The pzc of H+-kaolins determined by titration method is nearly pH = 3. The pzc of SiO2 + Al2O3 mixtures is not additive, and depends principally on Al2O3 content in mixture. The curve pzc—t°C (t°C = temperature of treatment of kaolins) has two maxima: 4·7 after treatment at 800-900°C, and 5 after treatment at 1300°C.

A bluish-green clay found in veins cutting across brecciated slates of the Llanvirnian stage at Huy, Belgium, is shown by X-ray diffraction and chemical analysis to be a lithium-bearing, aluminium-rich, regular mixed layer montmorillonite-chlorite with associated pyrophyllite, nacrite and quartz and smaller amounts of calcite and ankerite. The cation exchange capacity of the purified air-dry magnesium saturated clay is 49 mEq/100 g and its structural formula is

The problem of the nomenclature of regular mixed layer montmorillonite-chlorites is discussed.

A number of natural kaolinites from a variety of world sources have been investigated using electron spin resonance at both X-band and Q-band. The results show systematic differences some of which are related to the crystallinity of the material, some to the presence of transition metal ions other than Fe3+ and hole-trapping defects.

The results provide evidence for at least three sites for substitution of Fe3+ having large crystal fields : (i) a site with near maximum rhombic character having crystal field parameters D > 1·2, λ = ⅓ the occurrence of which is correlated with lack of crystalline perfection due to stacking defects or to the proximity of surfaces, (ii) a site with less rhombic character with λ = 0·234, D = 0·585 as likely parameters, and (iii) a site with parameters near the values λ = 0·207, D = 0·322.

Mössbauer and ESR evidence suggests that the principal sites of Fe3+ substitution are octahedral. The presence of Fe3+ in adjacent cation sites leads to a very broad resonance centred near geff = 2. Other resonances in the spectra are attributed to the effect of trapped holes, some at least of which are situated at oxygen sites adjacent to Al3+ ions substituting in sites normally occupied by Si4+.

Hyperfine effects due to the presence of the transition ions Mn2+ and (VO)2+ are also observed.

The adsorption of organic ions derived from ammonium, containing aromatic and saturated rings, was studied using different techniques. The ions with acid character produced a complicated set of reactions including aluminium extraction, proton adsorption, a real ion-exchange with the organic ions and an excess adsorption of ammonium salts. With non-acidic compounds only a stoichiometric ion-exchange process was observed. X-ray diffraction and infrared spectroscopy were used to determine the orientation of the organic ions and to characterize the nature of the co-adsorbed organic material.

The alteration of thirty-nine trioctahedral micas to vermiculite has been characterized by the K level, which is determined by repeated measurements of the stationary K concentration in the altering solution and provides a practical way of comparing the sensitivity to alteration. A calculated regression equation allows the K level of a sample to be predicted from its chemical composition. The model proposed for the alteration reaction outlines the physico-chemical meaning of the K level, with its experimental and theoretical limitations.

An unusual chlorite has been collected from amygdales in Miocene volcanic rock found at Taiheizan, Akita Prefecture, Japan. The mineral shows subtle variations from other chlorites and related minerals. These are: (a) no apparent expansion with water or ethylene glycol, (b) negligible or no collapse after NH4-saturation or heating at about 300°C, (c) a slow decrease in the basal spacing on heating from approximately 400°C to 760°C, (d) a small amount of low temperature or capillary water and (e) a DTA curve with a vermiculite-like system of peaks.

The mineral is identified as a highly chloritic vermiculite with a small proportion of imperfect hydroxy interlayer.

Le Grès à Voltzia des Vosges du Nord est formé de bancs gréseux et de lentilles argileuses. Les illites extraites des bancs gréseux montrent au microscope électronique des formes en lattes alors que celles des lentilles argileuses ont des contours pseudohexagonaux. Lorsqu'on broie une muscovite dans de l'eau désionisée avec du sable de Fontainebleau on retrouve ces deux formes, en lattes et pseudohexagonales. Les deux formes de particules peuvent donc être engendrées par un mème materiel initial.

Une hypothèse a été faite quant à la formation des illites en lattes. Elles seraient le résultat d'une dissection de particules micacées le long des rangées de substitution [10], [11] et [1] du silicium tétraédrique par de l'aluminium avec perte d'une partie de cet aluminium. Des analyses chimiques et des observations au microscope électronique ont été faites sur des particules de muscovite broyée. Les résultats obtenus vont dans le sens de l'hypothèse émise mais ne sont pas suffisants pour la démontrer pleinement.

