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This article describes the principal types of asbestos and explains the differences among Amphibole, Chrysotile, Crocidolite, Amosite, Anthophyllite & Tremolite Asbestos.
This article series describes the physical properties of asbestos including its mechanical, chemical, electrical and related properties both in pure asbestos form and when asbestos is mixed with other materials like cement or rubber. As the author points out, while this is a lenghty article, there is far more detailed information about asbestos properties, chemistry, etc. Page top photo: crocidolite asbestos in the laboratory - ©D Friedman.
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Types of Asbestos: properties of Amphibole, Chrysotile, Crocidolite, Amosite, Anthophyllite & Tremolite Asbestos
Properties of Amphibole Group Asbestos
A review will also be made of the amphibole group of minerals which is generally identified by the formula 2CaO.5MgO.8SiO2H20. The actual composition of the amphibole fibers varies greatly, particularly in comparison to chrysotile.
[Click to enlarge any image]
The variation in composition results in a physical property change of the fibers. This variation requires more rigid controls for obtaining and identifying shipments of amphibole fibers.
Properties of Chrysotile Asbestsos
Chrysotile asbestos in rock form is usually found in soft shades of green; these shades range from a very pale green to a dark green. The Arizona asbestos is often pale yellow.
However, despite its original color, it in- variably becomes white or grayish white when it is opened or fiberized. Its commercial usefulness depends not so much on its chemical composition but on its physical properties.
For textile products, chrysotile asbestos is the most important type of asbestos used because it has the best combination of strength and flexibility. Its resistance to alkalies is very good. However, its resistance to acids is lower than that of other varieties. its specific heat is 0.266 Btu per lb per °F.
From the point of view of structure, chrysotile asbestos is considered a silicate with a sheet structure; this factor makes it the magnesium analog of the kaolin group. In most of its occurrences, chryso'tile which has serpentine or olivine - as its source rock, shows either none or very little ' lime. Its chemical composition is Mg6(0H)6(S4011)H20 or 3MgO-2SiO2-2H20. Chemical composition of fibers can vary from mine to mine, but this variation is not great when compared to the other asbestos fibers.
Although the fibrous structure of many chrysotile fibers is similar, there is often a difference in the operation of separating the individual fibers. Techniques and experience are required both at the mining site and in the manufacturing process in order to obtain good quality and fibrous structures.
Crocidolite Asbestos Properties
When found in nature, the color varies from lavender blue to dark blue. Sometimes red and yellow streaks exist. When the fiber is opened, the dolor of the fiberized structure is lighter in shade than in its original form. The blue color is the result of the high soda content or the iron compounds associated with the rock formation.
Its general chemical formula is 3Na 2 O6FeO2Fe 2 O 3 16- Si0 2 11 2 0. Variation in the composition occurs where sodium may be replaced by potash, ferric or ferrous iron by magnesium or manganese and ferrous iron by aluminum.
The blue asbestos occurs only in very few localities and is mined only in large quantities in South Africa. Its predominate properties include high tensile strength, acid resistance, harshness and resistance to effects of outdoor exposure.
Amosite Asbestos Properties
Crocidolite as well as amosite occurs in metamorphosed siliceous-ferruginous sediments. The fibers are generally several inches long; however, the length is usually of no advantage inasmuch as its greatest use involves the manufacture of asbestos-cement products where fibers , of % in. or shorter are used. The more important features of amosite are its heat and acid resistant properties. In the rock form, it is gray to gray-green but when it is opened, it gives the appearance of a cloudy gray.
It may contain as much as 40 per cent iron oxide; sometimes, it is compared to anthophyllite. Unlike the true anthophyllites, amosite has long fibers and it is not as brittle.
Anthophyllite Asbestos Properties
Anthophyllite has a very limited use because of its weak fiber structure despite its resistance to high temperatures and chemicals.
Its low ignition loss is comparable to that of tremolite.
It is never known to occur with fibers that are sufficiently flexible to be spun.
Tremolite Asbestos Properties
Tremolite asbestos (shown at above left under the microscope, and at above right as fire insulation on the basement ceiling of a commercial building in White Plains, NY) generally has weak and brittle fibers; its color ranges from gray to white.
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Web search 01/20/2011, original source: http://epa.gov/asbestos/pubs/verm_questions.html
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