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 [[magnesium]] [[silicate]] [[hydroxide]]. It is extremely soft, with a greasy feel. It is translucent to opaque and has a pearly luster. Its color ranges from [[white]] to [[gray (color)|gray]] or [[green]], and its streak (color of the fine powder) is white. | '''Talc''' (derived from the [[Persian language|Persian]] via [[Arabic language|Arabic]] ''talq'') is a [[mineral]] composed of [[magnesium]] [[silicate]] [[hydroxide]]. It is extremely soft, with a greasy feel. It is translucent to opaque and has a pearly luster. Its color ranges from [[white]] to [[gray (color)|gray]] or [[green]], and its streak (color of the fine powder) is white. | ||
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| + | This mineral serves a number of uses. It is widely known for its use in [[baby powder]] and [[cosmetic]]s. It is also a [[lubricant]] and a filler in [[paper]] manufacture. Tailor's [[chalk]] and the chalk used for [[welding]] and [[metalworking]] often consist of talc. It is also an [[food additive|additive]] in some foods and pharmaceutical products. [[Soapstone]], a high-talc rock, is used for [[stove]]s, [[sink]]s, and [[electricity|electrical]] switchboards, among other applications. | ||
== Formation == | == Formation == | ||
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[[Image:Talcum Powder.JPEG|thumb|200px|Talcum powder.]] | [[Image:Talcum Powder.JPEG|thumb|200px|Talcum powder.]] | ||
| − | Talc finds use as a [[Cosmetics|cosmetic]] (talcum powder), a [[lubricant]], and a filler in [[paper]] manufacture. As a [[baby powder]], it is an [[astringent]] that helps prevent rashes in the area covered by a [[diaper]]. Most tailor's [[chalk]] is talc, as is the chalk often used for [[welding]] or [[metalworking]]. It is also an [[food additive|additive]] in some foods and pharmaceutical products.<ref>In the [[European Community]], the additive number is E553b.</ref> Moreover, [[soapstone]] or steatite—a coarse, grayish-green, high-talc rock—is used for stoves, sinks, electrical switchboards, | + | Talc finds use as a [[Cosmetics|cosmetic]] (talcum powder), a [[lubricant]], and a filler in [[paper]] manufacture. As a [[baby powder]], it is an [[astringent]] that helps prevent rashes in the area covered by a [[diaper]]. Most tailor's [[chalk]] is talc, as is the chalk often used for [[welding]] or [[metalworking]]. It is also an [[food additive|additive]] in some foods and pharmaceutical products.<ref>In the [[European Community]], the additive number is E553b.</ref> Moreover, [[soapstone]] or steatite—a coarse, grayish-green, high-talc rock—is used for stoves, sinks, and electrical switchboards, among other applications. |
== Safety == | == Safety == | ||
| − | Several studies have established preliminary links between talc and [[pulmonary]] problems,<ref> | + | Several studies have established preliminary links between talc and [[pulmonary]] problems,<ref>M.A. Hollinger, [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2198684&dopt=Abstract "Pulmonary toxicity of inhaled and intravenous talc,"] ''Toxicol. Lett.'' 52, no. 2 (1990): 121-27. Retrieved April 14, 2007.</ref> [[lung cancer]],<ref>National Toxicology Program, [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12616290&dopt=Abstract "NTP Toxicology and Carcinogenesis Studies of Talc (CAS No. 14807-96-6)(Non-Asbestiform) in F344/N Rats and B6C3F1 Mice (Inhalation Studies),"] ''Natl. Toxicol. Program Tech. Rep. Ser.'' 421 (1993): 1-287. Retrieved April 14, 2007.</ref><ref> [http://www.cdc.gov/niosh/pgms/worknotify/Talc.html "Health effects of mining and milling talc,"] ''NIOSH Worker Notification Program.'' Retrieved April 14, 2007.</ref> [[skin cancer]], and [[ovarian cancer]].<ref>B.L. Harlow et al., [http://www.meb.uni-bonn.de/cgi-bin/mycite?ExtRef=MEDL/92293722 "Perineal exposure to talc and ovarian cancer risk,"] ''Obstetrics and Gynecology'' 80 No.1 (1992): 19-26. Retrieved April 14, 2007.</ref> These studies have raised public concern, considering talc's widespread commercial and household use. However, no conclusive study has yet been made to determine the toxicity or carcinogenic nature of talc under normal conditions of human exposure. 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 [[carcinogen]]ic [[asbestos|asbestiform]] [[amphibole]] fibers—to be in the group of "[[Generally recognized as safe]]" (GRAS) materials that can be used in cosmetics. |
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| − | </ref> [[lung cancer]],<ref> | ||
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| − | </ref><ref> | ||
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| − | </ref> [[skin cancer]] and [[ovarian cancer]].<ref> | ||
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== See also == | == See also == | ||
Revision as of 21:34, 30 April 2007
| Talc | |
|---|---|
 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 magnesium silicate hydroxide. It is extremely soft, with a greasy feel. It is translucent to opaque and has a pearly luster. Its color ranges from white to gray or green, and its streak (color of the fine powder) is white.
