The textural evidence in septarian concretions shows that the septa formed as tensile fractures during burial and compaction of the host shale. Comparison of the combinations of vertical and horizontal stresses and pore-fluid pressure required for tensile fracture of cemented concretions and those likely to occur during shale burial indicates that septarian fracturing will be favoured by overpressuring and low horizontal stress, most likely to occur during times of rapid burial. Burial histories of septarian concretions from the Eocene London Clay and the Jurassic Kimmeridge Clay show that fracturing can form under as little as 50 m of sediment. By relating episodes of septarian fracturing to times of rapid burial, the timing of diagenetic cement formation can be constrained.

The literature on the complexes of n-alkylammonium ions with layer silicates is characterized by marked divergences, not only in the deductions and conclusions of the different investigators but also in their experimental results. An attempt is made to reconcile and rationalize the differences, and to form a self-consistent picture of these systems.

Given a saturating solution of sufficient concentration, the complexes tend during their formation to adopt an arrangement in which silicate layers are separated by double layers of ions oriented so that the alkyl chains are extended away from the silicate surfaces at a high angle. Water molecules, salt and free alkylamine may also be present in the interlayer spaces. When the excess material is removed by washing and the complexes dried, ideally the alkyl chains from opposing surfaces move over one another and interpenetrate so as to form a single layer of ions. During the contraction, however, the chains interact with one another and tend to stick at some point short of complete interpenetration. Weak attractive forces acting to bring the silicate layers together, and consisting mainly of electrostatic forces originating in the mineral layers and van der Waals interactions arising from increasing association of opposing alkyl chains with increasing interpenetration, are insufficient to overcome this tendency fully. As a result, an alkyl chain of given length can give rise to a series of complexes differing in their XRD characteristics.

Previous workers have noted the difficulty of achieving reproducible results and some have recommended grinding the complexes, but it appears that this treatment significantly alters the nature of the end-product.

Die kristallchemischen Strukturformeln von 2:1-Schichtsilikaten werden unter Voraussetzung der idealen Struktur mit 22 negativen Ladungen von 10 Sauerstoffen und 2 Hydroxylgruppen berechnet. Für die Verteilung der 22 Kationenladungen auf Tetraeder-, Oktaeder- und Zwischenschichtpositionen werden unter Berücksichtigung der direkt gemessenen Zwischenschichtladungen (Lagaly & Weiss 1971) bzw. Kationenumtauschkapazitäten Voraussetzungen und Berechnungsregeln angegeben. Als Beispiele werden die Formeln eines Glaukonits und eines Nontronits berechnet.

Die Verteilung der Kationenladungen in der Kristallstruktur von 2:1-Schichtsilikaten wird am besten in einem Dreiecksdiagramm mit den Ecken Pyrophyllit-Seladonit-Muskowit dargestellt. Jeder Punkt im Dreieck stellt die gesamte Kationenladung in der Formeleinheit gleich 22 dar. Es ist die Summe der Ladungen aus Tetraeder-, Oktaeder- und Zwischenschichtkationen.

Different forms of structural and chemical heterogeneity are considered including mixed-layer minerals, disordered layer structures containing rotational and translational stacking faults, interstratification of trans-vacant (tv) and cis-vacant (cv) layers in true micas, illites and illitesmectite (I-S), short-range order in isomorphous cation distribution etc.

Because determination of various structural and chemical imperfections requires elaboration of new diffraction and spectroscopic methodologies, special attention is paid to recent achievements in the development of new methodological approaches such as a multispecimen simulation of experimental X-ray diffraction (XRD) patterns from mixed-layer minerals, with account taken of layer-thickness fluctuations of the second type and possible difference between structures of outer and core layers; experimental determination of thickness distribution of illite crystals by HRTEMand the modified Bertaut-Warren-Averbach technique; XRD and thermal methods for determination of cv and tv layers in true micas, illites and I-S; generalization of Méring's rules to account for the behaviour of non-basal reflections for any defective structure in which two translations are irregularly interstratified; various ab initio calculations devoted to modelling infrared OH vibrations, octahedral cation distribution in dioctahedral 2:1 layer silicates, etc. It is shown that these recentlydeveloped methodologies have revealed new diversity in the structural and chemical heterogeneity of phyllosilicates and clay minerals, provided new insight into the structural mechanisms of their transformation in different geological environments, and discovered new natural processes.

