It is shown that order-disorder relations in the distribution of the isomorphous substitutions are important in the characterization of different 2/1 phyllosilicates and in the determination of their behavior. These order-disorder relations are shown by selected area diffraction patterns obtained from single crystals. The range of layer charges corresponding to smectites (charge per half-cell <0.6) is that for which phyllosilicates are stable with disordered substitutions. Phyllites with charge >0.6 show anomalous diffusions which indicate that the distributions of exchangeable Ba ions are partially ordered; this result is taken as evidence that the isomorphous substitutions also are partially ordered.

With the use of a BaCl2 solution containing radioactive Ba2+ ions, kinetics of cation exchange have been done on a Kenya vermiculite, natural on one hand and previously oxidized either by 50°C water or oxygenated water on the other hand. Correlatively, the quantity of ferric iron in the layer has been determined by E.P.R. These two methods have shown that during an oxidation the proportion of iron which stays in the octahedral layer depends upon the nature of the oxidizing agent. During a weak oxidation, the iron stays entirely in an octahedral layer and the exchange capacity of the vermiculite decreases; on the other hand, during an oxidation by oxygenated water, part of the iron is extracted from the octahedral layer and the exchange capacity of the vermiculite is not changed, as established by the studies of Farmer (Farmer et al., 1971). Kinetic data for Llano vermiculite also are reported and compared with those for the Kenya vermiculite.

A new model for the interpretation of dioctahedral mica infrared (IR) spectra in the OH stretching vibration region is proposed. It is based on the analysis of the main factors responsible for the observed sequence of the OH frequencies. In terms of this model, the simple analytical dependence between the OH frequencies and the mass and valency of cations bonded to OH groups has been found. The specific character of the interaction between octahedral Al and OH groups in the mica structures is assumed.

Integrated optical densities of the OH bands determined by the decomposition of the studied mica IR spectra are used for the quantitative analysis, that is, for the determination of a number of each type of octahedral cations per unit cell of the sample under study. A good agreement between the octahedral cation contents of 2:1 layers found from the IR spectra decomposition and the chemical analysis has shown that this technique may be used to study the local order-disorder of isomorphous cation distribution in mica structures.

The essential result obtained by the quantitative analysis of the mica IR spectra is the determination of Fe3+ cations in the tetrahedral sites of some samples. This means that the conventional presentation of structural formulae for Al-Fe3+-containing 2:1 layer silicates is unacceptable without consideration of tetrahedral Fe3+ by spectroscopic techniques and by the quantitative analysis of the IR spectra, in particular.

An improved model for the interpretation of thermal effects during dehydroxylation in aluminous dioctahedral 2:1 layer phyllosilicates considers trans-vacant (tv) and cis-vacant (cv) 2:1 layers and leads to very different temperatures of dehydroxylation for these tv and cv vacant modifications. In particular, smectites and illites consisting of cv 2:1 layers are characterized by dehydroxylated temperatures which are higher by 150°C to 200°C than those for the same minerals consisting of the tv 2:1 layers. A considerable lengthening of the OH-OH edges in cv 2:1 layers in comparison with the OH-OH edges in the tv 2:1 layers is postulated as the reason for the higher dehydroxylation.

Dehydroxylation in aluminous cv 2:1 layer silicates should occur in two stages. Initially, each two adjacent OH groups are replaced by a residual oxygen atom and the Al cations, which originally occupied cis -and trans-sites, become 5- and 6-coordinated, respectively. The structure of 2:1 layers corresponding to this stage of the dehydroxylation is unstable. Thus the Al cations migrate from the former trans-sites to vacant pentagonal prisms. The resulting dehydroxylated structure of the original cv 2:1 layers is similar to that of the former tv 2:1 layers.

Diffraction and structural features of the cv dehydroxylates predicted by the model are in agreement with X-ray diffraction effects observed for cv illite, illite-smectite and montmorillonite samples heated to different temperatures. In particular, the diffusion of Al cations to empty five-fold prisms during dehydroxylation of the tv 2:1 layers explains why dehydroxylation of reheated cv montmorillonites occurs at temperatures lower by 150°C to 200°C than samples that were not recycled.

