Electron spin resonance (ESR) spectroscopy and calorimetric methods were used to characterize conversion processes in multimineral samples from the Northampton ironstone (NIS) at temperatures between 25°C and 800°C. The beginning of the thermal conversion processes can be determined by the formation of asymmetric ESR spectra with g ≈ 2 at 250°C. The breakdown of the berthierine structure between 250°C and 520°C is indicated by the disappearance of the hyperfine splitting in the Mn2+ spectrum and the formation of magnetite. The decomposition of siderite and calcite was found by calorimetric methods at 580°C and 700°C, respectively. The hematite formation between 550°C and 800°C is explained by the decomposition of siderite but also by the oxidation of previously formed magnetite. The occurrence of hematite as the dominant ferric oxide at 800°C signifies the end of the conversion process of the major mineral phases in the NIS samples.

Detrital smectite in a sandy claystone and a phosphorite, and authigenic palygorskite in a dolomitic marl and a porcellanite from Cretaceous-Tertiary phosphorite deposits of the Ganntour Basin (Morocco) were purified using cation exchange resin, leached with dilute acid, and analysed for the contents and distribution patterns of their REE before and after acid treatment. The normalized patterns confirm a detrital origin for the smectite in the sandy claystone, whereas the origin of the smectite from the phosphorite is obscured by the addition of REE from the phosphogenic environment. The normalized REE patterns of the palygorskite suggest formation in non-oxidizing restricted environments. The Al2O3/ΣREE ratio of the two clay types suggests formation of diagenetic palygorskite (and mixed-layer illite-smectite) from Al-bearing detrital smectite by a dissolution-crystallization process.

La fixation du potassium par la montmorillonite sous l'effet des cycles d'humectation et de dessiccation est un phénomène bien connu. On ne peut cependant considérer ce dernier comme responsable de la rétrogradation du K dans les sols que si cette fixation peut se produire même en présence d'autres cations. Chaussidon (1963) avait étudié dans ce but l'évolution de la montmorillonite de Camp-Berteaux K-Ca soumise à des cycles d'humectation et de dessiccation, et avait observé aussi, dans ce cas, une fixation du K. Depuis, les auteurs de la présente communication ont pu proposer un mécanisme de fixation du K par la montmorillonite. A la lumière de ces résultats (aussi les résultats de Glaeser & Mering (1954)) l'étude de l'évolution de la montmorillonite biionique K-Ca sous l'effet des cycles d'humectation-dessiccation a pu être reprise et interprétée. Les résultats de Chaussidon sur la montmorillonite de Camp-Berteaux et ceux qui ont été obtenus sur celle du Wyoming permettent d'établir une comparaison entre les deux minéraux. Le mécanisme de fixation du K est identique et une interprétation des différences observées est proposée.

Halloysite in El-Gideda iron mine occurs as very soft, light and white-to-pinkish white pockets and lenses ranging in diameter from 50 cm to 1 m within the iron ore. Highly hydrated halloysite is the main constituent of these pockets beside some kaolinite and alunite. The diffraction pattern of the clay fraction (<2 mm) shows a rather broad and diffuse 001 reflection spread between 10.3 and 13.6°2θ. Upon treatment, the 001 reflection of halloysite expands up to 10.94 Å and 11.9 Å corresponding to ethylene glycol and dimethyl formamide treatment, respectively. After these treatments, kaolinite appeared with its characteristic basal spacing (~7 Å). The percentage of halloysite in halloysite-intercalated kaolinite ranged between 80 and 90%. Heating to 350°C, produces a kaolinite-like structure (~7.1 Å) that developed to a metakaolinite-structure when heated to 550°C. Morphologically, halloysite appears as well developed tubes composed entirely of SiO2 and Al2O3, while kaolinite is characterized by very fine platelets arranged in book-like or rosette-like shapes. A differential thermal analysis curve of the studied halloysite showed an endothermic peak at ~138°C due to the dehydration of interlayer water of halloysite. The small shoulder at ~540°C and the endothermic peak at ~593°C is attributed to the dehydroxylation of halloysite, kaolinite and alunite. On the other hand the exothermic peak that appeared at 995°C is due to the formation of new phases such as mullite and/or spinel. The infrared vibrational spectrum is typical of highly disordered halloysite and kaolinite.

