Isomorphous substitution pyrophyllite

Smectites, which are based on either the trioctahedral 2 1 (talc) or dioctahedral 2 1 (pyrophyllite) structure, differ from these neutral structures by the presence of isomorphous substitution in the octahedral or tetrahedral sheet. For example, the dioctahedral smectite, montmorillonite, has the general formula... 

Like the montmorillonites, the micas can be regarded as derived from talc or pyrophyllite by isomorphous substitution. Imagine that we start with pyrophyllite, i 2Si40io(OH)2, and replace one in four of the Si atoms by A1 this substitution would result in a charged lattice having the formula [Al2(Si8Al)Oio(OH)2] Note that the substituent A1 is written separately because it is in the silica, as distinct from the gibbsite layer. 

Al208(0H)2] asa pyrophyllite cluster model, A1 substituted HF/LANL2DZ, HF/ 6-31+G Geometry, isomorphous substitution effect of A1 by Mg and Fe 78... 

The least reactive type of surface site found on clay minerals is the neutral siloxane surface. Features associated with this type of site include no charge, no permanent dipole moment, and weak interactions with the hydrogen-bonded network of water molecules. Hydrophobic surfaces occur on 2 1 phyllosilicates, where there is no isomorphic substitution (e.g., talc and pyrophyllite), and also on the siloxane side of the kaolinite 1 1 TO unit. There is currently some question about the structural microscopic hydrophilicity of talclike surfaces (43) however, from a... 

Pyrophyllite, muscovite, margarite, beidellite, montmorillonite, illites MM lattice minimization (based on empirical potentials) Geometry, effect of isomorphic substitution 131... 

This particle is naturally occurring and found around the world. It is easily mined and purified. The reactor for the particle was a volcano. The ash from many volcanoes was spread around the earth during an intense period of activity many millions of years ago. This ash was transformed into clay (montmorillonoids or smectites) by natural processes, into uncharged species (talc and pyrophyllite) and charged species through isomorphic substitution of the crystal structure (hectorite, montmorillon-ite, saponite, suconite, volchonskoite, vermiculite, and nontronite). 

The minerals of the talc-pyrophyllite group have no isomorphous substitution giving rise to charge on the layer (minnesotaite is related to talc by substitution of Fe for Mg " ), and hence have a very low c.e.c. and do not swell in water or polar liquids. Pyrophyllite is monoclinic (Rayner and Brown [1966a]) with a basal spacing of 9.20 A (Heller et al. [1962]) and talc triclinic (Rayner and Brown [1966b]) with a basal spacing of 9.30 A (Brown [1961]). 

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