Particle-size analyses of brickearth and Clay-with-flints from Kent, England, are presented. A calcareous sample of brickearth is comparable to loess. In the clay fraction, there is more illite (or glauconite) than kaolin; and there is some chlorite. The clay fraction of the Clay-with-flints consists of smectite, illite and quartz and is probably derived directly from the Chalk. Black sand-grade nodules are manganiferous.

The amorphous mineral selectively dissolved from the clay (<2 μm) fractions of twenty-six ferruginous soils contains considerable iron in addition to silicon and aluminium. SiO2/Al2O3 and SiO2/R2O3 molar ratios are between 2·03-3·52 and 1·72-2·95 respectively. The model of the amorphous ferri-aluminosilicate (AFAS) consists mainly of negatively charged tetrahedrally coordinated silica-alumina phase Si3AlO6(OH)4 containing domains of neutral FeOOH, with an outer positively charged hydroxyaluminium polymeric component [Al(OH)2.5]n.The calculated hydroxyl water content of the AFAS averages 17·8%; cation exchange capacity varies from 48·6 to 112·0 mEq/100 g and shows a negative correlation with the outer hydroxyaluminium octahedral component and a positive correlation with the ratio of the tetrahedral Si-Al component to the octahedral hydroxyaluminium component. The K-fixation capacity (1·9-6·1 mEq/100 g) of the AFAS does not appear to be related to the chemical composition. The genesis of the amorphous mineral is discussed.

The nature and mineralogy of mixed Al and Fe(III) gels (initial Fe/Al molar ratios (Ri) of 1.0 and 2.5) formed at pH values ranging from 4.0 to 10.0, both in the presence and absence of citric acid (citrate/Fe + AI molar ratio (Rcit) of 0.01 and 0.1) and aged for a long period at room temperature and at 50°C have been studied. The complexes showed considerable differences in the mineralogy of the precipitation products. The samples formed at Ri = 1.0 contained ferrihydrite at pH 4.0, ferrihydrite + gibbsite at pH 5.0-7.0, and hematite + Al(OH)3 polymorphs + ferrihydrite at pH 9.0-10.0. The samples formed at Ri = 2.5 had greater quantities of poorly crystallized ferrihydrite. Large amounts of Fe+Al (25-82%) were solubilized from the samples aged for 60 days at 50°C by ammonium oxalate. The addition of increasing concentrations of citrate to the gel suspensions containing equimolar amounts of Fe and AI strongly inhibited the formation of Al(OH)3 polymorphs both at pH 5.0 or 8.5 by promoting the formation of short-range ordered materials. Citrate added initially to Fe-Al solutions (R*cit = 0.1) completely inhibited formation of crystals even after 135 days at 50°C.

The use of transmission electron microscopy in association with other methods is described for the characterization of Brazilian industrial clays, especially kaolinitic-halloysitic clays. Examples are presented from: (a) tubular 7 Å-halloysites and the characterization of mixtures with ordered and disordered kaolinites in residual china clays; (b) tubular kaolinitic clay from Piedade, São Paulo; (c) platey 10 Å-halloysite from Poģos de Caldas, Minas Gerais; (d) rolled forms similar to 10 Å-tubular halloysite formed by repeated K Ac intercalation in well ordered kaolinite; (e) use of particle shape and size of kaolinite crystals in the São Simão, São Paulo ball clays as orientation for good sanitaryware ball clays; (f) characterization of gibbsite crystals in high alumina gibbsite/kaolinite clays; (g) antigorite as a clay mineral; (h) electron optical studies of thermal phase transformations involving tubular kaolinite, halloysites, antigorite, chrysotile, talc and pyrophyllite mono crystals.

Reactions undergone by leadhillite from the type locality on heating to 1000°C have been followed by DTA, TG, DSC, evolved gas analysis, continuous-heating XRD and IR, and hot-stage microscopy. Intermediate decomposition products were identified by X-ray powder photography. At 80°C, biaxial leadhillite inverts to a uniaxial phase with properties similar to those of susannite, a naturally occurring polymorph of leadhillite, but this higher-temperature modification only partially reverts to the original structure on cooling (up to 24 hours at room temperature is required for complete reversion). Between 250 and 600°C the mineral undergoes two decomposition reactions: PbO.PbCO3 and PbO.PbSO4 form during the first reaction (PbCO3 may form in the initial stages) and 4PbO.PbSO4 during the second. α-2PbO.PbSO4 appears at 650°C due to solid-state reaction between the other lead oxysulphate products. Melting occurs above 850°C. The reaction products are discussed in relation to the phase diagrams for the systems PbO-CO2 and PbO-PbSO4.

In responding to the kind invitation of the Clay Minerals Group, may I say that my notes are intended to express appreciation by a geologist of the illuminating work of the Group, as well as a plea for many favours to come?

