Talc 31422 224308986 2008-07-08T07:39:46Z Benbest 167797 solubility {{Infobox mineral | name = Talc | category = Minerals | boxwidth = | boxbgcolor = | image = Talc block.jpg | caption = A block of talc | formula = [[Magnesium|Mg]]<sub>3</sub>[[Silicon|Si]]<sub>4</sub>[[Oxygen|O]]<sub>10</sub>([[Hydroxide|OH]])<sub>2</sub> | molweight = | color = white, gray, green or blue | habit = foliated to fibrous masses | system = [[Monoclinic]] or [[Triclinic]]<ref name="DHZ">''An Introduction to the Rock-Forming Minerals'', second edition, by W.A. Deer, R.A. Howie, and J. Zussman, 1992, Prentice Hall, ISBN 0-582-30094-0.</ref> | twinning = | cleavage = perfect [[basal cleavage]] | fracture = | mohs = 1 | luster = waxlike or pearly sometimes smooth | refractive = | opticalprop = | birefringence = | pleochroism = | streak = White | gravity = 2.5-2.8 | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = | other = }} '''Talc''' (derived from the [[Persian language|Persian]] via [[Arabic language|Arabic]] ''talq'') is a [[mineral]] composed of [[hydrate|hydrated]] [[magnesium]] [[silicate]] with the chemical formula [[Hydrogen|H]]<sub>2</sub>[[Magnesium|Mg]]<sub>3</sub>([[Silicate|SiO]]<sub>3</sub>)<sub>4</sub> or [[Magnesium|Mg]]<sub>3</sub>[[Silicon|Si]]<sub>4</sub>[[Oxygen|O]]<sub>10</sub>([[Hydroxide|OH]])<sub>2</sub>. In loose form, it is the widely used substance known as [[talcum powder]]. It occurs as foliated to fibrous masses, its [[monoclinic]] [[crystal]]s being so rare as to be almost unknown. It has a perfect [[basal cleavage]], and the folia are non-[[elastic (solid mechanics)|elastic]], although slightly flexible. It is [[sectile]] and very soft, with a [[Mohs scale of mineral hardness|hardness]] of 1 (Talc is the softest of the [[Mohs' scale of mineral hardness]], and can be easily scratched by a fingernail). It has a [[specific gravity]] of 2.5&ndash;2.8, a clear or dusty [[Lustre (mineralogy)|luster]], and is translucent to opaque. Talc is not soluble in water, but it is slightly soluble in dilute [[mineral acid]]s. Its colour ranges from [[white]] to [[grey]] or [[green]] and it has a distinctly greasy feel. Its streak is white. == Formation == Talc is a [[metamorphic rock|metamorphic mineral]] resulting from the metamorphism of magnesian minerals such as [[pyroxene]], [[amphibole]], [[olivine]] and other similar minerals in the presence of carbon dioxide and water. This is known as ''talc carbonation'' or ''steatization'' and produces a suite of rocks known as [[talc carbonate]]s. Talc is primarily formed via hydration and carbonation of serpentine, via the following reaction; ''[[Serpentine]] + [[Carbon Dioxide]] → Talc + [[Magnesite]] + [[Water]]'' :<math>2Mg_3Si_2O_5(OH)_4 + 3CO_2 \rarr Mg_3Si_4O_{10}(OH)_2 + 3MgCO_3 + 3H_2O</math> Talc can also be formed via a reaction between dolomite and silica, which is typical of [[skarn]]ification of dolomites via silica-flooding in contact metamorphic aureoles; ''[[Dolomite]] + [[Silica]] + Water → Talc + [[Calcite]] + Carbon Dioxide'' :<math>3CaMg(CO_3)_2 + 4SiO_2 + H_2O \rarr Mg_3Si_4O_{10}(OH)_2 + 3CaCO_3 + 3CO_2</math> Talc can also be formed from magnesian chlorite and quartz in [[blueschist]] and [[eclogite]] metamorphism via the following [[metamorphic reaction]]: ''[[Chlorite group|Chlorite]] + [[Quartz]] → [[Kyanite]] + Talc + H<sub>2</sub>O'' In this reaction, the ratio of talc and kyanite is dependent on [[aluminium]] content with more aluminous rocks favoring production of kyanite. This is typically associated with high-pressure, low-temperature minerals such as [[fengite|phengite]], [[garnet]], [[glaucophane]] within the lower [[Blueschist#Blueschist facies|blueschist facies]]. Such rocks are typically white, friable, and fibrous, and are known as ''whiteschist''. Talc is a tri-octahedral layered mineral; its structure is similar to that of [[pyrophyllite]], but with [[magnesium]] in the octahedral sites of the composite layers.