It is suggested (1) that large amounts of Al, Fe and Si carried in solution by fresh water are chemically precipitated as hydroxide gels in the brackish water environment of estuaries and deltas, and (2) that these gels are subsequently deposited in both the brackish water environment and in the neighbouring seas, where they become parental material for the neoformation of clay minerals, and various other silicate and iron minerals. The types of neoformed minerals will depend upon both the composition of the parental gels and the physico-chemical milieu of their crystallization. Evidence is discussed supporting this hypothesis from the following sources (1) the concentrations of Al, Fe and Si dissolved in fresh water and in sea-water, (2) experimental work on the crystallization of alumino-siliceous gels, and (3) a study of the precipitation of Si from the waters of the Mississippi River delta.

Because of the unusual sediment pattern of present times, this source of neoformed clay minerals and other minerals contributes only a small proportion of the sediments of the brackish parts of estuaries, deltas and the adjacent seas, which are dominated by fine-grained continental detritus. In earlier geological eras, when the world's river systems carried only relatively minor amounts of fine-grained continental detritus, this source of neoformed minerals is likely to have contributed a considerable proportion of the fine-grained sediments of these areas of sedimentation. Three possible examples are discussed.

Metamorphic isograd surfaces are mapped within the Morcles nappe using illite crystallinity (IC) and (clay-) mineral parageneses in 268 samples. The diagenesis-anchizone and the anchizone-epizone boundaries are nearly vertical surfaces which crosscut the present-day recumbent fold nappe structure. Frontal parts of the nappe are diagenetic (Tmax <200°C) whereas rear parts both in the normal and inverted limb are epizonal (Tmax >300°C). We demonstrate that the calcite content of shales, marls or limestones has no influence on the average IC. Deviations of individual samples from the mean IC of any given diagenetic and lower anchizonal site are very large, however, without it being possible to associate deviations with any obvious rock parameter. The standard deviations of populations of IC values decrease strongly with increasing metamorphic grade (toward smaller IC values). Mapping the diagenesis-anchizone boundary requires a much larger sampling effort than the same exercise for the anchizone-epizone boundary.

The clay mineralogy of Pleistocene sediments of eleven sediment cores at three ODP sites from 30°N to 60°N northwestern Atlantic Ocean has been investigated. The sediments are characterized by the presence of random illite-vermiculite mixed layers (I-V) (up to 32% of the clay mineral assemblage). The I-V clays are much more abundant during interglacial periods than during glacial ones. They are attributed to detrital supply through erosion of high-latitude continental areas from which they are derived mainly from chemical weathering of micaceous phyllosilicates. Their spatial distribution and the specific conditions for their formation through weathering suggest that I-V mixed layers are mainly derived from the Canadian Shield. They were transported from their source to marine deposition areas by rivers, deep water masses or nepheloid layers. Due to the specific conditions required for the formation of I-V, its occurrence and abundance are used as a palaeoclimate and palaeocirculation proxy for northwestern Atlantic Pleistocene sediment.

The work reported herein involves the characterization of natural zeolites from two different mines (San Andrés and Tasajeras; Cuba) using XRD, SEM, TG-DTA, ICP and surface area measurements. In addition, the chemical composition of zeolites, the heavy metal and environmental organic toxins content, the ion exchange rates, stability under biological conditions using simulated body fluids as well as the binding capacity for histamine have been investigated with a view to using them as medical products. The investigated zeolites contain clinoptilolite and mordenite as major phases. Furthermore, the samples are apparently free from fibrous materials according to SEM observations. In particular, the San Andrés zeolite binds remarkable amounts of histamine which are nearly irreversible under acidic (pH = 1; 12.4 mg/g) and neutral conditions (pH = 7; 15.7 mg/g), respectively. Thus, the San Andrés sample may well be applied as a medical product due to its excellent binding capacity for histamine along with its remaining optimum physico-chemical characteristics.

A study of soil formation on glauconitic parent materials in South-East England has included a mineralogical investigation of glauconite grains, heretofore identified solely by morphology. The grains have been subjected to X-ray diffraction, differential thermal and partial chemical analyses, and have been found to consist essentially of randomly interstratified micaceous and montmorillonitic clay mineral; thus all are glauconite sensu lato. Only small amounts of non-clay mineral impurities have been detected. The proportion of expandable layer material has been found to be related to the % K2O and cation exchange capacity of the specimens.

An interstratified clay mineral from Surges Bay, Tasmania, described by Cole & Carthew (1953) as containing a random stacking of illite and montmorillonite in the ratio of 3:2 and a regular stacking of illite and montmorillonite in the ratio of 1 : 1 is re-examined, after purification, and a new interpretation is made of the X-ray diffraction effects in terms of a single complex stacking model. The Fourier transform method of analysis used with an appropriate layer structure factor shows that the interstratification is produced by a three component stacking of 18% single mica layers (A), 10% double mica layers (ĀĀ) and 72% allevardite-like layers (ĀB̄) in which the A and ĀĀ layers are never together. This leads to the conclusion that the near regular interstratification of the mineral is due to structural and/or compositional variation from layer to layer within the parent crystals as suggested by Sudo, Hayashi & Shimoda (1962) to explain similar mineral types occurring in Japan.

