Resonance Raman spectroscopy has been used to observe the formation of cation radicals in the adsorption of N,N,N',N'-tetramethylbenzidine (TMBD), benzidine, N,Ndimethylaniline (DMA) and aniline on Na-, Cu- and Fe-montmorillonites. Cation radicals of benzidine and TMBD, and their dications were formed at acid sites on the montmorillonite surface, or through the reduction of Cu or Fe interlayer ions, and were adsorbed in the interlayer. Their structures are represented by biphenoquinone type structure, where the inter-ring CC bond and the ring C-N bond have double bond characters. It was demonstrated from Raman spectra that DMA and aniline adsorbed on Cu-montmorillonite from the vapour phase dimerize to form TMBD and benzidine dications.

Clay mineral abundances and illite-smectite (I/S) compositions have been determined by X-ray diffraction (XRD) in shales of Permo-Triassic to Quaternary age from seven wells in the Viking Graben and Moray Firth. Chemical analyses of size fractions provide evidence that diagenetic illitization of smectite has occurred during burial by uptake of Al and K, and release of Si. K-feldspar was probably the main source of K for illitization. The depth at which random I/S disappears occurs at similar temperatures (mean 93°C) in each well for which reliable measurements are available. Vitrinite reflectance measurements at this depth are also similar (mean 0·64% R0) and correspond to early oil generation. I/S diagenetic levels may have been imprinted by a Tertiary heating event.

Odinite is a Fe3+-rich green clay that is widespread in the form of infillings or replacements of microtests, bioclasts, faecal pellets, or mineral debris on shallow marine shelfs and reef lagoonal areas in tropical latitudes. The structure is based on a 1 : 1 serpentine-type layer that is intermediate between dioctahedral and trioctahedral. Octahedral cation totals range from 2·30 to 2·54 cations per 3·0 sites for 10 samples. The structural formula for the purest sample is Both monoclinic and trigonal polytypes are present in most samples, with 1M more abundant than 1T. Unit-cell dimensions are 1M: a = 5·373(3), b = 9·326(7), c = 7·363(6) Å, β = 104·0(1)°; 1T: a = 5·366(5), b = 9·334(9), c = 7·161(8), β = 90° (on orthohexagonal axes). The name is for Dr. Gilles Serge Odin, Département de Géologie Dynamique, Université Pierre et Marie Curie, Paris, who has done most of the pioneering work on this new mineral.

A comprehensive Mössbauer spectroscopic and X-ray diffraction study of six purified glauconites is presented. The Mössbauer spectra were computer-fitted with three Fe3+ and three Fe2+ doublets, both Fe species occupying the trans-OH and two cis-OH octahedral sites. In addition, a seventh smaller doublet is assigned to Fe3+ in tetrahedral coordination. It has been shown that an increasing IVFe3+ content directs VIFe3+ substitution to the cis-OH octahedrally coordinated sites. A correlation between the d(060) reflection and elemental composition is demonstrated.

A chlorite-smectite interstratified mineral in a pottery stone from Niwatorizawa mine, Izushi-Cho, Hyogo Prefecture (Japan), has been studied by means of Fourier transform methods, together with interlamellar sorption of ethylene glycol and glycerol. The calculations were carried out with the INTER program (using an Olivetti M-24 personal computer with MS-DOS operating system) which allows the analysis of two-component interstratified structures by two Fourier transform based methods: the X-ray diffraction intensity function method, and the interlayer distances distribution function method. The material studied contains a 1:1 chlorite-smectite interstratification and shows a marked tendency to alternation, i.e., the interstratification is almost regular.

The (02,11) X-ray diffraction band from a low-defect kaolinite from Cornwall (Hinckley index HI = 1·22) was examined to determine the defect structure. No combination of interlayer translations and admixing of dickite layers accurately modelled the observed diffraction pattern. Calculated diffraction patterns which gave a good agreement with the shape, position, and intensity of the observed peaks, uniformly had inter-peak intensities which were too weak. By treating the kaolinite as a mixture of low-defect (HI = 1·76) and moderate-defect (HI = 0·29) kaolinites, the agreement between the observed and calculated patterns was improved substantially. The existence of a mixture of two kaolinites was also found for a number of low-defect samples (HI > 0·4) from Georgia and Cornwall, and may be of even wider occurrence. The HI, which is very sensitive to the inner-peak intensities, does not estimate the types or abundances of various structural defects (the classical “crystallinity”), but is related directly, in a non-linear fashion, to the proportions of the two kinds of kaolinite which are present in the sample.

