Chrysotile
Encyclopedia
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
(Si
O
)(OH
).
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.
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.
, 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, and may be spun into thread and woven into cloth. They are also resistant to heat and are excellent thermal, electrical and acoustic insulators.
of chrysotile is Mg
(Si
O
)(OH
), 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. A related, but much rarer, mineral is pecoraite, in which all the magnesium cations of chrysotile are substituted by nickel
cations.
Chrysotile is resistant to even strong bases (asbestos is thus stable in high pH pore water of Portland cement
), 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 forsterite
(magnesium silicate), silica and water.
The global mass balance reaction of the chrysotile dehydration can be written as follows:
The chrysotile (serpentine) dehydration reaction corresponds in fact to the reverse of the forsterite (Mg-olivine
) hydrolysis in the presence of dissolved silica (silicic acid
).
Chrysotile has been included with other forms of asbestos
, in being 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
. which states "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". 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. Canada
, a major producer of the mineral, has been harshly criticized by the Canadian Medical Association
for its opposition to including chrysotile in the Convention.
Asbestos
Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. They all have in common their eponymous, asbestiform habit: long, thin fibrous crystals...
, 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
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
is Mg
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
(Si
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
)(OH
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...
).
Polytypes
Three polytypes of chrysotile are known. These are very difficult to distinguish in hand specimens, and polarized light microscopyMicroscopy
Microscopy is the technical field of using microscopes to view samples and objects that cannot be seen with the unaided eye...
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
International Mineralogical Association
The International Mineralogical Association is an international group of 38 national societies. The goal is to promote the science of mineralogy and to standardize the nomenclature of the 4000 plus known mineral species...
prefer to treat it as a single mineral with a certain variation in its naturally-occurring forms.
| Name | Crystal system Crystal system In crystallography, the terms crystal system, crystal family, and lattice system each refer to one of several classes of space groups, lattices, point groups, or crystals... |
Type locality Type locality (geology) Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified.... |
mindat.org Mindat.org Mindat.org is a non-commercial online mineralogical database, claiming to be the largest mineral database and mineralogical reference website on the internet.... reference |
Unit cell parameters | Crystal structure reference |
|---|---|---|---|---|---|
| Clinochrysotile | monoclinic | Złoty Stok*, Lower Silesia Lower Silesia Lower Silesia ; is the northwestern part of the historical and geographical region of Silesia; Upper Silesia is to the southeast.Throughout its history Lower Silesia has been under the control of the medieval Kingdom of Poland, the Kingdom of Bohemia and the Austrian Habsburg Monarchy from 1526... , Poland Poland Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north... |
a = 5.3 Å; b = 9.19 Å; c = 14.63 Å; β = 93° | ||
| Orthochrysotile | orthorhombic | Kadapa* district Kadapa district YSR Kadapa District is one of the 23 districts of Andhra Pradesh, India. On 8 July 2010, the government of Andhra Pradesh renamed the district in honor of Y. S... , Andhra Pradesh Andhra Pradesh Andhra Pradesh , is one of the 28 states of India, situated on the southeastern coast of India. It is India's fourth largest state by area and fifth largest by population. Its capital and largest city by population is Hyderabad.The total GDP of Andhra Pradesh is $100 billion and is ranked third... , India India India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world... |
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 Mindat.org Mindat.org is a non-commercial online mineralogical database, claiming to be the largest mineral database and mineralogical reference website on the internet.... . *Złoty Stok and Kadapa have formerly been known as Reichenstein and Cuddapah respectively, and these names may appear in some publications. |
|||||
Clinochrysotile is the commonest of the three forms, found notably at Asbestos, Quebec
Asbestos, Quebec
-Communities:*Asbestos*Trois-Lacs-External links:***...
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
. Its two measurable refractive indices
Refractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....
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, 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, although industrially-processed chrysotile usually has shorter fibre bundles. The diameter of the fibre bundles is 0.1–1 µmMicrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is 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, 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 chemical formulaChemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
of chrysotile is Mg
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
(Si
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
)(OH
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...
), although some of the magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
ions may be replaced by iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
or other cations. Substitution of the hydroxide
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...
ions for fluoride
Fluoride
Fluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are...
