Examination of the differential thermal characteristics of a normal montmorillonite saturated with a series of monovalent and divalent cations shows that the temperature of the main dehydroxylation peak is independent of valency but is apparently a parabolic function of ionic radius. NH4+, Cs+, Zn2+ and Cd2+ give anomalous results, but the apparent discrepancy of the former two ions can be fully accounted for. The results are believed to be consistent with evolution of water molecules through the hexagonal holes in the sheet surface and diffusion between the layers to the micelle edge. The significance of variation in the 800–1000°C region of the curve is briefly considered.

An ion-exchange adduct of saponite with tetra-n-decylammonium cation ((n-decyl)4N+) was prepared and dispersed in chloroform. The material was spread on a water surface to form a thin film at the air-water interface. From the measurements of surface pressure vs. area, it was concluded that the film consisted of the very thin layer which was a mixture of single and double layers of saponite adduct. A clay-modified electrode was prepared by depositing the film on a glassy carbon substrate using the Langmuir-Blodgett method. When the electrode was soaked in an aqueous solution of [Fe(phen)3](ClO4)2 (phen = 1,10-phenanthroline), (n-decyl)4N+ cations were replaced by [Fe(phen)3]2+ ions from solution. This process was followed by measuring the cyclic voltammogram.

Structural differences which occur on heating La-montmorillonite have been studied and compared with those for montmorillonite saturated with Na(I) and Li(I). Rehydration experiments show that La-montmorillonite swells after preheating up to 500°C. However, FT-IR spectra suggest partial migration of the La(III) cations from the interlamellar region to the structural sheets and(or) deprotonation of hydrated La(III) cations, followed by migration of the resulting protons to vacant octahedral sites. Additional measurements of X-ray absorption spectra (EXAFS, XANES) and heating to 700°C suggest that interlamellar hydrated La(III) partially deprotonates producing polyoxocations.

Lime-based mortars with admixtures of metakaolin (10, 20 and 30 wt.%) and fine sepiolite (5 wt.%) were prepared with the aim of facilitating their use as repair mortars in low-humidity conditions. The mechanical properties and the dynamic modulus of elasticity were studied after 28, 90 and 180 days of curing. With an increasing amount of metakaolin in lime mortars, improved mechanical strength was observed mainly after 90 days. Addition of fine sepiolite, due to its adsorption properties for storing water for later supply to the mortar system and its microfibrous morphology, led to an improvement of compressive and flexural strength of blended air lime/air lime-metakaolin mortars, espec ially at later ages of curing. Incorporation of fine sepiolite into air lime-metakaolin mortars resulted in comprehensive densification of the core of the mortars. Air lime mortar containing 5 wt.% of fine sepiolite and 20 wt.% of metakaolin appears to be an optimal admixture.

Montmorillonite is found to be a predominant clay mineral in the < 2µ fraction of the A2 horizon of podzol profiles in Fennoscandia, even when these are only 300 years old. In fractions between 2µ and 20µ vermiculite and hydrobiotite predominate, but are rarely detected in the fraction coarser than 20µ. Vermiculite and hydrobiotite are also found in the finer fractions of the B horizon, but are only rarely detected in the C horizon where their presence is apparently due to contamination with interglacial or older products of weathering. The presence of kaolinite in some profiles is explicable in the same way.

In a letter to “Nature” in 1937, Mitchell and Muir directed attention to the existence, in certain Scottish soils derived from basic igneous parent material, of a very high total cation exchange capacity relative to the clay content—as high as 9 m. eq./gm. clay in some cases. These values were so high as effectively to preclude the possibility of the clay itself being solely responsible for the cation exchange capacity, and in fact in those cases where it was very high relative to clay content, the clay content itself was generally low, so that the cation exchange capacity of the whole soil was quite moderate, of the order of 0·3 m. eq./gm. The high cation exchange capacity could not be due to organic material, for it often occurred in lower layers where the organic matter content was likely to be low.

