The present study examines the micro- and nano-texture and composition of ammonium-bearing and potassium micas in very-low grade metamorphic black Silurian shales from the SE Iberian Range (NE Spain). Two organic-rich shales were studied by X-ray diffraction (XRD), infrared spectroscopy (IR), transmission electron microscopy (TEM), analytical electron microscopy (AEM) and electron energy loss spectroscopy (EELS). The XRD showed the presence of two populations of micas: pure K micas with d001 = 9.98 Å and ammonium-bearing micas with larger d001 values (10.08 Å and 10.05 Å). The latter values indicate NH4 contents between 13 and 29% in the interlayer, which was confirmed by IR. Interstratifications of smectite and mica layers in the mica packets were not detected by XRD and TEM. Mica packets with sizes ranging from 100 to 250 Å show disordered polytypes and (001) lattice fringes that reflect the presence of K- and NH4-bearing layers (9.9–10.2 Å).

The combination of AEM and EELS analyses on powdered and lamellar samples indicates that micas have typical dioctahedral compositions with highly variable K contents. This variation in K is consistent with the presence of K and NH4 in the interlayers, even though the NH4 and K are not distributed homogeneously; rather they are segregated in nm-sized domains in the mica interlayer.

The effect of ulexite concentrator waste on the physical and mechanical properties and sintering behaviour of a standard floor tiles (FT) body fired at 1080°C was studied. The linear firing shrinkage, water absorption and fired bending strength of the floor tile/tiles were determined. X-ray diffraction analyses identified quartz, albite, mullite and hematite phases in the floor tiles containing 3 wt.% waste material. The FT body with the smallest water absorption (∼0.2%), the greatest bending strength (∼335 kgf/cm2) and the second greatest linear firing shrinkage values had optimal composition. In light of the excellent physical-mechanical properties and the results of the scanning electron microscopy-energy dispersive X-ray analyses, the authors determined that the sintering temperature of the FT body containing 3 wt.% ulexite concentrator waste was reduced by 100°C.

While the writer was working on an unusual form of calcium carbonate usually found in caves, he collected some material closely resembling it from an adit of the disused Odin Lead Mine, Near Castleton, Derbyshire.

This material was pure white in colour, tending in places to translucency. It had a S.G. of 2.125 and a R.I. of about 1.5, though determination of the latter was rendered uncertain on account of included water. It took the from of a rippled flow covering the Carboniferous Limestone walls and roof of the passage. It was very soft, being obviously in the process of formation, though in places it had dried to form a slightly resistant encrustation.

The Mamil Choique halloysite deposits of Patagonia, Argentina, contain randomly distributed green clay inclusions and patches within the halloysite mass. Halloysite has been formed from the thorough alteration of rhyolitic to dacitic ash fall tuffs and ignimbrites of the Huitrera Formation, Eocene age, under ambient conditions. The smectites present in the clay inclusions have been determined as ferruginous beidellites with variables amounts of Fe3+ in octahedral sites. The weathering activity that caused the formation of halloysite was also responsible for the genesis of the iron-bearing clay minerals, the formation of which was controlled mainly by permeability. Textural variations within the rock indicate favourable local geochemical environments for the formation of the green clay minerals.

The fluorination of montmorillonite by aqueous ammonium bifluoride solution (NH4HF2) has been investigated by chemical, sorptive, porosimetric and electron microscopic methods. Changes in the chemical composition of the montmorillonite during the fluorination were compared both in the crystal surface and in the bulk sample. The accumulation of fluorine was distinctly zonal, being present mainly in the surface layers. The electron microscope studies showed that the 300–400 nm thick macrodomains in the initial montmorillonite were cracked into small microdomains 20–30 nm in thickness, this resulting from disruption in the continuity of the octahedral sheets. These distinct changes in morphology of the montmorillonite aggregates particularly influenced the porosity and sorptive properties.

