Anisotropy in clay-rich sedimentary rocks is receiving increasing attention. Seismic anisotropy is essential in the prospecting for petroleum deposits. Anisotropy of diffusion has become relevant for environmental contaminants, including nuclear waste. In both cases, the orientation of component minerals is a critical ingredient and, largely because of small grain size and poor crystallinity, the orientation distribution of clay minerals has been difficult to quantify. A method is demonstrated that relies on hard synchrotron X-rays to obtain diffraction images of shales and applies the crystallographic Rietveld method to deconvolute the images and extract quantitative information about phase fractions and preferred orientation that can then be used to model macroscopic physical properties. The method is applied to shales from European studies which investigate the suitability of shales as potential nuclear waste repositories (Meuse/Haute-Marne Underground Research Laboratory near Bure, France, and Benken borehole and Mont Terri Rock Laboratory, Switzerland). A Callovo-Oxfordian shale from Meuse/Haute-Marne shows a relatively weak alignment of clay minerals and a random distribution for calcite. Opalinus shales from Benken and Mont Terri show strong alignment of illite-smectite, kaolinite, chlorite, and calcite. This intrinsic contribution to anisotropy is consistent with macroscopic physical properties where anisotropy is caused both by the orientation distribution of crystallites and high-aspect-ratio pores. Polycrystal elastic properties are obtained by averaging single crystal properties over the orientation distribution and polyphase properties by averaging over all phases. From elastic properties we obtain anisotropies for p waves ranging from 7 to 22%.

Late Miocene clayey sediments were deposited in lake-margin and shallow-lake environments of the southeastern Central Anatolian Volcanic Province (CAVP). Yellow to red mudstone, alternating with thin beds of conglomerate and sandstone in the Mustafapaşa Formation, is overlain by altered white Cemilköy ignimbrite. Grain size fines upward in each sequence (conglomerate, sandstone, and mudstone). The occurrence of reddish coloration upward, ripple marks, desiccation cracks, plant rootlets and remnants, and the development of initial-stage paleosols in association with smectite reveal that the area underwent alternating periods of siliciclastic and volcaniclastic sediment supply (wet) and drying. Micromorphologically, the development of spongy smectite in mudstone of the Mustafapaşa Formation and vermiform kaolinite in the Cemilköy ignimbrite on resorbed detrital feldspar and devitrified glass reveals in situ precipitation driven by dissolution and precipitation mechanisms. In addition, alteration of these sediments may have resulted in the depletion of soluble alkaline elements, such as Ca, Na, and K, from the ignimbrite downward into the Mustafapaşa Formation. Alternatively, the leaching of these elements — due to the hydrologically open system of the lake environment — may have resulted in the enhancement of Al+Fe/Si-favored precipitation of kaolinite in an acidic environmental condition, namely, of the altered Cemilköy ignimbrite at the top of the profile of the Mustafapaşa Formation, and of smectite in an alkaline setting within lower-level sediments where carbonate minerals were lacking. The coexistence of smectite with accessory illite indicates that illitization occurred via release of K and Al during excess desorption of feldspar. Large Ni and Co values in mudstone samples, and Fe oxidized and partly chloritized pyroxene and hornblende, indicate that the basin was also affected by ophiolite-related supply.

High-charge nontronites were synthesized at 75, 90, 100, 110, 125, and 150°C from a silicoferrous starting gel with Si2FeNa2O6.nH2O composition. This gel was oxidized in contact with air and then hydrothermally treated, for a period of 4 weeks, under equilibrium water pressure. The synthesized nontronites were similar to each other, regardless of the synthesis temperature. Their structural formula, obtained from chemical analysis, X-ray diffraction (XRD), and Fourier transform infrared (FTIR), Mössbauer, and X-ray absorption fine structure spectroscopies is: $\left({\text{Si}}_{3.25}{\text{Fe}}_{0.75}^{3+}\right){\text{Fe}}_2^{3+}{\text{O}}_{10}{\left(\text{OH}\right)}_2{\text{Na}}_{0.75}$$\left( {{\rm{S}}{{\rm{i}}_{3.25}}{\rm{Fe}}_{0.75}^{3 + }} \right){\rm{Fe}}_2^{3 + }{{\rm{O}}_{10}}{\left( {{\rm{OH}}} \right)_2}{\rm{N}}{{\rm{a}}_{0.75}}$. A strictly ferric end-member of the nontronite series was therefore synthesized for the first time. The uncommon chemistry of the synthesized nontronites, notably the high level of Fe-for-Si substitution, induced particular XRD, FTIR, and differential thermal analysis-thermogravimetric analysis data. The ethylene glycol expandability of the synthetic nontronites was linked to their crystallinity and depended on the nature of the interlayer cation, moving from smectite to vermiculite-like behavior. As the synthesis temperature increased, the crystallinity of the synthesized clays increased. The nontronite obtained at 150°C had the ‘best crystallinity’, which cannot be improved by increasing synthesis time or temperature.