Six deferrated clay (<2 µm) samples from the major B horizons of pedons derived from basaltic pyroclasts (Western Cameroon) were selected. These soil clays, which differ mainly in their contents of halloysite and kaolinite, represent the types of secondary constituents characteristic of different weathering stages in soils derived from such volcanic materials under humid tropical conditions. On these clays, Ca2+-K+ exchange equilibria were performed at pH 6 and 0·01 n chloride concentration. The amounts of K+ specific sites were estimated through a two-site modelling of the exchange isotherm curves. The total and external surface areas of the clays were measured by EGME retention and by the BET treatment of the N2 adsorption isotherm, respectively. Relative halloysite content was found to be directly related to all measured surface charge properties, i.e. CEC, amount of K+ specific sites, and total and internal surface areas. It was also observed that thermal collapse of halloysitic layers reduced both the CEC and the amount of K+ specific sites. All the surface properties observed point to the presence of smectite units intimately associated with halloysite in these clays. The results further suggest that the layer charge of these smectite units differs in different samples.

Adsorption isotherms of aniline and p-chloroaniline were determined from very dilute solutions on montmorillonite saturated with different cations (i.e. Na+, K+, Ca2+, Mg2+, Cu2+, Fe3+ and Al3+).

In all cases p-chloroaniline was absorbed to a greater extent than aniline. The shapes of the isotherms depend on the adsorbate and on the exchangeable cation and are interpreted in terms of adsorption mechanisms.

For aniline, the solvation of the adsorbate and the electronegativity of the saturating cation seem to be the main factors, whereas for p-chloroaniline the polarizing power of the exchange cation plays an important part. In the case of the Fe3+ ion the oxidizing power seems also be involved.

The enthalpy changes (ΔH°), calculated from the temperature coefficient of the equilibrium constant are exothermic but less exothermic as the polarizing power of the exchange cation increases. The adsorption of the amines on Na-, K- and Ca-, Mg-montmorillonite gives rise to an entropy loss which is higher for the divalent cations. This result is in good agreement with desorption curves obtained after several washings which indicated for the nature of the organo-clay complexes the decreasing order of stability, viz Mg2+ > Ca2+ > K+ > Na+.

The weathering of hornblende in the Rehiran profile has been investigated by optical, X-ray, infrared and differential thermal methods. Optical studies of the fresh hornblende show that it contains discrete lamellar intergrowths of another amphibole which, from infrared evidence, is of an iron-rich nature. This minor phase is selectively weathered in the lower horizons and yields a clay mineral which was identified as interstratified swelling chlorite-saponite. The major hornblende component remains relatively unchanged. Single crystal photographs indicate that the formation of the clay mineral is not structurally controlled by the parent hornblende, although there is a tendency towards alignment along cleavage planes. The clay mineral becomes unstable in the upper part of the profile and could not be detected in the A horizon. Comparisons are made with the findings of other workers.

A structural model is proposed for illite-smectite (I-S) from diagenetic environments which accounts for the presence of three different layer types which are defined as follows: montmorillonite (low-charge, octahedrally substituted, fully expandable), vermiculite (high-cha rge, octa- and tetrahed rally substitut ed, only partly expandabl e) and illite (K0.9Si3.3Al0.7R1.83+R0.22+O10(OH)2). All three layers may be found within the MacEwan crystallites, whereas external edges of the crystallites are only vermiculitic during the illitization process. In the proposed model, a layer is defined symmetrically on each side of the interlayer space, leading to the existence of polar 2:1 units. It is proposed that the I-S growth is a three step mechanism: (1) formation, from sediments of variable composition, of montmorillon ite crystallites; (2) vermiculitization of the montmorillonite crystallite interfaces and of inner montmorillonite layers; and (3) precipitation of illite of fixed chemical composition. The I-S crystal grows by addition of illite layers linked by K+ or NH4+ ions saturating the vermiculitic interfaces.