Halloysite was formed as a result of alteration of the overlying glauconite suggesting intensive chemical alteration during a humid wet period that prevailed in the Bahria Oasis during the late Eocene. Glauconite alteration releases K, Fe, silica and alumina. Iron forms at least part of the iron ore in the El-Gideda mine while alumina forms halloysite as well as alunite when interacted with silica in an acidic environment.

Three-component interstratification of layer silicate minerals in the clay fractions of soils and sediments is probably more common than is generally realized. However, interpretation of the proportion and arrangement of the various components from experimentally recorded X-ray diffraction curves is difficult and in this paper a series of calculated diffraction patterns are presented which illustrate the types of diffraction patterns obtained from interstratified mica-vermiculite-montmorillonite systems.

The Dalradian meta-limestones of the Banffshire coast have been investigated as part of a study of the mineralogy of Scottish sedimentary and metamorphic rocks, the main purpose of which is to assess the extent to which soil minerals are inherited from such parent rocks. Saponite was found to be a common constituent of the non-carbonate fraction. Thin sections of the limestones were examined microscopically and the textural relationships between the saponite and the other minerals, particularly those of undoubted metamorphic origin, suggest that the saponite was formed during the metamorphism. Recent reports of the hydrothermal synthesis of saponite at elevated temperatures and pressures support this hypothesis.

The reactivity of soils and sediments is often described by parameters such as the specific surface area (SSA) and the cation exchange capacity (CEC). Both, however, are bulk values controlled by the presence and crystallinity of different phases, e.g. clay minerals and iron oxides. Amongst the latter, ferrihydrite and goethite are the most abundant minerals. Goethite gradually forms from a ferrihydrite precursor, a process involving a decrease in surface area. Today the BET gas adsorption technique is the most common method to measure SSA. In this study, BET surface areas of synthetic and natural ferrihydrite and goethite of variable crystallinity were compared to (a) mineral-specific measurements, including infrared analysis (IR), differential thermal analysis (DTA), and (b) bulk methods, such as cation exchange capacity and oxalate-soluble iron. Correlations showed that the SSA can be indirectly inferred from all methods. There is no general correlation between IR and BET measurements due to the variability of adsorbed water, which depends on drying and ambient conditions. DTA, particularly using the dehydroxylation peak at 300°C, allows quantification of the goethite content, and hence the SSA, because adsorbed water does not affect this peak. The data set of the present study enabled us to estimate either SSA and/or the content of iron oxides, even in natural mixtures, e.g. those in which smectites determine the SSA.

Major and trace chemical elements from eleven Lower Pleistocene bentonite deposits from Eastern Milos Island, Aegean, Greece, were used for geochemical fingerprinting of the bentonites, by means of scatter binary and ternary plots and canonical discriminant analysis. The trace elements were selected according to their immobility during bentonite formation and subsequent hydrothermal alteration. The bentonites can be separated into at least four geographically distinct groups, each consisting of materials with similar geochemical affinities. The deposits of each group were derived from protoliths erupted from different volcanic centres, suggesting the existence of at least two distinct volcanic provinces, having rhyolitic and andesitic affinities respectively. Several deposits consist of more than one bentonite horizon, indicating that in some volcanic centres the character of volcanism changed with time. Geochemical fingerprinting, supplemented with geological, mineralogical, and textural evidence, may be useful for correlation and exploration of bentonites, in terrains with complex geological histories.

Five palygorskite samples with different chemical compositions and specific surface areas (SSA) were used for this study. Batch experiments in dilute salt solutions under neutral conditions were conducted to study the kinetics of clay hydrolysis. The rates of release of Mg and Si differ significantly among the palygorskite samples. It was found that differences in release rate of Mg among the palygorskite samples are due to differences in both surface area and chemical composition. The rate of release of Mg was greater in palygorskites with high SSA and high Mg and Fe contents than that in palygorskites with low SSA and high Al content. The rate of release of Si depends on the SSA of the mineral and is not related to chemical composition. The initial amount of Si released increases with SSA, while the Si rate of release decreases with increasing SSA. These data suggest that the decomposition of palygorskite in soils and sediments also takes place under neutral conditions.

