Low temperature nitrogen adsorption has been used to study the external and internal structure of a number of allophanic soil clays. The results indicate that allophane, in addition to having pores in the intermediate size range (2–10 nm radius), contains micropores of < 1 nm radius. The occurrence of hitherto unreported micropores in allophanic clays has necessitated re-evaluation of the validity of specific surface area measurements.

The controversy on the origin of the English Mesozoic fuller's earths is reviewed. Findings of (1) unaltered, devitrified, zeolitized and argillized glass, (2) fragments of holocrystalline and hypocrystalline igneous rocks, and (3) high temperature feldspar and sphene, conclusively demonstrate their volcanic origin. The bulk chemistries of the Bathonian and Lower Cretaceous earths are similar and suggest derivation from ash of trachytic composition. The two earths can be differentiated mineralogically and petrographically by: (a) the presence of sphene, and zeolites replacing glass in the Lower Cretaceous earths; (b) the presence of minor amounts of basaltic glass in the Bathonian earths.

K/Ar radioisotope dating on high-temperature alkali feldspar gives (1) 152–159 Ma for the Bathonian fuller's earth, and (2) 118–125 Ma and 142–148 Ma for the Lower Cretaceous fuller's earths. The distribution of the Mesozoic fuller's earths and the origin of their parent ash is discussed.

Die kristallchemischen Strukturformeln von 2:1-Schichtsilikaten werden unter Voraussetzung der idealen Struktur mit 22 negativen Ladungen von 10 Sauerstoffen und 2 Hydroxylgruppen berechnet. Für die Verteilung der 22 Kationenladungen auf Tetraeder-, Oktaeder- und Zwischenschichtpositionen werden unter Berücksichtigung der direkt gemessenen Zwischenschichtladungen (Lagaly & Weiss 1971) bzw. Kationenumtauschkapazitäten Voraussetzungen und Berechnungsregeln angegeben. Als Beispiele werden die Formeln eines Glaukonits und eines Nontronits berechnet.

Die Verteilung der Kationenladungen in der Kristallstruktur von 2:1-Schichtsilikaten wird am besten in einem Dreiecksdiagramm mit den Ecken Pyrophyllit-Seladonit-Muskowit dargestellt. Jeder Punkt im Dreieck stellt die gesamte Kationenladung in der Formeleinheit gleich 22 dar. Es ist die Summe der Ladungen aus Tetraeder-, Oktaeder- und Zwischenschichtkationen.

Imogolite structures in allophanic clays can be recognized and semi-quantitatively estimated by an absorption band at 348 cm−1. Allowance can be made for interference by aluminous dioctahedral layer silicates present in small amounts.

X-ray diffraction and electron microscopy show that halloysite occurs widely in soils derived from a variety of parent rocks (granite, gabbro, schist and slate) in north-east Scotland. Both tubular and non-tubular forms are observed, the latter being characterized by electron diffraction patterns with 001 reflection either absent or very weak and diffuse. Clay fractions from a poorly drained profile separated without prior drying of the soil samples contain essentially dehydrated halloysite at the surface, this becoming progressively more hydrated with depth. Since halloysite occurs extensively in soils of widely varying drainage class the mineral is probably not the result of recent soilforming processes but may have originated during Tertiary or interglacial weathering.

Commonly streaks and rarely extra spots are observed on the selected area diffraction patterns of beidellite. The streaks are non-radial, and are restricted along the direction parallel to [11], [11], and [01]. Extra spots appear instead of streaks between the normal Bragg spots along the direction parallel to [11] and [11]. These extra spots suggest the formation of a superlattice with the a and b cell parameters twice as large as those of the beidellite lattice. Dark-field images on the strong 020 reflection reveal the presence of a network of dislocations in some of the beidellite crystallites. These dislocations suggest that the chemistry is not uniform over the successive layers in these crystallites. The structural difference between the layers seems to be accommodated by the dislocations.

L'auteur étudie l'absorption par une montmorillonite H-AI, d'acides organiques extraits d'Andosols dans une gamme de pH allant de 1,5 à 5. Quand il y a absorption entre les feuillets, on observe une résistance particulière de la montmorillonite à l'écrasement après chauffage, même pour des températures supérieures à 500°C Un complexe organo-minéral ou organique résistant à la chaleur se forme entre les feuillets de la montmorillonite, comme le révèlent les courbes d'ATD et les spectres IR. On retrouve les propriétés originelles de la montmorillonite par peroxydation.

Des argiles gonflantes 2/1 à complexes organo-minéraux et/ou organiques entre les feuillets sont observées dans les Andosols. Les propriétés de telles argiles rappellent en partie celles des chlorites gonflantes ou des pseudochlorites.

L'étude de fire-clays provenant de deux séries continentales d'âge Eocène inférieur montre des corrélations très nettes entre la fréquence des défauts d'empilement des feuillets et certaines propriétés qui opposent les fire-clays aux kaolinites bien ordonnées: faible taux de ‘gonflement’ à l'hydrazine, capacité d'échange cationique élevée. Ces faits ainsi que les filiations observés dans l'une des séries étudiées entre interstratifiés smectitekaolinite et fire-clay condusient à émettre l'hypothèse que les défauts de structure des fire-clays sont dus à la présence de feuillets de type smectite, interstratifiés à faible fréquence, entre les feuillets de type kaolinite.