Chrysotile

This article is about the form of asbestos. For the types of gemstone, see Chrysolite.

Chrysotile or white asbestos is the most commonly encountered form of asbestos,^[5] accounting for approximately 95% of the asbestos in the United States^[6] and a similar proportion in other countries.^[7] It is a soft, fibrous silicate mineral in the serpentine subgroup of phyllosilicates; as such, it is distinct from other asbestiform minerals in the amphibole group. Its idealized chemical formula is Mg₃(Si₂O₅)(OH)₄.^[5] The material has physical properties which make it desirable for inclusion in building materials, but poses serious health risks when dispersed into air and inhaled.

Chrysotile
General
Category	Phyllosilicates Kaolinite-serpentine group
Formula (repeating unit)	Mg3(Si2O5)(OH)4 (ideal)
IMA symbol	Ctl^[1]
Strunz classification	9.ED.15
Crystal system	Monoclinic: clinochrysotile (most common) Orthorhombic: orthochrysotile and parachrysotile (both rare)
Crystal class	Clinochrysotile: prismatic (2/m) Orthochrysotile and parachrysotile: pyramidal (mm2)
Space group	Clinochrysotile: C2/m Orthochrysotile and parachrysotile: Ccm21
Identification
Formula mass	277.11 g/mol (ideal)
Colour	White to greyish green
Crystal habit	Acicular
Fracture	Fibrous
Mohs scale hardness	2.5–3
Lustre	Silky
Streak	White
Diaphaneity	Translucent
Density	2.53 g/ml
Optical properties	Biaxial (+)
Refractive index	nα = 1.569, nγ = 1.570
Birefringence	0.001 (max)
Dispersion	Relatively weak
Extinction	parallel
Melting point	600–850 °C (1,112–1,562 °F) (decomposes)
Fusibility	dehydrates at 550–750 °C (1,022–1,382 °F)
Diagnostic features	White to grayish green thin, flexible curved fiber
Solubility	Insoluble in water Fibres degrade in dilute acid
References	^[2]^[3]^[4]

Polytypes

Three polytypes of chrysotile are known.^[8] These are very difficult to distinguish in hand specimens, and polarized light microscopy^[6] 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.^[9]

Name	Crystal system	Type locality	mindat.org reference	Unit cell parameters	Crystal structure reference
Clinochrysotile	monoclinic	Złoty Stok*, Lower Silesia, Poland	1071	a = 5.3 Å; b = 9.19 Å; c = 14.63 Å; β = 93°	^[10]
Orthochrysotile	orthorhombic	Kadapa* district, Andhra Pradesh, India	3025	a = 5.34 Å; b = 9.24 Å; c = 14.2 Å	^[11]
Parachrysotile	orthorhombic	uncertain	3083	a = 5.3 Å; b = 9.24 Å; c = 14.71 Å	^[12]
Source: mindat.org. *Złoty Stok and Kadapa have formerly been known as Reichenstein and Cuddapah respectively, and these names may appear in some publications.

Clinochrysotile is the most common of the three forms, found notably at Val-des-Sources, Quebec, Canada. Its two measurable refractive indices tend to be lower than those of the other two forms.^[13] 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.^{[citation needed]}

Physical properties

 

SEM photo of chrysotile

Bulk chrysotile has a hardness similar to a human fingernail and is easily crumbled to fibrous strands composed of smaller bundles of fibrils. Naturally-occurring fibre bundles range in length from several millimetres to more than ten centimetres,^[5] although industrially-processed chrysotile usually has shorter fibre bundles. The diameter of the fibre bundles is 0.1–1 µm, and the individual fibrils are even finer, 0.02–0.03 µm, each fibre bundle containing tens or hundreds of fibrils.^[7]

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.^[5][7]

Chemical properties

The idealized chemical formula of chrysotile is Mg₃(Si₂O₅)(OH)₄, although some of the magnesium ions may be replaced by iron or other cations. Substitution of the hydroxide ions for fluoride, oxide or chloride is also known, but rarer.^[5] A related, but much rarer, mineral is pecoraite, in which all the magnesium cations of chrysotile are substituted by nickel cations.^{[citation needed]}

Chrysotile is resistant to even strong bases (asbestos is thus stable in high pH pore water of Portland cement), but when 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 (1,022 °F), at which temperature it starts to dehydrate. Dehydration is complete at about 750 °C (1,380 °F), with the final products being forsterite (magnesium silicate), silica and water.^[7]

The global mass balance reaction of the chrysotile dehydration can be written as follows:

${\displaystyle {\ce {{\overset {Chrysotile\ (serpentine)}{2Mg3Si2O5(OH)4}}->[{750^{\circ }C}][{dehydration}]{\overset {Forsterite}{3Mg2SiO4}}+{\overset {silica}{SiO2}}+{\overset {water}{4H2O}}}}}$ 

The chrysotile (serpentine) dehydration reaction corresponds to the reverse of the forsterite (Mg-olivine) hydrolysis in the presence of dissolved silica (silicic acid).

