Tremolite, layered silicate

The Fibrous Minerals. The fibrous minerals contain very long silicate ions in the form of tetrahedra condensed into a chain, as shown in Figure 31-6. These crystals can be cleaved readily in directions parallel to the silicate chains, but not in the directions which cut the chains. Accordingly crystals of these minerals show the extraordinary property of being easily unravelled into fibers. The principal minerals of this sort, tremolite, C.a.jMg..Si 022(0H)2, and chrysotile, Mg6Si40u(0H)p/H20, are called asbestos. Deposits of these minerals are found, especially in South Africa, in layers several inches thick. These minerals are shredded into fibers, which are then spun or felted into asbestos yarn, fabric, and board for use for thermal insulation and as si heat-resistant structural material. 

The term asbestos is usually applied to a fibrous group of minerals that includes the amphiboles, such as tremolite, Ca2(OH)2Mg5(S 14011)2, with double-chain structures, and chrysotile, Mg3(0H)4Si205. In chrysotile, the dimensions of the silicate and magnesium layers are different, resulting in a curling that forms the characteristic cylindrical fibers. 

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