cathodic sites that reduce water, causing the loss of magnesium. Controlling

2800-503: The typical 100 km (60 mi) thickness of mature oceanic or non-cratonic, continental lithosphere. At that depth, craton roots extend into the asthenosphere , and the low-velocity zone seen elsewhere at these depths is weak or absent beneath stable cratons. Craton lithosphere is distinctly different from oceanic lithosphere because cratons have a neutral or positive buoyancy and a low intrinsic density. This low density offsets density increases from geothermal contraction and prevents

2856-455: The upper mantle has held up well with subsequent observations. The properties of mantle xenoliths confirm that the geothermal gradient is much lower beneath continents than oceans. The olivine of craton root xenoliths is extremely dry, which would give the roots a very high viscosity. Rhenium–osmium dating of xenoliths indicates that the oldest melting events took place in the early to middle Archean. Significant cratonization continued into

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2912-505: The very stable calcium silicate. The Mg/Ca ratio of the precursors can be adjusted by the addition of MgO or CaO. The Pidgeon and the Bolzano process differ in the details of the heating and the configuration of the reactor. Both generate gaseous Mg that is condensed and collected. The Pidgeon process dominates the worldwide production. The Pidgeon method is less technologically complex and because of distillation/vapour deposition conditions,

2968-609: Was approximately 1,100 kt in 2017, with the bulk being produced in China (930 kt) and Russia (60 kt). The United States was in the 20th century the major world supplier of this metal, supplying 45% of world production even as recently as 1995. Since the Chinese mastery of the Pidgeon process the US market share is at 7%, with a single US producer left as of 2013: US Magnesium, a Renco Group company located on

3024-469: Was by accretion at continental margins. The origin of the roots of cratons is still debated. However, the present understanding of cratonization began with the publication in 1978 of a paper by Thomas H. Jordan in Nature . Jordan proposes that cratons formed from a high degree of partial melting of the upper mantle, with 30 to 40 percent of the source rock entering the melt. Such a high degree of melting

3080-423: Was possible because of the high mantle temperatures of the Archean. The extraction of so much magma left behind a solid peridotite residue that was enriched in lightweight magnesium and thus lower in chemical density than undepleted mantle. This lower chemical density compensated for the effects of thermal contraction as the craton and its roots cooled, so that the physical density of the cratonic roots matched that of

3136-541: Was the source of orogenic belts and the current configuration of the craton. The São Francisco Craton around 1.0 Ga ago was in the south of the supercontinent Rodinia , and after the fragmentation of Rodinia in the late Proterozoic (700 Ma) became a member of the supercontinent Gondwana until it fragmented in the Jurassic (about 180 Ma). The subsequent opening of the Atlantic Ocean left Southern Africa in

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