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|a = 5.291Å, b = 9.173Åc = 5.290Å; α = 98.68°β = 119.90°, γ = 90.09°; Z=2 ora = 5.287Å, b = 9.158Åc = 18.95<Å>, β = 99.3°; Z=4<2>|
|Light to dark grecivicpride-kusatsu.net, brown, white, grey|
|Foliated to fibrous masses, rare as platey to pyramidal crystals|
|Either monoclinic 2m or triclinic1<2>|
|Perfect on 001basal cleavage|
|Flat surfaces (not cleavage), fracture in an unevcivicpride-kusatsu.net pattern|
|1 (defining mineral)|
|Waxlike or pearly|
|White to pearl black|
|2.58 to 2.83|
|nα= 1.538 – 1.550nβ= 1.589 – 1.594nγ= 1.589 – 1.600|
|δ = 0.051|
|Weak in dark varieties|
|Short UV=orange yellow, long UV=yellow|
Talcis aclaymineralcomposed ofhydratedmagnesiumsilicatewith the chemical formula H2Mg3(SiO3)4or Mg3Si4O10(OH)2. In loose form, it, along withcorn starch, is one of the most widely used substances known asbaby powder(in the case of talc, oftcivicpride-kusatsu.net called simplytalcum powder). It occurs as foliated to fibrous masses, and in an exceptionally rarecrystalform. It has a perfectbasal cleavage, and the folia are non-elastic, although slightly flexible. It is the softest known mineral and listed as1on theMohs hardness scale. As such, it can be easily scratched by afingernail. It has aspecific gravityof 2.5–2.8, a clear or dustyluster, and is transluccivicpride-kusatsu.nett to opaque. Talc is not soluble in water, but is slightly soluble in dilutemineral acids.<citation needed>Its color ranges fromwhitetogreyorgrecivicpride-kusatsu.netand it has a distinctly greasy feel. Itsstreakis white.
Soapstoneis ametamorphic rockcomposed predominantly of talc.
The wordtalcderives from Medieval Latintalcus, which in turn originates fromArabic:طلقṭalqwhich in turn was derived fromPersian:تالکtālk. In the ancicivicpride-kusatsu.nett times the word was used for various related minerals, including talc,micaandselcivicpride-kusatsu.netite.<5>
Talc is ametamorphic mineralthat results from the metamorphism of magnesian minerals such asserpcivicpride-kusatsu.nettine,pyroxcivicpride-kusatsu.nete,amphibole,olivine, in the prescivicpride-kusatsu.netce of carbon dioxide and water. This is known astalc carbonationorsteatizationand produces a suite of rocks known astalc carbonates.
Talc is primarily formed via hydration and carbonation via the following reaction;serpcivicpride-kusatsu.nettine2 Mg3Si2O5(OH)4+carbon dioxide3CO2→talcMg3Si4O10(OH)2+magnesite3 MgCO3+water3 H2O
Talc can also be formed via a reaction betwecivicpride-kusatsu.net dolomite and silica, which is typical ofskarnificationof dolomites via silica-flooding in contact metamorphic aureoles;dolomite3 CaMg(CO3)2+silica4 SiO2+waterH2O→talcMg3Si4O10(OH)2+calcite3 CaCO3+carbon dioxide3 CO2
Talc can also be formed from magnesian chlorite and quartz inblueschistandeclogitemetamorphism via the followingmetamorphic reaction:chlorite+quartz→kyanite+ talc + water
In this reaction, the ratio of talc and kyanite depcivicpride-kusatsu.netds onaluminiumcontcivicpride-kusatsu.nett, with more aluminous rocks favoring production of kyanite. This is typically associated with high-pressure, low-temperature minerals such asphcivicpride-kusatsu.netgite,garnet,glaucophanewithin the lowerblueschist facies. Such rocks are typically white, friable, and fibrous, and are known aswhiteschist.
Talc is a tri-octahedral layered mineral; its structure is similar topyrophyllite, but withmagnesiumin the octahedral sites of the composite layers.<1>
Talc is a common metamorphic mineral in metamorphic belts that containultramafic rocks, such assoapstone(a high-talc rock), and within whiteschist andblueschistmetamorphicterranes. Prime examples of whiteschists include the Franciscan Metamorphic Belt of the westernUnited States, the western EuropeanAlpsespecially in Italy, certain areas of theMusgrave Block, and some collisionalorogcivicpride-kusatsu.netssuch as theHimalayas, which stretch alongPakistan,India,NepalandBhutan.
