Chrysotile composition

TM Tubular morphology, not sufficiently characteristic for classification as chrysotile CM Characteristic chrysotile rmrphology CD Chrysotile SAED pattern CQ Chrysotile composition by quantitative EDXS CMQ Chrysotile morphology and composition by quantitative EDXS... 

The extent of substitution of magnesium and siUcon by other cations in the chrysotile stmcture is limited by the stmctural strain that would result from replacement with ions having inappropriate radii. In the octahedral layer (bmcite), magnesium can be substituted by several divalent ions, Fe ", Mn, or Ni ". In the tetrahedral layer, siUcon may be replaced by Fe " or Al ", leaving an anionic vacancy. Most of the other elements which are found in vein fiber samples, or in industrial asbestos fibers, are associated with interstitial mineral phases. Typical compositions of bulk chrysotile fibers from different locations are given in Table 3. 

Nanostructured materials are nothing new. Chrysotile fibers are an example (Fig. 16.22), as are bones, teeth and shells. The latter are composite materials made up of proteins and embedded hard, nanocrystalline, inorganic substances like apatite. Just as with the imitated artificial composite materials, the mechanical strength is accomplished by the combination of the components. 

Antigorite is another serpentine mineral. It is similar in composition to chrysotile except that small amounts of Fe substitute for some of the Mg" in its structure (see Table 2.2). This subtle difference in composition produces a limited sheet structure with corregated stacking of the octahedral-tetra-... 

MMMF are synthetics that have crystalline rather than amorphous structures. Not surprizingly, early examples are reminiscent of the naturally occurring fibers synthetic chrysotile (lander and Wuhrer, 1938) and needles of amphibolelike composition and crystal structure (Shell et al., 1958). However, the bulk of the crystalline synthetic fibers, both in use and under investigation, do not have mineral equivalents therefore, we chose to use the term whiskers to distinguish crystalline man-made inorganic fibers from their natural relatives. 

Synthetics and mineral fibers have other parallels. A few synthesized fibers show a higher level or secondary ordering of the crystalline structure, such as that described for chrysotile. Composed entirely of carbon, graphite fibers are synthetic fibers with such a secondary structure (see the following section). Tubular fibers of other compositions, such as aluminum silicate polymers, have also been synthesized (Farmer et al., 1977). 

Type I (OT) silicates include kaolinite, Al2Si205(0H)4 (Section 10.3.21) and dickite with the same composition. These are true clay minerals. Clay minerals are layer silicates with a grain size < 2 pm. The serpentines also are Type I minerals, include antigorite, Mg3Si2Os(OH)4 (Section 10.3.20) and chrysotiles with the same composition. Chrysotiles include clinochrysotile and orthochrysotile. 

By the formation of an infinite series of tetrahedra connected by common corners, silicates of the (stoichiometric) composition A2Si03 are produced. Examples of these structures are to be found in the fibrous silicates, such as asbestos (chrysotile) and diopside, CaMg(Si03)2. By the coupling of two parallel... 

Keane MJ, Stephens JW, Zhong B-Z, et al. 1999. A study of the effect of chrysotile fiber surface composition on genotoxicity in vitro. J Toxicol Environ Health A 57 529-541. 

Asbestos— A general term applied to certain polysilicate fibrous minerals displa5dng similar physical characteristics although differing in composition. The most common asbestos mineral (over 95% of U.S. production) is chrysotile, a variety of serpentine, a metamorphic mineral. 

The different chemical composition and structures of chrysotile and amphibole asbestos have a considerable influence on their physical properties. 

The macroscopic individual fibers of chrysotile asbestos consist of more or less parallelly oriented fibrils, which have a diameter of 15 to 40 nm and according to electron microscopic investigations are composed of carpet roll-like hollow fibers. The wall partitions of these small rolls consist of double layers of the composition Mg3(OH)4Si205, in which one brucite Mg(OH)2- and one Si205- layer are condensed with one another. These crystal lattices not fitting precisely with one another leads to curvature and hence a hollow fiber. Chrysotile asbestos is, as a result, easily fragmented into very fine fibers, which are soft and flexible and hence, of all the asbestos types, they lend themselves most easily to spinning. Industrially, however, chrysotile is always present as fiber bundles. 

Muscovite and biotite have very similar compositions. Why is one "white mica" and the other "black mica" In the same vein, talc is white, chrysotile is while asbestos, crocidolite is blue asbestos and amosilc is a gray-bruwm asbestos. 

Layers of type (c) only. The pure Mg layer occurs in chrysotile, (0H)4Mg3Si20s, in which the structural unit is a kaolin-like layer of this composition, instead of (0H)4Al2Si205 as in Fig. 23.16. Since the dimensions of the brucite (Mg(OH)2) part of the composite layer do not exactly match those of the Si205 sheet, the layer curls up, the larger (brucite) portion being on the outside. The fibres are built of curled ribbons forming cylinders several thousand A long with a dozen or so layers in their walls and overall diameters of several hundred the detailed structures of chrysotiles are still not known, nor is the... 

Clnysotile belongs to the serpentine group of minerals, v arieties of which are found in most of the important mountain ranges and precambrian shields (8). Only a small part of these serpentine occurrences are in the asbestiform clnysotile variety. Chrysotile fibers are found as veins in serpentines or related minerals in serpentinized ultramafic rocks and in serpentinized dolomitic marbles (9). It has been suggested that the ultrabasic rocks (forsterite, Mg-rich pyroxenes, and ampliiboles) are first attacked in an hydrothermal process and transformed in serpentines in a later hydrothermal event, the serpentines are partially redissolved and crystallized as chrysotile fibers (9). (Heady, the genesis of each chrysotile deposit must have involved specific features related to the composition of the precursor minerals, the stress and defomiations in the host matrix, the water content, the temperature cycles, etc. Nonetheless, it is generally observed that the chemical composition of the fibrous phase is closely related to that of the surrounding rock matrix (9). 

Chrysotile is a hydrated magnesium silicate and its stoichiometric chemical composition may be given as AIg3SyOs(OH)4 [12001 -29-5]. However, the geothermal processes which yield the chrysotile fiber formations usually involve the co-deposition of various other minerals. These mineral... 

---