Distribution coefficients and isotherms for the adsorption of radioiodide, caesium and strontium ions (125I−, 134Cs+ and 85Sr2+) were determined in untreated vermiculite and in vermiculite treated with the chloride salt of hexadecylpyridinium (HDPy+). Experimental data reveal that some of the alkylammonium ions were incorporated as HDPyCl ion pairs into the vermiculite. The fraction of ion pairs adsorbed is reflected by an increase in distribution coefficients with increasing saturation levels. Consequently, a considerable part of the iodide adsorption could be attributed to an anion exchange process. At smaller amounts of Cs+ and Sr2+ adsorbed, distribution coefficients of the modified clay mineral are significantly reduced in comparison with the original material. These differences are less pronounced when greater amounts of cations are adsorbed. Generally, larger distribution coefficients were found for the Cs+ compared with the Sr2+ ion in the untreated and modified samples.

Imogolite structures in allophanic clays can be recognized and semi-quantitatively estimated by an absorption band at 348 cm−1. Allowance can be made for interference by aluminous dioctahedral layer silicates present in small amounts.

This study focused on whether the presence of clay minerals (montmorillonite and kaolinite) in marine or coastal environments contaminated with high concentrations of heavy-oil spills were able to support the growth of hydrocarbon degraders to enable bioremediation. The bacterial growth experiment utilizing ~150 g/l of heavy oil (from the Nakhodka oil spill) was conducted with 1500 mg/l of montmorillonite or kaolinite. Bacterial strain Pseudomonas aeruginosa (isolated from Atake seashore, Ishikawa Prefecture, Japan), capable of degrading heavy oil, was employed in combination with other hydrocarbon degraders inhabiting the heavy oil and seawater (collected from the Sea of Japan). The interactions among microbial cells, clay minerals and heavy oil were studied. Both clays were capable of promoting microbial growth and allowed microorganisms to proliferate (to a greater degree than in a control sample which contained no clay) in an extremely high concentration of heavy oil. Observation by transmission electron microscopy of the clay-oil-cell complexes showed that microbial cells tended to be bound primarily on the edges of the clays. X-ray diffraction analysis showed that the clay-oil and clay-oil-cell complexes involved the adsorption of microbial cells and/or heavy oil on the external surfaces of the clays. How do the interactions among clay minerals, microbial cells and heavy oil contribute to environmental factors influencing the bioremediation process? To our knowledge, there are no previous reports on the use of clay minerals in the bioremediation of the Nakhodka oil spill in combination with biofilm formation.

X-ray diffraction (XRD) patterns of a pore-lining diagenetic chlorite (14 Å) from a reservoir sandstone, offshore Norway, show broad odd-order and sharp even-order basal reflections indicating that it contains 7 Å layers. Using NEWMOD, simulated XRD patterns with 15% 7 Å serpentine layers and a maximum crystallite thickness of 30 layers match the natural mineral well. Microprobe analyses of the 7 Å-14 Å mineral indicate that it is Fe-rich and aluminous suggesting that it is interstratified berthierine-chamosite. Apparent octahedral vacancies, however, suggest a significant dioctahedral component, and an alternative interpretation is interstratified kaolinite-chlorite. Indeed, chemical analyses of the mineral suggest a mixture of chlorite with 15% kaolinite, precisely the proportion of 7 Å layers indicated by XRD. Two other examples from the literature, previously identified as diagenetic chlorite, are probably also 7 Å-14 Å interstratified minerals, and the proportion of 7 Å layers indicated by XRD is also correlated with their structural formulae, if the 7 Å layers are, in fact, kaolinitic. This type of interstratification could explain why Fe-rich diagenetic chlorites appear to be compositionally distinct from metamorphic chlorites. The structure and chemistry of the Norwegian chlorite tend to support the idea that pore-lining chlorites form early in the diagenetic history, inhibiting the precipitation of later diagenetic minerals, and hence preserving abnormally high porosity at greater depths.

