Chrysotile 426184 220599560 2008-06-20T17:15:20Z 84.44.219.225 {{Infobox mineral | name = Chrysotile | category = Silicate mineral<br/>([[serpentine group]]) | boxwidth = 200px | boxbgcolor = | image = Chrysotile.jpg | imagesize = | caption = Chrysotile serpentine from the [[Salt River (Arizona)|Salt River]] area, [[Arizona]] | formula = [[Magnesium|Mg]]{{sub|3}}([[Silicon|Si]]{{sub|2}}[[Oxygen|O]]{{sub|5}})([[Hydroxide|OH]]){{sub|4}}<br/>(''ideal'') | molweight = 277.11 g/mol<br/>(''ideal'') | color = grey to green | habit = acicular | system = [[monoclinic]] or [[orthorhombic]] | twinning = | cleavage = | fracture = fibrous | tenacity = | mohs = 2½–3 | luster = silky | polish = | refractive = 1.545–1.569; 1.553–1.571 | opticalprop = | birefringence = 0.008 (max) | dispersion = relatively weak | pleochroism = | fluorescence= | absorption = | streak = white | gravity = | density = 2.53&nbsp;g/ml | melt = | fusibility = [[Dehydration (chemistry)|dehydrates]] at 550–750&nbsp;°C | diagnostic = | solubility = insoluble in water<br/>fibres degrade in dilute acid | diaphaneity = translucent | other = | references = }} '''Chrysotile''' or '''white asbestos''' is the most commonly encountered form of [[asbestos]],<ref name="11thRoC">[[United States Department of Health and Human Services|U.S. Department of Health and Human Services]] (2005). "[http://ntp.niehs.nih.gov/ntp/roc/eleventh/profiles/s016asbe.pdf Asbestos]." ''[http://ntp.niehs.nih.gov/index.cfm?objectid=32BA9724-F1F6-975E-7FCE50709CB4C932# Report on Carcinogens, Eleventh Edition].''</ref> accounting for approximately 95% of the asbestos in place in the United States<ref name="29CFR1910J">[[Occupational Safety and Health Administration]], [[United States Department of Labor|U.S. Department of Labor]] (2007). [http://edocket.access.gpo.gov/cfr_2007/julqtr/pdf/29cfr1910.1001.pdf 29&nbsp;C.F.R.&nbsp;1910.1001]. Appendix&nbsp;J.</ref> and a similar proportion in other countries.<ref name="INRS">[[Institut national de recherche sur la sécurité]] (1997). "[http://www.inrs.fr/inrs-pub/inrs01.nsf/IntranetObject-accesParReference/FT%20145/$File/ft145.pdf Amiante]." ''Fiches toxicologiques.'' n° 167. (in French)</ref> It is a soft, fibrous [[silicate mineral]] in the [[serpentine group]] of [[phyllosilicate]]s: as such, it is distinct from other asbestiform minerals in the [[amphibole group]]. Its idealized [[chemical formula]] is [[Magnesium|Mg]]{{sub|3}}([[Silicon|Si]]{{sub|2}}[[Oxygen|O]]{{sub|5}})([[Hydroxide|OH]]){{sub|4}}, in which some of the [[magnesium]] ions may be substituted by [[iron]] or other cations. Substitution of the [[hydroxide]] ions for [[fluoride]], [[oxide]] or [[chloride]] is also known, but rarer.<ref name="11thRoC"/> A related, but much rarer, mineral is [[pecoraite]], in which all the magnesium cations of chrysotile are substituted by [[nickel]] cations. == Polytypes== Three [[polytype]]s of chrysotile are known.<ref>''Can. Mineral.'' '''13''' (1975): 227–43.</ref> These are very difficult to distinguish in hand specimens, and [[polarized light]] [[microscopy]]<ref name="29CFR1910J"/> must normally be used. Some older publications refer to chrysotile as a group of minerals—the three polytypes listed below, and sometimes [[pecoraite]] as well—but the 2006 recommendations of the [[International Mineralogical Association]] prefer to treat it as a single mineral with a certain variation in its naturally-occurring forms.