This study characterizes the effects of fluid migration into a predominantly shale cover which seals the active geothermal system of Mt. Amiata (Tuscany, Italy). During Alpine orogenesis the shale unit was affected by regional metamorphism at the limit of the diagenesis-anchizone. Subsequently, the phyllosilicate clay minerals of the shales underwent significant alteration at diagenetic temperatures (175±25ºC as determined by the geochemical model) by the pervasive circulation of fluids activated by the geothermal field. The overall mineralogical assemblages indicate that the main transformations consisted mostly of destabilization of illite and formation of kaolinite together with large amounts of I-S mixed layers, with higher smectite content and decreased Reichweite I-S ordering (from R3 to R1) with respect to the original, unaltered phases. Application of computer modelling indicates that the circulation of CO2-rich geothermal fluids into the shale unit was responsible for the observed phyllosilicate clay mineral transformations.

Des lizardites substituées (Mg,Fe,Ni)3Si2O5(OH)4 ont été étudiées par spectrométrie en réflectance diffuse de 340 à 2500 nm, de manière à déterminer l'environnement de Mg2+, Ni2+ et Fe2+, en particulier la symétrie des sites et les distances métal-ligands. L'examen de la structure de la lizardite sensu stricto ayant conduit à définir pour Mg2+ deux sites hexacoordonnés M1 et M2 non équivalents dans la couche octaédrique du feuillet serpentineux, l'interprétation, à l'aide de la théorie du champ cristallin, des spectres d'absorption de lizardites de compositions chimiques variées a fourni les résultats suivants: 1. Le site M1 a la symétrie C2v: octaèdre orthorhombique. 2. Le site M2 a la symérie C3v: octaèdre rhomboédrique. 3. Fe2+ est hexacoordonné, et occupe les deux sites M1 et M2 si sa teneur est supérieure à environ 2%. Pour une teneur inférieure, Fe2+ n'occupe que M1. 4. Dans une lizardite Mg + Fe + Ni, Ni2+ est hexacoordonné et occupe le site M2. Ce site du nickel est plus grand en présence de Fe2+, que lorsque le nickel y est seul (népouite). Ni2+ y occupe une position plus rapprochée du centre de la couche octaédrique que Mg2+, ce qui contribue à réduire la flexion du plan des cations dans cette couche. 5. Dans une lizardite proche du pôle nickelifère (népouite), il y a réorganisation de la structure autour d'un site hexacoordonné unique de symétrie C3v. Ce site est déformé, et plus petit: distance moyenne métal-ligand r = 2·06 Å dans la népouite, r = 2·11 Å dans la lizardite magnésienne sensu stricto. Cette réduction de la taille du site ne peut se concevoir que par la réduction de l'épaisseur de la couche octaédrique: 2·20 Å (pôle Mg) à 2·16 Å (pôle Ni).

Chlorite belonging to subfamily C, vermiculite 2MB-VII-meso, talc and a monoclinic amphibole were identified in rocks from a contact zone between highly tectonized granite and serpentinite at Jordanów, Lower Silesia, Poland. K-saturated vermiculite readily produced a phlogopite-like structure 1M-I (3TA-IV) indicating trioctahedral mica to be its precursor. Spatial relations of the mineral assemblages were compared with published experimental data and used to produce a tentative model of the geological evolution of the rocks and minerals, which include four episodes of mineral development separated by three tectonic events.

Phyllosilicate associations in hydrothermally altered fluorite ore bodies are: Li-chlorite ± pyrophyllite ± interstratified minerals ± muscovite +± kaolinite. Chlorites, the main alteration minerals, are dioctahedral, d060 = 1.489-1-490/~,, of Ia polytype. The structural formulae indicate substitution of AI for Si from 0.61-0.78 atoms. The total octahedral occupancy ranges from 4.52-4-71 atoms, with 0.49-0-69 Li atoms per half cell unit. This composition indicates that the chlorites are intermediate members of the donbassite-cookeite series proposed by Sudo (1978). The mineralogical associations and textural relations suggest that after intensive silicification which produced alkali alteration under acid conditions, pyrophyllite was produced at the expense of muscovite and then Li-bearing donbassite formed from the pyrophyllite. The Li needed for the formation of the chlorites could be genetically related to granitic batholiths which occur close to the fluorite ores.

K+ ⇋ Ca2+ exchange was performed on a mixed-layer (phlogopite-vermiculite) sample from Palabora, Republic of South Africa. Exchange isotherms, X-ray diffraction patterns and far infrared (FIR) spectra of the mineral were obtained. Different mineralogical phases were identified during the exchange process: K-vermiculite, Ca-vermiculite and a regular mixed-layer (VK–VCa) phase. Two types of exchange sites for K+ were identified by FIR during the exchange process. The first type, dominant in the K-vermiculite, gives an absorption band at 76 cm–1. The other, which was the most pronounced site in the mixed-layer phase, gives an absorption band at 72 cm–1. The mixed-layer phase was formed only when oxidation of Fe2+ resulted in the internal compensation of part of the negative charge of vermiculite. This study shows that the high selectivity displayed by vermiculite for K+ is enhanced by the formation of the mixed-layer phase.

Les nontronites ne présentent pas les propriétés caractéristiques des phyllosilicates 2:1 magnésiens ou alumineux à substitutions tétraédriques: domaines d'hydratation homogène, isotherme de désorption d'eau avec paliers, organisation structurale ordonnée ou semi-ordonnée. Or les analyses structurales montrent que ce sont des beidellites ferriffères et l'étude de l'effet Hofmann–Klemen confirme le taux très faible de lacunes et de substitutions octaédriques. Diverses hypothèses justifiant ces propriétés sont présentées et discutées.