Concrete and bentonite are being considered as engineered barriers for the deep geological disposal of high-level radioactive waste in argillaceous rocks. Three hydrothermal laboratory experiments of different scalable complexity were performed to improve our knowledge of the formation of calcium aluminate silicate hydrates (C-A-S-H) at the interface between the two materials: concretebentonite transport columns, lime mortar-bentonite transport columns and a portlandite- (bentonite and montmorillonite) batch experiment. Precipitation of C-A-S-H was observed in all experiments. Acicular and fibrous morphologies with certain laminar characteristics were observed which had smaller Ca/Si and larger Al/Si ratios with increasing temperature and lack of accessory minerals. The compositional fields of these C-A-S-H phases formed in the experiments are consistent with Al/(Si+Al) ratios of 0.2– 0.3 described in the literature. The most representative calcium silicate hydrate (C-S-H) phase from the montmorillonite–cement interface is Al-tobermorite. Structural analyses revealed a potential intercalation or association of montmorillonite and C-A-S-H phases at the pore scale.

Low crystallinity of unsubstituted goethites is characterized by a small coherently diffracting domain, which may be accompanied by another type of disorder revealed by broader IR half-absorbance band widths. Inside the unit cell, the H-bond is weaker, which increases the OH stretching frequency and lowers the bending frequencies. Also, an increase in parameter a and a change in Fe-O bonds, which might correspond to a minor tilting of octahedra, occur along with a lowering of the frequency of the 630 cm−1 band.

The distribution of Fe3+-kaolinite, Al-goethite and Al-hematite and their contents of Fe and Al in bauxites and ferricretes are controlled by water activity, dissolved silica activity, temperature and particle size. The proposed model, based on ideal solid-solution equilibria in the Fe2O3-Al2O3-SiO2-H2O system, takes into account water and silica activities. By using the same considerations as those previously developed for the Fe2O3-Al2O3-H2O system, the model calculates the amounts of coexisting phases, Al or Fe substitution ratios in goethite, hematite or kaolinite, and the stability field distributions of the minerals under various conditions. Thermodynamic equilibrium conditions and element distributions within the mineral constituents are shown to be dependent on the parameters cited above. The model yields results compatible with natural observations on lateritic profiles.

The oxidation of benzidine to benzidine-blue on silicate minerals is shown to occur at aluminium atoms exposed at crystal edges and at transition metal atoms in the higher valency state present in the silicate lattices. The transition metals in the silicate lattice undergo chemical oxidation-reduction reactions.

Changes in the colour of the benzidine-blue radical cation with the conditions of reaction are discussed in terms of the solvent used for the reaction and its influence on the pH of the mineral surface.

The OH-OD exchange of kaolin minerals through contact with D2O introduced into interlayer space via intersalation resulted in a partial shift of the OH absorption bands. The total decrease in OH absorbance upon deuteralion was 52, 56, and 47% for the kaolinite, dickite-nacrite, and halloysite respectively, but the percentage decrease differed for the different absorption maxima of any one mineral. A secondary OH—OD exchange in the deuterated specimens was also observed upon heating to 350 and 400° C. These data together with the lack of deuteration in montmorillonite, and available orientation data on the kaolin OH groups by infrared spectroscopy, suggest that only two-thirds of the inner-surface OH groups form the interlayer OH—O bonds.