<ref>Burke, Ernst A. J. (2006). "[http://article.pubs.nrc-cnrc.gc.ca/ppv/RPViewDoc?_handler_=HandleInitialGet&journal=mineral&volume=44&articleFile=tcm-155744-6.pdf A Mass Discreditation of GQN Minerals]." ''Can. Mineral.'' '''44''': 1557–60.</ref> {| class="wikitable" |- ! Name ! [[Crystal system]] ! [[Type locality (geology)|Type locality]] ! [[mindat.org]] reference ! [[Unit cell]] parameters ! Crystal structure reference |- | Clinochrysotile | [[monoclinic]] | [[Złoty Stok]]*, [[Lower Silesia]], [[Poland]] | <span class="reflink plainlinksneverexpand">[http://www.mindat.org/min-1071.html 1071]</span> | ''a''&nbsp;= 5.3&nbsp;Å; ''b''&nbsp;= 9.19&nbsp;Å; ''c''&nbsp;= 14.63&nbsp;Å; β&nbsp;= 93° | <ref>Whittaker, E. J. W. (1956). "The structure of chrysotile II. Clinochrysotile." ''[[Acta Crystallographica|Acta Crystallogr.]]'' '''9''': 855–62.</ref> |- | Orthochrysotile | [[orthorhombic]] | [[Kadapa district|Kadapa* district]], [[Andhra Pradesh]], [[India]] | <span class="reflink plainlinksneverexpand">[http://www.mindat.org/min-3025.html 3025]</span> | ''a''&nbsp;= 5.34&nbsp;Å; ''b''&nbsp;= 9.24&nbsp;Å; ''c''&nbsp;= 14.2&nbsp;Å | <ref>Whittaker, E. J. W. (1956). "The structure of chrysotile III. Orthochrysotile." ''[[Acta Crystallographica|Acta Crystallogr.]]'' '''9''': 862–64.</ref> |- | Parachrysotile | [[orthorhombic]] | uncertain | <span class="reflink plainlinksneverexpand">[http://www.mindat.org/min-3083.html 3083]</span> | ''a''&nbsp;= 5.3&nbsp;Å; ''b''&nbsp;= 9.24&nbsp;Å; ''c''&nbsp;= 14.71&nbsp;Å | <ref>Whittaker, E. J. W. (1956). "The structure of chrysotile IV. Parachrysotile." ''[[Acta Crystallographica|Acta Crystallogr.]]'' '''9''': 865–67.</ref> |- | colspan=6 | <small>''Source'': [[mindat.org]].<br/>*Złoty Stok and Kadapa have formerly been known as Reichenstein and Cuddapah respecively, and these names may appear in some publications.</small> |} Clinochrysotile is the commonest of the three forms, found notably at [[Asbestos, Quebec]], [[Canada]]. Its two measurable [[Refractive index|refractive indices]] tend to be lower than those of the other two forms.<ref>In principle, all polytypes of chrysotile should have three independent refractive indices: in practice, two of the three are so close as to be indistinguishable by experimental measurement.</ref> The orthorhombic paratypes may be distinguished by the fact that, for orthochrysotile, the higher of the two observable refractive indices is measured parallel to the long axis of the fibres (as for clinochrysotile); whereas for parachrysotile the higher refractive index is measured perpendicular to the long axis of the fibres. ==Physical and chemical properties== Bulk chrysotile, whose hardness is about the same as that of a human [[fingernail]], is easily crumbled to fibres that are, in fact, bundles of fibrils. Naturally-occurring fibre bundles range in length from several millimetres to more than ten centimetres,<ref name="11thRoC"/> although industrially-processed chrysotile usually has shorter fibre bundles. The diameter of the fibre bundles is 0.1–1&nbsp;[[micrometre|µm]], and the individual fibrils are even finer, 0.02–0.03&nbsp;µm, each fibre bundle containing tens or hundreds of fibrils.