History repeats itself. Forty years ago, when the coarser detrital and authigenic constituents of sediments were first being systematically examined, it became evident that their significance could not be assessed until we knew, in broad outline at least, the characters of the assemblages in all the major stratigraphical divisions. The more finely-grained materials were at that time in the main intractable: their investigation has had to await the development of the now familiar techniques utilized by the Group.

The use of thermal analysis for the identification of clay minerals differs from its use for the determination of phase transitions in that the latter are, in theory at least, reversible and occur at definite temperatures while the dehydration reactions utilized in the identification of clays are monotropic, irreversible decompositions proceeding at a velocity which increases continuously as the temperature is raised. There is, therefore, no definite transformation temperature and the temperature of the arrest registered on a heating curve depends on the heating rate employed.

In view of the increasing importance of thermal analysis it was decided that an attempt should be made to study the implications of this. An investigation of the kinetics of the dehydration reaction seemed the most obvious approach.

A unified system of vector representation of chemical composition is proposed for the phyllosilicates based on projection of the composition, as given by crystallochemical formula, onto a field with orthogonal axes chosen for octahedral divalent cations, R2+, and Si (X, Y, respectively), and oblique axes for octahedral trivalent cations, R3+, and vacancies, □, (V, Z, respectively). Point coordinates for each set of axes were used to define the direction and length of the unit vectors for phyllosilicates belonging to different groups. Parallel to these fundamental directions the composition isolines were drawn in the projection fields. Applied to micas, this system enables control of the chemical composition by the general crystallochemical formula covering all varieties of Li-free dioctahedral and trioctahedral micas:

where z (number of vacancies) = (y-x+ m)/2; m (layer charge) =1; u+y+z = 3. There is a similar formula for vacancy-free lithian micas:

where w = m — x+y;m=1; u+y+w = 3, and for Li-free brittle micas:

where z = (y — x+m)/2; m = 2; u+y+z = 3. Projection fields were used to classify micas.

Separation of nitrogen, the major impurity of natural gas, is necessary for quality improvement of the gas. In this study, purified and some ion-exchanged forms of clinoptilolite were used to separate N2 from natural gas. Competitive adsorption of mixtures of N2, CH4 and C2H6 by Cu2+ (Cu-Cp)-, Zn2+ (Zn-Cp)-, Ni2+ (Ni-Cp)- and Mn2+ (Mn-Cp)-exchanged samples was studied at different pressures and ambient temperature. Among the cations studied, Cu2+ has the lowest selectivity towards N2. Samples were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, BET N2 adsorption and wet chemical analysis techniques.

The composition of the soil solution of various horizons of Galician soils was studied to gain insight into the direction of the processes of weathering and neoformation by means of stability diagrams of the clay minerals. The soil solution was extracted by compression at various pF values.

The most significant results are as follows. In all the cases studied the mineral in equilibrium with the soil solution is a 1:1 philosilicate. As the pF at which the soil solution is extracted increases, corresponding to smaller pore size, pH increases and silica concentration falls. The stable mineral does not vary significantly between different horizons of the same profile. Each parent material gives rise to a different zonation in the stability diagrams. The predictions of the stability diagrams are in general agreement with the mineralogical data of the clays of the horizons in question.

Finally, weathering processes in Galicia are briefly commented on.

Thermal analysis (DTA-TG-DTG), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, nitrogen adsorption and mercury intrusion porosimetry techniques were used to assess the structural changes induced upon heating of two hydrotalcite-phenol (trichloro- and trinitrophenol, HT-TCP and HT-TNP) complexes, and the results were compared with those obtained for the original hydrotalcite (HT) sample. The DTA revealed thermal effects that depended on the nature of the interlayer ion in the complexes. The total weight loss (TG-DTA) increased from 37% for the original HT to 40% for HT-TCP and 77% HT-TNP, as the amount of phenol increased. The XRD and FTIR spectroscopy showed that the calcination product (550°C) of the HT-phenol complexes was indistinguishable from that formed from the original HT. Since HT-phenol complexes were prepared by phenol adsorption on calcined HT, our results confirm the recyclability of HT-like compounds as sorbents for phenols.

The contamination of water bodies in urban areas is a serious problem, which may increase when wastewater is discharged without complete remediation. Due to their high adsorption capacity and ion-exchange properties, zeolites, such as clinoptilolite, can be used successfully to detoxify the wastewater before discharging it into the water body. In this study, experimental use of clinoptilolite is presented for water remediation. A static flow (A) and a laminar flow (B) method were applied in order to evaluate the efficiency of clinoptilolite for reducing different contaminants in the outflow wastewater of an old municipal treatment plant in Bologna District (Northern Italy). Mesocosm experiments were performed in order to achieve reduction of the microbial faecal indicators and of the excess nutrients and heavy metals in the effluent. During the experiments, pathogenic microorganisms, ammonium and heavy metals were reduced by as much as between 78 and 95% within 24 h, highlighting the great efficiency of this low-cost material for water remediation.

