Magnesite 611537 219909896 2008-06-17T12:25:50Z 212.98.237.146 :''Magnesite is not to be confused with [[Magnetite]] or [[Magnemite]].'' {{Infobox mineral | name = Magnesite | category = | boxwidth = | boxbgcolor = | image = Mineraly.sk - magnezit.jpg | caption = | formula = [[magnesium]] [[carbonate]]:MgCO<sub>3</sub> | molweight = | color = White | habit = usually massive, rarely as rhombohedrons or hexagonal prisms | system = [[trigonal]]; bar 3 2/m | twinning = | cleavage = [1011] Perfect, [1011] Perfect, [1011] Perfect | fracture = Brittle - Conchoidal | mohs = 3.5 - 5 | luster = Vitreous | refractive = Uniaxial (-) nω=1.508 - 1.510 nε=1.700 | opticalprop = | birefringence = | pleochroism = | streak = white | gravity = 3.0 - 3.2 | melt = | fusibility = infusible | diagnostic = | solubility = Effervesces in hot HCl | diaphaneity = | other = }} '''Magnesite''' is [[magnesium carbonate]], [[magnesium|Mg]][[carbon|C]][[oxygen|O]]<sub>3</sub>. [[Iron]] (as [[iron|Fe]]<sup>2+</sup>) substitutes for [[magnesium]] (Mg) with a complete solution series with [[siderite]], FeCO<sub>3</sub>. [[Calcium]], [[manganese]], [[cobalt]], and [[nickel]] may also occur in small amounts. [[Dolomite]], (Mg,[[calcium|Ca]])CO<sub>3</sub>, is almost indistinguishable from magnesite. === Occurrence === Magnesite occurs as veins in and an alteration product of [[ultramafic rocks]], [[serpentinite]] and other magnesium rich rock types in both contact and regional [[metamorphic rock|metamorphic]] terranes. These magnesites often are cryptocrystalline and contain silica as [[opal]] or [[chert]]. Magnesite is also present within the [[regolith]] above ultramafic rocks as a secondary carbonate within soil and subsoil, where it is deposited as a consequence of dissolution of magnesium-bearing minerals by carbon dioxide within groundwaters. == Formation == Magnesite can be formed via [[talc carbonate]] [[metasomatism]] of [[peridotite]] and other ultrabasic rocks. Magnesite is formed via carbonation of [[olivine]] in the presence of water and carbon dioxide, and is favored at moderate temperatures and pressures typical of [[Greenschist#Greenschist facies|greenschist facies]]; Magnesite can also be formed via the carbonation of magnesian [[serpentine]] (lizardite) via the following [[Metamorphic reaction|reaction]]:<br> ''Serpentine + carbon dioxide → Talc + magnesite + Water'' :<math>2Mg_3Si_2O_5(OH)_4 + 3CO_2 \rarr Mg_3Si_4O_10(OH)_2 + 3MgCO_3 + H_2O</math> [[Forsterite]] magnesia-rich [[olivine]] compositions favor production of magnesite from peridotite. [[Fayalite|Fayalitic]] (iron-rich) olivine favors production of magnetite-magnesite-silica compositions. [[Image:Magnezyt, porcelanit; 4Czechy Masyw Czeski Vezna.jpg|thumb|left|180px|Magnesite]] Magnesite can also be formed from metasomatism in [[skarn]] deposits, in [[Dolomite|dolomitic]] [[limestone]]s, associated with [[wollastonite]], [[periclase]], and [[talc]]. ==Uses== Magnesite can be used as a [[slag]] former in steelmaking furnaces, in conjunction with [[lime (mineral)|lime]], in order to protect the [[magnesium oxide]] lining. It can also be used as a catalyst and filler in the production of synthetic rubber and in the preparation of magnesium chemicals and fertilizers. Similar to the production of lime, magnesite can be burned in the presence of charcoal to produce MgO, otherwise known as [[periclase]]. Such periclase is an important product in refractory materials. == References and external links == *Dana's Manual of Mineralogy ISBN 0-471-03288-3 *Smithsonian Rock and Gem ISBN 0-7566-0962-3 * [http://mineral.galleries.com/minerals/carbonat/magnesit/magnesit.htm Mineral Galleries] *[http://webmineral.com/data/Magnesite.shtml Webmineral.com] *[http://www.mindat.org/min-2482.html Mindat.org] *[http://www.minerals.net/mineral/carbonat/magnesit/magnesit.htm Minerals.net] [[Category:Magnesium minerals]] [[Category:Carbonate minerals]] [[Category:Calcite group]] [[da:Magnesiumcarbonat]] [[de:Magnesiumcarbonat]] [[fi:Magnesiitti]] [[fr:Magnésite]] [[it:Magnesite (minerale)]] [[hu:Magnezit]] [[he:מגנזיט]] [[ja:菱苦土鉱]] [[nl:Magnesiet]] [[pl:Magnezyt (minerał)]] [[pt:Magnesita]] [[sk:magnezit]] [[ru:Магнезит]] [[sr:Магнезијум карбонат]] [[tr:Magnezit]]