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Asbestos - Classification And Properties

minerals chrysotile amphibole amosite

The various minerals that make up the asbestos group are so diverse that they share only one major property, their fibrous character. The form known for the longest time and most widely used is chrysotile, or white asbestos, a member of the serpentine asbestos family. Its fibers are long, hollow cylinders with a diameter of about 25 nanometers (10-9 meter). The fibers are strong and relatively inflexible. The chemical formula assigned to chrysotile is Mg3Si2O5(OH). Like other forms of asbestos, chrysotile is noncombustible. The whole class of minerals was, in fact, named after the Greek word asbeston, for noncombustible. The amphibole asbestos minerals are:

  • riebeckite (Na Fe2+3Fe3+2Si8O22(OH)2)
  • anthophyllite (Mg7Si8O22(OH))
  • actinolite (Ca2(Mg,Fe2+)5Si8O22(OH)2)
  • tremolite (Ca2Mg5Si8O(OH)2).

Riebeckite is also called crocidolite, or blue asbestos.

The asbestos amosite is sometimes included among the amphibole asbestos minerals and sometimes placed in its own group. Amosite (Fe 7Si8O22(OH)) is also called grenerite. It is typically ash-gray in color.

In general, amphibole minerals and amosite tend to have longer, more rigid fibers with a lower melting point than that of chrysotile. This fact makes them less desirable as fireproofing materials.

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