The growth and decay rates of rapid, induced electro-optical phenomena in dilute colloidal suspensions are characteristic of the geometry of the solute particles. The speed of measurement renders such methods especially relevant for fast, in situ analyses of the size and size distribution of colloids in practical, industrial situations where these properties may be undergoing continuous change. The principles of the measurement of electrically induced birefringence using pulsed fields is outlined and used to study vermiculite suspensions as they undergo size reduction in an ultrasonic field. The high sensitivity of the method to both the particle size range and the form of the distribution function is indicated. The use of the method for on-line monitoring of dilute mineral suspensions for the indication and control of aggregated, dissolving or growing media is discussed.

Layer silicates are generally assumed to be insulators, but electron transport may take place in nm thick particles. A combined scanning tunnelling-atomic force (STM-AFM) instrument using a conducting AFM tip has been constructed to investigate this conduction. Some layer silicates, e.g. micas (muscovite and biotite), are in fact semiconductors, conduction taking place through free electrons in the tetrahedral sheet (n-type semiconductivity) and probably through polaron hopping in the octahedral sheet. This implies that these minerals can be investigated by STM. Furthermore, micas show negative differential resistance (decreasing current with increasing voltage) at 2 – 5 V.

Molecular simulations using the Cerius2 modelling environment have been used to investigate the structure of montmorillonite (MMT) intercalated with Zn cations. Basal spacing and bonding of Zn2+ cations in the interlayer have been investigated with regard to their dependence on the water content. In the first part of the work, Zn cations in the interlayer are coordined by six water molecules and the energy of the system is discussed. The energy discussion is focused on the influence of the different starting orientations of the Zn octahedron, and different positions of Mg atoms in the octahedral sheet. An energy scan at fixed d-spacing was carried out. Later the hydration simulation giving the hydration curve (i.e. the dependence of d-spacing on the number of water molecules in the interlayer) was also carried out. Two different hydration states were found — for certain humidity ranges there is almost constant d-spacing and between these intervals there is a sharp edge. Finally the structure of totally dehydrated Zn-MMT was simulated.

The weathering of two co-existing sodic (glaucophane) and calcic (actinolite) amphiboles in a glaucophane-schist was studied by optical microscopy. XRD and the electron microprobe. In the early stages of weathering, two trioctahedral expandable phases occur as internal weathering products in the amphiboles: a sodic saponite in the glaucophane and a calcic ‘hectorite’ in the actinolite. Further weathering leads to the replacement of the ‘hectorite’ by a calcic saponite in the actinolite, while the saponites formed in the weathered glaucophane exhibit progressive calcium enrichment in their interlayer sites. These observations demonstrate the influence of the primary mineral compositions on initial weathering products.

INTERSTRAT is designed to help clay mineralogists identify clay minerals from powder X-ray diffraction data and is especially useful as an aid in the interpretation of interstratified clay minerals. This paper illustrates the use of the INTERSTRAT program in the identification of a set of interstratified clay minerals. One of the examples has been matched against the PDF and the answers compared with those obtained by INTERSTRAT. The most useful features of the program are the knowledge bases of diffraction parameters for the interstratified clay minerals, the ability of the program to compare the clays identified in more than one state and the hierarchical clay text file.

Des études expérimentales sont réalisées afin de préciser les relations entre la vermiculitisation des biotites (ouverture par NaCl N) et les phénomènes d'oxydation (par l'eau ou par H2O2). Les évolutions sont suivies par diffraction des rayons X et en spectroscopie d'absorption infra-rouge; l'oxydation du fer est appréciée sur l'échantillon par spectroscopie Mössbauer. Les résultats montrent que si une certaine oxydation accompagne normalement la vermiculitisation, une oxydation intense provoque une expulsion de fer et la formation de vermiculite hydroxy ferrique.

In 2019, BYK Additives (Widnes, UK; www.byk.com) marked the 55th anniversary of the discovery by Dr Barbara Zsusanna (Susanna) Neumann of the extraordinary product known as Laponite®. The range of Laponite® products developed in the UK during the early 1960s is one of the first examples of truly nanodimensional materials manufactured on an industrial scale, at a time when the field of nanotechnology was only being hinted at (Feynman, 1959). These hectorite-like synthetic nanoclays with very unusual properties have been an enduring commercial success for the UK company that first patented and introduced them to the market, Laporte Industries, which is now a part of the BYK company. The Laponite® brand has proved tremendously popular with academic and industrial scientists worldwide, being cited in >3000 patents and >2500 published academic articles.