The pH of aqueous bentonite suspensions is known to be influenced by carbonates present even in minor amounts. On the other hand, at high solid:liquid ratios (at standard pH measurement conditions: 2% w/w suspension), the type of exchangeable cation in the smectite is also known to determine pH (particularly Na+ or Ca2+). By cation-exchange tests we proved that exchanging the Ca2+ for Na+ results in an increase in the pH. However, this increase in pH was only found if excess salts were removed from the system (by washing or dialysis, respectively). The effect of the type of exchangeable cation can, at least partially, be explained by hydrolysis of Ca2+. On the other hand, a pronounced alkalinity of Na bentonites is observed which can, at least partially, be attributed to the hydrolysis of montmorillonite (Na+ is exchanged for H+ of water). The increase in the volume of the Stern layer, caused by increasing the degree of delamination, is also suggested to play a role. H+ and Na+ are concentrated in the Stern layer. Hence, increasing the Stern layer volume decreases the amount of H+ and Na+ in solution and thus increases pH. Unfortunately, both processes, montmorillonite hydrolysis and delamination, depend on the ionic strength. Distinguishing the processes quantitatively, therefore, is an analytical challenge, and impossible based on the data presented here.

To model the pore-water chemistry of clays and clay stones, all of the above-mentioned processes have to be considered. It is possible that other reactions, not identified in the present work, contribute toward the pH values of aqueous bentonite suspensions.

The structural significance of micas with Na-K intermediate composition, and their chemical and structural evolution at increasing metamorphic grade have been investigated in Triassic rocks from the transition between the Maláguide and Alpujárride complexes (Internal zones of the Betic Cordillera, Spain). Micas were studied by X-ray diffraction (XRD) and by scanning and transmission electron microscopy (SEM/TEM). Three samples, belonging to the late diagenesis and to the low and medium anchizone, were selected for this study. Na-bearing mica appears as submicroscopic packets intergrown in parallel with K-mica, becoming more compositionally uniform with increasing grade. The diagenetic sample contains illite, minor paragonite, and two main populations of intermediate Na-K micas, with average compositions Ms60Prg40 and Ms35Prg65, respectively, where Ms represents muscovite and Prg, paragonite. The lattice-fringe images of mica packets with intermediate compositions suggest the presence of random mixed-layered paragonite-muscovite. Under low anchizonal conditions the amount of discrete paragonite increases and the Na-K intermediate mica has a mean composition of Ms40Prg60. The TEM images suggest that the packets with intermediate composition are solid solutions of paragonite and illite. Micas with Na-K intermediate composition are lacking in the sample with the highest metamorphic grade. In this sample, paragonite and muscovite coexist with mica, with composition intermediate between paragonite and margarite. The lattice-fringe images of these Na-Ca-bearing packets suggest that they consist of irregularly shaped domains enriched either in Na or in Ca.

Our data indicate that Na+K-bearing micas have several origins: detrital stacks of K- and Na-bearing micas coexist with authigenic phases, formed from dickite in the diagenetic, coarse-grained samples, and perhaps from smectite-bearing mixed-layers or detrital illite, in the fine-grained rocks. The changes observed at increasing metamorphic grade can be related to the influence of the lithology, the metamorphic grade, and the different geological settings. Intermediate Na-Ca mica appears to have grown from paragonite, with calcite as the source of Ca.

Samples from different depths in the Oligocene Frio formation (offshore Gulf of Mexico) were studied by X-ray diffraction (XRD), thermal analyses, and scanning electron microscopy. The experimental XRD patterns recorded from oriented and ethylene glycol (EG) solvated clay fractions of the samples were similar to those typical of random, mixed-layered illite-smectite (R0 I-S). The experimental XRD patterns recorded in air-dried (AD) and EG states were simulated using three different models. One of them corresponds to R0 I-S for which thickness and content of the interstratified layers were determined by the Środoń technique. The second model is represented by a single homogeneous I-S in which illite and smectite layers are interstratified with a tendency to segregation. The expandability of the segregated I-S model varies from 48% to 75% without any rational relationship between the smectite layer content and depth.