A green smectitic mineral from Jordan with 16% Cr2O3 (almost 22% on an ignited basis) has been shown by chemical, X-ray, electronoptical, electron microprobe, infrared and thermoanalytical evidence to be an iron-free volkonskoite of composition:

The octahedral occupancy of 4·7, with only Mg2+ and Cr3+ in octahedral positions (in a ratio of 1·14), suggests that the mineral is intermediate between di- and trioctahedral—an inference supported by the uniformity of composition of individual particles (as revealed by the microprobe) and IR evidence, which indicates that it is predominantly dioctahedral but with certain trioctahedral characteristics. A volkonskoite sample from the type area in the USSR, examined for comparison, contained 23·5% Cr2O3 (about 29% on an ignited basis), but proved on electron microprobe examination to be a mixture of at least three species, one of which was aluminium-rich. IR and thermoanalytical characteristics are discussed in relation to the existence of tri-dioctahedral species.

The < 2 µm fractions of two fluvio-glacial sediments from East Greenland have been analysed chemically and by XRD and Mössbauer spectroscopy. The bulk of each < 2 µm fraction consists of feldspars and micas (biotite) which are important constituents of the Precambrian igneous and metamorphic rocks of the area. Significant amounts of vermiculitic and smectitic minerals are also present. Compared with similar minerals present in Danish soil clays, the Greenland vermiculite and smectite are characterized by a high degree of crystallinity and it is concluded that these minerals have been formed from biotite through K release and lattice expansion. These processes appear to have proceeded at a sufficiently high rate to yield significant amounts of vermiculite and smectite despite the cold climate prevailing in the area.

During investigations on clays and minerals, of which only small amounts were readily available, it became necessary to find an accurate micro-method for determining cation-exchange capacities. Usual methods, which are far too numerous to detail here (see, e.g., Kelley, 1948) required considerably more than the 10-50 mg. of material that could be spared. Three possible methods were tested, viz., (a) an adaptation of the manganese method of Bower and Truog (1940 a); (b) a method employing saturation with strontium and utilising spectrographic determination of the sorbed strontium; (c) an adaptation of the usual ammonium acetate method (Schollenberger and Dreibelbis, 1930; Jackson and Truog, 1939).

The results obtained by the first two methods were usually somewhat high—not surprising, as polyvalent ions would have difficulty in bridging exchange spots any distance apart and might consequently be sorbed as M(OH)+ rather than as M++ (Bower and Truog, 1940 b). Method (c) gave results in very good agreement with those obtained with the macro-method normally employed and was the one finally adopted. A complete description and assessment of the method is at the moment in the press (Mackenzie, 1951) and only a brief indication need be given here.

Diagenetic evolution of illite-smectite in shales corresponds more closely than in other rocks to the thermal history of a sedimentary basin. In bentonites, illitization can be significantly retarded by the diffusion of K+ (Altaner et al., 1984; Clauer et al., 1997), and in sandstones it can be related to a localized hot fluid flow (e.g. Whitney & Northrop, 1987). Thus, extracting the diagenetic ages of illite-smectite from shales remains an important opportunity for the verification of basin history models.

Syntheses of Na-magadiite were performed under hydrothermal conditions in a water/alcohol medium. It is only possible to obtain a pure and well crystallized magadiite sample using a water/ethanol medium at a water/ethanol molar ratio of ∼0.12. As shown by thermal analysis and 1H liquid nuclear magnetic resonance spectroscopy, ethanol is not incorporated into the magadiite. Intercalation of dodecyl- and hexadecyltrimethylammonium cations in the interlayer space of Na-magadiite at different theoretical ion-exchange rates shows that the experimental ion-exchange rates are in good agreement with the theoretical ones. However, scanning electron micrographs of the sample having a theoretical ion exchange rate of 25–75% shows that the exchanges are not homogeneous (both thin and thick platelets are present). Attempts to obtain a Si-pillared compound starting from C16TMA-magadiite as the host material leads to a microporous compound having a BET surface area of 778 m2g-1.