Illite/smectite mixed-layered minerals (I/S) occurring in hydrothermally altered dacite from the island of Martinique were studied using X-ray powder diffraction, electron microprobe and CEC measurement techniques. Microprobe analyses and X-ray identification of high- and low-charge smectite layers indicate that the I/S hydrothermal alteration operates from wall-rock to hydrothermal veins, with conversion of high-charge to low-charge smectite and formation of illite layers. The overall alteration reaction can be expressed as: mixed-layered high-charge smectite + Si4+ + K+ → mixed-layered low-charge smectite + illite. This reaction requires Si and K from external sources and differs from the currently invoked mechanisms for diagenetic illitization where Si is released. The proposed reaction appears, therefore, to be the first step of I/S alteration under low-temperature hydrothermal conditions, prior to the crystallization of newly-formed I/S.

Maghemite with acicular morphology occurs as an oriented growth on fresh quartz surfaces in the magnetic sandy fraction of the B horizon of a Typic Rhodoxeralf from southern Portugal. The maghemite was characterized by Mössbauer spectroscopy, X-ray diffraction and electron microscopy (scanning and transmission), and on the basis of a structural similarity between quartz and maghemite, a mechanism has been proposed for the formation of the oriented overgrowth. Correlation with an interpretative chemical model is discussed, assuming active sites over quartz surfaces. Infrared absorption data agree with the proposed models.

Vermiculite prepared from biotite by interlayer cation exchange was reacted with solutions exhibiting redox potentials between 625 and 765 mV. The redox potential was controlled by the Fe2+/Fe3+ activity ratio, measured with a Pt electrode, and kept constant by addition of hydrogen peroxide to balance electron transfer from structural Fe2+ to Fe3+ in solution. Oxidation of structural Fe2+ was followed by Eh-stat titration and the rate of oxidation was shown to depend on the amount of Fe3+ penetrating into interlayer positions. Consequently, it was affected not only by the redox potential, but also by the activity between Fe3+ and all other cations present in solution or in an exchangeable state. Oxidation and cation exchange are coupled reactions. In contrast to the redox potential in solution, the effective redox potential controlling the oxidation of structural Fe2+ was increased by preferential sorption of the Fe3+ ion.

Intercalated compounds of montmorillonite and poly-6-amide were prepared by heating mixtures of ɛ-caprolactam and 5, 10, 15 and 30 wt% of montmorillonite, cation-exchanged with NH3+(CH2)11COOH, at 250°C in a nitrogen atmosphere, and examined by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), gel permeation chromatography (GPC) and elemental analysis. ɛ-caprolactam was polymerized to poly-6-amide by the heat treatment. The mean number-average molecular weight decreased from 3·6 × 104 to 0·8 × 104 with increasing montmorillonite content. TEM showed that considerable swelling had taken place subsequent to polymerization and that the clay layers were uniformly distributed in the final clay/poly-6-amide products. Both XRD and TEM showed that the basal spacing of the compound increased from 51 Å to 210 Å with increasing polyamide content. The driving force for the swelling was considered to be a combination of the polymerization energy of ɛ-caprolactam and the attractive interaction between the interlayer cation and ɛ-caprolactam.

Mössbauer spectra of several smectites demonstrate the existence of at least three phases with distinct Fe populations: (i) a component with very low Fe content (< 1%), which shows slowly-relaxing paramagnetic hyperfine structure at both 4·2 K and 77 K; (ii) a component with intermediate Fe content (∼ 1–10%) which is seen as doublets in the spectra at 4·2 K, 77 K and ambient temperature; (iii) an Fe-rich phase (> 30% Fe), which shows magnetic ordering at 4·2 K and 77 K. These data are consistent with components (i) and (ii) corresponding to Fe incorporated in aluminosilicate structures from distinct phases, whereas (iii) is characteristic of an iron oxide phase, probably goethite in most cases. These conclusions are supported by EPR measurements which show magnetically-dilute Fe in more than one type of structural environment plus an additional component with magnetically-interacting ions.

Mössbauer spectra of three natural ferrihydrites of different crystallinities were collected between 295 and 4·2 K. Optimal fits of the room-temperature spectra were obtained using distributions of quadrupole-split doublets; half-widths of the distributions (0·71–0·86 mm/s) increased, and maxima (at 0·62–0·78 mm/s) shifted to higher quadrupole splittings with decreasing crystallinity. Rather poorly-defined magnetically-ordered spectral components appeared and gradually replaced the superparamagnetic doublets as temperatures were reduced. Blocking temperatures between 115 and 28 K, derived from the relative areas under the doublets and magnetic sextets, indicated average particle sizes between ∼ 5 and 3 nm. The sextets were relatively broad and could be fitted with distributions of hyperfine fields. These distributions narrowed and their maxima shifted to higher fields as temperatures decreased; the influence of superparamagnetism was no longer apparent at 4·2 K.