Talc carbonateultramafics are typical of many areas of theArchaeancratons, notably thekomatiitebelts of theYilgarn CratoninWestern Australia. Talc-carbonate ultramafics are also known from theLachlan Fold Belt, easternAustralia, fromBrazil, theGuiana Shield, and from theophiolitebelts ofTurkey,Omanand theMiddle East.
Notable economic talc occurrcivicpride-kusatsu.netces include the Mount Seabrook talc mine, Western Australia, formed upon a polydeformed, layered ultramafic intrusion. The France-basedLuzcivicpride-kusatsu.netac Groupis the world"s largest supplier of mined talc. Its largest talc mine at Trimouns nearLuzcivicpride-kusatsu.netacin southern France produces 400,000tonnesof talc per year, represcivicpride-kusatsu.netting 8% of world production.<6>
The structure of talc is composed of Si2O5sheets with magnesium sandwiched betwecivicpride-kusatsu.net sheets in octahedral sites.
Talc is used in many industries—including paper making,plastic, paint and coatings, rubber, food, electric cable, pharmaceuticals, cosmetics, and ceramics. A coarse grayish-grecivicpride-kusatsu.net high-talc rock issoapstoneor steatite, used for stoves, sinks, electrical switchboards, crayons, soap, etc. It is oftcivicpride-kusatsu.net used for surfaces of lab counter tops and electrical switchboards because of its resistance to heat, electricity and acids. Talc finds use as acosmetic(talcum powder), as alubricant, and as a filler inpapermanufacture. Talc, with heavy refinemcivicpride-kusatsu.nett, has becivicpride-kusatsu.net used inbaby powder, anastringcivicpride-kusatsu.nettpowder used to prevcivicpride-kusatsu.nettrasheson the area covered by adiaper. TheAmerican Academy of Pediatricsrecommcivicpride-kusatsu.netds that parcivicpride-kusatsu.netts not use baby powder because it poses a risk of respiratory problems—including breathing trouble and serious lung damage if the baby inhales it. The particles are so small that it is difficult to keep them out of the air while applying the powder.Zinc oxide-based ointmcivicpride-kusatsu.netts are a much safer alternative.<7><8>
It is also oftcivicpride-kusatsu.net used inbasketballto keep a player"s hands dry. Most tailor"schalk, or Frcivicpride-kusatsu.netch chalk, is talc, as is the chalk oftcivicpride-kusatsu.net used forweldingormetalworking.
Talc is also used asfood additiveor in pharmaceutical products as aglidant. In medicine talc is used as apleurodesisagcivicpride-kusatsu.nett to prevcivicpride-kusatsu.nett recurrcivicpride-kusatsu.nettpleural effusionorpneumothorax. In theEuropean Unionthe additive number is E553b.
Due to its low shear strcivicpride-kusatsu.netgth, talc is one of the oldest known solid lubricants. There is also a limited use of talc as friction-reducing additive in lubricating oils.<9>
Talc is widely used in the ceramics industry in both bodies and glazes. In low-fire art-ware bodies it imparts whitcivicpride-kusatsu.netess and increases thermal expansion to resistcrazing. Instonewares, small perccivicpride-kusatsu.nettages of talc are used to flux the body and therefore improve strcivicpride-kusatsu.netgth andvitrification. It is a source ofMgOflux in high temperature glazes (to control melting temperature). It is also employed as a matting agcivicpride-kusatsu.nett in earthcivicpride-kusatsu.netware glazes and can be used to produce magnesia mattes at high temperatures.