This mineral serves a number of uses. It is widely known for its use in baby powder and cosmetics. It is also a lubricant and a filler in paper manufacture. Tailor's chalk and the chalk used for welding and metalworking often consist of talc. It is also an additive in some foods and pharmaceutical products. Soapstone, a high-talc rock, is used for stoves, sinks, and electrical switchboards, among other applications.
Formation
Talc is a metamorphic mineral. It is produced by the metamorphism of magnesian minerals—such as pyroxene, amphibole, or olivine—in the presence of carbon dioxide and water. This process, called talc carbonation or steatization, produces a suite of rocks known as talc carbonates.
Talc is formed primarily via hydration and carbonation of serpentine, via the following reaction:
Serpentine + Carbon Dioxide → Talc + Magnesite + Water
Talc can also be formed by a reaction between dolomite and silica:
Dolomite + Silica + Water → Talc + Calcite + Carbon Dioxide
Another reaction that produces talc involves magnesian chlorite and quartz in blueschist and eclogite metamorphism:
Chlorite + Quartz → Kyanite + Talc + H2O
In this last reaction, the proportions of talc and kyanite depend on aluminum content, with the production of kyanite being favored when the rock is more aluminous.
Occurrence
Talc is a common mineral in metamorphic belts that 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.
A notable talc mine of economic importance is at Mount Seabrook in Western Australia. It is formed on a polydeformed, layered, ultramafic intrusion.
Characteristics
The chemical formula of talc may be written as Mg3Si4O10(OH)2 or H2Mg3(SiO3)4. The mineral occurs as foliated to fibrous masses. Its monoclinic crystals are so rare as to be almost unknown. It has a perfect basal cleavage, and the folia are non-elastic, although slightly flexible. It is the softest material on the Mohs scale of mineral hardness—its hardness rating is 1. Its specific gravity is in the range of 2.5–2.8.
Uses
Talc finds use as a cosmetic (talcum powder), a lubricant, and a filler in paper manufacture. As a baby powder, it is an astringent that helps prevent rashes in the area covered by a diaper. Most tailor's chalk is talc, as is the chalk often used for welding or metalworking. It is also an additive in some foods and pharmaceutical products.[1] Moreover, soapstone or steatite—a coarse, grayish-green, high-talc rock—is used for stoves, sinks, and electrical switchboards, among other applications.
Safety
Several studies have established preliminary links between talc and pulmonary problems,[2] lung cancer,[3][4] skin cancer, and ovarian cancer.[5] These studies have raised public concern, considering talc's widespread commercial and household use. However, no conclusive study has yet been made to determine the toxicity or carcinogenic nature of talc under normal conditions of human exposure. 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.
- ↑ M.A. Hollinger, "Pulmonary toxicity of inhaled and intravenous talc," Toxicol. Lett. 52, no. 2 (1990): 121-27. Retrieved April 14, 2007.
- ↑ National Toxicology Program, "NTP Toxicology and Carcinogenesis Studies of Talc (CAS No. 14807-96-6)(Non-Asbestiform) in F344/N Rats and B6C3F1 Mice (Inhalation Studies)," Natl. Toxicol. Program Tech. Rep. Ser. 421 (1993): 1-287. Retrieved April 14, 2007.
- ↑ "Health effects of mining and milling talc," NIOSH Worker Notification Program. Retrieved April 14, 2007.
- ↑ B.L. Harlow et al., "Perineal exposure to talc and ovarian cancer risk," Obstetrics and Gynecology 80 No.1 (1992): 19-26. Retrieved April 14, 2007.
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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