Micas formulas

Properties A vanadium-bearing species of mica. Formula variable with V203 up to 28%. Occurs as minute scales with micaceous cleavage, dark green to brown in color, pearly luster, Mohs hardness 2.5, d 3.0. 

Red clays used for the manufacture of terra cotta products are actually natural mixtures with a complex composition. They generally contain kaolinite, illite and/or other clays rich in alkaline, sand, mica (formula Si3Al3Oi0(OH)2), goethite (FeO(OH)) and/or hematite (Fe203), organic matter and, very often, calcium compounds. The latter, just like the micas and the other alkaline-rich compounds, help lower the firing temperature of the shard. 

The structure leads to a general formula for the micas namely, KXMY.1Oio(OH,r )2, with 2 < < 3, in which X represents cations of coordination number 6 (Al+3, Mg+, Fe++, Fe+3, Mn++, Mn+3, Ti+ Li+, etc.) and Y cations of coordination number 4 (Si+4, A1+3, etc.). The subscript n can have any value between 2 (hydrargillite layer) and 3 (complete octahedral layer). K+ can be partially replaced by Na+ and possibly to some extent by Ca++. This formula represents satisfactorily the.numerous recently published mica analyses almost without exception.6 The distribution of the various ions X and Y must be such as to give general agreement with the electrostatic valence rule. 

Mauguin showed that for various micas the unit of structure uniformly contains the number of atoms 0 + F given by the above formula. 

Silicates also exist in which each silicon atom bonds to one outer oxygen and to three inner oxygen atoms. The result is a linked network in which every silicon atom forms three Si—O—Si links, giving a planar, sheet-like structure. The empirical formula of this silicate is S12 O5. In many minerals, aluminum atoms replace some of the silicon atoms to give aluminosilicates. The micas—one has the chemical formula... 

Later in the simulations, the zeolite analcime (NaAlSi206 H20) begins to form, largely at the expense of micas, which serve as proxies for clay minerals. In the NaOH flood, the overall reaction (expressed per formula unit of analcime) is,... 

Muscovite or white mica has the formula KAl2(OH)2(AlSi3Oio). Since they are not... 

Similarly to Mn(IV)- and Fe(III)-oxides, some primary minerals were shown to promote polymerization of hydroquinone (19). Olivines, pyroxenes, and amphiboles accelerated the polymerization reaction to a greater extent than micas and feldspars. Microcline and quartz were ineffective- The effect was greatest for tephroite, a manganese-bearing silicate with the ideal chemical formula M SiO. Fayalite, the corresponding Fe(II) analog (Fe2Si0 ), was effective, but to a lesser extent. 

Micas are classified according to the charge of the mixed layer per formula unit. This depends on the diadochy level of AF (or Fe or, more rarely, Be ) with in tetrahedral groups, and on the charge (and occupancy) of the cation in the intermediate octahedral sheet. 

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.)... 

Table 5.55 Chemical analyses of natural micas (from Deer et al., 1983). Note that ionic fractions are retrieved on a 24-anion basis—i.e. double the canonical formula. (1) Muscovite from a low-grade metamorphic prasinite schist (2) glauconite from a sandstone (3) phlogopite from a marble (4) biotite from a quartz-bearing latite (5) lepidolite from a pegmatite. ...

The 2-3 subscript for the B site in the formula expresses the fact that there are two families of mica structures, the dioctahedral and trioctahedral micas, based on the composition and occupancy of the intralayer octahedral sites. The trioctahedral micas have three divalent ions—for example, Mg or a brucitelike [Mg(OH)2] intralayer, and the dioctahedral group—two tri-valent ions—for example, Al or a gibbsitelike [AlfOHfa] intralayer, between the tetrahedral sheets. In the dioctahedral micas, therefore, one-third of the octahedral sites are vacant or unoccupied (Fig. 2.12C). 

Fig. 2.13 The 1 1 and 2 1 layer arrangements in the sheet structure minerals and the (010) view of the structures of the serpentine, clay, talc, pyrophyllite, mica, and chlorite minerals. X = layer charge per formula unit. [From Bailey (1980), Fig 1.1, p. 3 Fig 1.2, p. 6.1...

The chlorites are a group of sheet silicate minerals similar to the micas and talc. The general formula, A5 6T40io(OH) j, is deceptively simple. The range of possible substitutions is enormous, for example, A = Mg, Al, Fe, ... 

It can be surmised that even though X-ray data indicated only expandable material, there must be significant interlayering with illite or other non-expandable mica-like phases such as glauconite-celadonite in order to give such a high structural charge imbalance. If not, one wonders why illites, with a similar chemical formula, are not expandable as well. 

There are several varieties of mica which contain this element lepidolite, one of the simplest, has the type-formula R3Al(SiC>3)3, and it contains from 4 to 6 per cent, of lithia. It occurs in scaly masses, the crystals are monoclinic red, violet, grey, yellow, or white in colour sp. gr., 2 8 hardness, 2 5. After calcination, it is decomposed by hydrochloric acid with the separation of gelatinous silica. A variety found in pegmatite veins (Wisconsin) is called irvingite another rather... 

B.D. Burlutskii, Ibid 1969, (67/24), pp 186-201 CA 73, 16940z(1970) (Industrial efficiency of the expl breakdown of mica-contg rocks in open pit mines of the Aldan mica combine was detd. A new formula for calcn... 

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