Dolomite and calcite in Bavarian bentonites, southern Germany, were investigated using petrography, field-emission scanning electron microscopy and stable isotope geochemistry to explore the role of authigenic carbonate formation during bentonitization. Pedogenic, palustrine and groundwater carbonates were distinguished on the basis of X-ray diffraction, micromorphological and stable isotope analysis. The δ13CV-PDB and δ18OV-PDB values of dolomite range from −8.0% to −6.1% and −5.4% to −3.4%, respectively. Calcites show a range from −11.9% to −8.1% for carbon and from −9.1% to −6.2% for oxygen. Carbon isotope compositions imply a C3-plant-dominated carbon source and repeated wetting and drying cycles. The oxygen isotope data points to an evaporation and temperature controlled δ18OV-SMOW value of meteoric water of −7.0% to −4.8%. A syngenetic to early diagenetic timing of dolomitization is indicated, suggesting both dolomite and bentonite formation in non-saline, non-arid and repeatedly partially-oxygenated and reducing soil and groundwater environments during pedogenesis.

(1) Long spacings (29·6 and 26·7Å) are confirmed from certain clays from Japan. (2) These clays have very complicated clay mineral compositions including kaolin minerals, chlorite, sepiolite and montmorillonite. (3) Each long spacing can be explained by a regular interstratification between two kinds of lattices selected from the following ones: montmorillonite (cell ht. 15·4Å), a magnesian chlorite (14·5Å), sepiolite (12·7Å), and a new lattice (14·0Å); the last is a regular interstratitication of gibbsite and silicate (pyrophyllite unit) layers. The new lattice is proposed not only to explain the spacing but all other mineralogical properties of the clay. Thus the 29·6Å spacing agrees well with that of a 15·4/14·0Å super-lattice, and the 26·7 Å spacing with a 12·7/14·5Å super-lattice. (4) These long spacings are liable to be found in a clay in which several kinds of clay minerals co-exist, and such a complex clay tends to be found in special conditions, such as a boundary area between two different kinds of alteration zones, and/or an area affected by successive hydrothermal alteration.

Pedogenic alteration of illite from red earth sediments in Jiujiang in subtropical China was investigated using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Illite, hydroxy-interlayered vermiculite (HIV), kaolinite and mixed-layer illite-HIV (I-HIV) are present in the soils. The characteristic reflections of the clay phases were 14 Å, 10–14 Å, 10 Å, and 7 Å, respectively. After Mg-glycerol saturations, the 14 Å peak of the samples did not expand, and after heating at 350°C and 550°C it shifted to 13.8 Å and 12 Å respectively, with no residual 14 Å reflection, suggesting the occurrence of hydroxy-interlayered vermiculite. The randomly interstratified I-HIV clays were characterized by a broad peak at 10–14 Å, which did not change its position after Mg-glycerol saturation, but collapsed to 10 Å after heating at 350°C and 550°C. HRTEM analysis showed different lattice fringes of 12 Å, 10 Å and 7 Å . Mixed-layer I-HIV, HIV-K and illite-kaolinite (I-K) were observed in the HRTEM images which represented the intermediate phases during illite alteration. The merging of two 10 Å illite layers into a 12 Å HIV layer, lateral transformation of one HIV layer into one kaolinite layer and alteration of one illite layer into two kaolinite layers illustrated the mechanisms of illite-to-HIV, HIV-to-kaolinite and illite-tokaolinite transformation, respectively. The proposed pedogenic alteration of illite and the weathering sequence of the clay minerals in Jiujiang is illite → I-HIV → HIV → HIV-K → kaolinite. In addition, illite may transform directly to kaolinite.

A method is given for calculation of X-ray scattering from interstratified materials which is applicable to components that do not possess centres of symmetry. This procedure allows contributions from interlamellar material to be included in the calculation without any assumptions being imposed by the method on the composition of the components. The method is in fact a simplification of the general formula given by Kakinoki & Komura (1965).

Sepiolites are rare minerals in Great Britain, there being hitherto only two recorded occurrences. The identity of the present sample has been established by means of X-ray diffraction, differential thermal analysis, thermogravimetry, chemical analysis, and infra-red absorption analysis, and some speculations on its genesis are offered.

