Chrysotile or white asbestos is the most commonly encountered form of

asbestos Asbestos () is a naturally occurring fibrous silicate mineral. There are six types, all of which are composed of long and thin fibrous crystals, each fibre being composed of many microscopic "fibrils" that can be released into the atmosphere b ...

, accounting for approximately 95% of the asbestos in the United States

Occupational Safety and Health Administration The Occupational Safety and Health Administration'' (OSHA ) is a large regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. Congress established the agenc ...

U.S. Department of Labor The United States Department of Labor (DOL) is one of the United States federal executive departments, executive departments of the federal government of the United States, U.S. federal government. It is responsible for the administration of fede ...

(2007)
29 C.F.R. 1910.1001
Appendix J. and a similar proportion in other countries.Institut national de recherche sur la sécurité (1997).
Amiante
." ''Fiches toxicologiques.'' n° 167. (in French) It is a soft, fibrous

silicate mineral Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, silica (silicon dioxide, ) is usually consid ...

in the

serpentine subgroup Serpentine subgroup (part of the kaolinite-serpentine group in the category of phyllosilicates) are greenish, brownish, or spotted minerals commonly found in serpentinite. They are used as a source of magnesium and asbestos, and as decorative s ...

phyllosilicate Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, silica (silicon dioxide, ) is usually consid ...

s; as such, it is distinct from other asbestiform minerals in the

amphibole group Amphibole () is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is A ...

. Its idealized

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...

is Mg( Si O)( OH). 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.

Polytypes

Three

polytype In materials science, polymorphism describes the existence of a solid material in more than one form or crystal structure. Polymorphism is a form of isomerism. Any crystalline material can exhibit the phenomenon. Allotropy refers to polymorphism ...

s of chrysotile are known. These are very difficult to distinguish in hand specimens, and polarized light

microscopy Microscopy is the technical field of using microscopes to view objects and areas of objects that cannot be seen with the naked eye (objects that are not within the resolution range of the normal eye). There are three well-known branches of micr ...

must normally be used. Some older publications refer to chrysotile as a group of minerals—the three polytypes listed below, and sometimes

pecoraite Pecoraite is a nickel silicate mineral and a member of the serpentine group. It was named after geologist William Thomas Pecora. It is monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crys ...

as well—but the 2006 recommendations of the

International Mineralogical Association Founded in 1958, the International Mineralogical Association (IMA) is an international group of 40 national societies. The goal is to promote the science of mineralogy and to standardize the nomenclature of the 5000 plus known mineral species. Th ...

prefer to treat it as a single mineral with a certain variation in its naturally occurring forms. Clinochrysotile is the most common of the three forms, found notably at Val-des-Sources, Quebec,

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

. Its two measurable

refractive indices In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...

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.

Physical properties

Bulk chrysotile has a hardness similar to a human

fingernail A nail is a claw-like plate found at the tip of the fingers and toes on most primates. Nails correspond to the claws found in other animals. Fingernails and toenails are made of a tough protective protein called alpha-keratin, which is a polymer ...

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, 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. Chrysotile fibres have considerable

tensile strength Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or F_\text within equations, is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials t ...

, and may be spun into thread and woven into cloth. They are also resistant to heat and are excellent thermal, electrical and acoustic insulators.

Chemical properties

The idealized

of chrysotile is Mg( Si O)( OH), although some of the

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...

ions may be replaced by

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...

or other

cations An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by con ...

. Substitution of the

hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. I ...

ions for

fluoride Fluoride (). According to this source, is a possible pronunciation in British English. is an inorganic, monatomic anion of fluorine, with the chemical formula (also written ), whose salts are typically white or colorless. Fluoride salts typ ...

oxide An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...

chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts ...

is also known, but rarer. A related, but much rarer, mineral is

, in which all the magnesium cations of chrysotile are substituted by

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to ...

cations. Chrysotile is resistant to even strong bases (asbestos is thus stable in high pH pore water of Portland

cement A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel ( aggregate) together. Cement mix ...

), but when the fibres are attacked by acids, the magnesium ions are selectively dissolved, leaving a

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

skeleton. It is thermally stable up to around , at which temperature it starts to

dehydrate In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...

. Dehydration is complete at about , with the final products being

forsterite Forsterite (Mg2SiO4; commonly abbreviated as Fo; also known as white olivine) is the magnesium-rich end-member of the olivine solid solution series. It is isomorphous with the iron-rich end-member, fayalite. Forsterite crystallizes in the orthor ...

(magnesium silicate), silica and water. The global mass balance reaction of the chrysotile dehydration can be written as follows: :\overset ->[][] \overset + \overset + \overset The chrysotile (serpentine) dehydration reaction corresponds to the reverse of the forsterite (Mg-olivine) hydrolysis in the presence of dissolved

(

silicic acid Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

Applications

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

Magnesium sulfate Magnesium sulfate or magnesium sulphate (in English-speaking countries other than the US) is a chemical compound, a salt with the formula , consisting of magnesium cations (20.19% by mass) and sulfate anions . It is a white crystalline solid, ...