The dominant source of oxalate-soluble Al in the B horizon of a brown podzolic soil developed on andesite appears to be hydroxyaluminium interlayers in a dioctahedral vermiculite in the clay and silt fractions, of which the latter contributes most to the total extractable Al and fluoride reactivity of the whole soil. Cold sodium carbonate solutions extract as much interlayer Al as does oxalate, indicating that this fraction of the interlayer material is highly reactive, and sharply distinguished from more resistant interlayers which are also present.

The study of 13C NMR spectra of polystyrene thermally obtained on clays shows that thermal polymerization of styrene on these minerals proceeds by two parallel reaction mechanisms: the radical mechanism due to the thermal effect, and the cationic mechanism in which the initiatory cation H+ is provided by the clay. The latter mechanism, accelerated by increase in temperature, becomes more important as the clay content increases in the reaction medium. Otherwise, the thermal polymerization on clays is accompanied by the hydrogenation of some α carbons of the polystyrene molecule and the oxidation of certain aromatic carbons.

Pillared smectites in which the pillars consist of iron oxide are expected to have interesting and unusual magnetic properties. Several possible routes by which such materials might be made have been investigated, namely intercalation of hydroxy-Fe(III) polycations, mixed hydroxy-Fe(III)/Al polycations, phenanthroline-Fe(II) cations, and trinuclear Fe(III) acetato cations into Na-montmorillonite. Only the last of these yielded a pillared clay (PILC) on calcination. The products have been characterized using X-ray powder diffraction and 57Fe Mössbauer spectroscopy. The precursor Fe-PILC has a d-spacing of 21 Å and expands to 23 Å on solvation with glycol. The calcined Fe-PILC has a d-spacing of 19 Å (gallery height 9·4 Å) and does not expand with glycol, confirming cross-linking of the layers. From Mössbauer spectra at 4·2 K it is estimated that there are of the order of some hundred Fe atoms per pillar.

Decomposition of decylammonium cations on vermiculite surfaces as a result of acidity has been studied. The vermiculite-decylammonium complex was treated with solutions of HCl in water and butanol, and solutions of chlordimeform in butanol. X-ray powder diffraction and IR spectroscopy data showed the presence after treatment of ammonium cations in addition to aliphatic chain compounds in the interlamellar space. The ammonium cation is produced by breaking of the C-N bond of alkylammonium due to the low pH of the medium and, when using butànol as solvent, to the dissociation of the scarce water molecules on the clay surface. The influence of the different solutions on the period of decomposition of alkylammonium cations is discussed. Vermiculite-decylammonium complex treated with HCl solutions for a year released structural Mg2+ due to the acidity of the medium. This Mg2+ partially displaced ammonium cations from the interlamellar space.

Imogolite, protoimogolite and two synthetic allophanes (A and B) with very different Si/Al ratios have been pyrolysed over a range of temperatures, and the reactions followed by high-resolution solid-state 27AI and 29Si nuclear magnetic resonance (NMR) spectroscopy. The Si(OAloct)3OH groups of protoimogolite are destroyed at relatively low (∼ 200°C temperatures, whereas the same structures in imogolite are stable to ∼ 300°C. During pyrolysis of both materials there is little change in the observed coordination of AI at temperatures of < 500°C but at 500°C or higher, ∼25% of the NMR-visible Al is converted to tetrahedral coordination. The mechanism of decomposition of both protoimogolite and imogolite is shown to involve the formation of highly branched Si-O-Si chains. As far as can be discerned by 27Al and 29Si NMR, allophanes A and B both appear to produce products similar to protoimogolite on pyrolysis.

The clay fraction of soils from a toposequence developed on a sandy clay Tertiary sediment in the Brazilian Amazonia was studied. Clayey Acrorthox located at the upper part of the sequence have transformed progressively into sandy Tropohumods down the slope. Along the slope important chemical and mineralogical changes linked to modifications in the weathering conditions were observed. In the Acrorthox the hydrolysis process largely prevails and the clay fraction is composed mainly of Fe-rich kaolinite. Fe and Al amorphous compounds become increasingly abundant along the slope. In the Spodosols, hydrolysis and acidocomplexolysis processes have both been effective, and the clay fractions contain not only more gibbsite, but also amorphous materials which are particularly abundant in the Bh horizons.

The study of M and Mg ion exchange (M = Co, Ni, Cu, Zn), between silicate gels SiO2.q(M, Mg)O.nH2O and amino acid (glycine) saline aqueous solutions (M, Mg)SO4, shows that the introduction of the complexing agent completely upsets the original distribution equilibria of M and Mg between the two types of phases. The values of the measured bulk distribution coefficient

are lowered considerably relative to the inorganic reference distribution coefficients. The lowering of D may be accounted for by calculating the contents of the different species, MA, MA+, M2+, under which the metallic element M is present in the solutions. The values of

resulting from the calculated M2+ contents are identical to the values of Dref, determined in systems without a complexing agent.