Asbestos is a group of six minerals that are classified as silicate minerals, composed of fibers that are formally referred to as thin fibrous crystals. In fact asbestos fibers are in most cases somewhat flexible, very durable and have very high levels of resistance to fire. The earliest industrial uses of asbestos were in the form of textiles woven from asbestos fibers that were used as fire curtains in theaters or for fire resistant clothing for steel and refractory workers.
By far the most common form of asbestos found naturally and used industrially is chrysotile asbestos, also known as white asbestos. This form of the mineral differs from the other five defined types of asbestos in that its fibers are serpentine, or curly in nature. The remaining types of asbestos are all composed of straight, thin, needle-like fibers that are not as flexible as those found in chrysotile. Ninety to ninety five percent of all asbestos used for the manufacture of products in the United States has been chrysotile.
Chrysotile fibers are typically the form of asbestos used as a cement additive, as a binding material in sealants of various types, and in the many types of linoleum and floor tiles developed during the Twentieth Century. Congoleum products all used chrysolite asbestos as an additive; it was also the standard form of asbestos used in gasket materials for cars and for pumps. Chrysotile asbestos is the principal component found in asbestos roofing materials that were used extensively as shingles and in several forms of home siding marketed after World War II and into the 1970s.
The term amphibole asbestos refers to the remaining five types of the mineral, differentiated from chrysotile which falls into the serpentine class. These other five types of asbestos that have been identified and mined commercially include amosite, a trade name name given to brown asbestos that is found in South African mines. Amosite is in fact an acronym for ‘asbestos mines of South Africa’. Blue asbestos bears the name crocidolite. It is found in mines in Africa and in Australia. Blue asbestos has been mined commercially and is still being produced in small amounts by African mines still in operation. Amosite is also still being produced in South Africa.
Tremolite asbestos is another amphibole form of the mineral that has been mined commercially to some extent and was a common addition to talcum powder when the use of asbestos in commercial products was legal. Tremolite is also the form of asbestos that contaminated the vermiculite mine in Libby Montana operated by W.R. Grace for several decades during the Twentieth Century. That mine has been an environmental disaster for residents of the area and workers who operated the facility.
Anthophyllite asbestos has a more brittle fiber than other forms of the mineral and is formed by the breakdown of talc, thus resulting in it being a common presence in talc that is mined for commercial purposes. It has not been commercially mined except in small, isolated instances. Actinolite asbestos, the fifth member of the amphibole class, is commonly found in a number of rock forms, including iron ore. It has not been mined commercially but nevertheless may be found as a contaminant in asbestos products or in products derived from other mined minerals.