Chrysotile crystal structure

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. 

In contrast to chrysotile fibers, the atomic crystal structure of amphiboles does not inherendy 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 structures of the two varieties do not exhibit substantial differences. Nonfibrous amphiboles also exhibit preferential cleavage directions, yielding fiber-shaped fragments. 

Plesiopjc seres. The crystal structures of the members of these series are based on modules which have common features but may contain additional peculiar details. The family of serpentine-like structures (lizardite, chrysotile, antigorite, carlosturanite) is an example reported by Makovicky (1997). The members of this plesiotypic series are based on variously curled, reversed and/or interrupted TO (serpentine) layers. 

The serpentine group of minerals, which include chrysotile asbestos, are almost identical in composition. The chemical composition of unit cell is Mg6(OH)8Si40io. Chrysotiles have layered or sheeted crystal structure containing a silica sheet of (Si20s) in which silica tetrahedra point one way (Streib 1978). A layer of brucite, Mg(OH)2, joins the silica tetrahedra on one side of the sheet structure. Two out of every three —OH are replaced by oxygen atoms. X-ray and electron microscope studies indicate... 

Mechanisms based on electron transfer and active oxygen species have been proposed to explain asbestos-induced toxicity and lung disease. Fisher et al. (1987) studied the effect of heat treatment on chrysotile asbestos toxicity. The in vitro study showed that heat treatment reduced cytotoxicity. Infra red spectra indicated a reduction of external hydroxyl group population, which repopulated after irradiation. There is, apparently, an electron transfer from the asbestos matrix to biological receptors. In an earlier study, Fisher and coworkers (1985) reported that irradiation of chrysotile samples heated to 400°C (752°F) restored the biological activity to near-control values. X-ray diffraction pattern showed no change in the crystal structure. Brucite, present as a surface contaminant, was removed by heating. 

Warren Bragg (1931) Warren, B.E. Bragg, W.L. The crystal structure of chrysotile H4Mg3Si209 Zeitschrift fuer Kristallographie, Kristallgeometrie, Kristallphysik,... 

Chrysotile, sometimes called white asbestos, with its unique fibrous form, is an expression of the subtle structural variations that can be found in crystalline solids. These characteristics illustrate the need to go beyond the simple, or standard, chemical and crystal analyses used for identification, to understand the distinctive qualities of fibrous inorganic materials. 

Two molecular types of silicates are referred to as asbestos. Chrysotile is a magnesium silicate built upon a layered structure of silicate rings and Mg(OH)2. The layered structure causes the sheets to roll into cylinders approximately 200A in diameter. Amphibole asbestos may contain a variety of cations but is built upon a double chain silicate structure. The chrysotile asbestos is always found as an asbestiform crystal while the amphiboles may be either acicular or asbestiform. 

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. 

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. 

Chry sotile is decomposed at temperatures below those generated on the surface of automobile and truck brakes. Hydrate water is lost at higher temperatures and chrysotile fibers turn to nonfibrous dust, another example where molecular structure dictates crystal morphology. When the shape molecules change, morphology converts from a fiber to a particulate dust with little or no fibrous nature. 

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. 

Falini, G., Foresti, E., Lesci, G. Roveri, N. (2002) Structural and morphological characterization of synthetic chrysotile single crystals. Chemical Communications, 1512-1513. 

The formation of chrysotile was never observed. However, evidence of Mg or Co talc could be detected with the characteristic line at 0.95 nm. in the absence of magnesium, a badly crystallized Co talc was obtained together with CuO. in the presence of Mg, the Mg talc structure seemed to be favoured but the degree of crystallization remained low. 

Consequently, the introduction of copper in the chrysotile stucture appears very difficult. This fact has already been pointed out by Wey et al. (ref. 16) and explained by a Jahn-Teller effect, which makes the structure distorted and creates an unstability for the whole crystal. 

The structure of chrysotile has been extensively investigated in recent years by Whittaker and ZussMAN [1956], Whittaker [1953, 1956a, 1956b, 1957), and Zussman et al. [1957]. Zvyagin [1967] reports many studies of single crystals of chrysotile. The most common form of the mineral was named clinochrysotile by Whittaker and Zussman. It has a two-layer structure with a = 5.34 A,b = 9.20 A, c = 14.65 A, jS = 93.16°. The a and b dimensions are slightly smaller than those of cronstedite because of the presence of smaller Mg " " and Al ions in octahedral positions. 

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