A large and representative collection of clay-size dioctahedral mica minerals differing in their chemical compositions has been studied by infrared (IR) spectroscopy in the OH stretching vibration region. Decomposition of the IR spectra in the individual OH bands has provided unambiguous identification of the band positions for each defined pair of octahedral cations bonded to OH groups. The presence of pyrophyllite-like local structural environments in samples having a deficiency of K in interlayers has been established. A set of the relationships between the OH frequencies corresponding to pairs of cations having different valency and mass has been found.

We recently reported on the radio-frequency attenuation length of cold polar ice at Summit Station, Greenland, based on bi-static radar measurements of radio-frequency bedrock echo strengths taken during the summer of 2021. Those data also allow studies of (a) the relative contributions of coherent (such as discrete internal conducting layers with sub-centimeter transverse scale) vs incoherent (e.g. bulk volumetric) scattering, (b) the magnitude of internal layer reflection coefficients, (c) limits on signal propagation velocity asymmetries (‘birefringence’) and (d) limits on signal dispersion in-ice over a bandwidth of ~100 MHz. We find that (1) attenuation lengths approach 1 km in our band, (2) after averaging 10 000 echo triggers, reflected signals observable over the thermal floor (to depths of ~1500 m) are consistent with being entirely coherent, (3) internal layer reflectivities are ≈–60$\to$–70 dB, (4) birefringent effects for vertically propagating signals are smaller by an order of magnitude relative to South Pole and (5) within our experimental limits, glacial ice is non-dispersive over the frequency band relevant for neutrino detection experiments.

Over the last 25 years, radiowave detection of neutrino-generated signals, using cold polar ice as the neutrino target, has emerged as perhaps the most promising technique for detection of extragalactic ultra-high energy neutrinos (corresponding to neutrino energies in excess of 0.01 Joules, or 1017 electron volts). During the summer of 2021 and in tandem with the initial deployment of the Radio Neutrino Observatory in Greenland (RNO-G), we conducted radioglaciological measurements at Summit Station, Greenland to refine our understanding of the ice target. We report the result of one such measurement, the radio-frequency electric field attenuation length $L_\alpha$. We find an approximately linear dependence of $L_\alpha$ on frequency with the best fit of the average field attenuation for the upper 1500 m of ice: $\langle L_\alpha \rangle = ( ( 1154 \pm 121) - ( 0.81 \pm 0.14) \, ( \nu /{\rm MHz}) ) \,{\rm m}$ for frequencies ν ∈ [145 − 350] MHz.

This study provides insights about the diversity, prevalence and distribution of alpine wild galliformes gastrointestinal parasite community, trying to fill a gap in the scientific information currently available in scientific literature. The analysis included three host species: 77 rock partridge (Alectoris graeca saxatilis), 83 black grouse (Tetrao tetrix tetrix) and 26 rock ptarmigan (Lagopus muta helveticus) shot during the hunting seasons 2008–2015. Parasites isolated were Ascaridia compar, Capillaria caudinflata and cestodes. The rock ptarmigan was free from gastrointestinal parasites, whereas the most prevalent helminth (37%) was A. compar in both black grouse and rock partridge. C. caudinflata occurrence was significantly higher in black grouse (prevalence = 10%, mean abundance = 0.6 parasites/sampled animal) than in rock partridge (prevalence = 1.20%, mean abundance = 0.01 parasites/sampled animal). Significant differences were detected among hunting districts. A. compar was found with a significant higher degree of infestation in the hunting districts in the northern part of the study area whereas cestodes abundance was higher in Lanzo Valley. Quantitative analysis of risk factors was carried out using a generalized linear model (GLM) only on the most common parasite (A. compar). Latitude was the only factors associated with infestation risk (OR = 52.4). This study provides information on the composition and variability of the parasite community in the alpine Galliformes species.