Two natural clays (kaolinite and montmorillonite) were deposited onto a platinum electrode surface using two deposition techniques and under different experimental variables. For both clays, the percentages of surface coverage (%θ) were optimized in the 75–96% range. A greater surface coverage was observed at higher temperatures for both clays, which confirms the endothermic nature of the deposition process. The maximum surface coverage (96%) was achieved for kaolinite. The surface coverage of kaolinite on a platinum electrode was constant for deposition times between 6 and 20 h. A surface coverage of 91% with montmorillonite particles was achieved. There was a very small increase in surface coverage by increasing the concentration of clay in the modified solution. The maximum surface coverage was observed under acidic conditions and smaller coverage values were reported for neutral and basic solutions. For both clays, a complete surface coverage for the electrode surface was achieved using the spin-coating technique. The experimental variables that affect the deposition of the clay, such as the stoichiometric ratio of clay/PVC and centrifugation speed and time, were studied and optimized to obtain full surface coverage. The spin-coating method achieved the required durability and stability for the modified-electrode. The characterization showed that the metallic surface chemistry of the platinum electrode was totally suppressed. Both modified electrodes were found to be useful for determination of Ag(I) ion with a detection limit as small as 1.00×10–10 M. The analytical precision was also satisfactory (RSD <5.0%).

The mineralogical, geochemical and micromorphological features of an isalteritic clay facies, which originated from weathering of an anorthosite, were compared to those of clay facies derived from the degradation of a bauxite developed from the same rock. The isalteritic clay was formed by the hydrolytic alteration of plagioclase, whereas the degraded clays were formed by decomposition of gibbsite and neoformation of kaolinite. This resilification process resulted from the reintroduction of silica via the oscillation of the phreatic level and/or the decomposition of organic matter on the surface. The degradation process was gradual and yielded two different facies: (a) degraded clays with almost total decomposition of gibbsite, and (b) degraded clays with gibbsite nodules. Morphologically, the isalteritic clays differ from the degraded clays because they contain larger hexagonal and pseudo-hexagonal crystals. The degraded clays have more irregular crystal shapes, ranging from laths to anhedral shapes.

The object of this study was to find a structural explanation for the corrosion figures produced in biotites having different chemical compositions and to apply this information to other di- or trioctahedral micas. The biotites investigated were used in earlier studies of epitaxial growth, so that previous knowledge of their surface behaviour was available. The biotites studied were from Evje, Norway (number 1), Guomum, Czechoslovakia (number 2), and Tanokami Yama, Japan (number 3). All were very dark in colour due to their high iron content.

A new approach to understanding illite-smectite interstratification is formulated which incorporates the concepts of interparticle diffraction and elementary illite particles. The analysis shows that nearest-neighbour ordering, non-nearest-neighbour ordering, ordering at the illite end of the composition scale, and the lack of ordering at the smectite end can be explained by expandable interfaces between elementary, i.e. two silicate layers, and larger illite particles. Ordering in I/S clays is significant only when the probability of occurrence of illite is ∼80%. New concepts proposed are an order parameter (ω) and an expansion parameter (β). Interparticle diffraction implies that I/S clays are unusual among all crystalline materials since their XRD size is equal to or larger than the size of their constituent physically separable particles.

Both kaolinite and its thermal decomposition products are to be regarded as “active” solids in that they have a fairly large specific surface area, of the order of 10 square metres per gram. It was therefore thought worth while to apply some of the procedures which proved useful in the investigation of other surface active solids, to the problem of the dehydration of kaolinite. The techniques chosen were: (a) the resorption of water by the dehydration product; (b) the sorption isotherm of a vapour (carbon tetrachloride) on the dehydration product, in order to estimate its surface area; (c) the apparent density of the product in a suitable, inert, immersing liquid; (d) X-ray examination of the product (through the kindness of Dr Clark and Mr Parker of English Clays Lovering Pochin Ltd.).

Microscopic observation is valuable for elucidating diagenetic phenomena in clays subsequent to deposition. Examples:—

1. (1) Pressure can enlarge the regions of parallel orientation in kaolinite (Fig. 1), even giving zoned regions (Figs. 2, 3).

