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+.

Volume resistivities of various homoionic montmorillonite films and their polyacrylonitrile (PAN) complexes were determined with a high-resistance meter. It was found that: (i) electrical conductivities of the homoionic montmorillonite films decreased in the order: Li- > Na- > K- > Mg- > Ca- > Sr- > Ba-montmorillonite, (ii) conductivities of the PAN-complex films varied with the amount of polymer present in the interlaminar space, and (iii) heating the PAN-complex films for 12 h at 150°C generally resulted in an increase in conductivity due to carbonization of the polymer.

Some predominantly kaolinitic tropical soil clays when examined by DTA in a nitrogen atmosphere gave two exothermic reactions (at ∼880°C and ∼950°C) instead of the usual single exotherm. During heating, iron present in the samples is reduced, possibly by organic carbon, and reacts with the metakaolin phase to form hercynite (FeAl2O4). The presence of Fe2+ also causes mullite to form at a lower temperature than normal. These reactions accompany the lower-temperature exotherm. The higher-temperature exotherm is due to formation of γ-alumina. Although this exothermic doublet is an artifact of the experimental conditions, its occurrence may help to elucidate the sequence of reactions involved in the metakaolinite recrystallization process.

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.

An Illite/Montmorillonite mineral found in a porphyritic rock of Alpe di Siusi has an I/M ratio of 80:20. Introducing proper chemical parameters in a Q-Mode program of sixty-six Illites and Illite/Montmorillonite from the literature suggests the possibility of distinguishing Illites from Illite/Montmorillonite.

Clay mineral assemblages from a Quaternary sequence, sampled near the estuary of the Arno River, commonly contain some intergrade minerals, associated with other 14 Å phases and with illite and subordinate amounts of a kaolin mineral. The X-ray diffraction characteristics of such intergrade phases and their thermal modifications (100–600°C) are analysed and described.

The effectiveness of some chemical treatments for removal of interlayer material is investigated and the results discussed on the basis of X-ray diffraction pattern and C.E.C. changes. Finally the properties of these intergrades are compared with those of the 14 Å phases present in the sediments carried by the Arno River and its tributary the Era River as well as with those of a soil from the Era watershed. Hypotheses are expressed about the probable relationships between degree of chloritization and characteristics of the depositional environments.

Des zéolites de la famille Heulandite-Clinoptilolite se rencontrent dans toute la série cénomanienne littorale péri-armoricaine dans des faciès pétrographiques variés. Souvent présentes à l'étal de traces, leur abondance apparait liée à certaines conditions pétrogénétiques qui peuvent se réaliser localement à diverses périodes mais se généralisent au Cénomanien supérieur provoquant une régionalisation de la ‘paragenèse’: Clinoptilolite, Smectites, Cristobalite.

L'étude au microscope pétrographique et au microscope à balayage des échantillons les plus riches montre que la clinoptilolite se présente en cristaux automorphes dans des pores de dissolution intrasédimentaire. Son origine diagénétique est ici évidente; elle est postérieure à la dissolution des spicules de spongiaires et antérieure à la genèse de certaines sphérules de cristobalite. Ces néoformations se réalisent à partir des solutions interstitielles alimentées, au moins en partie, par l'altération de spicules de spongiaires, feldspaths détritiques, paillettes de mica, glauconie ...

L'origine détritique de la clinoptilolite des sédiments crétacés de la bordure occidentale du bassin de Paris qui avait été envisagée doit donc être écartée; deplús la paragenèse zéolitesmectites-cristobalite ne peut ici être utilisée comme l'indice d'une activité volcanique en cours de dépôt. Une partie des smectites, qui remplit certains pores de dissolution, prend également naissance par diagenèse précoce.