The general approach to the problem of the real structure of smectites requires an analysis based on the relationship between structural characteristics and diffraction patterns. This paper, which considers only the models corresponding to dioctahedral smectites saturated by K-cations and collapsed, includes: 1. Successive consideration of all models which are crystallochemically possible. These models may differ in (i) the structure and chemical composition of layers and interlayer spaces; (ii) the azimuthal orientations, translations and the mode of alternation of the layers; (iii) independent parameters which describe quantitatively the models (e.g. abundance of each type of layer, probability parameters defining the succession of layers, …). 2. Calculation, in all accessible domains of reciprocal space, of the distribution of intensities and profile variations, obtained by changing only one parameter at a time, that defines one type of structural feature (e.g. cation distribution in individual layers, stacking of the layers, nature of stacking faults, …). 3. A systematical analysis of the calculated diffraction patterns to establish the diffraction criteria which will help to interpret the experimental data explicitly.

Hofmann & Klemen ont observé qu'en chauffant modérément (200-220°C) une smectite dioctaèdrique à substitutions octaàdriques saturée par du lithium, celle-ci perdait sa capacité d'échange cationique et son pouvoir de solvatation. Les auteurs ont attribué cet effet à la migration des cations Li vers la couche octaèdrique. Nous avons, en utilisant essentiellement la diffraction X aux grands angles et la microscopie électronique, caractérisé de manière quantitative la structure d'une smectite à déficit de charge mixte (c'est-à.-dire ayant 30% de substitutions dans les couches téraèdriques et 70% dans les couches octaèdriques) saturée par du nickel, avant et après chauffage. Nous avons ainsi pu montrer en éudiant les réflexions 00l qu'après un chauffage à 400°C, les cations interfoliaires migrent vers la cavité octaèdrique vacante pour compenser la totalité des charges négatives dues aux substitutions Al → Mg et qu'il existe une distribution inhomogène de la charge entre les couches octaèdriques et tétraèdriques au sein d'un même cristal. Certains feuillets ont des substitutions uniquement dans la couche octaèdrique, d'autres uniquement dans la couche tétraèdrique, et toutes les possibilités peuvent exister entre ces deux pôles extrèmes.

Nous décrivons un montage expérimental permettant d'obtenir, avec une bonne précision, des diagrammes de diffraction X de poudre d'argile dans un état hydraté homogène et de suivre la cinétique du processus d'hydratation. Nous avons pu déterminer, dans le cas de l'état homogène à une couche d'eau d'une beidellite sodique, la position des cations échangeables, le nombre total de molécules d'eau par maille et leurs coordonnées z, en utilisant une méthode de modèle basée sur la comparaison des profils expérimentaux et calculés des réflexions 00l. De plus nous avons comparé les caractéristiques structurales et en particulier le mode d'empilement des feuillets de l'état monocouche avec celui des états anhydre et bicouche. L'analyse du profil des réflexions 00l montre l'existence de fluctuations autour d'un espacement basal moyen . Ces fluctuations sont interprétées comme provenant de l'hétérogénéité de la distribution des charges dans le feuillet. Enfin, un processus théorique d'hydratation et de déshydratation est proposé.

Iron-rich dioctahedral 2:1 clays were sampled in metalliferous sediments from Atlantis II Deep (Red Sea), and studied by XRD, TEM, FTIR and Mössbauer spectroscopy. One sample with the structural formula (Si3·94Fe3+0·06)(Fe3+1·90Mg0·10)K0·1(Mg, Ca)0·03 is closer to the theoretical end-member ferripyrophyllite Si4Fe3+2O10(OH)2 than any other Fe-rich clay previously described. Other samples appear as mixed-layered clays: ferripyrophyllite-hydroferripyrophyllite or hydroferripyrophyllite-celadonite.

A method is given for quantitative analysis of IR spectra of dioctahedral micas in the OH-stretching region, which involves spectral decomposition and correlation of octahedral cation contents with integrated optical densities of the corresponding bands. It provides a basis for the study of order-disorder in these minerals and has allowed revision of the crystallochemical formulae of some glauconites and celadonites.