Rock weathering has been investigated from atomic to global scales through the different but complementary approaches of mineralogy, petrography, geomorphology and geochemistry. The sequences of mineral reactions involved in the alteration process are now well known. They explain the global trend of weathering phenomena but do not account for the actual rock transformation dynamics. In particular, they ignore the intimate relation of the mineral reaction progress with the increase in connected porosity. At the hand specimen scale, heterogeneity is the rule: mineral reactions are controlled by local physicochemical conditions. Alteration processes depend largely on the rock microstructure properties. They proceed through nearly-closed, semi- and completely open microsystems which are interconnected by fractures or pores. Before being leached out by the solutions which flow in the large fractures (flux), the soluble elements migrate inside the connected porosity through chemical diffusion. The dissolution of the primary minerals is mediated through local gradients of chemical potential. With increasing alteration, the rock porosity increases, as does the length of the fluid passageways and their constrictivity and tortuosity. Consequently, the apparent diffusion coefficient for the most soluble elements decreases. The amplitude of the chemical potential gradients for the most soluble elements is reduced by the progressive coating of the reactive surfaces by clays and Fe oxyhydroxides. The residence time of these elements inside the weathered rock increases as alteration progresses; an effect enhanced by their temporary adsorption on the exchangeable sites of clays and Fe oxyhydroxides. Consequently, the weathering rate decreases with time. A possible new way to calculate weathering rates could be to measure the residence time of soluble elements inside the different microsystems during their migration towards the diluted solution which occurs in the large fractures.

Syntheses of ferric smectites were performed at low temperature (75° C by aging coprecipitated gels of silica and Fe2+-sulphate under initially reducing then oxidizing conditions. Under strictly reducing conditions only nuclei of a trioctahedral ferrous stevensite were observed and crystal growth did not take place. When a spontaneous oxidization, in contact with air, was effected, the ferrous smectite nuclei transformed rapidly into a ferric, nontronite-like, smectite. Crystallogenesis of the ferric smectite was studied by XRD, IR, DTA, Mössbauer and EPR spectroscopies. The end-synthesis smectite contained only Fe3+ ions, all located in the octahedral sheet. This clay was mixed with a cryptocrystalline iron oxide phase containing one-third of the iron atoms and undetectable by XRD.

Strongly held carbonates anions in the interlayer region of pyroaurite-type compounds, [MlII1−xM2IIIx(OH)2]x+[(CO3)x/2yH2O]x− (x = 0·15−0·44), can be relatively easily exchanged by other anions such as NO3−, Cl− or SO42− dissolved in heated glycerol. Some Fe(III) of pyroaurite is reduced to Fe(II) by the glycerol treatment. If pyroaurite is treated with glycerol in the absence of dissolved anions or with glycerol vapour at 120°C, glycerol becomes intercalated in the interlayers. In all examples the interlayer CO32− is partially or completely lost as CO2. In aqueous salt solutions a glycerol intercalated form allows other anions to substitute in the interlayer. Expansion in the c-axis direction following glycerol treatment depends on (1) the method of glycerol treatment, (2) the trivalent metal in the octahedral sheet, and (3) the interlayer anions. Heated glycerol causes a different expansion to that produced by its vapour phase at 120°C. The variation in d(003) follows the series: hydrotalcitevap. > pyroauritevap. > hydrotalciteliquid > pyroauriteliquid > SO42−-pyroauritevap. > SO42−-hydrotalcitevap., where liquid refers to glycerol used at 160–180°C and vap. refers to glycerol vapour at 120°C Carbonate-free, glycerol-intercalated pyroaurite compounds may serve as re-usable anion absorbers. Glycerol intercalates of pyroaurite-type compounds may also be useful to study and identify stacking sequences and interlayer compositions in these minerals.

The Biga Peninsula of NW Turkey is host to six major halloysite deposits in the Go¨nen, Yenice and Balya districts. Mineralization took place in areas of Permian limestone blocks where the Triassic Karakaya Complex is in contact with early Miocene calc-alkaline volcanic rocks. Hypogene halloysite mineralization was controlled by the intersection of minor faults in the vicinity of clay deposits. During the Pleistocene, activity of the North Anatolian Fault (NAF) brought ascending geothermal solutions through the fault zones to the surface, which led to hydrothermal alteration and halloysite formation. N-MORB normalized element values for each halloysite deposit and the volcanic rocks suggest genetic links. Alunite and halloysite were formed in the Turplu area where upwelling hydrothermal waters contained major H2S and SO2 acids. Only halloysite mineralization occurred in outflow areas of the same fossil geothermal field.

