This study deals with the analysis of dielectric measurements made on montmorillonites saturated by bivalent cations. These measurements are performed between — 150°C and +30°C at frequencies ranging from 300 to 10,000 Hz. Their interpretation is based on a numerical analysis allowing determination of the dielectric losses due to free charge carriers conductivity phenomena and losses due to relaxation phenomena. The free charge carriers conductivity is due to the movement of protons. It depends very much on the nature of compensating cations and on the water content and seems to be closely related to the characteristics of the swelling.

Two types of relaxation phenomenon are described: a Debye relaxation due to electric dipole rotations and a Maxwell-Wagner relaxation due to heterogeneity effects. The analysis of the first phenomenon leads to the examination of the values of the relaxation time. It appears that the rotations of water molecules are difficult with bivalent cations. This essentially is shown by the high activation energy of the phenomenon. The discussion of these parameters shows that the state of adsorbed water molecules are certainly different as compared to the state of water molecules in ice or in liquid water. The characteristics of the second relaxation phenomenon are closely dependent on the free carriers charge conductivity.

Heats of compression of glass bead-water and clay-water mixtures were determined from the peak heights of the thermograms produced when these mixtures were subjected to pressure in a Calvet differential microcalorimeter. It is known that the heat of compression is directly proportional to the peak height. When the latter quantity was plotted against the pressure applied to any mixture, two intersecting straight lines were obtained. The change in slope at the point of intersection was interpreted as being the result of a pressure-induced higher-order phase transition in the water.

The differential peak height, ε, was defined as the rate of change of peak height with pressure/g of water present in the mixture. Hence, it is directly proportional to the rate of change of the heat of compression with pressure/g of water. Values of ε were determined for both glass bead-water and clay-water mixtures containing different proportions of solids. It was found that ε remained nearly constant with increasing proportions of glass beads, whereas, it varied in a non-uniform way with increasing proportions of clay. Also, its values in the clay-water mixtures were relatively high. Calculations showed that the difference in ε values for the two mixtures could not be ascribed to the exchangeable cations associated with the clay particles. Consequently, it was ascribed to the effect of the particle surfaces on the structure of the vicinal water.

The effects of bending on diffraction profiles and intensities have been directly evaluated. It has been shown that:

1. (1) bending may cause large reductions in intensities or even the total loss of them

2. (2) due to bending, the profile of the reflection may become asymmetrical and it may display two or more maxima

3. (3) bending effects vary with the class of reflections and they become larger with the increasing order of diffraction, and

4. (4) the interference function for a bent lattice must be evaluated for each set of lattice parameters, whereas the interference function for an undeformed lattice can be made invariant with respect to lattice parameters.

A closed form equation is derived for the calculation of the oriented diffraction pattern given by single particle size layer silicates having randomly interstratified interlamellar species. A general method for treating any particle size distribution is indicated and closed form results are presented for the Poisson, normal, gamma and binomial distributions. No restriction is placed on the number of interlayer types. The structure factors for these types are explicitly introduced. Graphs of two of the variables appearing in the equations applicable to particle size distributions provide a means of visualizing the effects of both interstratification and particle size on observed X-ray patterns.

The mineral in monomineralic glauconite pellets is an iron-rich mixed-layer illite-smectite (here called glauconite), often composed almost entirely of illite layers. The nature of the interlayering is closely analagous to that of aluminous illite-smectite and varies with the proportions of the layer types: >30 per cent smectite, randomly interstratified; 15–30 per cent smectite, allevardite-like ordering; < 15 per cent smectite, ‘IMII’ ordering.

Glauconite is analagous to aluminous illite-smectite chemically as well as structurally. A good correlation has been found between the number of potassium atoms per O10(OH)2 in structural formulas calculated from the chemical analyses and the proportion of illite layers as determined by X-ray powder diffraction methods. This relationship indicates a remarkably systematic increase in the potassium content of the illite layers with an increasing proportion of illite layers. This feature and the existence of ordered interlayering at high proportions of illite layers can be explained by crystal-chemical effects of illite layers on neighboring smectite layers. Glauconite differs from aluminous illite-smectite in that glauconite contains significantly less potassium per illite layer than does aluminous illite-smectite with the same proportion of illite layers except near the pure illite composition. The strength with which the interlayer potassium is held and the ease of conversion of smectite to illite layers in glauconite may be attributed to its 1M structure and, perhaps, to its high octahedral iron content, which lead to stronger bonding of potassium by allowing a higher tilt angle of the O-H axis of hydroxyls adjacent to the potassium ion.

