Interlayer Bonding in Kaolinite, Dickite and Nacrite

The orientation of the OH-vectors in hydroxyl groups of micas of different compositions, polytype modifications, and symmetry were calculated by the method of minimization of electrostatic energy. The orientations are strongly affected by the peculiarities of structures, and even slight deviations from the ideal dioctahedral periodicity can introduce a correction of as much as 10 ~ to the value of the polar angle. Ordering of cations in octahedra lead to twisting of the OH-bond towards the octahedron with lower charge and larger dimension. The latter is less true for cation ordering in tetrahedra. Because of these factors and the dependence of the hydrogen position on the coordinates of heavy atoms, such calculations can give reliable results only if the structure has been refined with high precision. Different polytypes of micas displayed the same orientation of the OH-vectors with respect to the axes of a separate layer, if the stacking sequence did not introduce specific distortions of the 2:1 layer.

Section: Influence Of Structural Distortions Of Polyhedramentioning

confidence: 72%

Factors Affecting Orientation of OH-Vectors in Micas

Bookin

1982

“…The symmetry of these polytypes depends on the relative orientation of neighboring layers. In turn, the orientation of the hydroxyl groups of octahedral sheets is determined by the layer stretching (Giese and Datta, 1973) as well as by the symmetry of the crystal field in which the Fe z+ is located. The linewidths of the halloysites are also very narrow: F = 0.39 mm/sec for the Dunino sample, and F = 0.48 mm/sec for the Michalovce sample.…”

Section: Clays and Clay Mineralsmentioning

confidence: 99%

Application of Electron Paramagnetic Resonance and Mössbauer Spectroscopy in the Investigation of Kaolinite-Group Minerals

Komusinski¹,

Stoch²,

Dubiel

1981

Abstract--Samples of nacrite, dickite, kaolinite, and halloysite were investigated using X-band electron paramagnetic resonance (EPR) and Mbssbauer spectroscopy. Fe 3+ gave rise to EPR signals at g = 4 which differed with the individual polytype. Only nacrite had no resonance in this region of the spectrum, but it had one at g ~ 2. Dickite had a quadruple line, kaolinite a triple line, and halloysite a single line in this region. The EPR spectra of these minerals are apparently dependent also on the orientation of adjacent layers in the structures. Other resonances were attributed to (1) clusters of ferric ions giving rise to broad resonance near g = 2, (2) trapped holes, and (3) free radicals linked with organic matter. The Mbssbauer spectroscopic results suggest that iron occurs in the ferric state (except in nacrite where Fe 2+ is present also) as an ionic substitution (IS) in octahedral layers. This suggestion follows from the difference is the IS values between octahedral and tetrahedral symmetry sites occupied by Fe a+ equal to -0.4 mm/sec. Linewidths depend mainly on the way the layers stack; for monoclinic modifications represented by nacrite and dickite, the linewidths are narrow (F = 0.45 mm/sec and 0.56 mm/sec, respectively); pseudomonoclinic halloysites also gave narrow linewidths (F = 0.39 mm/sec and 0.48 mm/sec). The widest line was observed for triclinic kaolinite (F = 0.62 mm/sec and 0.71 mm/sec).

“…Since then, little additional information has been obtained on the non-H structure, but there remains little agreement on the locations of the H atoms. H-atom orientations were originally inferred from infrared spectroscopic data, and positions were later modeled by Giese and Datta (1973) and Giese (1982) using electrostatic energy calculations. More recently, Suitch and Young (1983) and Young and Hewat (1988) refined H-atom positions using neutron powder diffraction data but assuming the space group of P1.…”

Section: Introductionmentioning

confidence: 99%

Rietveld Refinement of the Kaolinite Structure at 1.5 K

Bish

1993

483

278

Abstract--The crystal structure of Keokuk kaolinite, including all H atoms, was refined in space group C1 using low-temperature (1.5 K) neutron powder diffraction data (~ = 1.9102 A) and Rietveld refinement/ difference-Fourier methods to R,,,p = 1.78%, reduced x 2 = 3.32. Unit-cell parameters are: a = 5,1535 ( (5) ik ~. Unit-cell parameters show that most of the thermal contraction occurred along the [001] direction, apparently due to a decrease in the interlayer distance. The non-H structure is very similar to published C1 structures, considering the low temperature of data collection, but the H atom positions are distinct. The inner OH group is essentially in the plane of the layers, and the inner-surface OH groups make angles of 600-73 ~ with the (001) plane. Difference-Fourier maps show minor anisotropy of the inner-OH group in the [001] direction, but the inner-surface OH groups appear to have their largest vibrational (or positional disorder) component parallel to the layers. Although no data indicate a split position of any of the H sites in kaolinite, there is support for limited random positional disorder of the H atoms. However, these data provided no support for a space group symmetry lower than C1.