The third model assumes that the clay fraction is a physical mixture of smectite and an R0 I-S. In this model the I-S contains 65% illite and 35% smectite layers independent of depth, whereas the smectite content varies from 28% to 63%. This model has consistently smaller profile factors, Rp, for both EG and AD XRD scans compared with the Rp values determined for the other two models.

The mineralogical association, volcanic origin, narrow stratigraphic interval (427 m), and low maximum temperature (42°C) of the studied Frio Formation are considered. These features are completely consistent with the two-phase model and so the segregation model must be rejected. An authigenic origin of the pure smectite and an alternative detrital or authigenic origin of the R0 I-S are discussed.

The preparation of porous materials from clay minerals by selective leaching is of interest because it yields residues with large specific surface areas that can be used as adsorbents of contaminants or as catalysts. Grinding produces surface modifications and therefore may significantly influence the leaching behavior. The aim of this paper is to study the effect of grinding and leaching on the structure of the vermiculite from Santa Olalla, Spain, using 57Fe Mössbauer spectroscopy, X-ray diffraction, infrared spectroscopy, and specific surface area (SBET) measurements. The study shows that grinding destroys the long range order of the vermiculite, but leaves the local structure in the environment of the Fe atoms intact, at least up to a grinding time of 10 min. The Mössbauer study shows that there is no Fe3+ in the tetrahedral sheets and that grinding does not lead to a significant oxidation of the structural Fe. Vermiculite ground for 4 min and leached with 1 M HCl solution at 80°C over a 24 h period was decomposed to X-ray amorphous silica with a very large specific surface area (SBET = 720 m2g−1) and with total pore volume of 0.586 cm3 g−1, whereas an unground sample leached with the same acid concentration yielded a specific surface area of only 504 m2 g−1. Most of the Mg2+ and Al3+ are removed from the ground sample after leaching with 1 M HCl, while large percentages of Fe2O3 remain with the X-ray amorphous silica. In unground vermiculite leached with 1 M HCl, a considerable amount of vermiculite remains in the residue. A sample ground for 4 min and treated with 0.25 M HCl also shows the typical vermiculite Mössbauer spectrum with an Fe2+/Fe3+ ratio similar to that of the unground vermiculite. The samples ground for 2 or 4 min and treated with 1 M HCl solution have an orange color and, according to the Mössbauer spectra, only Fe3+ remains. Mössbauer spectra of these samples taken at 4.2 K reveal the presence of akaganéite.

Particle-size distribution (PSD) is a fundamental soil property usually reported as discrete clay, silt, and sand percentages. Models and methods to effectively generate a continuous PSD from such poor descriptions using another property would be extremely useful to predict and understand in fragmented distributions, which are ubiquitous in nature. Power laws for soil PSDs imply scale invariance (or selfsimilarity), a property which has proven useful in PSD description. This work is based on two novel ideas in modeling PSDs: (1) the concept of selfsimilarity in PSDs; and (2) mathematical tools to calculate fractal distributions for specific soil PSDs using few actual texture data. Based on these ideas, a random, multiplicative cascade model was developed that relies on a regularity of scale invariance called ‘log-selfsimilarity.’ The model allows the estimation of intermediate particle size values from common texture data. Using equivalent inputs, this new modeling approach was checked using soil data and shown to provide greatly improved results in comparison to the selfsimilar model for soil PSD data. The Kolmogorov-Smirnov D-statistic for the log-selfsimilar model was smaller than the selfsimilar model in 92.94% of cases. The average error was 0.74 times that of the selfsimilar model. The proposed method allows measurement of a heterogeneity index, H, defined using Hölder exponents, which facilitates quantitative characterization of soil textural classes. The average H value ranged from 0.381 for silt texture to 0.838 for sandy loam texture, with a variance of <0.034 for all textural classes. The index can also be used to distinguish textures within the same textural class. These results strongly suggest that the model and its parameters might be useful in estimating other soil physical properties and in developing new soil PSD pedotransfer functions. This modeling approach, along with its potential applications, might be extended to fine-grained mineral and material studies.