A smectite formed by weathering of mica in a laterite pallid zone at Boddington, Western Australia has been investigated by analytical electron microscopy. The evidence suggests that this mineral has the chemical composition and swelling properties of ideal beidellite but is anomalous in containing abundant non-exchangeable K. This K balances half of the layer charge that arises mostly from tetrahedral substitution of Al3+ for Si4+, with the K+ occupying one sixth of the sites occupied by K in mica.

Early Cretaceous glauconite from the Xiala section, southwestern Tibet, China, was investigated by petrographic microscopy and scanning electron microscopy (SEM), X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy, and electron probe microanalysis (EPMA). The investigations revealed that the glauconite in both sandstones and limestone is highly evolved. The glauconite in sandstone is autochthonous, but in limestone it may be derived from the underlying glauconitic sandstone. Based on analyses of the depositional environments and comparisons of glauconite-bearing strata in Zanda with sequences in adjacent areas, we conclude that the glauconitization at Zanda was probably associated with rising sea levels during the Late Albian, which represent the final separation of the Indian continent from the Australian-Antarctic continent. After the separation of the Indian continent from the Australian-Antarctic continent, cooling of the Indian continent resulted in subsidence and northward subduction of the Indian plate. A gradually rising sea level in Zanda, located along the northern margin of the Indian continent, was the cause of the low sedimentation rate. Continued transgression resulted in the occurrence of the highly evolved glauconite in this area.

Dehydration and rehydration of a phlogopitic vermiculite saturated with either Sr2+ or Ba2+ were studied by thermoanalysis (TG, DSC, DTA) and by in situ X-ray powder diffractometry. A detailed analysis of the relationship between temperature and state of hydration of the vermiculites close to equilibrium at atmospheric pressure was rendered possible by use of low heating rates in combination with a fast recording position-sensitive detector. For Sr-vermiculite, the results reveal the existence of a number of distinct states of hydration characterized by basal spacings of 1.54, 1.51, 1.49, 1.23, 1.21 and 0.96 nm. The Ba-vermiculite failed to develop a two-layer hydrate even in contact with water. Its one-layer hydrate (1.24 nm) was reversibly transformed into an incompletely dehydrated ordered ‘mica-structure’ (1.00-0.99 urn), before an irreversibly dehydrated structure was attained at temperatures exceeding 700°C The formation of regular 1:1 interstratification was confirmed for all transformations characterized by a change in the number of water layers. The concluding compilation summarizes basal spacings, stacking orders, layer translations and specific water contents for all discrete states of hydration observed in our experiments at saturation of vermiculite with different alkaline earth cations.

Kaolinite- and halloysite-potassium acetate complexes were synthesized by cogrinding with solid potassium acetate (mechanochemical intercalation). The efficiency of mechanochemical intercalation was compared to the intercalation in solution and by homogenization. The effects of ageing and grinding parameters (grinding time, sample:grinding body mass ratio (SGMR), rotational speed) and the humidity on the intercalation were studied. The degree of intercalation increased exponentially with ageing of the samples prepared by mechanochemical and homogenization techniques. For the mechanochemical and homogenization techniques the required amount of potassium acetate per gram of kaolin (∼0.4 g/g) was two orders of magnitude lower than that for the solution intercalation (78.6 g/g). The highest degree of intercalation (86%) and the lowest structural deformation were achieved by the mechanochemical method (¼ h of co-grinding with 1:2 SGMR at 300 rpm), followed by 16 h ageing at 57% relative humidity.

Sixteen montmorillonites (8 normal and 8 abnormal using DTA dehydroxylation criteria) from the Gurasada bentonite deposits, Romania, were investigated by ESR. The spectra showed two features: a g = 4·3 signal attributed to isolated Fe3+ ions and a broad resonance with g ∼ 2·0 which was interpreted as arising from exchange interactions between clusters of Fe3+ ions. Additional experiments suggested that the latter resonance could have a structural component. The line-shape of the two resonances varied between normal and abnormal montmorillonites, indicating that the distribution of the Fe3+ ions between internal phase (montmorillonite lattice) and external phase (montmorillonite surface) was different for the two varieties.

Numerous exposures of highly altered kimberlites in exploratory trenches and pits have afforded an opportunity of studying the very great changes which take place chemically and mineralogically under conditions of tropical weathering in Sierra Leone.