The synthesis of magnesium smectite from heated slurries of magnesium hydroxide, silica and lithium fluoride proceeds through ready formation of torroidal structures visible under the electron microscope. These are associated with the synthesis of a smectite-like material with, however, only half the expected requirement for silica. True smectite only forms significantly with Si/Mg ratios > 1 and reaction times (at reflux) > 1-3 days.

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).

The acid strength and the number of acid sites on various clays were determined by observing the colouration of Hammett indicators adsorbed on them and by titrating benzene suspensions of them with n-butylamine, respectively. H(Al)-saturated allophane behaves as a strong acid (Ho; −5·6 ∼ 1·5) in a relatively dry environment (relative humidity 10-55%), but its acid strength is very much reduced either by increasing its water content or by saturating it with alkali or alkali earth metal cations. Imogolite shows only a very weak acidity (Ho; 4·6 ∼ 6·8) under medium dry to moist conditions (relative humidity; 30-100%). Both allophane and imogolite show a marked enhancement of acidity (Ho; −8·2 ∼ 1·5) when they have been dried over P2O5 or heated to result in dehydroxylation. H(Al)-saturated montmorillonite, kaolinite and halloysite show stronger acidities (Ho; −5·6 ∼ 1·5) than allophane (Ho; 1·5 ∼ 6·8) in a relatively moist environment (relative humidity; >60%). The n-butylamine titre and CEC show a good agreement for montmorillonite, but a poor agreement for allophane. The latter discrepancy which is larger for allophane when it has been heated at 150 and 300°C, is also found for imogolite when similarly heated. In these titrations, excess butylamine is found in supernatants at end-points. Therefore, the n-butylamine titre as such can not be used for the estimation of the number of acid sites on imogolite and allophane. The origin, structure and transformation of the acid sites on these clays is discussed.

Specimens of palygorskite from Warren Quarry, Enderby, Leicestershire, have been studied in the laboratories. The mineral is found in dioritic rocks in association with angular dolomitic rock fragments as the filling material of a joint, the walls of which are sometimes lined with calcite and dolomite. Palygorskite occurs as 3-10 mm long bundles of fibres, 0·03-0·1 μm wide. X-ray diffraction data indicate that the mineral may occur in the monoclinic form. The structural formula for the half-unit cell is Si8(Al1.89Fe0.053+Ti0.01Mg1.99)O20(OH)2(OH2)4 3·61 H2O.Ca0.07. Data obtained from differential thermal and infrared analyses are comparable with those for palygorskite in the literature, but the six-sided transversal cross-section of the fibres as revealed by electron microscopy is unexpected. The mineral was formed after the deposition of the overlying basal Triassic rocks when ground waters penetrated cracks in the dioritic rocks, causing Si and Mg to be released there and above the unconformity.

The Coalgate Bentonite deposit has been formed by the alteration of cryptocrystalline basaltic ash erupted in Upper Miocene to Pliocene times and deposited in a freshwater lake on a land surface of earlier tholeiitic flows. Physical and chemical analysis shows the bentonite to consist essentially of non-swelling (Ca2+ and Mg2+) ferriferous-beidellite with minor ferriferous montmorillonite. The process of montmorillonitization probably involved a crystal chemical structural reorganization without solution or precipitation and occurred in a mildly alkaline environment in which initial reducing conditions become oxidizing.

Initial exchange of Cu(II)-montmorillonite by tetrapropylammonium (TPA) or tetramethylammonium (TMA) ions results in segregation of different ions in randomly interstratified layers, with particular preference for TPA over Cu(II) during exchange. More complete exchange reverses this preference and both Cu(II)-TPA and Cu(II)-TMA clays become more homogeneous. The copper ions of the homogeneous Cu(II)-TPA clays are not fully hydrated while the TMA ions have less effect than TPA on the hydration of copper, probably a result of the smaller radius and higher hydration energy of TMA. Methods of X-ray diffraction, thermogravimetric analysis, BET surface area determinations, as well as infrared and electron spin resonance spectroscopy, are used in supplying evidence of cation distribution and hydration properties of these clays. Definite changes in the properties of hydrated copper when associated with tetraalkylammonium ions on the clay surface are indicated.

Synthetic kaolinites of varying crystallinity, and in some instances with ideal morphology, have been produced by hydrothermal reaction of aluminiosilicate gels. Synthetic kaolinites doped with Mg2+ and Fe3+ were also obtained.

Synthetic kaolinite doped with Fe3+ produced an ESR spectrum at g = 4 identical to spectra observed in natural kaolinites. Following X-irradiation and annealing at ~200°C, synthetic kaolinite doped with Mg2+ exhibited an ESR signal at g = 2·0 identical to a resonance observed in natural kaolinites. It is concluded that the g = 2·0 signal in kaolinite is due to a defect centre stabilized by Mg2+ substitution.