(MgSO₄) may be produced by treating chrysotile with

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...

(H₂SO₄).

Safety concerns

Chrysotile has been included with other forms of

in being classified as a human

carcinogen A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive substan ...

by the

International Agency for Research on Cancer The International Agency for Research on Cancer (IARC; french: Centre International de Recherche sur le Cancer, CIRC) is an intergovernmental agency forming part of the World Health Organization of the United Nations. Its role is to conduct and ...

(IARC)

(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
.'' and by the U.S. Department of Health and Human Services. These state that "Asbestos exposure is associated with parenchymal

asbestosis Asbestosis is long-term inflammation and pulmonary fibrosis, scarring of the human lung, lungs due to asbestos, asbestos fibers. Symptoms may include shortness of breath, cough, wheezing, and chest pain, chest tightness. Complications may include ...

, asbestos-related

pleural The pleural cavity, pleural space, or interpleural space is the potential space between the pleurae of the pleural sac that surrounds each lung. A small amount of serous pleural fluid is maintained in the pleural cavity to enable lubrication bet ...

abnormalities, peritoneal mesothelioma, and

lung cancer Lung cancer, also known as lung carcinoma (since about 98–99% of all lung cancers are carcinomas), is a malignant lung tumor characterized by uncontrolled cell growth in tissue (biology), tissues of the lung. Lung carcinomas derive from tran ...

, and it may be associated with cancer at some extra-

thoracic The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the crea ...

sites".

Agency for Toxic Substances and Disease Registry The Agency for Toxic Substances and Disease Registry (ATSDR) is a federal public health agency within the United States Department of Health and Human Services. The agency focuses on minimizing human health risks associated with exposure to haz ...

(ATDSR), U.S. Department of Health and Human Services (2007).
Asbestos Toxicity
." ''Case Studies in Environmental Medicine.'' In other scientific publications, epidemiologists have published peer reviewed scientific papers establishing that chrysotile is the main cause of pleural mesothelioma. 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 listed, exports of chrysotile would only be permitted to countries that explicitly consent to imports.

, a major producer of the mineral, has been harshly criticized by the

Canadian Medical Association The Canadian Medical Association (CMA; french: Association médicale canadienne, AMC) is a national, voluntary association of physicians and medical learners that advocates on national health matters. Its primary mandate is to drive positive ch ...

for its opposition to including chrysotile in the Convention. According to EU Regulation 1907/2006 ( REACH) the marketing and use of chrysotile, and of products containing chrysotile, are prohibited.

Critics of safety regulations

1990s: Canada-European dispute GATT dispute

In May 1998, Canada requested consultations before the

WTO The World Trade Organization (WTO) is an intergovernmental organization that regulates and facilitates international trade. With effective cooperation in the United Nations System, governments use the organization to establish, revise, and e ...

and the

European Commission The European Commission (EC) is the executive of the European Union (EU). It operates as a cabinet government, with 27 members of the Commission (informally known as "Commissioners") headed by a President. It includes an administrative body o ...

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 The General Agreement on Tariffs and Trade (GATT) is a legal agreement between many countries, whose overall purpose was to promote international trade by reducing or eliminating trade barriers such as tariffs or quotas. According to its prea ...

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.EC measures affecting asbestos products
World Trade Organization News. 29 October 1998

2000s: Canadian exports face mounting global criticism

In the late 1990s and early 2000s, the

Government of Canada The government of Canada (french: gouvernement du Canada) is the body responsible for the federal administration of Canada. A constitutional monarchy, the Crown is the corporation sole, assuming distinct roles: the executive, as the ''Crown ...

continued to claim that chrysotile was much less dangerous than other types of asbestos. Chrysotile continued to be used in new construction across Canada, in ways that are very similar to those for which chrysotile was exported. 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". 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. However, under increasing criticism by environmental groups, in May, 2012, the Canadian government stopped funding the Chrysotile Institute. As a result, the Chrysotile Institute has now closed. 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 The Rotterdam Convention (formally, the Rotterdam Convention on the Prior Informed Consent Procedure for Certain Hazardous Chemicals and Pesticides in International Trade) is a multilateral treaty to promote shared responsibilities in relation ...

hearings regarding chrysotile. The

CFMEU The Construction, Forestry, Maritime, Mining and Energy Union (CFMMEU, though most commonly still referred to as CFMEU) is Australia's main trade union in construction, forestry, maritime, mining, energy, textile, clothing and footwear producti ...

pointed out that most exports go to developing countries. Canada has pressured countries, including

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

, and other UN member states to avoid chrysotile bans. In September 2012, governments in Quebec and Canada ended official support for Canada's last asbestos mine in Asbestos, Quebec.

References

External links

The Chrysotile Institute
*
"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'', , 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. {{Phyllosilicates Serpentine group Magnesium minerals Luminescent minerals Asbestos IARC Group 1 carcinogens Monoclinic minerals Minerals in space group 12 Orthorhombic minerals Minerals in space group 36