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.
Types of asbestos and associated fibres
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.
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.
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 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.