The weathering of two co-existing sodic (glaucophane) and calcic (actinolite) amphiboles in a glaucophane-schist was studied by optical microscopy. XRD and the electron microprobe. In the early stages of weathering, two trioctahedral expandable phases occur as internal weathering products in the amphiboles: a sodic saponite in the glaucophane and a calcic ‘hectorite’ in the actinolite. Further weathering leads to the replacement of the ‘hectorite’ by a calcic saponite in the actinolite, while the saponites formed in the weathered glaucophane exhibit progressive calcium enrichment in their interlayer sites. These observations demonstrate the influence of the primary mineral compositions on initial weathering products.

Sixteen glauconite samples from different locations in Belgium and Northern France were investigated by 57Fe Mössbauer spectroscopy at room temperature. The spectra were fitted with three Fe3+ and two Fe2+ doublets, both Fe species occupying M1(trans) and M2(cis) sites in the T-O-T layers. The third Fe3+ doublet was assigned to interlayer ferric complexes. The observed Mössbauer parameters did not show significant variations from sample to sample. No direct relation between K and Fe content was observed, although within some distinct groups (e.g. Bande Noire, Cenomanian) the amount of Fe2+ increased with increasing K content.

Smectites were synthesised hydrothermally from zeolites in an Mg-rich brine at 300°C under a confining pressure of 30 MPa and characterized by XRD using the Greene-Kelley Li-saturation test and the K+-saturation/glycolation test. The synthetic smectites were found to be dioctahedral with only tetrahedral negative layer charge; the layer charge was also deduced to be low and they are classified as beidellites. The mechanism of formation includes H+ saturation of zeolites by the hydrolysis of Mg2+ under hydrothermal conditions, followed by decomposition of the zeolites and recrystallization to beidellites. These results show that solution chemistry is an important factor affecting stability of zeolites under hydrothermal conditions.

Le mécanisme de rètention de l'octylbenzènesulfonate de sodium (OBSNa) en milieu aqueux pur sur les argiles correspond essentiellement à une précipitation du sel de calcium (OBS)2Ca. L'adsorption, proprement dite, atteint à peine 2 à 3 µEq/g d'argile. En présence de KCl, la part de l'adsorption devient plus importante à cause de l'augmentation de la solubilité du sulfonate de calcium. L'affinité des monomères du tensio-actif pour l'interface solide-liquide est accrue. On montre que l'adsorption varie avec les propriétés de l'argile, en particulier, avec le nombre et la nature de ses cations échangeables. L'équilibre d'adsorption dépend de l'état d'avancement des réactions d'échange entre les cations échangcables de l'argile, les cations apportés par l'électrolyte (KCl) et le monomère (Na+), et les cations adsorbés sur les micelles. II existe, pour chaque argile, une concentration limite en KCl, d'autant plus grande que la teneur en calcium de l'argile est élevée, et à partir de laquelle le tensio-actif ne précipite plus. La rétention se fait alors uniquement par adsorption. Suivant les conditions de pH, elle a lieu sur les cations échangeables de l'argile et les sites positifs à la périphérie des cristaux (kaolinite) ou seulement sur les cations échangeables (illite et chlorite). Dans les procédés de récupération assistée du pétrole, l'addition de chlorure de potassium au fluide de balayage permettra de réduire la précipitation du tensio actif. Même, si l'adsorption augmente, cet effet est souvent suffisant pour que, globalement, la rétention diminue.

The Wash drainage basin contains four principal river systems. Samples were collected from the freshwater and estuarine reaches of each of these, and silt- and clay-grade fractions were separated and examined by XRD. The clay mineralogy of each of the rivers is different; in the north the Witham sediments contain chlorite, the Welland and Nene samples contain vermiculite, with a higher proportion of kaolinite in the former, while in the south the Ouse sediments contain smectite. The clay fractions of the samples from the estuarine reaches all contain chlorite, confirming that non-fluvial sources must contribute to the sediments of the Wash. Comparison of this pattern of clay mineralogy with that for the underlying Jurassic and Cretaceous rocks shows that there was relatively little modification during the Pleistocene glacial periods. Such a pattern supports recent work which suggests that ice moved through the Wash gap and then fanned out from the Fenland area, rather than entering the region from the north.

Les hydrates à une couche des vermiculites présentent cinq modes d'empilement. Aux cations de petit et de grand rayon ionique (Li et Ba) correspondent des modes d'empilement particuliers. Les cations (Na, Mg, Ca et Sr) conduisent chacun à deux modes d'empilement correspondant à deux stades différents d'hydratation.

Transmission powder patterns of random and of highly oriented samples of natural micas have been recorded and compared with those calculated from structural data with the aid of the DIFK computer program modified to correct for preferred orientation. Intensities calculated from structural data for random and for highly oriented samples (symmetrical and oblique settings) are presented for 1M, 2M1, 2M2, 3T polytypes of muscovite, 1M, 2M1, 3T polytypes of paragonite and 1M (C2/m and C2 space groups), 2M1, 2M2, 3T polytypes of lepidolite.

Mathematically, it is well established that besides the Fourier coefficients, the natural characteristics of any distribution are its moments. The use of the second moment, called variance, as a measure of line broadening has already gained wide popularity because of its several merits relative to other empirically devised parameters. In recent decades, the fourth moment has been recognized as an important parameter; its theoretical significance has been discussed by Mitra (1964), who developed the moment range function for the estimation of crystallite size and distortion in cold-worked metal. However, owing to the requirements of high degree of accuracy of intensity measurement coupled with cumbersome calculations, this parameter did not find much general application. Modern diffractometers and sophisticated computers have helped ease the problem and in recent years several workers (Kagan & Snovidov, 1965; Kulshreshtha et al., 1971; Mukherjee, 1981) have successfully used this parameter for defect analysis in various non-ideal forms of materials.

Aluminium-substituted goethites are found in many soils and can also be synthesised readily in the laboratory. In recent years, synthetic substituted goethites have been examined by various techniques including XRD, IR, TEM and dissolution kinetics (Thiel, 1963; Jonas & Solymar, 1970; Fey & Dixon, 1981; Fysh & Fredericks, 1983; Schulze & Schwertmann, 1984; Schwertmann, 1984). Transmission electron microscopy (TEM) studies have shown that as Al substitution rises above 10%, the goethite needles become shorter and also thicker in the a direction. Furthermore, crystals which at zero substitution consist of domains parallel to the c axis become less domainic with increasing Al substitution (Schulze & Schwertmann, 1984).

The object of this study was to find a structural explanation for the corrosion figures produced in biotites having different chemical compositions and to apply this information to other di- or trioctahedral micas. The biotites investigated were used in earlier studies of epitaxial growth, so that previous knowledge of their surface behaviour was available. The biotites studied were from Evje, Norway (number 1), Guomum, Czechoslovakia (number 2), and Tanokami Yama, Japan (number 3). All were very dark in colour due to their high iron content.