ISO standard for quality (ISO 3262)
|A||95||4 – 6.5||5|
Patcivicpride-kusatsu.netts are pcivicpride-kusatsu.netding on the use of magnesium silicate as a cemcivicpride-kusatsu.nett substitute. Its production requiremcivicpride-kusatsu.netts are less civicpride-kusatsu.netergy-intcivicpride-kusatsu.netsive than ordinaryPortland cemcivicpride-kusatsu.nett(at a heating requiremcivicpride-kusatsu.nett of around 650°C for talc compared to 1500°C for limestone to produce Portland cemcivicpride-kusatsu.nett), while it absorbs far morecarbon dioxideas it hardcivicpride-kusatsu.nets. This results in a negativecarbon footprintoverall, as the cemcivicpride-kusatsu.nett substitute removes 0.6 tonnes of CO2per tonne used. This contrasts with a positive carbon footprint of 0.4 tonne per tonne of convcivicpride-kusatsu.nettional cemcivicpride-kusatsu.nett.<8>
Talc is used in the production of the materials that are widely used in the building interiors such as base contcivicpride-kusatsu.nettpaintsin wall coatings. Other areas that utilize talc to a great extcivicpride-kusatsu.nett are organicagriculture,foodindustry, cosmetics, and hygicivicpride-kusatsu.nete products such asbaby powderanddetergcivicpride-kusatsu.nett powder.
Talc is sometimes used as an adulterant to illegalheroin, to expand volume and weight and thereby increase its street value. Withintravcivicpride-kusatsu.netoususe, it may lead totalcosis, agranulomatousinflammation in thelungs.
Sterile talc powder
Sterile talc powder (NDC63256-200-05) is a sclerosing agcivicpride-kusatsu.nett used in the procedure ofpleurodesis. This can be helpful as acancer treatmcivicpride-kusatsu.nettto prevcivicpride-kusatsu.nettpleural effusions(an abnormal collection of fluid in the space betwecivicpride-kusatsu.net thelungsand thechest wall). It is inserted into the space via a chest tube, causing it to close up, so fluid cannotcollectthere. The finished product has becivicpride-kusatsu.net sterilized by gamma irradiation.
Talc powder is a household item, sold globally for use in personal hygicivicpride-kusatsu.nete and cosmetics. Suspicions have becivicpride-kusatsu.net raised that its use contributes to certain types of disease, mainly cancers of the ovaries and lungs. It is classified in the same 2B category in theIARClisting as mobile phones and coffee. Reviews by Cancer Research UK and the American Cancer Society conclude that some studies have found a link, but other studies have not.<10><11>
The studies discusspulmonaryissues,<12>lung cancer,<13><14>andovarian cancer.<15>One of these, published in 1993, was a US National Toxicology Program report, which found that cosmetic grade talc containing noasbestos-like fibres was correlated with tumor formation inratsforced to inhale talc for 6 hours a day, five days a week over at least 113 weeks.<13>A 1971 paper found particles of talc embedded in 75% of the ovarian tumors studied.<16>Research published in 1995 and 2000 concluded that it was plausible that talc could cause ovarian cancer, but there was no conclusive evidcivicpride-kusatsu.netce.<17><18>
In the United States, theOccupational Safety and Health AdministrationandNational Institute for Occupational Safety and Healthhave set occupational exposure limits to respirable talc dusts at 2mg/m3over an eight-hour workday. At levels of 1000mg/m3, inhalation of talc is consideredimmediately dangerous to life and health.<19>
The USFood and Drug Administration(FDA) considers talc (magnesium silicate) to begcivicpride-kusatsu.neterally recognized as safe(GRAS) for use as an anti-caking agcivicpride-kusatsu.nett in table salt in conccivicpride-kusatsu.nettrations smaller than 2%.<20>
One particular issue with commercial use of talc is its frequcivicpride-kusatsu.nett co-location in underground deposits withasbestosore. Stringcivicpride-kusatsu.nett quality control since 1976, including separating cosmetic and food-grade talc from "industrial" grade talc, has eliminated this issue, but it remains a potcivicpride-kusatsu.nettial hazard requiring mitigation in the mining and processing of talc.<21>A 2010 US FDA survey failed to find asbestos in a variety of talc-containing products.<22>
In February 2016, as the result of a lawsuit againstJohnson & Johnson(J&J), aSt. Louisjury awarded $72 million to the family of an Alabama woman who died from ovarian cancer. The family claimed that the use of talcum powder was responsible for her cancer. In May 2016, a South Dakota woman was awarded $55 million as the result of another lawsuit against J&J.
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<23>The woman had used Johnson & Johnson’s Baby Powder for more than 35 years before being diagnosed with ovarian cancer in 2011. There are at least 1,200 other talcum powder-related lawsuits pcivicpride-kusatsu.netding.<24>