Micas chemistry

EFFECTS OF PETROLOGIC FACTORS ON WHITE MICA CHEMISTRY... 

Earlier, clay mineralogists anticipated that mica chemistry could be estimated rapidly in some detail from a simple X-ray measurement of the b dimension. It is now appreciated that there are too many independent variables involved to allow this to be successful. An alternative approach, which has proved useful, however, is to attempt to estimate (for example) the octahedral Mg and Fe content of biotites from the relative intensities of a few X-ray reflections. Early studies of this problem were made by Brown [1955] and Gower [1957], and a more recent study based on new structural information is that of Franzini and Schiaffino [1965]. They have claimed that, using the relative intensities of the 004, 005, and 006 reflections only, the octahedral Mg and Fe may be estimated, with an error for the six octahedral sites of not more than 0.5 atoms. Their technique seems quite satisfactory, provided their recommended precautions in measuring relative intensities are observed. 

In 1963, Armin Weiss (then at the University of Heidelberg, Germany) reported the intercalation of amino acids and proteins in mica sheet silicates (Weiss, 1963). Some years later, U. Hoffmann, also from Heidelberg, published an article titled Die Chemie der Tonmineralien (The Chemistry of Clay Minerals), in which he mentioned possible catalytic activity of clays in processes which could have led to the emergence of life (Hoffmann, 1968). 

Table 5.53 lists the general classification of micas with their main compositional terms. Stoichiometry obeys the general formula XF2 3Z40io(OH,F)2, where X = interlayer cations, Y = octahedrally coordinated cations of the 2 1 mixed layer, and Z = tetrahedrally coordinated cations of the 2 1 mixed layer. It must be noted that several compositional terms are indeed solid mixtures of more elementary components. In particular, glauconite has a complex chemistry and an Al Si diadochy of 0.33 3.67. (R and R terms in table 5.53 identify generic divalent and trivalent cations, respectively.)... 

The intrinsic stability of micas as a function of P and T intensive variables and chemistry is essentially related to the capabihty of the tetrahedral and octahedral... 

Bailey S. W. (1984b). Crystal chemistry of true micas. In Reviews in Mineralogy, vol. 13, P. H. 

When three of the oxygens in the tetrahedra are shared (Si O ratio = 2 5), the complex ions that form take on a sheetlike configuration. The sheets can be stacked, and the associated cations are found between the sheets. Micas and clays are sheet-structure minerals with distinctive habits and physical properties, that reflect the planar silicate sheet structure (Fig. 2.1G). These normally platey minerals may also occur with fibrous-growth habits. The special crystal chemistry that produces such a distinctive habit is discussed later. 

Fig. 2.12E. From Bailey, S. W. (1984). Crystal Chemistry of the True Micas. Figs. 3 and 4, p. 15. In Micas, S. W. Bailey, ed. Reviews in Mineralogy 13, Min. Soc. America, Washington, D.C. With permission of Min. Soc. America and the author.

If then illite, or a potassic, mica-like mineral, is present in most of the geologic environments, the variations of its structure and chemistry must be examined with care in order to establish its chemical stability relative to the system in which it is found. 

Flotation - [AMINES - FATTY AMINES] (Vol 2) - [FLOTATION] (Vol 11) - [FOAMS] (Vol 11) - [METALLURGY-SURVEY] (Vol 16) -dye water effluent treatment [DYES, ENVIRONMENTAL CHEMISTRY] (Vol 8) -isopropyl xanthates for [PROPYL ALCOHOLS - ISOPROPYL ALCOHOL] (Vol 20) -of lead ore [LEAD] (Vol 15) -formica [MICA] (Vol 16) -m paper recycling [RECYCLING - PAPER] (Vol 21) -ofpotassium chlonde [POTASSIUM COMPOUNDS] (Vol 19) -silicates for [SILICON COMPOUNDS - SYNTHETIC INORGANIC SILICATES] (Vol 22) -use of copper composition [COPPER COMPOUNDS] (Vol 7) -usmgSCFs [SUPERCRITICAL FLUIDS] (Vol 23)... 

Aluminum occurs widely in nature in silicates such as micas and feldspars, complexed with sodium and fluorine as cryolite, and in bauxite rock, which is composed of hydrous aluminum oxides, aluminum hydroxides, and impurities such as free silica (Cotton and Wilkinson 1988). Because of its reactivity, aluminum is not found as a free metal in nature (Bodek et al. 1988). Aluminum exhibits only one oxidation state (+3) in its compounds and its behavior in the environment is strongly influenced by its coordination chemistry. Aluminum partitions between solid and liquid phases by reacting and complexing with water molecules and anions such as chloride, fluoride, sulfate, nitrate, phosphate, and negatively charged functional groups on humic materials and clay. 

It is clear that the Wacker cycle in a CuPdY zeolite incorporates the traditional features of the homogeneous catalysis combined with typical effects of a zeolite (303, 310). It also follows that whereas other cation exchangers in principle will show Wacker activity after cation exchange with Cu/Pd ions, the cage and pore architecture will probably be less suitable for Wacker chemistry than those of the faujasite structure. This is the case for fluoro-tetrasilicic mica, a synthetic layer silicate that swells under reaction conditions and allows access to the interlayer space (311). 

N. Farrell, Y. Qu, U. Bierbach, M. Valsecchi, E. Menta, in Cisplatin. Chemistry and Biochemistry of a Leading Anticancer Drug , Ed. B. Lippert, Verlag Helvetica Chi-mica Acta, Zurich, 1999, p. 479. 

Recognizing the applicability of XRD to occupational health chemistry, Lennox and Leroux (1) suggested a number of chemical species which would be suitable for XRD analysis arsenic trioxide, beryllium oxide, mica, vanadium oxides, calcium fluoride in ceramic materials, as well as a number of organics such as DDT, lindane and chlordane. Unfortunately, the general application of XRD to the quantitation of industrial hygiene samples has not been realized and the majority of these analyses are restricted to free silica and to a lesser extent asbestos and talc. 

Table 1. Structure and chemistry of Mica-type layered silicates...

Aluminosilicates form an extensive family of compounds that include layered compounds (such as clays, talc, and micas), 3-D compounds, (e.g. feldspars, such as granite), and microporous solids known as molecular sieves. The structural diversity of these materials is contributed to by aluminum s ability to occupy both tetrahedral and octahedral holes as it also does in y-Al203. Thus, aluminum substitution for silicon in silicate minerals may lead to replacement of silicon in tetrahedral sites or the aluminum can occupy an octahedral environment external to the silicate lattice. Replacement of Si with Al requires the presence of an additional cation such as H+, Na+, or 0.5 Ca + to balance the charge. These additional cations have a profound effect on the properties of the aluminosilicates. This accounts for the many types of layered and 3-D structures (see Silicon Inorganic Chemistry). 

Aluminum is a constituent of many minerals, including clay (ka-olinite), mica, feldspar, sillimanite, and the zeolites. Some of these minerals are discussed under the chemistry of silicon, in Chapter 31. Aluminum oxide (alumina), occurs in nature as the mineral corundum. Corundum is the hardest of aU naturally occurring substances except diamond it scratches all other minerals, but is itself scratched by diamond, and also by the artificial substances boron carbide, and silicon carbide, SiC. Corundum and impure corundum (emery) are used as abrasives. 

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