2. (2) Solution and re-precipitation may give vermicular kaolinite (Figs. 4,5), “fluidic” halloysite (Fig. 6), or vermicular dickite on nuclei of hydrargillite (Fig. 7).

3. (3) Montmorillonite may form from halloysite by action of basic siliceous waters (Fig. 8); or (together with halloysite) from kaolinite (Fig. 9).

4. (4) Illite may recrystallise, giving large hexagonal forms (Fig. 10).

Among the lithological types making up the northern Appennines, an important part is played by the (occasionally schistose) clays which make up the main bulk of an enormous nappe (“liguride,” according to Stille) which has slipped from the Ligurian region towards the Po valley. These clays are particularly well developed in the mid-mountain region, and can, because of their plasticity, insinuate into the more recent formations.

Within the argillaceous nappe, frequent nuclei of basic and ultrabasic rocks (gabbros, diabases, serpentines) are observed, of size ranging from that of a pebble to masses of many thousands of cubic meters (Monte Penna, Sasso Tignoso), which appear immersed in the clay mass without having produced in it the well-known contact phenomena.

In a high-level radioactive waste repository, bentonite may react with the alkaline solution produced by cement degradation. In this study, bentonite was mixed with alkaline solution in a closed system and reacted for 3–24 months. Furthermore, swelling tests were conducted on the alkaline-dissolved bentonite immersed in distilled water. The swelling deformation decreased significantly with increases in the concentration of NaOH solution and reaction time, and this was mainly due to montmorillonite dissolution. The fractal e–p relationship (e is the void ratio and p is the vertical pressure) with two calculation coefficients (the swelling coefficient and the fractal dimension) was employed to determine the swelling of alkaline-dissolved bentonite. The fractal dimension increased slightly with increasing reaction time or concentration of NaOH solution, as the dissolution traces caused by the alkaline solution favoured an increase in the irregularity and fractality of the bentonite surface. The swelling coefficient decreased linearly with decreasing montmorillonite content. In addition, the swelling coefficient and the fractal dimension were related exponentially to the reaction time in alkaline solution. A relationship between the swelling of alkaline-dissolved samples and the reaction time was proposed, which might be used to assess the swelling properties of bentonite barriers that would be affected by long-term dissolution of the alkaline solution in a closed repository.

Clay often has severe detrimental impacts on cement-based materials. Therefore, it is necessary to investigate the mechanism causing the deterioration to improve the service life of cement-based materials. Based on accurate dimensional analysis, a mechanism that influences clay is proposed: the intercalation of the side chains of superplasticizer molecules in the interlayer space of the clay. To lessen this harmful effect, a new clay-resistant admixture (CRA) possessing cationic groups of small molecular size was synthesized through a novel dimensional design. The length and width of the side chains of this superplasticizer molecule were 9.50–17.50 and 0.25–0.40 nm, respectively, with a radius of ~3.74 nm in solvent, which is larger than the interlayer spacing of montmorillonite (i.e. 1.09–2.14 nm). The longitudinal and latitudinal lengths of the CRA molecule were 0.468 and 9.456 nm, respectively, ensuring intercalation in the interlayer of montmorillonite. The increase in interlayer spacing of the clay was 0.364 nm following addition of polycarboxylate superplasticizer (PCE) plus CRA and 0.632 nm following addition of PCE, which suggests that the CRA plays the role of a ‘sacrificial agent’ that is preferentially intercalated into the interlayer space of clay to further prevent the side chains of the superplasticizer molecules from entering the interlayer. The aim of this study was to propose a suitable means of synthesizing a new CRA to address the impact of clay through dimensional design and mechanism analysis, which contributes to the theoretical study and technological improvement of cement-based materials.