The apparent octahedral cation occupancy in excess of two-thirds of the octahedral positions in many glauconites appears largely attributable to the presence of significant amounts of interlayer hydroxy-iron, aluminum and magnesium complexes in the smectite layers.

The Si/Al ratio of an hydrothermal system plays an important role in kaolinite synthesis. If the atomic Si/Al ratio of a system is greater than 2-0, kaolinite will disappear at 345 + 5°C and 2 kbars water pressure according to the reaction kaolinite + 2 quartz → pyrophyllite + H2O. If the atomic Si/Al ratio is less than 2-0, however, kaolinite will persist until 405°C where it will react according to the equation 2 kaolinite → pyrophyllite + 2 boehmite + 2 H2O. The Si/Al ratio of the system and temperature are also factors in determining whether b-axis ordered or disordered kaolinite will crystallize. The ordered variety is favored by a lower Si/Al ratio and a higher temperature than is the disordered form.

Hydrothermal experiments also show that kaolinite can be synthesized at 150°C and 5 bars pressure in distilled water from amorphous starting materials. Previous investigators were unsuccessful in forming kaolinite under these conditions because their systems were contaminated with alkalis.

Attempts to synthesize halloysite and dickite failed, but halloysite was converted to kaolinite at 150°C, suggesting that halloysite can be synthesized only at low temperatures.

Electron microscope microprobe analysis (EMMA) has been applied to the determination of the elemental compositions of the kaolinite particles (Mg, Al, Si, K, Ti and Fe) contained in the 0·2-0·3 µm e.s.d., the 0·9-1·0 µm e.s.d. and the 1·9-2·0 µm e.s.d. fractions of an English kaolin and an American kaolin. Particles with masses as small as 10-13 g were analysed. An EMMA-4 instrument (A.E.I. Ltd.) equipped with linear fully focussing spectrometers was used. The ratio method of analysis was employed. The operating procedures used to obtain the required high experimental precision in the measurement of Al:Si atom ratio are discussed.

Statistical analysis of the results gives the estimated mean and spread of the Al:Si atom ratios. In the English kaolin the mean Al:Si atom ratio differs from the ideal 1:1 at the 0·05 significance level. There is evidence for a variation in composition from kaolinite particle to kaolinite particle in the 1·9-2·0 µm fraction of each kaolin. In the 0·9-1·0 µm fractions, the mean Fe:Si atom ratio was close to 0·002 showing the presence of iron in the kaolinite structure. The mean K:Si ratio was about 0·002 which would be equivalent to 1 unit muscovite layer associated with a 0·175 µm thick kaolinite particle. In the American clay the Ti:Si atom ratio was 0·002 suggesting that some 12 per cent of the 'titania' found by conventional chemical analysis was associated with the kaolinite particles either as titania itself or as an isomorphous substituent.

With the use of a BaCl2 solution containing radioactive Ba2+ ions, kinetics of cation exchange have been done on a Kenya vermiculite, natural on one hand and previously oxidized either by 50°C water or oxygenated water on the other hand. Correlatively, the quantity of ferric iron in the layer has been determined by E.P.R. These two methods have shown that during an oxidation the proportion of iron which stays in the octahedral layer depends upon the nature of the oxidizing agent. During a weak oxidation, the iron stays entirely in an octahedral layer and the exchange capacity of the vermiculite decreases; on the other hand, during an oxidation by oxygenated water, part of the iron is extracted from the octahedral layer and the exchange capacity of the vermiculite is not changed, as established by the studies of Farmer (Farmer et al., 1971). Kinetic data for Llano vermiculite also are reported and compared with those for the Kenya vermiculite.

The present paper presents the mineralogical composition of sediments from the Spanish Wealdian facies, selected from four stratigraphic sections of several regions in the Southern Cordillera Iberica.

Three of these sections show an irregular alternation of kaolinite rich sandy and silty-clay beds. The fourth section which contains calcareous layers, is very important from a geological point of view, because it is located where the structures of two ranges, the Iberian and the Betics, converge.

The clays of about 80 samples from these sections always consist of illite, kaolinite and interstratified clay minerals. The sandy layers also contain quartz, as well as potash and calcic-sodic felspars. The fine fraction (< 2 µm) is composed of kaolinte, between pM and T types, swelling illite and randomly interstratified clay minerals of the type (10I-14M), richer in 10 Å layers.

From the mineralogical and crystalchemical data and field observations, it is deduced that these sediments are mainly detrital. This and the layer alternation suggest, for the Upper Jurasic and Lower Cretaceous (Wealdian facies), a climate alternating from biostatic to rhexistatic. Alternating laterization and erosion might supply the materials to the Wealdian sedimentary basin.