AskDefine | Define talcum

Dictionary Definition

talcum

Noun

1 a fine grained mineral having a soft soapy feel and consisting of hydrated magnesium silicate; used in a variety of products including talcum powder [syn: talc]
2 a toilet powder made of purified talc and usually scented; absorbs excess moisture [syn: talcum powder]

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English

Etymology

Late Latin

Noun

talcum
  1. powdered and perfumed talc for toilet use

Related terms

Translations

Extensive Definition

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. In loose form, it is the widely used substance known as talcum powder. 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, and can be easily scratched by a fingernail). It has a specific gravity of 2.5–2.8, a clear or dusty luster, and is translucent to opaque. 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 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
2Mg_3Si_2O_5(OH)_4 + 3CO_2 \rarr Mg_3Si_4O_(OH)_2 + 3MgCO_3 + 3H_2O
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
3CaMg(CO_3)_2 + 4SiO_2 + H_2O \rarr Mg_3Si_4O_(OH)_2 + 3CaCO_3 + 3CO_2
Talc can also be formed from magnesian chlorite and quartz in blueschist and eclogite metamorphism via the following metamorphic reaction:
Chlorite + QuartzKyanite + 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.
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. lung cancer, skin cancer and ovarian cancer. 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. However, the U.S. Food and Drug Administration (FDA) considers non-asbestiform talc, that is talc which does not contain potentially carcinogenic asbestiform amphibole fibers, to be Generally recognized as safe (GRAS) for use in cosmetics.
talcum in Arabic: تلك
talcum in Bulgarian: Талк
talcum in Catalan: Talc
talcum in Czech: Mastek
talcum in Danish: Fedtsten
talcum in German: Talk (Mineral)
talcum in Spanish: Talco
talcum in Esperanto: Talko
talcum in Basque: Talko
talcum in French: Talc
talcum in Galician: Talco
talcum in Croatian: Talk
talcum in Italian: Talco
talcum in Hebrew: טלק
talcum in Latvian: Talks
talcum in Lithuanian: Talkas
talcum in Hungarian: Zsírkő
talcum in Dutch: Talk (mineraal)
talcum in Japanese: 滑石
talcum in Norwegian: Talk
talcum in Polish: Talk
talcum in Portuguese: Talco
talcum in Romanian: Talc
talcum in Russian: Тальк
talcum in Slovenian: Lojevec
talcum in Serbian: Талк
talcum in Finnish: Talkki
talcum in Swedish: Talk
talcum in Tamil: டால்க்
talcum in Thai: ทัลก์
talcum in Turkish: Talk
talcum in Ukrainian: Тальк
talcum in Chinese: 滑石
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