The weathering of biotite in Quaternary lahars from Monti Ernici (Central Italy) via interstratification stages has been studied by X-ray diffraction of both the interstratified minerals and the initial (biotite) and final (vermiculite) end-members. The structure of the biotite and vermiculite is described by means of monodimensional Fourier series. The interstratified phases have been studied using the INTER program which permits an analysis of two interstratified components by Fourier transform methods. It is shown that in the alteration range for biotite to vermiculite even small samples have different spatial concentrations of biotite, vermiculite and an intermediate biotite-vermiculite-type phase. Hydrobiotite and a rare biotite-hydrobiotite with a tendency to regularity have also been documented. Chemically, the process involves considerable oxidation of Fe2+ and the removal of most of the elements, corresponding to a 34% loss in matter. The sequence of the element losses is: K+ > Fe2+ > F− > Mn2+ > Si4+ > Mg2+ > Al3+ > Ti4+. There are also some gains in the order: H+ > Ca2+ > Fe3+ > Na+.

The electrical conductivity of synthetic zeolites, types X and Y has been studied to give information about the distribution and possibility of migration of the exchangeable cations, located at various sites. The Na+ samples were exchanged with K+, Cs+, Ag+, Li+, and NH4+. The various cationic forms were pressed into pellets and treated at 430°C under high vacuum for 24 hours. After cooling, the electrical conductivity and capacity was measured as a function of frequency (500–20,000 c/s) at various temperatures from −20°C up to 500°C. For each sample the reversibility was investigated. The experimental results allow the calculation of the specific conductivity, the real (ε′) and imaginary (ε″) part of the complex dielectric constant (ε*) and the loss factor tgδ.

The results show an ionic conductivity: the specific conductivity depends on the nature of the exchangeable cations as follows: Cs+ > K+ > Ag+ > Na+ > Li+. There is a different conductivity mechanism in the high temperature region compared with the low temperature region. At high temperatures (T > 400°K) the activation energy is independent of frequency. At low temperatures, a dielectuc absorption phenomenon occurs. The activation energy, calculated for this process was somewhat higher, but of the same order of magnitude as that of the high temperature region. It is suggested that the migration of the exchangeable cations in the supercage to interstitial positions gives rise to this dipole absorption phenomenon.

A comparison of the decationated Y zeolites with Na+Y and Na+X made it possible to attribute the conductivity to the cations in the supercage only. The exchangeable cations in the cubo-octahedra and in the hexagonal prisms lower the activation energy of the moving cations. Thus the energy of activation of X zeolites is lower than of Y zeolites.

A series of Mn-goethites was synthesized at highly alkaline conditions. The samples were aged for 15 days at a final [KOH] of 0.3 M. Products were washed free from non-goethite phases using 3 M H2SO4. The bulk mineralogy of the samples was determined by X-ray diffraction and verified on selected individual crystals by electron diffraction. The samples had a relatively low magnetic susceptibility (300≤MS≤400×10-9 m3/kg). As revealed by total acid dissolution, the Mn mole fraction XMn ranged from zero to 0.125. Five samples (XMn: 0.025, 0.050, 0.077, 0.099, 0.125) were selected to investigate the variability of the XMn value in single goethite needles (crystals) by analytical electron microscopy (AEM) using rastered and spot analyses. Linear regressions of both as a function of total Mn yielded unit slopes and zero intercepts, indicating that acid dissolution gave the same results as AEM. Spot AEM, however, revealed significant variation of Mn distribution within individual crystals which argues in favour of Mn zoning in goethite. Inhomogeneous transformation of ferrihydrite to goethite may partly explain the Mn zoning.

Six clays from various deposits were studied for their use in the production of structural clay products. The clays were characterized using chemical (X-ray fluorescence), mineralogical (X-ray diffraction) and thermal (differential scanning calorimetry/thermogravimetry) analyses. Particle-size distribution was determined by laser diffraction, plasticity by the Pfefferkorn method and the residue by the sieve-size method. Next, specimens were formed by extrusion and characterized by their linear thermal shrinkage (on drying and firing), water absorption, bulk density, porosity and compressive strength. The clays were, in general, suitable for the manufacture of structural ceramics, mainly bricks. The clays from flooded pits (AV1 and AV2) were classified as floodplain clays and alluvial clays. The clays mined in mountainous regions (AM1 and AM2, as well as AV1) were characterized as siliceous clays due to the abundance of free SiO2 phases.

