Difference between revisions of "Talc" - New World Encyclopedia
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− | '''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>Mg<sub>3</sub>(SiO<sub>3</sub>)<sub>4</sub> or Mg<sub>3</sub>[[Silicon|Si]]<sub>4</sub>[[Oxygen|O]]<sub>10</sub>([[Hydroxide|OH]])<sub>2</sub>. | + | '''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>Mg<sub>3</sub>(SiO<sub>3</sub>)<sub>4</sub> or Mg<sub>3</sub>[[Silicon|Si]]<sub>4</sub>[[Oxygen|O]]<sub>10</sub>([[Hydroxide|OH]])<sub>2</sub>. |
+ | |||
+ | Its color ranges from [[white]] to [[gray (color)|gray]] or [[green]] and it has a distinctly greasy feel. Its streak is white. | ||
== Formation == | == 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 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. | ||
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== Occurrence == | == Occurrence == | ||
+ | |||
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 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]]. | ||
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Notable economic talc occurrences include the Mount Seabrook talc mine, Western Australia, formed upon a polydeformed, layered ultramafic intrusion. | Notable economic talc occurrences include the Mount Seabrook talc mine, Western Australia, formed upon a polydeformed, layered ultramafic intrusion. | ||
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+ | == Characteristics == | ||
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+ | 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]]). It has a [[specific gravity]] of 2.5–2.8, a waxlike or pearly [[luster]], and is translucent to opaque. | ||
== Uses == | == Uses == | ||
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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]]. | 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. | + | Talc is also used as [[food additive]] or in pharmaceutical products.<ref>In the [[European Community]], the additive number is E553b.</ref> |
== Safety == | == Safety == |
Revision as of 02:29, 24 April 2007
Talc | |
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A block of talc |
|
General | |
Category | Mineral |
Chemical formula | Mg3Si4O10(OH)2 |
Identification | |
Color | white to gray or green |
Crystal habit | foliated to fibrous masses |
Crystal system | Monoclinic |
Cleavage | perfect basal cleavage |
Mohs Scale hardness | 1 |
Luster | waxlike or pearly |
Streak | White |
Specific gravity | 2.5-2.8 |
{{{density}}} | |
Talc (derived from the Persian via Arabic talq) is a mineral composed of hydrated magnesium silicate with the chemical formula H2Mg3(SiO3)4 or Mg3Si4O10(OH)2.
Its color ranges from white to gray or green and it has a distinctly greasy feel. Its streak is white.
Formation
Talc is a 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 carbonates.
Talc is primarily formed via hydration and carbonation of serpentine, via the following reaction;
Serpentine + Carbon Dioxide → Talc + Magnesite + Water
Talc can also be formed via a reaction between dolomite and silica, which is typical of skarnification of dolomites via silica-flooding in contact metamorphic aureoles;
Dolomite + Silica + Water → Talc + Calcite + Carbon Dioxide
Talc can also be formed from magnesian chlorite and quartz in blueschist and eclogite metamorphism via the following reaction:
Chlorite + Quartz → Kyanite + Talc + H2O
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 phengite, garnet, glaucophane within the lower blueschist facies. Such rocks are typically white, friable, and fibrous, and are known as whiteschist.
Occurrence
Talc is a very common metamorphic mineral in metamorphic belts which contain ultramafic rocks, 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 orogens such as the Himalayas.
Talc carbonated ultramafics are typical of many areas of the Archaean cratons, notably the komatiite belts of the Yilgarn Craton in Western Australia. Talc-carbonate ultramafics are also known from the Lachlan Fold Belt, eastern Australia, from Brazil, the Guyana 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.
Characteristics
It occurs as foliated to fibrous masses, its monoclinic crystals being so rare as to be almost unknown. It has a perfect basal cleavage, and the folia are non-elastic, although slightly flexible. It is sectile and very soft, with a hardness of 1 (Talc is the softest of the Mohs' scale of mineral hardness). It has a specific gravity of 2.5–2.8, a waxlike or pearly luster, and is translucent to opaque.
Uses
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 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.[1]
Safety
Several studies have established preliminary links between talc and pulmonary issues,[2] lung cancer,[3][4] skin cancer and ovarian cancer.[5] This is a significant concern, considering talc's widespread commercial and household use. However, no conclusive study has yet been made to determine either the toxicity or carcinogenic nature of talc. The long history of safe use suggests that these concerns are unfounded. The U.S. Food and Drug Administration (FDA) considers non-asbestiform talc—that is, talc that does not contain potentially carcinogenic asbestiform amphibole fibers—to be in the group of "Generally recognized as safe" (GRAS) materials that can be used in cosmetics.
See also
Notes
- ↑ In the European Community, the additive number is E553b.
- ↑ Hollinger (1990). Pulmonary toxicity of inhaled and intravenous talc..
- ↑ National Toxicology Program (1993). NTP Toxicology and Carcinogenesis Studies of Talc (Non-Asbestiform) in Rats and Mice (Inhalation Studies)..
- ↑ NIOSH Worker Notification Program. Health effects of mining and milling talc..(historical)
- ↑ Harlow, Cramer, Bell, et al. (1992). Perineal exposure to talc and ovarian cancer risk..
ReferencesISBN links support NWE through referral fees
- Farndon, John. 2006. The Practical Encyclopedia of Rocks & Minerals: How to Find, Identify, Collect and Maintain the World's best Specimens, with over 1000 Photographs and Artworks. London: Lorenz Books. ISBN 0754815412.
- Klein, Cornelis, and Barbara Dutrow. 2007. Manual of Mineral Science. 23rd ed. New York: John Wiley. ISBN 978-0471721574.
- Pellant, Chris. 2002. Rocks and Minerals. Smithsonian Handbooks. New York: Dorling Kindersley. ISBN 0789491060.
- Shaffer, Paul R., Herbert S. Zim, and Raymond Perlman. 2001. Rocks, Gems and Minerals. Rev. ed. New York: St. Martin's Press. ISBN 1582381321.
External links
- The Mineral Talc. Amethyst Galleries. Retrieved April 13, 2007.
- Talc Mineral Data. Webmineral.com. Retrieved April 13, 2007.
- Talc. Mindat.org. Retrieved April 13, 2007.
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