Après avoir rappelé l'importance du mode de préparation des associations montmorillonite-acides humiques sur leurs propriétés d'hydratation, nous présentons les résultats obtenus par adsorption d'azote.

L'ensemble des résultats obtenus sur ces associations indique que la localisation de la matière organique dans l'espace poral de l'argile joue un grand rôle, localisation qui varie avec le mode de préparation des échantillons et la teneur en carbone.

On donne une interprétation générale des courbes représentant la variation des quantités d'eau fixées par ces associations, quand la teneur en carbone augmente.

Dickites with well-ordered crystal structures and with relatively high dehydroxylation temperatures develop a 14 Å phase when heated to temperatures in the range 550–800°C. The actual spacing is close to 13·7–13·8 Å. Dickites with less well-ordered structures and with lower dehydration temperatures give less development of this phase or none at all. Other kaolinite group minerals do not produce a similar phase. Thermal weight-change and differential thermal analysis data show that the 14 Å phase develops to a maximum as hydroxyl ions are eliminated from the dickite structure and infrared spectroscopic data are consistent with this result. AIKα fluorescence wavelength measurements indicate that the Al ions are in four-fold coordination in the 14 Å phase. Absence of other diffraction data makes structure analysis impossible. The description ‘chlorite-like’ for the 14 Å phase is of questionable validity.

Dioktaedrische Smektite aus 19 Bentonitproben werden abgetrennt. Aus den chemischen Analysen errechnen sich unter Berücksichtigung der direkt gemessenen Zwischenschichtladungen (nach Lagaly & Weiss, 1971) kristallchemische Strukturformeln von exakt dioktaedrischen Mineralen. Die Tetraederzentren in der Struktur sind fast ausschliesslich von Si4+ besetzt; nur zwei der untersuchten Minerale zeigen eine beidellitische Komponente. Die gemessenen mittleren Zwischenschichtladungen der Montmorillonite (0·33 bis 0·39) ergeben sich allein aus der oktaedrischen Substitution von Me3+ durch Me2+. Im Gegensatz zu der grossen Variation der Strukturformeln von dioktaedrischen Smektiten in der älteren Literatur sind die kristallchemischen Unterschiede der hier untersuchten gereinigten Smektite sehr klein.

Im Vergleich zu den Rohbentoniten sind die Konzentrationen der meisten Spurenelemente in den abgetrennten Montmorilloniten erheblich verringert. Nur Mn, Zn, Co und Ni scheinen in die Kristallstruktur eingebaut zu sein. Die übrigen analysierten Spurenelemente sind adsorbtiv gebunden oder in akzessorischen Mineralen enthalten.

Mössbauer spectra have been obtained at room temperature on a series of phlogopites and biotites which have also been characterized by chemical analyses, I.R. and N.M.R. The distribution of the Fe2+ ions on the two possible octahedral sites is on the average nearly random. A clear example of tetrahedrally coordinated Fe3+ ions in a natural phlogopite is given. This phlogopite has a very high vermiculitization ability. The Fe3+ content of the samples has been determined by two different chemical methods and it is shown that even when precautions are taken to minimize oxidation, the agreement with Mössbauer spectra is poor.

Three-component interstratification of layer silicate minerals in the clay fractions of soils and sediments is probably more common than is generally realized. However, interpretation of the proportion and arrangement of the various components from experimentally recorded X-ray diffraction curves is difficult and in this paper a series of calculated diffraction patterns are presented which illustrate the types of diffraction patterns obtained from interstratified mica-vermiculite-montmorillonite systems.

XRD, DTA and IR patterns showed clay veins filling fissures in a granite of the Bayerischer Wald (eastern Bavaria) to consist mainly of hydrated halloysite of low crystallinity with traces of gibbsite, 2:1 (mixed layer) clay minerals and iron oxides. The halloysite forms thin plates which exhibit varying degrees and types of enrolment, resulting in platy, tubular and spheroidal crystals within the same sample. Concentrations of the trace elements Rb, Sr, Ba, Zr, Y, Ce, Pb, Zn and Cu indicate halloysite formation to have taken place via an aqueous phase under the influence of vadose waters circulating in fissures.

Les auteurs étudient les produits de l'altération fumerollienne et météorique de Vulcano, Iles Eoliennes, Italie. Ces produits sont étudiés par diffraction des rayons X, analyse chimique classique, microscopie électronique et microsonde.

The chemical composition of nine samples of Lower and Middle Chalk from the Givendale area of Yorkshire was determined; acetic acid residues were mechanically, chemically and mineralogically analysed. All nine chalk samples proved to be exceptionally pure calcium carbonate (96±1·5%), with only small amounts of MgO (1·03±0·53%), Al2O2 (0·33±0·28%) and Fe2O2 (0·20±0·14%). Insoluble residues ranged from 1·07 to 4·46%. Clay formed 56–88% of the insoluble residue. The non-clay fraction consisted of flint, quartz, collophane, limonite, feldspar, tourmaline and zircon. The clay fractions were dominated by montmorillonite (50%) with secondary illite (30%), apatite (3%), and quartz (8–30%). Kaolinite was detected by X-ray diffraction in the Lower Chalk.

Silicifications and smectite-dominated clay assemblages are associated in the marine Cretaceous sediments of England. Both are neoformed, and have developed at approximately the same time in the host sediment. Two silicification types, opal-CT and α-quartz, have a distribution pattern unrelated to the stratigraphy or lithology of the Lower Greensand, Upper Greensand and Lower Chalk. The petrography of five examples suggest that the two silicification types were both precipitated from the porewaters of their host sediment, and their silica mineralogy and their associated silicate minerals were controlled generally by the silica concentration of the porewaters and more locally by the pH gradients.