X-ray photoelectron diffraction data from single crystals of a biotite containing ∼1% Ti show that although this element is located entirely in octahedral sites, the Ti sites are not precisely equivalent to those of Mg and Fe. Comparisons of Ti 2p X-ray photoelectron spectra from two biotites and from two titaniferous phlogopites (∼0·3–·5% Ti) with those from Ti(II), Ti(III) and Ti(IV) oxides indicate that this element is present as Ti(III) rather than Ti(IV) in all four micas.

Calculations previously used to distinguish between methanol adsorbed in micropores between clay microcrystals (external) and that present in the interlamellar space (internal) of variable charge Ca-montmorillonites have been extended to homoionic Li-, Na- and Bamontmorillonites. It is shown that both the shape and the magnitude of the internal isotherms are in good agreement with X-ray diffraction data. Furthermore, the apparent molecular packing of methanol in the interlamellar space is related specifically to the nature of the charge balancing cation.

In previous papers of this series it was shown that it is possible to determine both the amount of methanol adsorbed in the interlamellar space of charge-deficient Ca-montmorillonite or of homoionic clays and the amount of methanol occluded in a system of micropores between clay particles. This paper deals with the distinction between methanol molecules in the cation coordination shell within the interlamellar space from those not directly influenced by the cation. An OH stretching band at about 3520 cm−1 or an OD stretching band in the 2600–2650 cm−1 region permits this distinction. At 35°C and at relative methanol vapour pressures between 0·1 and 0·9, one molecule of CH3OD is influenced directly by Na+, 2 molecules are influenced by Ba2+, 1·3–1·8 molecules by Li and 4 molecules by Ca2+. Thus, only 20–50% of the adsorbed alcohol molecules may be within the coordination shell of the cation in the interlamellar space.

L'organisation de l'espace interlamellaire des vermiculites a été comparée en fonction: (i) de la nature du cation (Mg, Ni, Ca, Sr et Ba) et de son état d'hydratation (bicouche, monocouche et anhydre), (ii) de la nature du feuillet (charge et localisation des substitutions). Le facteur prépondérant, celui qui confère à l'espace interlamellaire son caractère ordonné ou non, est la nature du cation en particulier sa taille et son degré d'hydratation. La charge du feuillet apparaît comme un facteur complémentaire, elle limite la taille des domaines ordonnés.

Se realiza un estudio detallado de las distintas fases minerales (caolínicas y silíceas) que aparecen en rocas silicificadas tanto graniticas como sedimentarias de la provincia de Avila.

Las técnicas utilizadas (A.T.D., difracción de rayos X, microscopía electrónica de trasmisión y de barrido) permiten establecer una clasificación de estos minerales segun sus propiedades térmicas, parámetros cristaloquímicos, y morfologías identificadas al scaning.

Sa dá una interpretación genética a cada uno de los tipos de caolinitas encontrados (macrocaolinitas en acordeón, microcaolinitas en gusanillo y criptocaolinitas). Los dos primeros tipos pueden ser explicados por procesos conjuntos de alteración hidrotermal y ‘weathering’ de feldespatos y micas. El tercer tipo (criptocaolinitas) es de más difícil interpretación al aso-ciarse con ópalo C-T en diques que cortan a rocas granitoideas y otras veces al presentarse como matriz de areniscas sedimentarias.

Experimental transformations of feldspars and muscovites following additions of magnesite and dolomite have been studied at PH2O = 1 kbar, T = 200–600°C. Formation of layer silicates such as smectite, 7 Å (Mg,Al)-serpentine, some mixed-layer phases and other minerals is shown to be a function of the composition of the starting materials, temperature and run duration. It is established that 1 M- and 2 M1-phlogopites are formed from 1 M- and 2 M1-muscovites, respectively, under Mg-bearing hydrothermal conditions. Some causes of variations in the composition of 7 Å (Mg,Al)-serpentines at elevated temperature as a function of the composition of hydrothermal media are given. These data may be used to explain the main characteristics of clay mineral formation from feldspar- and muscovite-bearing sedimentary rocks during their alteration in postdiagenetic and metasomatic processes.

The Weissenberg method has been used to study crystalline fragments of hydrobiotites from Stupná near Křemže, Czechoslovakia. The intensity distribution for basal reflections recorded in zero-level photographs indicates that most ‘single crystals’ are nearly regular interstratifications of vermiculite and biotite. Proportions of vermiculite in these interstratifications lie between 12 and 60%.

Im klassischen Lössprofil von Stillfried an der March wurden in der oberen Humuszone des Stillfrieder Komplexes Mineralbestand und Mikrogefüge mittels Röntgendiffraktometeranalyse und Rasterelektronenmikroskopie untersucht. In der Schluffund Tonfraktion fand sich neben anderen Tonmineralen Palygorskit, der vor allem in Form feinstrukturierter Mineralanhäufungen über Karbonatknollen auftritt.

Die charakteristische Morphologie der dünnstengeligen und faserförmigen Einzelkristalle sowie die Bildungsbedingungen bei alkalischem Milieu und hohem Mg-Gehalt der Bodenlösung sprechen für eine pedogenetische Neubildung des Palygorskit.

The vertical clay mineral distribution pattern in two sediment cores taken from two East African lakes has been studied in detail. In the core from Lake Albert (Mobutu Sese Seko) a clay assemblage consisting principally of smectite with some illite and kaolinite in the uppermost segment of the core changed with depth into first a mixed-layer illite-smectite dominated clay and then at 6·60 m into an iltite dominated clay. Lower in the core there was again a transition towards interlayer mixtures, and in the bottom segment towards smectite. These changes are interpreted as a diagenetic transformation of smectite into illite, effected by saline palaeo-lake water with an unusually high K/Na ratio. Three smectite→illite-smectite→illite transition cycles were recognized in a 56 m deep sediment core from Lake Manyara. The sections in which illite dominated contained silt-sized analcime, while those with interlayer mixtures contained alkaline zeolites. The diagenetic illitization of smectite appeared to parallel the process of analcime formation, the K necessary for illitization being released during K,Na-zeolite→analcime transformation. These occurrences suggest that high temperature and pressure may not constitute absolute prerequisites for the diagenetic illitization of smectite.