Asbestos

Asbestos (Greek ????????: a-, "not"; sbestos, "extinguishable") describes any of a group of fibrous metamorphic minerals of the hydrous magnesium silicate variety. 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. It 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 deposits.

Types of asbestos

• Chrysotile, or white asbestos, CAS No. 12001-29-5, is obtained from Canadian serpentine rocks. It is less friable (and therefore less likely to be inhaled) than the other types and is the type most often used industrially. Chrysotile should not be confused with chrysolite, a synonym of olivine. There is some evidence that this form of asbestos is not actually harmful when inhaled. However it should be noted that there is also 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 Na₂Fe²⁺₃Fe³⁺₂Si₈O₂₂(OH)₂.
• Amosite, CAS No. 12172-73-5, also known as Grunerite or brown asbestos, is an amphibole from Africa, named as an acronym from Asbestos Mines of South Africa. One formula given for Amosite is Fe₇Si₈O₂₂(OH)₂.
• Crocidolite, or blue asbestos, CAS No. 12001-28-4, is an amphibole from Africa and Australia. It is the fibrous form of 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.

Notes: Serpentine rocks are those with curled fibres. Amphiboles have straight, needle-like fibres.

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The amphiboles, in their fibrous form, are friable and therefore the most carcinogenic, although they also exist in safer non-fibrous forms. Asbestos with particularly fine fibers is also referred to as "amianthus".

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Other asbestos minerals, such as tremolite, CAS No. 77536-68-6, Ca2Mg5Si8O22(OH)2; actinolite (or smaragdite), CAS No. 77536-66-4, Ca2(Mg, Fe)5Si8O22(OH)2; and anthophyllite, CAS No. 77536-67-5, (Mg, Fe)7Si8O22(OH)2; are less-used industrially but can still be found in a variety of construction materials and insulations and occur in a few consumer products, such as talcum powders and vermiculite. In the United States, the Environmental Protection Agency (EPA) has banned all construction-related products that have asbestos content of 1% or greater. It has also banned asbestos in all other friable (easily crushed by finger pressure) products.

Related Topics:
Tremolite - Actinolite - Anthophyllite - Environmental Protection Agency

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