Asbestos

Asbestos (Greek a-, "not"; sbestos, "extinguishable") is a group of fibrous metamorphic mineralss. Asbestos was historically used for lamp wicks from which the name derives. It was also in fabrics such as Egyptian burial cloths and Charlemagne's tablecloth which legend says he threw in a fire to clean. The fibres are typically mixed with cement or woven into fabric or mats. It is used in buildings for its flame-retardant and insulating properties, its tensile strength, flexibility, and its resistance to chemicals, but is now known to be carcinogenic and is banned in many countries.

Types of asbestos

Chrysotile, or white asbestos, 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.
Amosite, or brown asbestos, is an amphibole from Africa.
Crocidolite, or blue asbestos, is an amphibole from Africa and Australia. It is the fibrous form of riebeckite.

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

The amphiboles, in their fibrous form, are friable and therefore the most carcinogenic, although they also exist in safer non-fibrous forms.

Other asbestos minerals, such as tremolite, actinolite and anthophyllite are not used industrially but occur in traces.

Asbestosis and Cancer

The fine asbestos fibres are easily inhaled, and can cause a number of respiratory complaints, including a potentially serious lung fibrosis asbestosis. Exposure to asbestos has also been determined to cause a very serious form of cancer, mesothelioma, that occurs in the chest and abdominal cavities. This aggressive disease is not properly referred to as a lung cancer, as the malignant cells are derived from the mesothelium, a tissue found on the inner walls of the chest and abdominal cavities and on the outer surface of the lungs rather than in the lung itself.

In the United States, asbestos was one of the first hazardous air pollutants regulated under Section 112 of the Clean Air Act of 1970.