The distribution of Fe3+-kaolinite, Al-goethite and Al-hematite and their contents of Fe and Al in bauxites and ferricretes are controlled by water activity, dissolved silica activity, temperature and particle size. The proposed model, based on ideal solid-solution equilibria in the Fe2O3-Al2O3-SiO2-H2O system, takes into account water and silica activities. By using the same considerations as those previously developed for the Fe2O3-Al2O3-H2O system, the model calculates the amounts of coexisting phases, Al or Fe substitution ratios in goethite, hematite or kaolinite, and the stability field distributions of the minerals under various conditions. Thermodynamic equilibrium conditions and element distributions within the mineral constituents are shown to be dependent on the parameters cited above. The model yields results compatible with natural observations on lateritic profiles.

A technique for preparing vermiculites for examination by high-resolution transmission electron microscopy (HRTEM) has been developed. A TEM-stable expanded phase can be obtained by intercalating n-alkylammonium ions between the silicate layers of a parent biotite. The vermiculite particles were embedded in Spurr resin and centrifuged to improve orientation. Ultra-thin specimens were prepared using an ultramicrotome, the quality and thickness of the sections being monitored by TEM. Lattice images of biotite, Ba-vermiculite and octylammonium-vermiculite, the latter showing a perpendicular arrangement of the alkyl chains relative to the silicate layers, were obtained with a resolution ∼2 Å. The reliability of these images was confirmed by computer simulation.

Talc is very often an important constituent of suspended matter in marine and lacustrine environments but is rarely detected in sediments. The presence of talc is usually attributed to its industrial and agricultural application. Its recent anthropogenic use, long residence time in the water column due to its small particle size, transport by surface currents and winds, and its tendency to resuspension from the sediment are factors which contribute to the preferential detection of talc in suspended matter.

Des phases transitoires ont été préparées par activation thermique de deux montmorillonites, l'une calcique et l'autre sodique, dans le domaine de température 650–950°C, puis étudiées par spectroscopie infrarouge. Le coefficient de désordre à courte distance, défini à partir de l'élargissement et l'intensité de certaines bandes caracteristiques, présente ses valeurs maximales avec les phases transitoires obtenues à 800°C et 820–850°C respectivement pour la couche de silice et la couche d'alumine. Ce résultat a pu être corrélé à plusieurs données expérimentales concernant la cinétique de dissolution de ces phases transitoires dans l'acide fluorhydrique dilué ou dans des solutions saturées d'hydroxyde de calcium. En outre, l'accroissement particulièrement marqué du désordre à courte distance mis en évidence au niveau de la transition V→IV de la coordinance de l'aluminium, confirme l'hypothèses émise antérieurement par d'autres auteurs pour expliquer le troisième effet endothermique de faible intensité observé sur les courbes ATD des montmorillonites entre 800° et 900°C.

The oxidation state and mineralogical distribution of Fe in two different shale sequences have been studied by Mössbauer spectroscopy and chemical methods. Kimmeridge Clay Formation sediments proved to be richer in total Fe than Gulf Coast shales. In such sediments, Fe may be present in clay minerals (Fe(II) in chlorite, Fe(III) in illite and illite/smectite), pyrite, and ferroan carbonates (siderite, dolomite and ankerite). Pyrite accounts for a much greater proportion of the total Fe in the Kimmeridge Clay samples in which it is difficult to reconcile chemical data with Mössbauer data. There is major doublet overlap of Fe(III) in silicates with Fe(II) in pyrite and spectra cannot be satisfactorily deconvoluted. This would appear to be a fundamental limitation for simple applications. In the pyrite-poor Gulf Coast material, however, chemical and spectroscopic evaluations of overall valence state are much more consistent. Confidence in both determinative techniques is generated, and useful information documenting progressive reduction and redistribution of Fe with burial is obtained.

The REE contents in the clay-sized fractions of nineteen Cretaceous and Pliocene continental sediments, Portugal, were found to be correlated with kaolinite. No correlation is apparent between clay mineralogy and La/Lu or Eu/Sm ratios. The Eu anomaly is generally smaller (or even absent) in the clay-sized fraction than in the corresponding whole sediment, probably due to a greater ability of the clay minerals to accommodate Eu (as Eu2+) rather than the other REE released during weathering.

Primary kaolins, related to Pliocene-Pleistocene volcanic rocks of acid to intermediate composition from the southern part of Kimolos island contain kaolinite and quartz ± cristobalite. Smectite is rarely present whereas alunite is common and more prevalent than baryte or gypsum. The kaolinites show structural disorder (Hinckley indices ranging from 0·6 to 1·1) and contain faults along the c*-axis. The elements Nb, Th, Ce and Sr, La, V constitute two groups with a strong intercorrelation and the kaolins are enriched in these elements compared to the parent rocks. K, Rb, Y and Ba are positively correlated with feldspar content and decrease with the intensity of kaolinization. The mineral assemblages suggest a zonal pattern which is thought to be related to different types of hydrothermal alteration. Starting from the triple point of the alunite-K-feldspar-K-mica-quartz association encountered in Kimolos, a tentative path is presented showing the approximate ranges in concentrations of K2SO4 and H2SO4 required for the formation of the various mineral assemblages.

Five areally distinct mineral assemblages are recognized in the Inferior Oolite of S. England. In each area, vertical (stratigraphic) variations are insignificant. The five assemblages comprise varying proportions of illite, illite-smectite, kaolinite, chlorite and kaolinite-smectite, the mixed-layer clays being largely poorly crystalline and randomly interstratified. A predominantly detrital rather than authigenic origin is suggested for most of the clays. Shallow-water platform carbonates contain kaolinite with illite and illite-smectite. Kaolinite decreases in abundance away from former mid-Jurassic land areas, the deeper shelf and more basinal facies being dominated by illite and/or illite-smectite. Possible volcanic contributions to clay suites are suggested but cannot yet be fully evaluated. The palaeogeographic usefulness of clay mineral suites is confirmed, even in carbonate-dominated systems.

Room-temperature dehydration of aqueous coal slurries, coal extraction residue, or coal ash results in spontaneous luminescence. The phenomenon is characterized by a monotonic decay in photon activity which precedes a sharp rise in photon release. A maximum is reached within several minutes but subsequent decay is slower and photon emission continues for an extended period of time. The magnitude of photon activity is severely limited by the thickness of the strongly absorbing coal slurry. Prior removal of mineral matter from the coal appears to curtail the dehydration-induced phenomena, suggesting that clays or clay-organic interactions are responsible. Data also suggest that air is required as a medium for discharging the excited species.