Ka Loko Dam, in Kauai, Hawaii, failed suddenly and catastrophically on March 14, 2006. The resulting breachwas marked by three topographic benches, the lowest of which exposed native volcanic deposits once resident in the dam foundation. These deposits were found to contain outcrops of a waxy, gel-like material that appeared to result from in situ weathering processes. This unusual material was found to be highly enriched in halloysite. Gravel-size pieces in the hydraulic fill of the embankment derived from these materials also exhibited significant in situ weathering and significant halloysite content. Engineers and geologists generally recognize that bedrock materials weather progressively into soil constituents over ‘geological time’, and that this process is accelerated in tropical environments. Still, the strength, stiffness and durability of bedrock, earth and embankment materials are not expected to vary significantly over the geologically short life of a dam. In the case of Ka Loko Dam, however, the volcaniclastic sediments that comprise the local bedrock experienced substantial in situ weathering over its geologically brief 115-year operational lifetime. Prolonged exposure to seepage of anoxic water weathered the sediments completely to saprolite, including weak, sensitive, fine, spherical halloysite.

Mathematically, it is well established that besides the Fourier coefficients, the natural characteristics of any distribution are its moments. The use of the second moment, called variance, as a measure of line broadening has already gained wide popularity because of its several merits relative to other empirically devised parameters. In recent decades, the fourth moment has been recognized as an important parameter; its theoretical significance has been discussed by Mitra (1964), who developed the moment range function for the estimation of crystallite size and distortion in cold-worked metal. However, owing to the requirements of high degree of accuracy of intensity measurement coupled with cumbersome calculations, this parameter did not find much general application. Modern diffractometers and sophisticated computers have helped ease the problem and in recent years several workers (Kagan & Snovidov, 1965; Kulshreshtha et al., 1971; Mukherjee, 1981) have successfully used this parameter for defect analysis in various non-ideal forms of materials.

Spongolite from the State of Mato Grosso do Sul, Brazil, contains the remains of fossil sponges and hollow needles or microcapillaries with uniform surfaces. The central tunnels are ∼1/10 to 1/2 of the cylinder's diameter. The material is essentially X-ray amorphous though it contains small amounts of orthosilicic acids. The other main elements were Ti and Fe. Spongolite may have uses as a sorbent, as a bioavailable silicon source or, after blending with glass waste, it can be used in the fabrication of lightweight products having a closed-cell structure, potentially useful as an industrial insulator.

Only recently has it been possible to perform quantitative mineralogical analysis of clays and to establish the crystallochemical and morphological characteristics of the different clay minerals. The classification and nomenclature of these minerals is complicated by the existence of mixed-layer structures which are essentially epitaxial assemblages.

The Fe3+ uptake from aqueous and methanol solutions of FeCl3·6H2O in two vermiculites from Santa Olalla and Ojén (Spain) and in a montmorillonite from Wyoming has been investigated by Mössbauer spectroscopy at room temperature and 4.2 K. The samples were further characterized by X-ray diffraction. The low temperature Mössbauer spectra reveal the deposition of akaganeite and perhaps some ferrihydrite on the external surface of the clay minerals. The room temperature spectra exhibit two Fe3+ quadrupole doublets in addition to the Fe2+ components of the structural iron in the sheet silicates. On treatment in ⩾0.04 M Fe3+ solutions the Fe3+ quadrupole splittings of 0.90 mm/s and 0.55 mm/s can be assigned to the mineral akaganeite; at smaller Fe3+ concentrations one of these doublets has a quadrupole splitting similar to that of the Fe3+ in the original vermiculites, the other one a quadrupole splitting of 0.6–0.7 mm/s, which can be considered as a hint for an uptake of Fe dimers in the interlayer space irrespective of the solvent used for iron deposition. Preliminary results show that the adsorption of pyrrole in all of our Fe3+-containing samples, regardless of the preparation in aqueous or methanol solution, results in the formation of polypyrrole and a concomitant reduction of some of the Fe3+. An uptake of pyrrole into the interlayer space has been observed only in the Fe3+-containing Wyoming montmorillonite and in the Ojén vermiculite treated with the methanol solution of iron chloride.