Fibrous variety of the magnesium silicate mineral serpentine; it is the most important asbestos mineral. Individual fibres are white and silky, but the aggregate in veins is usually green or yellowish. Chrysotile fibres have a high tensile strength, similar to that of other asbestos minerals (see amphibole asbestos). The largest deposits of chrysotile are in Quebec and in the Ural Mountains.
Learn more about chrysotile with a free trial on Britannica.com.
Chrysotile or white asbestos is the most commonly encountered form of asbestos, accounting for approximately 95% of the asbestos in place in the United States and a similar proportion in other countries. It is a soft, fibrous silicate mineral in the serpentine group of phyllosilicates: as such, it is distinct from other asbestiform minerals in the amphibole group. Its idealized chemical formula is Mg(SiO)(OH), 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. A related, but much rarer, mineral is pecoraite, in which all the magnesium cations of chrysotile are substituted by nickel cations.
|Name||Crystal system||Type locality||mindat.org reference||Unit cell parameters||Crystal structure reference|
|Clinochrysotile||monoclinic||Złoty Stok*, Lower Silesia, Poland||a = 5.3 Å; b = 9.19 Å; c = 14.63 Å; β = 93°|
|Orthochrysotile||orthorhombic||Kadapa* district, Andhra Pradesh, India||a = 5.34 Å; b = 9.24 Å; c = 14.2 Å|
|Parachrysotile||orthorhombic||uncertain||a = 5.3 Å; b = 9.24 Å; c = 14.71 Å|
| Source: mindat.org.|
*Złoty Stok and Kadapa have formerly been known as Reichenstein and Cuddapah respecively, and these names may appear in some publications.
Clinochrysotile is the commonest of the three forms, found notably at Asbestos, Quebec, Canada. Its two measurable refractive indices tend to be lower than those of the other two forms. 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.
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.
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 °C, at which temperature it starts to dehydrate. Dehydration is complete at about 750 °C, with the final products being silica and forsterite (magnesium silicate).
Chrysotile, as well as other forms of asbestos, is considered to be a human carcinogen by the International Agency for Research on Cancer (IARC) and by the U.S. Department of Health and Human Services. Asbestos exposure is associated with parenchymal asbestosis, asbestos-related pleural abnormalities, mesothelioma, and lung cancer, and it may be associated with cancer at some extra-thoracic sites. Chrysotile has been recommended for inclusion in the Rotterdam Convention on Prior Informed Consent, an international treaty that restricts the global trade in hazardous materials. If approved by the parties to convention when they meet in October 2008, exports of chrysotile would only be permitted to countries explicitly consenting to receive it. Canada, the major producer of the mineral, is currently resisting efforts to include it in the treaty. All other forms of asbestos are already listed in the treaty.
Ban All Production and Export of Chrysotile Asbestos/ Il faut interdire toute la production et l'exportation de l'amiante chrysotile
Sep 01, 2010; The disturbing image on the cover of this issue of the Canadian Journal of Public Health shows a child in Indonesia sifting...