Nous présentons une méthode de calcul de l'énergie totale d'une structure cristallińe (énergie électrostatique, énergie de van der Waals, et énergie de répulsion). Nous utilisons ensuite cette méthode pour étudier une série de phyllosilicates (talc, pyrophyllite, muscovite et phlogopite), pour comparer et discuter leurs propriétés physico-chimiques en particulier l'énergi de liaison interfoliaire et la distance interlamellaire. Nous constatons que des méthodes de calcul, basées sur des expressions empiriques différentes de l'énergie de répulsion, conduisent à des résultats relatifs analogues. Nous vérifions que la distance interlamellaire calculée approche la distance mesurée à 0·1 Å près. Nous calculons des énergies de liaison interfoliaire du talc et de la pyrophyllite (de l'ordre de 30 Kcal/mol) plus faibles que celles de la muscovite et de la phlogopite (de l'ordre de 60 Kcal/mol).

Vermiculite single crystals immersed in aminoacid solutions of varying concentration and pH, form complexes characterized by discrete basal spacings. Organic molecules enter in the interlayer space as cations and as dipolar ions through mechanisms of ion exchange and dipole adsorption.

The basal spacings of the complexes were recorded. Based on these results the possible arrangements of the aminoacid molecules have been discussed.The main assumptions used are: (a) the electropositive groups NH3+ penetrate into the holes formed by the basal oxygens of the silicate; (13) the C-N bonds are perpendicular to the silicate sheets; (c) the hydrogen atoms of the —CH2 groups are directed towards the sheet surfaces; (d) the —COO− and —COOH groups are located in the middle plane of the interlayer space, halfway between the negative structural charges; and (e) double hydrogen bonds are formed between —COOH groups belonging to organic cations adsorbed onto opposite surfaces.

In solutions of higher concentration the crystals swell to the gel state. This phenomenon is due to: (a) the different nature of interlayer cohesion after substitution of the inorganic cations by the aminoacid cationic form; and (b) the appearance of repulsive forces between —COO− groups of adsorbed dipoles, that overcome cohesive forces.

Three soils of the Strathdon area, Aberdeenshire, derived from a biotite-rich quartz-gabbro and representing well-drained, imperfectly drained and poorly drained types, were studied. The 50–200 µ fractions contained mainly plagioclase feldspar, amphibole (tremolite and hornblende), biotite and quartz and the following order of relative stability was established: quartz > amphibole > plagioclase feldspar > biotite. In all soils biotite was found to weather to a 14 Å aluminous vermiculite-chlorite with zones of kaolinite. The clay mineral composition of three soils was identical, consisting of trioctahedral vermiculite-chlorite, trioctahedral illite, kaolinite and gibbsite. These minerals originated in various ways through the decomposition of biotite which thus plays a key role in the origin of the clay fraction. It is suggested that the clay mineral constituents of the soils were formed in a regolith predating the last glacial period, and that post glacial soil-forming processes have modified them only slightly.

Samples of the mineral pyroaurite, formed from the weathering of partially serpentinised harzburgite (olivine + pyroxene) were found in an arid region of the Sultanate of Oman. These were either golden or silver in colour depending on the horizon from which they were derived. Chemical analysis showed that the colour variation was primarily due to the differing conditions in the hydrological environment. The golden colour was attributed to small Fe(III) oxide particles detected by Mössbauer spectroscopy. In addition, the samples were examined by X-ray diffraction, scanning electron microscopy, and glycerol intercalation. These results were compared with a synthetic pyroaurite sample prepared under conditions (previously reported) similar to those in nature. These conditions are shown to approximate to those found in the hydrological environment in the zones of the natural pyroaurite formation.

The adsorption of methylene blue (MB) on montmorillonite from acid solutions has not yet been studied in detail. In this paper the adsorption of this dye on Ca/SAz montmorillonite from 0.32, 0.80 and 1.60 M HCl solutions at ambient temperature and after 2 hours leaching was carefully studied and evaluated. Under the above conditions the MB/SAz intercalates formed are practically insoluble. In contrast to the adsorption of methylene blue on montmorillonite from aqueous solutions, the adsorption from acid solutions consists of two adsorption waves. The intercalated samples from the first and second waves were studied using X-ray powder diffraction (XRD), FTIR, Vis spectroscopy, and scanning electron microscopy (SEM) equipped with a microprobe system. The adsorption of MB in the first wave is attributed to ion exchange of the dye cationic species (MB+, MB22+, H-aggregates, MBH2+ and H+) for the original interlayer cations of montmorillonite. The percentages of MBH2+ and H+ based on total adsorbed MB were estimated for varying HCl concentrations. The second adsorption wave is linked to the precipitation of MB species on the outer MB/SAz surface.