Applications

Previously, in the 1990s it was used in asbestos-cement products (like pipes and sheets).^[14]

Magnesium sulfate (MgSO₄) may be produced by treating chrysotile with sulfuric acid (H₂SO₄).^[15]

Safety concerns

 

Chrysotile asbestos

Chrysotile has been included with other forms of asbestos in being classified as a human carcinogen by the International Agency for Research on Cancer (IARC)^[16] and by the U.S. Department of Health and Human Services.^[5] These state that "Asbestos exposure is associated with parenchymal asbestosis, asbestos-related pleural abnormalities, peritoneal mesothelioma, and lung cancer, and it may be associated with cancer at some extra-thoracic sites".^[17] In other scientific publications, epidemiologists have published peer-reviewed scientific papers establishing that chrysotile is the main cause of pleural mesothelioma.^[18][19][20]

Chrysotile has been recommended for inclusion in the Rotterdam Convention on Prior Informed Consent,^[21] an international treaty that restricts the global trade in hazardous materials. If listed, exports of chrysotile would only be permitted to countries that explicitly consent to imports. Canada, a major producer of the mineral, has been harshly criticized by the Canadian Medical Association^[22][23] for its opposition to including chrysotile in the convention.^[24]

According to EU Regulation 1907/2006 (REACH) the marketing and use of chrysotile, and of products containing chrysotile, are prohibited.^[25]

Critics of safety regulations

1990s: Canada-European dispute GATT dispute

In May 1998, Canada requested consultations before the WTO and the European Commission concerning France's 1996 prohibition of the importation and sale of all forms of asbestos. Canada said that the French measures contravened provisions of the Agreements on Sanitary and Phytosanitary Measures and on Technical Barriers to Trade, and the GATT 1994. The EC claimed that safer substitute materials existed to take the place of asbestos. It stressed that the French measures were not discriminatory under the terms of international trade treaties, and were fully justified for public health reasons. The EC further claimed that in the July consultations, it had tried to convince Canada that the measures were justified, and that just as Canada broke off consultations, it (the EC) was in the process of submitting substantial scientific data in favour of the asbestos ban.^[26]

2000s: Canadian exports face mounting global criticism

In the late 1990s and early 2000s, the Government of Canada continued to claim that chrysotile was much less dangerous than other types of asbestos.^[27] Chrysotile continued to be used in new construction across Canada, in ways that are very similar to those for which chrysotile was exported.^[28] Similarly, Natural Resources Canada once stated that chrysotile, one of the fibres that make up asbestos, was not as dangerous as once thought. According to a fact sheet from 2003, "current knowledge and modern technology can successfully control the potential for health and environmental harm posed by chrysotile".^[29] The Chrysotile Institute, an association partially funded by the Canadian government, also prominently asserted that the use of chrysotile did not pose an environmental problem and the inherent risks in its use were limited to the workplace.^[30]

However, under increasing criticism by environmental groups, in May, 2012, the Canadian government stopped funding the Chrysotile Institute.^[31][32] As a result, the Chrysotile Institute has now closed.^[33][34][35]

The Canadian government continues to draw both domestic and international criticism for its stance on chrysotile, most recently in international meetings about the Rotterdam Convention hearings regarding chrysotile. The CFMEU pointed out that most exports go to developing countries. Canada has pressured countries, including Chile, and other UN member states to avoid chrysotile bans.^[36]

In September 2012, governments in Quebec and Canada ended official support for Canada's last asbestos mine in Asbestos, Quebec,^[37] now renamed as Val-des-Sources.

See also

• Erionite
• Serpentinite reactions – Rock formed by hydration and metamorphic transformation of olivine
• Antigorite