<ref name="INRS"/> Chrysotile fibres have considerable tensile strength, and may be spun into thread and woven into cloth. They are also resistant to heat and are excellent thermal, electrical and acoustic insulators.<ref name="11thRoC"/><ref name="INRS"/> Chrysotile is resistant to even strong bases, but the fibres are attacked by acids: the magnesium ions are selectively dissolved, leaving a [[silica]] skeleton. It is thermally stable up to around 550&nbsp;°C, at which temperature it starts to [[Dehydration (chemistry)|dehydrate]]. Dehydration is complete at about 750&nbsp;°C, with the final products being silica and [[forsterite]] (magnesium silicate).<ref name="INRS"/> == Safety concerns == [[Image:Asbestos1USGOV.jpg|thumb|Chrysotile asbestos]] Chrysotile, as well as other forms of [[asbestos]], is considered to be a human [[carcinogen]] by the [[International Agency for Research on Cancer]] (IARC)<ref name="IARCs7">[[International Agency for Research on Cancer]] (1998). "Asbestos." ''[http://monographs.iarc.fr/ENG/Monographs/suppl7/suppl7.pdf IARC Monographs on Evaluating the Carcinogenic Risks to Humans. Supplement 7].''</ref> and by the [[United States Department of Health and Human Services|U.S. Department of Health and Human Services]].<ref name="11thRoC"/> Asbestos exposure is associated with [[Asbestosis|parenchymal asbestosis]], asbestos-related [[Pleural cavity|pleural]] abnormalities, [[mesothelioma]], and [[lung cancer]], and it may be associated with cancer at some extra-[[Chest|thoracic]] sites.<ref name="ATSDR">[[Agency for Toxic Substances and Disease Registry]] (ATDSR), [[United States Department of Health and Human Services|U.S. Department of Health and Human Services]] (2007). "[http://www.atsdr.cdc.gov/csem/asbestos/cover2.html Asbestos Toxicity]." ''Case Studies in Environmental Medicine.''</ref> ==References== {{Reflist}} ==External links== *{{ICSC|0014|00}} *[http://webmineral.com/data/Chrysotile.shtml Webmineral] *[http://www.mindat.org/min-1071.html Mindat clinochrysotile] *[http://www.mindat.org/min-3025.html Mindat orthochrysotile] *[http://www.mindat.org/min-3083.html Mindat parachrysotile] *[http://ibe.sagepub.com/cgi/content/abstract/14/1/83 "Asbestos-containing Floor Tile and Mastic Abatement: Is there Enough Exposure to Cause Asbestos-related Disease?"] *Deer William Alexander, Howie Robert Andrew, Zussman Jack, ''An Introduction to the rock-forming minerals'', ISBN 0-582-30094-0, OCLC 183009096 pp. 344-352, 1992 *Ledoux, RL (ed), ''Short course in mineralogical techniques of asbestos determination'', Mineralogical Association of Canada, pp. 35-73, 185, 1979. *http://www.microlabgallery.com/ChrysotileFile.aspx Photomicrographs of parachrysotile and clinochrysotile *Nolan, RP, Langer AM, Ross M, Wicks FJ, Martin RF (eds), "The health effects of chrysotile asbestos", ''The Canadian Mineralogist'', Special Publication 5, 2001. *http://www.chrysotile.com/en/news/news.aspx/?id=44&lang=en [[Category:Phyllosilicates]] [[Category:Magnesium minerals]] [[Category:Hydroxide minerals]] [[Category:Asbestos]] [[Category:IARC Group 1 carcinogens]] [[ca:Crisòtil]] [[de:Chrysotil]] [[es:Crisotilo]] [[fr:Chrysotile]] [[nl:Chrysotiel]] [[pl:Chryzotyl]] [[pt:Crisótilo]] [[sk:Chryzotil]]