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Asbestos (a misapplication of Latin: asbestos "quicklime" from Greek; a, "not"
and sbestos, "extinguishable") describes any of a group of minerals that can be
fibrous, many of which are metamorphic and are hydrous magnesium silicates.
These minerals, together with their occurrences, uses, and associated hazards,
have been discussed in detail by Guthrie and Mossman (1993).
The name is derived for its historical use in lamp wicks; the resistance of
asbestos to fire has long been exploited for a variety of purposes. Asbestos
was used in fabrics such as Egyptian burial cloths and Charlemagne's tablecloth
(which according to legend, he threw in a fire to clean). Asbestos occurs
naturally in many forms (see below); it is mined from metamorphic rocks.
When asbestos is used for its resistance to fire or heat, the fibers are often
mixed with cement or woven into fabric or mats. Asbestos is used in brake shoes
and gaskets for its heat resistance, and in the past was used on electric oven
and hotplate wiring for its electrical insulation at elevated temperature, and
in buildings for its flame-retardant and insulating properties, tensile
strength, flexibility, and resistance to chemicals. The inhalation of some
kinds of asbestos fibers, however, can cause a number of serious illnesses,
including cancer. Many uses of asbestos are banned in many countries.
"White" asbestos
Chrysotile, CAS No. 12001-29-5, is obtained from serpentine rocks. Chrysotile is
the type most often used industrially. It is more flexible than other types of
asbestos; it can be spun and woven into fabric. This is the kind of asbestos of
which theatre curtains are made, as well as firefifgters' suits, and possibly
Charlemagne's tablecloth. There is evidence that this type of asbestos is
harmful, although not perhaps as harmful as other forms(refer to UK Health
& Safety Commission report Asbestos: Effects on health of exposure to
asbestos, 1985). One formula given for Chrysotile is Mg3(Si2O5)(OH)4.
"Brown" asbestos
Amosite, CAS No. 12172-73-5, is a trade name for the amphiboles belonging to
the Cummingtonite - Grunerite solid solution series, commonly from Africa,
named as an acronym from Asbestos Mines of South Africa. One formula given for
Amosite is Fe7Si8O22(OH)2. This type of asbestos is highly biohazardous.
"Blue" asbestos
Riebeckite, CAS No. 12001-28-4, also known under the variety name of
Crocidolite, is an amphibole from Africa and Australia. It is the fibrous form
of the amphibole riebeckite. Blue asbestos is commonly thought of as the most
dangerous type of asbestos (see above and below). One formula given for
Crocidolite is Na2Fe2+3Fe3+2Si8O22(OH)2. This type of asbestos is highly
biohazardous.
Notes: chrysotile commonly occurs as soft friable fibers. Asbestiform amphibole
may also occur as soft friable fibers but some varieties such as amosite are
commonly straighter. All forms of asbestos are fibrillar in that they are
composed of fibers with widths less than 1 micrometer that occur in bundles and
have very long lengths. Amphiboles most commonly occur in nature in a safer
nonfibrous form. Asbestos with particularly fine fibers is also referred to as
"amianthus".
Other asbestos
Other regulated asbestos minerals, such as tremolite asbestos, CAS No.
77536-68-6, Ca2Mg5Si8O22(OH)2; actinolite asbestos (or smaragdite), CAS No.
77536-66-4, Ca2(Mg, Fe)5Si8O22(OH)2; and anthophyllite asbestos, CAS No.
77536-67-5, (Mg, Fe)7Si8O22(OH)2; are less commonly used industrially but can
still be found in a variety of construction materials and insulation materials
and have been reported in the past to occur in a few consumer products. Other
natural and not currently regulated asbestos minerals, such as richterite,
Na(CaNa)(Mg,Fe++)5[Si8O22](OH)2, and winchite, [
](CaNa)Mg4(Al,Fe3+)Si8O22(OH)2, may be found as a contaminate in products such
as the vermiculite containing Zonolite insulation manufactured by W.R. Grace
and Company. These forms of asbestos are no less harmful than chrysotile,
amosite, or crocidolite.
Source: http://en.wikipedia.org/wiki