Amphiboles and Chrysotile

Asbestos may also be released to indoor air from the use of asbestos-contaminated household water (Hardy et al. 1992 Webber et al. 1988). Limited studies indicate that both amphibole and chrysotile... 

Churg A, Wright JL. 1989. Fibre content of lung in amphibole- and chrysotile-induced mesothelioma Implications for environmental exposure. lARC Sci Pub 90 314-318. 

Both amphibole and chrysotile asbestos in air and water may be analyzed by TEM. Accnracies above 90% may be obtained on chrysotile fibers of >1 pm (Steel and Small... 

Judging by the differences in iron-contents of crocidolite and chrysotile. Hardy and Aust (1995) proposed that the high iron content of the amphibole asbestos fiber, crocidolite, was the cause of its much greater carcinogenicity than the chrysotile fiber, which, indeed, contains forty times less iron than crocidolite or amosite. However, the fibrous zeolite erionite, also contains much less iron (about 18 times less iron than the amphiboles, and is also much less tightly bound cf. van Oss et al.(1999). As the mechanisms of pulmonary carcinogenesis of amphibole asbestos needles and of erionite needles are remarkably similar, the differences in the iron contents of amphibole and chrysotile asbestos species appear to be irrelevant. 

Chrysotile is a noncombustible fibrous solid that has been widely used as a fireproof thermal insulator, for brake linings, in construction materials, and for filters under the name of asbestos. It decomposes with loss of water at 600-800 °C, eventually forming forsterite and silica at 810-820 °C. Because it is more resistant to attack by alkalis than are the amphibole asbestoses, chrysotile has been used in chloralkali cell membranes and in admixture with Portland cement for making sewer pipes (Chapter 11). 

Smith AH. 1998. Amphibole fibers, chrysotile fibers, and pleural mesothelioma [Letter]. Am J Ind Med 33 96. 

Chiysotile belongs to the serpentine group, all other asbestos listed are of amphibole type chrysotile, crocidolite, and amosite are of commercial use. 

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. 

In counting thin chrysotile fibers, the SEM method may produce lower results than the TEM technique, but for coarser amphibole fibers such an effect is not likely. A large number of amphibole and nearly all chrysotile fibers are undetectable using OM. Definitive identification of a chrysotile can only be made if a characteristic SAED pattern is recorded for a tubular morphology fiber and the EDX spectrum is quantitatively consistent. Not all these elements may be either necessary or desirable for any or all fibers in every sample. This means that the level to which each fiber has been identified needs to be recorded to... 

Carcinoma of the lung was correlated with a markedly elevated asbestos content of lung tissue (Roggli and Sanders 2000). Asbestos content was recorded as total asbestos fibres, commercial am-phibole fibres, noncommercial amphibole fibres, and chrysotile fibres 5 gm or greater in length per gram of wet lung tissue. 

Talc is in the same acceptance class as saccharin. It is another case of familiarity breeding acceptance. Talcum has never caused me a problem, why should it cause me a problem now It has been claimed for many years that some talcum powders contain several percent amphibole asbestos. This is strange because, as noted above, the chemical formulas of talc and chrysotile are very similar. Neither talc nor chrysotile are amphiboles. It would be expected that if talc were to contain a fibrous component it would be one of similar composition, but this is not the case. The structure of chrysotile is almost unbelievable and perhaps talc does not provide a proper environment for this crystal growth. 

When the contents of these Gooch crucibles were vacuum dry, the crucibles were again heated to constant weight. An analysis was the difference in weight of a crucible before and after the precipitate was filtered and heated. Chrysotile would never have withstood treatments that crocidolite endured. This is partly because crocidolite contains double chains of an amphibole, while chrysotile does not, a major difference in these asbestoses, and few other substances other than crocidolite could have been substituted in this application. 

Whereas fibers of chrysotile resemble rolls of newspapers when viewed as a cross section of fibers, crocidolite is an amphibole and its fibers are laves with a trapezoidal cross section. As mentioned, this behavior is related to the cross-linked double chains of silicate from which these fibers are formed. Like [NaCa(P03)3]n which is grown as single crystals and must be milled to be converted to fibers, crocidolite is not a natural fiber as it is mined. It must be milled before it is cleaved to fibers. Unmilled crocidolite mineral is a beautiful stone known as either Cat s eye or Tiger s eye. It is also known as Riebeckite Asbestos. ... 

Termolite is also an amphibole and its structure is more acicular, tubular, or lamellar. Its crystals are reported to be monoclinic. Termolite is probably the most used fibrous amphibole asbestos -type fiber, but crocidolite has been equally popular. Both fibers have been little more than specialty items in the United States with chrysotile fortunately being the primary fiber of choice. 

Chrysotile fibers have a much faster clearance than amphiboles, and evaluation of exposures to this variety of asbestos (De Vuyst 1994) by analysing lung tissue (De Vuyst et al. 1998 Rees et al. 2001), BALF or sputum (Paris et al. 2002) samples is difficult. 

Figure 9.3 The crystalline structure of the two major forms of asbestos (after Hodgson [2]). (a)Amphibole and (b) chrysotile.

The two main amphibole asbestos fibers are amosite and crocidoHte, and both are hydrated siHcates of iron, magnesium, and sodium. The appearance of these fibers and of the corresponding nonfibrous amphiboles is shown in Figure 1. Although the macroscopic visual aspect of clusters of various types of asbestos fibers is similar, significant differences between chrysotile and amphiboles appear at the microscopic level. Under the electron microscope, chrysotile fibers are seen as clusters of fibrils, often entangled, suggesting loosely bonded, flexible fibrils (Fig. 2a). Amphibole fibers, on the other hand, usually appear as individual needles with a crystalline aspect (Fig. 2b). 

In contrast to chrysotile fibers, the atomic crystal stmcture of amphiboles does not inherentiy lead to fiber formation. The formation of asbestiform amphiboles must result from multiple nucleation and specific growth conditions. Also, whereas the difference between asbestiform and massive amphibole minerals is obvious on the macroscopic scale, the crystalline stmctures of the two varieties do not exhibit substantial differences. Nonfibrous amphiboles also exhibit preferential cleavage directions, yielding fiber-shaped fragments. 

The morphological variance appears more important with chrysotile than with amphiboles. The intrinsic stmcture of chrysotile, its higher flexibiUty, and interfibnl adhesion (10) allow a variety of intermediate shapes when fiber aggregates are subjected to mechanical shear. Amphibole fibers are generally more britde and accommodate less morphological deformation during mechanical treatment. 

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