En utilisant des méthodes diffractométriques avec des smectites mal cristallisées, il n'est pas possible de déterminer de façon précise la répartition des atomes dans le feuillet. Il est particulièrement difficile de confirmer si le mineral est di- ou trioctaédrique, ou de déterminer la position de la vacance (position cis ou trans) dans la couche octaédrique. De même la nature polytypique de ces minéraux est difficile à preciser. La détermination de ces paramètres est difficile car les modulations (hkl) obtenues par diffraction des rayons X avec les smectites sont faibles et très peu marquées. Ce travail montre qu'en utilisant le césium comme cation interfoliaire, il y a non seulement augmentation de l'ordre dans l'empilement des feuillets mais aussi que son grand facteur de diffusion augmente l'intensité des modulations (hkl). En supposant que la substitution par du césium ne modifie pas la répartition des atomes dans le feuillet (il affecte seulement la distorsion de la couche tétraédrique), il est alors possible de déterminer cette répartition.

Le remplissage des cavités karstiques de la région d'Ain Khamouda (Tunisie Centrale) est partiellement constitué d'une argile blanche. Son étude par diffraction X. ATD et analyse chimique traditionnelle montre qu'il s'agit d'un mélange d'halloysite prédominante et de smectite, renfermant plusieurs pourcents de ZnO. Une étude plus détaillée mettant en oeuvre un diffractométre à détecteur linéaire et à ambiance contrôlée, la microscopie électronique à transmission et la microscopie électronique à transmission en balayage (STEM) a permis de préciser les points suivants. En dehors de l'halloysite totalement dépouvue de zinc, il existe deux phases porteuses de ce métal: une sauconite et un hydroxyde de zinc à peu près amorphe. En outre, les faibles quantités (0.2%) de MgO contenues dans l'échantillon sont localisées à l'intérieur des tubes d'halloysite. De plus, ce minéral est présent sous la forme de deux phases, l'une hydratée, l'autre anhydre. Enfin, ces argiles renferment un peu d'argent sous la forme de microparticules de 3 à 10 nm de diamètre.

Celadonite and glauconite samples heated at different temperatures were studied by X-ray and electron diffraction. For dioctahedral micas the in-plane component of the translation between layers (ccosβ/a), which is strongly dependent on the position of the vacant octahedral site, significantly decreases at temperatures greater than the temperature of maximum dehydroxylation. The simulation of XRD patterns from different structural models reveals the actual crystal structure of dehydroxylated samples as well as the dynamics of the structural transformations. In the nonheated state the samples consist of tv (trans-vacant) 2:1 layers. During dehydroxylation, cations migrate from cis- into trans-octahedra and have 5-fold coordination. In the averaged unit-cell the ‘residual’ anions formed after the dehydroxylation reaction occupy the former OH sites with probability equal to 0.5. The migration of octahedral cations is accompanied by the transformation of the C-centred layer unit-cells into primitive ones. In contrast to Fe, Al and Mg cations have a greater ability to migrate.

Glauconites are dioctahedral, microdivided, Fe-containing silicates whose idealized structure may be described as a stacking of 2 : 1 layers with the same azimuthal orientation. The diffractometric and crystallochemical data do not coincide with this idealized structural model. For each glauconite studied the best fit between experimental and theoretical XRD patterns was obtained using the same model. It was possible to describe the stacking by an equally probable occurrence of layers rotated by multiples of 60°. The layer types alternate with a definite tendency to segregation. The model is characteristic for all glauconites, irrespective of composition, age and type of host rock. The alternation of layers rotated by 60° in the structure leads to both octahedral and prismatic coordination for the interlayer K+ cation.

A trioctahedral, ferrous smectite has been located in the uppermost deposits of Atlantis II Deep, SW basin, Red Sea. This clay is very unstable when removed from its environment of formation and, for example, oxidizes during desiccation under laboratory conditions. Only X-ray transmission diffraction study of the mud itself demonstrates the trioctahedral character of the clay. Electron-optical investigation shows that oxidation within the octahedral sheet creates a juxtaposition of dioctahedral and trioctahedral sub-lattices in the same particle. Ferrous smectite authigenesis is located near the hydrothermal spring outlets of the Atlantis II Deep.