Pyrite and alunite samples from the Turplu deposits have δ34S values of 0.6–1.8% and 4.8–7.9%, respectively, with values for gypsum of 3.1–3.5%. The δ34S values of pyrite suggest that local meteoric waters had partially mixed with the dominant fluid during the closure stage of fossil hydrothermal activities. The range of δD values of halloysite samples from Turplu is –58.4 to –68.6%. The δ18O values for halloysite are in the range 16.7–18.1%. All halloysite deposits in the study areas are either overlying or adjacent to limestone blocks, and these provide excellent drainage for the discharging geothermal waters. Subsurface drainage systems in the karstic environment and the SO2-bearing thermal waters indicate the importance of acidic waters and the continuous leaching of elements in forming relatively pure hydrated halloysite. A steam-heated dissolution-precipitation model is proposed for the occurrence of all halloysite and alunite deposits. Sulphur gases (H2S-SO2) of hypogene origin rose from deep in the fault zone to the surface where they encountered oxygenated groundwater at the water table. The occurrence of H2SO4 in this hydrothermal system enhanced the acidity of geothermal waters provoking advanced argillic alteration. Hypogene alunite deposits also have large P2O5 contents, suggesting a parent material with a magmatic origin deeper than the alkaline tuffs. Halloysite is a fast-forming metastable precursor to kaolinite.

Recent examination of clay-materials from several different sources has suggested to us the existence of a type of chlorite capable of the same kind of expansion along the c-axis by imbibition of glycerol, as is shown by montmorillonoids, vermiculites and halloysites. The expansion occurs within the range of 14 kX to 18 kX.

It is necessary to discuss the definition of chlorite in this connexion, since such expansion is not regarded as characteristic of any of the minerals to which the name has been given. The characteristics by which chlorites are generally identified from their X-ray diffraction patterns are twofold: (1) they give basal reflexions at approximately 14 kX and submultiples, the first four orders being usually strong and of comparable intensity, though differing in different species of chlorite; (2) these reflexions persist after heating at 500°C.

The influence of grinding on colour and particle-size properties of talc and smectite from a white bentonite were studied and compared with a fine-grained calcite from a chalk. Grinding decreased the grain size of all three minerals. The crystallite size and structure of smectite was not affected but the crystallite size of talc decreased. The Si–O–Mg and Mg–O bonds of talc were disrupted and cation exchange capacity increased with increasing grinding. Delamination of talc crystallites was observed in the initial stages of grinding, whereas with more intense treatment, amorphous material was formed. Comminution improved the colour properties of all three minerals, namely brightness, L* (lightness) and ΔE*ab (deviation from perfect white diffuser). Grinding time exerts greater influence on the reflectance from calcite surfaces than from clay minerals. This difference is attributed to continuous formation of progressively smaller diffuse reflection units forming a smoother calcite surface. Decrease of grain size does not form considerably smaller diffuse reflection units in clay minerals unless delamination takes place. With prolonged grinding, amorphization forms additional diffuse reflection units and a smoother surface due to comminution.

To provide fundamental knowledge for studying the relative content of vacant sites and exploring the mechanism of interaction between Pb2+ and birnessite, Fourier transform infrared spectroscopy (FTIR) of birnessites with different Mn average oxidation states (AOS) before and after Pb2+ adsorption were investigated. The number of absorption bands of FTIR spectra was determined by using the second derivatives of the original spectra. The band at 899–920 cm–1 was assigned to the bending vibration of -OH located at vacancies. The bands at 1059–1070, 1115–1124 and 1165–1171 cm–1 could be attributed to the vibrations of Mn(III)-OH in MnO6 layers, and the intensities of these bands increased with decreasing Mn AOS. The bands at 990 and 1023–1027 cm–1 were ascribed to the vibrations of Mn(III)-OH in the interlayers. Mn(III) in MnO6 layers partially migrated to interlayers during Pb2+ adsorption, which led to an increased intensity of the band at 990 cm–1. The band at 564–567cm–1 was assigned to the vibration of Mn-O located at vacancies. This band could split by coupling of vibrations due to Pb2+ and/or Mn2+ adsorbed at vacant sites. The large distance between the band at 610–626 cm–1 and that at 638–659 cm–1 might reflect small Mn(III) ions located in Mn(III)-rich rows.