<ref name="DHZ" /> == Occurrence == [[Image:2005talc.PNG|thumb|left|Talc output in 2005]] Talc is a very common metamorphic mineral in metamorphic belts which contain [[ultramafic rock]]s, such as [[soapstone]] (a high-talc rock), and within whiteschist and [[blueschist]] metamorphic terranes. Prime examples of whiteschists include the Franciscan Metamorphic Belt of the western [[United States]], the western European [[Alps]] especially in Italy, certain areas of the [[Musgrave Block]], and some collisional [[Orogeny|orogens]] such as the [[Himalayas]]. [[Talc carbonate]]d ultramafics are typical of many areas of the [[Archaean]] [[craton]]s, notably the [[komatiite]] belts of the [[Yilgarn craton|Yilgarn Craton]] in [[Western Australia]]. Talc-carbonate ultramafics are also known from the [[Lachlan Fold Belt]], eastern [[Australia]], from [[Brazil]], the [[Guiana Shield]], and from the [[ophiolite]] belts of [[Turkey]], [[Oman]] and the [[Middle East]]. Notable economic talc occurrences include the Mount Seabrook talc mine, Western Australia, formed upon a polydeformed, layered ultramafic intrusion. == Uses == {{Unreferencedsection|date=January 2008}} [[Image:Talcum Powder.JPEG|thumb|Talcum Powder]] A coarse grayish-green high-talc rock is [[soapstone]] or steatite and has been used for stoves, sinks, electrical switchboards, etc. Talc finds use as a [[Cosmetics|cosmetic]] (talcum powder), as a [[lubricant]], and as a filler in [[paper]] manufacture. Talc is used in [[baby powder]], an [[astringent]] powder used for preventing rashes on the area covered by a [[diaper]] (see [[diaper rash]]). Most tailor's [[chalk]] is talc, as is the chalk often used for [[welding]] or [[metalworking]]. Talc is also used as [[food additive]] or in pharmaceutical products. In medicine talc is used as a [[pleurodesis]] agent to prevent recurrent pneumothorax. In the [[European Union]] the additive number is E553b. == Safety == Several studies have established preliminary links between talc and [[pulmonary]] issues,<ref> {{cite journal |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2198684&dopt=Abstract |title=Pulmonary toxicity of inhaled and intravenous talc. |author=Hollinger |year=1990 }} </ref> [[lung cancer]],<ref name="NTP"> {{cite journal |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12616290&dopt=Abstract |title=NTP Toxicology and Carcinogenesis Studies of Talc (Non-Asbestiform) in Rats and Mice (Inhalation Studies). |author=National Toxicology Program|year=1993}} </ref><ref> {{cite journal |url=http://www.cdc.gov/niosh/pgms/worknotify/Talc.html |title=Health effects of mining and milling talc. |author=NIOSH Worker Notification Program }}(historical) </ref> [[skin cancer]] and [[ovarian cancer]].<ref> {{cite journal |url=http://www.meb.uni-bonn.de/cgi-bin/mycite?ExtRef=MEDL/92293722 |title=Perineal exposure to talc and ovarian cancer risk. |author=Harlow, Cramer, Bell, et al. |year=1992}} </ref> This is a major concern considering talc's widespread commercial and household use. In 1993, a US National Toxicology Program report found that cosmetic grade talc caused tumours in animals, even though it contained no asbestos-like fibres.<ref name="NTP" /> Scientists have been aware of the toxicity of talc since the late 1960s, and in 1971 researchers found particles of talc embedded in 75 percent of the ovarian tumors studied.<ref> {{cite journal |url=http://www.ncbi.nlm.nih.gov/pubmed/5558843 |title=Talc and carcinoma of the ovary and cervix. |author=Henderson WJ, Joslin CA, Turnbull AC, Griffiths K|year=1971 |journal=J Obstet Gynaecol Br Commonw|volume=78|issue=3|pages=266–272}} </ref>{{Fact|date=June 2007}} However, the U.S. [[Food and Drug Administration]] (FDA) considers non-asbestiform talc, that is talc which does not contain potentially [[carcinogen]]ic [[asbestos|asbestiform]] [[amphibole]] fibers, to be [[Generally recognized as safe]] (GRAS) for use in cosmetics. <ref> {{cite web | author = CFSAN/Office of Food Additive Safety | title = Food Additive Status List | publisher = U.S. Food and Drug Administration |date=July 2006 | url =http://www.cfsan.fda.gov/~dms/opa-appa.html#ftnT | accessdate = December 2007 }} </ref> == See also == {{commonscat|Talc}} * [[List of minerals]] * [[Serpentinite]] * [[Talc carbonate]] * [[Magnesite]] * [[Blueschist]] * [[Metamorphic rocks]] * [[Asbestos]] * [[French chalk]] == References == * [http://mineral.galleries.com/minerals/silicate/talc/talc.htm mineral.galleries.com] * [http://webmineral.com/data/Talc.shtml Webmineral.com] * [http://www.mindat.org/min-3875.html www.mindat.org] <references/> [[Category:Phyllosilicates]] [[Category:Magnesium minerals]] [[Category:Symbols of Vermont]] [[Category:Cosmetic chemicals]] [[ar:تلك]] [[bg:Талк]] [[ca:Talc]] [[cs:Mastek]] [[da:Fedtsten]] [[de:Talk (Mineral)]] [[es:Talco]] [[eo:Talko]] [[eu:Talko]] [[fr:Talc]] [[gl:Talco]] [[hr:Talk]] [[it:Talco]] [[he:טלק]] [[lv:Talks]] [[lt:Talkas]] [[hu:Zsírkő]] [[nl:Talk (mineraal)]] [[ja:滑石]] [[no:Talk]] [[pl:Talk]] [[pt:Talco]] [[ro:Talc]] [[ru:Тальк]] [[sl:Lojevec]] [[sr:Талк]] [[fi:Talkki]] [[sv:Talk]] [[ta:டால்க்]] [[th:ทัลก์]] [[tr:Talk]] [[uk:Тальк]] [[zh:滑石]]