The intercalation process of crown-ethers and cryptands into Ba2+- and Na+-montmorillonites leads to H-type adsorption isotherms according to the Giles et al. classification. The experimental monolayer capacity shows that 1:1 or 2:1 macrocyclic ligand/interlayer cation complexes can be produced. Kinetic experiments at different temperatures indicate that the intercalation is diffusion-controlled. The activation energies deduced from Arrhenius plots are 25–38 kJ mol−1.

The purpose of this study was to investigate the impact of redox-induced changes in the organization of the clay fraction of a bulk vertisol using transmission electron microscopy. Chemical and X-ray powder diffraction (XRD) analyses indicated that the oxidized clay was composed of 32% kaolinite and 68% non-pure smectitic material, mostly a dioctahedral beidellite with octahedral Fe, according to Quantarg2 and DecompXR models.

The cation exchange capacity of the soil increased from 26.1 to 65 cmolc+ kg-1 due to structural iron (FeStr) reduction and dissolution of oxide coatings. Transmission electron micrographs revealed dramatic changes upon reduction. Oxides were dissolved and the smectite increased in particle darkness, lateral extension, thickness, compactness and stacking order. These changes were interpreted to be a consequence of sorption of ferrous Fe and reduction of FeStr, as found in previous studies on pure Fe-bearing smectites.

The mineralogical and chemical changes of sheridanite were followed in different alteration horizons as weathering of its host amphibolite increased. Microscopic and microprobe analyses of phases produced in or around the chlorite allowed a classification of the different alteration stages relative to their position in the profile. In the unweathered rock, prehnite and a sericite—kaolinite assemblage appear to have formed at grain boundaries between chlorites and plagioclases. These represent low-pressure (PH2O < 2.5 ± 1 Kb) and low-temperature (320–360°C) metamorphic phases. In the saprock, where initial rock structure is still preserved, chlorites weather to a more or less regular mixed-layer chlorite-vermiculite. In the saprolite, large-grain (20 µm) vermiculite forms in the clayey zones (plasma) when rock structure is destroyed. The chemical composition of these newly-formed minerals is influenced by the original chlorites and mixed-layer minerals.

Griffithite is a trioctahedral smectite with dioctahedral domains, found in the <2 μm fraction of weathered basic rock from Griffith Park, California, USA. Crystalline admixtures (albite, calcite, quartz and maghemite) are concentrated in the 0.2 – 2 μm fraction, while the <0.06 μm fraction contains only trace amounts of other minerals. Griffithite is primarily an Fe–rich saponite with negative charge located in the tetrahedral sheets. The octahedral occupancy is ∼91%, and ∼26% of the octahedra contain trivalent atoms imparting a net positive charge to the octahedral sheet. Medium levels of Fe(III) reduction in griffithite, up to 60% of total Fe, can be achieved by adding solid sodium dithionite to clay dispersions in a citrate–bicarbonate buffer. By contrast >90% reduction of Fe(III) to Fe(II) is achieved in nontronites using the same method. The lower reducibility of Fe(III) in griffithite relative to nontronites may be due to structural differences between griffithite and nontronites, such as a more negative tetrahedral charge and a positive octahedral charge.

Polyamine is a novel inhibitor applied to water-based drilling fluids in order to reduce hydration of clays, especiallymontmorillonite (MT). In the present study, thewater-adsorption properties of montmorillonite intercalated with polyamine were characterized by X-ray diffraction (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) and adsorption isotherm tests using water, benzene and heptane. According to the XRD, DRIFT and water-adsorption test results, polyamine (PA)- intercalated montmorillonite (PA-MT) adsorbs less water than either K+- or NH+4-intercalated montmorillonite (K-MT, NH4-MT). The surface energy of MT was analysed using the van Oss- Chaudhury-Good (VCG) approach based on thewater, benzene and heptane adsorption results. The surface energy between PA-MTand water was less than that of NH4-MT and K-MT. Compared with K-MT and NH4-MT, the surface energy of the Lewis acid portion of PA-MT underwent a more significant decrease, suggesting that the hydration of unexchanged Na+ did not make a discernible contribution. The experimental water-adsorption data were fitted using Langmuir, Brunauer-Emmett-Teller (BET), and Freundlich adsorption models. The Langmuir adsorption models can be used to fit the data for water adsorption on PA-MTacross the entire p/p0 range. After plotting the experimental data in the linear format of the Freundlichmodel, only one linear region for PA-MTwas observed, indicating a singlewater-adsorption mechanism for PA-MT. When compared with PA in the absence of clay, DRIFT spectroscopy showed that the NH2 bending mode for PA-MT shifted from 1571 cm–1 to 1619.7 cm–1. This suggested an increase in hydrogen bonding (H bonding) between the ammonium group and the interlayer water. Across the entire p/p0 range, water is suggested to have adsorbed onto PA-MT through H-bonding interactions between the ammonium group and the interlayer water.