All synthetic and natural kaolinites exhibit an additional resonance at g = 2·0 following X-irradiation which can be repeatedly created and destroyed by irradiation and annealing. This resonance is attributed to defects possibly associated either with the substitution of Al3+ for Si4+ in kaolinite or with lattice vacancies.

The distribution of 2:1-2:2 intergrade clays has been investigated in some podzolized soils from Norway. In some of the profiles the intergrade clay mineral appears to be concentrated in the A2 horizon; in others, where smectite is predominant in the surface horizon, the maximum accumulation of the intergrade is observed in the B2 horizon. Smectite and vermiculite have been found to be the precursors of the intergrades of the A2 and B2 horizons respectively. A possible explanation to account for the observed variable pattern of occurrence of intergrades in soils is suggested.

It is shown from studies of synthetic kaolinites doped with Fe3+ that the ESR spectrum of kaolinite at g = 4 consists of two components attributed to Fe3+ ions occupying two distinct substitutional sites (Centres I and II). The relative intensity of the two components can be correlated with the X-ray crystallinity of the samples. The ESR spectrum is influenced by artificial changes in crystallinity produced by subjecting samples to high stresses or by intercalation. It is concluded that Centre II is due to Fe3+ replacing Al3+ in the octahedral layer in a region of high crystallinity. Centre I is assigned to Fe3+ occupying Al3+ sites distorted by changes in the hydroxyl orientations associated with layer stacking disorder or disruption of interlayer bonding.

A stable defect centre in kaolinite which produces an ESR spectrum at g = 2·0 is attributed to either a hole centre located on an Si—O bond adjacent to an Mg2+ octahedral impurity or to an O2− ion trapped within the lattice.

The less than 10 μm and less than 3 μm fractions of the heterogenous Haldon Gravels have been examined by X-ray diffractometry. Kaolinite of high to low crystallinity is the dominant clay mineral, with variable amounts of illite (clay mica) ; quartz, a little feldspar and anatase also occur. The kaolinite has been ranked using the crystallinity index of Hinckley and also by indices derived from the ratio of peak height to background height for the 10 and 11 peaks.

Clay from the matrix of the psaphitic members of the Buller's Hill Gravel contains intermediate grade kaolinite with a little illite, but clay bodies included in this formation contain only low grade kaolinite with a high, but variable proportion of illite. The Tower Wood Gravel contains two distinct populations; one is identical to that of the Buller's Hill Gravel, the other consists of high crystallinity kaolinite with a little illite. Head Gravel formed from the Buller's Hill Gravel by solifluction contains intermediate to low crystallinity kaolinite.

The very fine (<0·04 µm) clay fraction of a Denchworth series subsoil in weathered Oxford Clay has been investigated in detail. It contains a layer silicate mineral, almost free from impurities, that is a randomly interstratified mixture of approximately 45% expanding and 55% non-expanding interlayers with the following unit formula: Na0.33K0.29(Al1.41Fe0.34Mg0.26)(Si3.60Al0.40)O11. Computer-simulated diffraction patterns showed that experimental patterns are best matched when an average diffracting packet consists of between 4 and 5 2:1 layer silicate units. Correction of the chemical composition for external exchangeable ions associated with such small packets gives non-expanding interlayers a charge density of 0·69K/Si4O11 and expanding interlayers one of 0·57M+/Si4O11. The relationship between these values and those of mica and regularly expanding minerals is briefly discussed.

Investigation of the clay mineralogy of forty-seven samples of sediments from boreholes in the western Nile Delta, an area little studied hitherto, and from surface sites on the mouth of the Nile and adjacent coast shows that the clay fractions consist of dominant iron-rich, dioctahedral, randomly interstratified smectite-illitcs together with kaolinite, illite and chlorite.

Amounts of the constituent minerals of the clay fractions are estimated from their X-ray diffraction intensities, supported by selective dissolution chemical data, and a new method is used to estimate the proportion of expanding layers in randomly interstratified smectite-illite. The results, which confirm and extend the work of previous investigators, also show that there is little correlation between the clay mineral composition and texture of the sediments, only kaolinite being weakly linearly correlated with clay content. Transformation of 2:1 layer silicate minerals occurs within the buried sediments ; chlorite is transformed and smectite and illite interlayers redistributed within randomly interstratified smectite-illites.

Sorption of molecular amines by montmorillonite involves protonation of the amine group and hydrolysis of the interlayer cation. Sorption and subsequent desorption of amines may render some of the interlayer cations non-exchangeable, thus causing partial 'chloritization' of the montmorillonite. The effect is stronger with interlayer Al than Ca ions and depends upon the amine sorbed.