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Wednesday, November 3, 2010
Asbestos is the generic term for a group of naturally occurring, fibrous minerals with high tensile strength, flexibility, and resistance to heat, chemicals, and electricity. The three most common types of asbestos are: a) chrysotile, b) amosite and c) crocidolite. Chrysotile, also known as white asbestos and a member of the Serpentine mineral group is the commonest. Asbestos can only be identified under a microscope. Asbestos differs from other minerals in its crystal development. The crystal formation of asbestos is in the form of long thin fibers. Asbestos is divided into two mineral groups:Serpentine and Amphibole. The division between the two types of asbestos is based upon the crystalline structure. Serpentines have a sheet or layered structure where amphiboles have a chain-like structure. As the only member of the serpentine group, Chrysotile( A, B) is the most common type of asbestos found in buildings. Chrysotile makes up approximately 90%-95% of all asbestos contained in buildings in the United States.
Asbestos was a popular component in commercial products from the early 1900’s to the 1970’s and is found in building construction materials such as:
sprayed-on fireproofing
sprayed-on or textured ceiling material
pipe and boiler insulation
floor tiles and associated mastics
cement pipe and sheeting
roofing felts and shingles
ceiling tiles
drywall and joint compounds
acoustical products.
In the amphibole group, there are five types of asbestos. As an acronym for the Asbestos Mines of South Africa, Amosite is the second most prevalent type of asbestos found in building materials. Amosite is also known as "brown asbestos." Next, there is Crocidolite or "blue asbestos," which is an asbestos found in specialized high temperature applications. The other three types (Anthophyllite, Tremolite, and Actinolite) are rare and found mainly as contaminants in other minerals. Asbestos deposits can be found throughout the world and are still mined in Australia, Canada, South Africa, and the former Soviet Union.
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