Les hydrates à deux couches et à une couche d'une saponite calcique ont été étudiés par infrarouge. Les résultats expérimentaux indiquent que dans l'hydrate à deux couches les molécules d'eau directement coordinées à l'ion calcium sont liées par liaisons hydrogène fortes d'une part aux atomes d'oxygène de surface chargés négativement et d'autre part à d'autres molécules d'eau. En revanche, dans l'hydrate à une couche où chaque ion calcium est solvaté par un minimum de 2 molécules d'eau, il n'y a pas de liaison hydrogène intermoléculaire. La plupart des molécules d'eau donnent une seule liaison hydrogène forte. Chacune des molécules d'eau forme un pont hydrogène, l'une avec le feuillet supérieur et l'autre avec le feuillet inférieur.

In the Maastrichtian-Danian chalk in the North Sea, discrete intervals, appearing as normal white chalk, contain up to 60% α-quartz <2 μm in size. Atomic force microscopy (AFM) reveals that the particles are of nm size, appearing as spherical particles and aggregates. Similar particles consisting of opal-CT were found in surface exposures of chalk in Denmark. Two new abiogenic pathways of silica formation in chalk are proposed. The first model proposes that SiO2 nano-size particles and aggregates precipitated and flocculated in the free-water phase as opal and were diagenetically transformed from opal-CT at low temperature to α-quartz at elevated temperature. In the second model, the dominance of radiolarians in the deep-water environment of the North Sea resulted in low dissolution supply with subsequent precipitation and flocculation of nano-size α-quartz particles. In the shallower water of the shelf environment of the present onshore chalk, the abundance of sponges and their dissolution supplied enough Si to precipitate opal-CT in the free-water phase.

Clay mica is the predominant component of the fine-grained siliciclastic sediments of the Western European Permo-Trias and it may occur as the sole component of the clay assemblage. Its characteristics have been studied by chemical analysis, radioisotope (K/Ar) data, X-ray diffraction and electron microscopy in the clay assemblages from Triassic and Permian sediments in Spain, Western Approaches, South Devon and East Yorkshire. The clay mica is a ferric dioctahedral mineral containing on average 6.5% Fe2O3 and 7.5% K2O. Crystal thickness ranges from 8 × 10 Å to 115 × 10 Å, and varies with geological, stratigraphical and grain-size factors. Radioisotope data and geological considerations suggest that much of the Permo-Triassic clay mica was formed originally in coeval desert soils rather than being derived from pre-existing rocks. It was then eroded, sometimes mixed with much older material, and deposited as fine-grained detritus in adjacent areas. Upon deep burial, this detrital mica assemblage underwent recrystallization with the development of euhedral crystals and the alteration of the K/Ar values.

Neutron diffraction experiments can provide an extremely high-resolution structural picture of clay-fluid systems. Here we describe the application of time-of-flight neutron scattering to hydrated clays, including discussion of issues such as isotopic labelling, sample containment, and data analysis. Recent studies of hydrated vermiculites under ambient conditions are used as an example. We then describe a new high-pressure/high-temperature sample environment that is being used to study clay-fluid interactions, in situ under hydrostatic sedimentary basin conditions. This environment enables us to approximate conditions encountered during burial, at depths of up to 10 km.

The alteration and transformation behaviour of Ceca smectite in two acid and saline solutions (NaCl and KCl) was studied in batch experiments. This type of smectite is proposed as potential backfill material for nuclear waste storage sites. The initial solution was enriched with 500 ppm of U, Th and Eu. The evolution of pH and solution concentrations were measured over a period of 25 months. The mineralogical and chemical evolution of the clays was also studied. X-ray diffraction revealed a significant loss of diffraction intensity and the clays became amorphous to Xrays with increasing reaction time. Deconvolution of the XRD data indicated a continuous collapse of the smectite layers but no illitization. Infrared spectroscopy revealed unchanged smectite spectra at the end of the experiment. Thorium precipitated as amorphous ThO2, but showed an incipient crystallization after 500 days. The Th, Eu and U were neither adsorbed onto the clays nor incorporated into a secondary phase.