References

1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
2. Mineralienatlas
3. Chrysotile on Mindat.org
4. Chrysotile data on Webmineral
5. "Asbestos" (PDF). Report on Carcinogens, Eleventh Edition. U.S. Department of Health and Human Services. 2005.
6. Occupational Safety and Health Administration, U.S. Department of Labor (2007). 29 C.F.R. 1910.1001. Appendix J.
7. Institut national de recherche sur la sécurité (1997). "Amiante 2008-06-25 at the Wayback Machine." Fiches toxicologiques. n° 167. (in French)
8. Wicks, F. J.; Whittaker, E. J. W. (1975). "A reappraisal of the structures of the serpentine minerals". The Canadian Mineralogist. 13 (3): 227–243.
9. Burke, Ernst A. J. (2006). (PDF). The Canadian Mineralogist. 44 (6): 1557–60. Bibcode:2006CaMin..44.1557B. doi:10.2113/gscanmin.44.6.1557. Archived from the original (PDF) on 2012-03-26. Retrieved 2010-11-30.
10. Whittaker, E. J. W. (1956). "The structure of chrysotile. II. Clino-chrysotile". Acta Crystallographica. 9 (11): 855–62. doi:10.1107/S0365110X5600245X.
11. Whittaker, E. J. W. (1956). "The structure of chrysotile. III. Ortho-chrysotile". Acta Crystallographica. 9 (11): 862–64. doi:10.1107/S0365110X56002461.
12. Whittaker, E. J. W. (1956). "The structure of chrysotile. IV. Para-chrysotile" (PDF). Acta Crystallographica. 9 (11): 865–67. doi:10.1107/S0365110X56002473.
13. 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.
14. Pigg, B. J. (August 1994). "The uses of chrysotile". The Annals of Occupational Hygiene. 38 (4): 453–458, 408. doi:10.1093/annhyg/38.4.453. ISSN 0003-4878. PMID 7978966.
15. Bedelova, Zh. D.; Tabylganova, A. N; Homyakov, A. P.; Dagubaeva, A. T. (2017). "DEVELOPING THE TECHNOLOGY OF WASTE SULFURIC ACID LEACHING OF CHRYSOTILE ASBESTOS PRODUCTION" (PDF). Machines. Technologies. Materials. National center on complex processing of mineral raw materials of the Republic of Kazakhstan. 4: 288–290. eISSN 1314-507X. ISSN 1313-0226.
16. International Agency for Research on Cancer (1998). "Asbestos." However, the study states " In some of these case reports and in other studies, asbestos fibres have been identified in the lung. Amphibole fibres have usually predominated, but in a few cases mainly or only chrysotile fibres were found." IARC Monographs on Evaluating the Carcinogenic Risks to Humans. Supplement 7 2008-03-06 at the Wayback Machine.
17. Agency for Toxic Substances and Disease Registry (ATDSR), U.S. Department of Health and Human Services (2007). "Asbestos Toxicity June 6, 2011, at the Wayback Machine." Case Studies in Environmental Medicine.
18. (PDF). Archived from the original (PDF) on 2010-06-09. Retrieved 2011-10-03.{{cite web}}: CS1 maint: archived copy as title (link) See e.g., Smith, Allen "Chrysotile is the main cause of pleural mesothelioma", Amer.J.Indus.Med., Vol. 32, pp. 252 to 266 (1996)
19. [1] Tossavainen A, "Asbestos, asbestosis, and cancer: the Helsinki criteria for diagnosis and attribution" Scand J Work Environ Health 1997;23(4):311–316 (stating that all types of malignant mesothelioma can be induced by asbestos, with the amphiboles showing greater carcinogenic potency than chrysotile)
20. Lemen, Richard A. (2010). "Chrysotile Asbestos and Mesothelioma". Environmental Health Perspectives. 118 (7): a282. doi:10.1289/ehp.1002446. PMC 2920924. PMID 20601327.
21. Rotterdam Convention: Chrysotile
22. Attaran, Amir; Boyd, David R.; Stanbrook, Matthew B. (October 2008). "Asbestos mortality: a Canadian export". CMAJ. 179 (9): 871–2. doi:10.1503/cmaj.081500. PMC 2565724. PMID 18936444.
23. Collier, Roger (December 2008). "Health advocates assail Canada's asbestos stance". CMAJ. 179 (12): 1257. doi:10.1503/cmaj.081806. PMC 2585122. PMID 19047602.
24. MITTELSTAEDT, MARTIN (September 10, 2008). "Canada still blocking action on asbestos". The Globe and Mail. Toronto. Retrieved 2008-10-01.
25. Amtsblatt der Europäischen Union, L 396 from 30-12-2006 (PDF 1,8 MB; S. 129)
26. EC measures affecting asbestos products. World Trade Organization News. 29 October 1998
27. Harper, Tim (3 July 2011). . The Chronicle Herald. Archived from the original on 20 November 2012. Retrieved 28 September 2012.
28. Versailles, Guy (8 July 2015). "What Exactly Is Asbestos?". South Bay Mitigation.
29. (PDF). Natural Resources Canada. 3 February 2009. Archived from the original (PDF) on 27 September 2007. Retrieved 2010-01-12.
30. Vongdouangchanh, Bea (5 July 2011). "NDP MP Martin's one-man battle to ban asbestos mining in Canada gains traction". The Hill Times.
31. . Archived from the original on 2012-07-10. Retrieved 2018-10-04.
32. . Archived from the original on 28 June 2011. Retrieved 28 September 2012.
33. R.I.P. Chrysotile Institute, The Mad Scientist Blog>
34. Asbestos Advocacy Group Shuts Its Doors, Vancouver Sun, 29 April 2012^{[permanent dead link]}
35. . Archived from the original on 2019-04-04. Retrieved 2012-09-28.
36. Stop Canada's Export Of Asbestos CFMEU July 10, 2010, at the Wayback Machine
37. Daniel Lak (17 Oct 2012). "Canada axes support for asbestos mining". Al Jazeera.

External links

• The Chrysotile Institute
• International Chemical Safety Card 0014
• "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.