Occurrence and Extraction

98% of the worldwide production of asbestos (3.110 t/a in 1993, see Table 5.2-4) is chry.sotile. The most important deposits are in Canada and the former States of the USSR with the largest amphibole asbestos deposit being in South Africa. The worldwide reserves have been estimated to be 100 to 150 lO t/a and should at current consumption levels (2 I O t/a in 1997) last for 50 to 75 years. The asbestos content of the stone from economically workable deposits is ca. 4 to 10% (Quebec, Urals), the minimum level for economic workability being ca. 3%. 

The wet process enables a narrower fiber length distribution to be obtained for amphibole asbestos. In this process the asbestos fibers are separated from the rock in the crushed mixture by using a hydrocyclone and the longer and shorter fibers separated with a rotary sieve. 

The classification of asbestos fibers is carried out on the basis of type and deposits, important classification criteria are also, however, fiber length, degree of decomposition and fiber texture. This leads to a grouping according to industrial application (Table 5.2-, i). 

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