, oxide
Oxide
An oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....
or chloride
Chloride
The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...
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
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
cations.
Chrysotile is resistant to even strong bases (asbestos is thus stable in high pH pore water of Portland cement
Cement
In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed...
), 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 forsterite
Forsterite
Forsterite is the magnesium rich end-member of the olivine solid solution series. Forsterite crystallizes in the orthorhombic system with cell parameters a 4.75 Å , b 10.20 Å and c 5.98 Å .Forsterite is associated with igneous and metamorphic rocks and has also been found in meteorites...
(magnesium silicate), silica and water.
The global mass balance reaction of the chrysotile dehydration can be written as follows:
- Chrysotile (serpentine) → Forsterite + silica + water
→ 
The chrysotile (serpentine) dehydration reaction corresponds in fact to the reverse of the forsterite (Mg-olivine
Olivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....
) hydrolysis in the presence of dissolved silica (silicic acid
Silicic acid
Silicic acid is a general name for a family of chemical compounds of the element silicon, hydrogen, and oxygen, with the general formula [SiOx4-2x]n...
).
Safety concerns
Asbestos
Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. They all have in common their eponymous, asbestiform habit: long, thin fibrous crystals...
, in being considered to be a human carcinogen
Carcinogen
A carcinogen is any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes...
by the International Agency for Research on Cancer
International Agency for Research on Cancer
The International Agency for Research on Cancer is an intergovernmental agency forming part of the World Health Organisation of the United Nations....
(IARC) and by the U.S. Department of Health and Human Services
United States Department of Health and Human Services
The United States Department of Health and Human Services is a Cabinet department of the United States government with the goal of protecting the health of all Americans and providing essential human services. Its motto is "Improving the health, safety, and well-being of America"...
. which states "Asbestos exposure is associated with parenchymal asbestosis
Asbestosis
Asbestosis is a chronic inflammatory and fibrotic medical condition affecting the parenchymal tissue of the lungs caused by the inhalation and retention of asbestos fibers...
, asbestos-related pleural
Pleural cavity
In human anatomy, the pleural cavity is the potential space between the two pleura of the lungs. The pleura is a serous membrane which folds back onto itself to form a two-layered, membrane structure. The thin space between the two pleural layers is known as the pleural cavity; it normally...
abnormalities, peritoneal mesothelioma
Peritoneal mesothelioma
Peritoneal mesothelioma is the name given to the cancer that attacks the lining of the abdomen. This type of cancer affects the lining that protects the contents of the abdomen and which also provides a lubricating fluid to enable the organs to move and work properly.The peritoneum is made of two...
, and lung cancer
Lung cancer
Lung cancer is a disease characterized by uncontrolled cell growth in tissues of the lung. If left untreated, this growth can spread beyond the lung in a process called metastasis into nearby tissue and, eventually, into other parts of the body. Most cancers that start in lung, known as primary...
, and it may be associated with cancer at some extra-thoracic
Chest
The chest is a part of the anatomy of humans and various other animals. It is sometimes referred to as the thorax or the bosom.-Chest anatomy - Humans and other hominids:...
sites". 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
Rotterdam Convention
The Rotterdam Convention on the Prior Informed Consent Procedure for Certain Hazardous Chemicals and Pesticides in International Trade, more commonly known simply as the ', is a multilateral treaty to promote shared responsibilities in relation to importation of hazardous chemicals...
, 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
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, a major producer of the mineral, has been harshly criticized by the Canadian Medical Association
Canadian Medical Association
The Canadian Medical Association , with more than 70,000 members, is the largest association of doctors in Canada and works to represent their interests nationally. It formed in 1867, three months after Confederation...
for its opposition to including chrysotile in the Convention.
External links
- The Chrysotile Institute
- Webmineral
- Mindat clinochrysotile
- Mindat orthochrysotile
- Mindat parachrysotile
- "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 mineralsAn Introduction to the Rock-Forming MineralsAn Introduction to the Rock-Forming Minerals, by W A Deer, R A Howie, and J Zussman, is a book often considered the "bible" of mineralogy. It covers hundreds of minerals, with details of their structure, chemistry, optical and physical properties, distinguishing features, and paragenesis...
, 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.