Fresh samples of some Scottish basic igneous rocks contain two-component interstratified minerals consisting mainly of layers of chlorite, swelling chlorite and saponite in different combinations. The differential thermal curves are characteristic of swelling chlorite.

A method is described whereby differentiation between clay minerals may be rapidly effected. The method depends upon the differential moisture adsorption of clay minerals. There seems no reason why reasonably quantitative results may not be obtained. An application to the Etruria Marl is given.

Clay from the Fuller's Earth formation is shown to contain mainly illite, kaolinite and calcite, in contrast to the Fuller's Earth Bed in which montmorillonite is the main clay mineral. A negative correlation has been demonstrated between the calcite content and the plasticity as measured by the Atterberg limits. Fresh samples from the Fuller's Earth Bed have a higher plasticity than those of the fuller's earth clay with similar calcite percentages, due to the relative increases in the expanding lattice clay mineral. Weathering of the fuller's earth clay typically reduces the calcite content and increases the percentage of montmorillonite, resulting in a higher plasticity.

Measurements have been made of the transient changes in the polarized components of fluorescence when aqueous suspensions of dye-tagged sepiolite particles were subjected to pulses of high frequency alternating electric field. The dye was acridine orange, a planar, cationic molecule. From these measurements, the size and electrical prolarizability of the sepiolite particles was evaluated and the directions of the absorption and emission transition moments responsible for the fluorescence of the dye located. The dye molecules were shown to adsorb on the clay surface with their long axes parallel to the sepiolite rods. Adsorption of the dye molecules in the surface channels of the clay was indicated. The electrical polarizability was considered and compared with the cation exchange capacity of the mineral. A novel, rapid means of studying clay minerals is indicated hereby.

The sorption of potassium by mica partially depleted of potassium was studied by adding potassium to a solution of sodium chloride in quasi-equilibrium with the mica. The concentration of potassium in the solution was increased 1·5 times before reverse exchange was initiated. Potassium resorbed by the depleted mica was extracted more readily than potassium from the original mica. Potassium exchange from mica is not reversible; there is irreversible change in the mica when potassium is exchanged and also an additional hysteresis in the forward and reverse exchange.

The hydrothermal reactivity of a Mg-vermiculite from Santa Olalla (Spain) was studied experimentally at 150 and 300ºC, 75 and 100 bars, respectively, in (Na,K,Ca,Mg) chloride and sulphate solutions (liquid/solid ratio = 10). The formation of mixed-layer clays is demonstrated by FT-IR spectroscopy, X-ray diffraction (XRD) and electron microprobe. The gradual decrease of the 3220 cm–1 infrared band intensity, characteristic of free water, is interpretated as the dehydration of the interlayer Mg cation of the vermiculite. The presence of ‘brucite type’ sheets is also observed by the increase of 3555 cm–1 and 3420 cm–1 band intensities. The XRD results show that run products are able to expand when glycolated. Microprobe analyses document the decrease of IVSi content and a significant enrichment in Mg in the run products. The formation of a mixed-layer clay comprising saponite and chlorite layers is proposed.

The distribution of octahedral cations in the two component layers of a 7 Å–14 Å interstratified mineral with a bulk chemical composition (Fe4.122+Mg0.07Mn0.01Al1.69□0.11)(Si2.56Al1.44) O10(OH)8 was investigated using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) in combination with the image simulations. In the 14 Å component layers, comparison between the observed and simulated images revealed that the M4 sites of the interlayer sheets were occupied preferentially by Al together with a small amount of Fe; the other M1, M2 and M3 sites were occupied by dominant Fe and residual Al in equal proportions. Two types of octahedral sheets with disordered and ordered cation distributions were recognized in the 7 Å component layers. The two types of sheets were similar to the octahedral sheet of the 2:1 layer and the interlayer sheet in the 14 Å layer above, respectively. Irregular vertical stacking and lateral contact of the different component layers in structure and chemistry characterized the interstratification, which may be caused by rapid precipitation and accretion of the component layers in hydrothermal environments.

Back-scattered electron images of clay minerals from sandstones are used, together with complementary micro-analytical methods, to identify and quantify mineral microporosity and geochemistry. Clay minerals typically have a range of microporosity from 10 to >90% dependent on texture and paragenesis. Fibrous clays are highly microporous; detrital clays have low microporosity but specific clay minerals have broad ranges of microporosity. The often quoted mineral-chemical association between thorium (Th) and kaolinite cannot be substantiated by micro-analysis. The Th content of clay minerals is associated with micro-inclusions within the kaolinite which form diagenetically or are derived from precursor minerals.

The flocculation of a Na-montmorillonite suspension by Na, Ca, and Al chlorides was investigated using the optical absorbance method. The flocculation of the clay was found to be irreversible with a degree of irreversibility that increases with electrolyte concentration. The flocculation values of Na, Ca and Al chlorides were found to be equal to 8, 0·25 and 0·032 mmol/l respectively. The ratio of the flocculation values of the different salts is in reasonable agreement with the ratio predicted by current theories of colloid stability.

To enhance the catalytic activities of zeolites for the polycondensation reactions of humic precursors, Fe was loaded into a zeolite via an ion-exchange reaction and the resulting product was subjected to calcination at 773 K. Two types iron-loaded zeolites were prepared using one equivalent (Fe-Z-1) and 10-equivalents (Fe-Z-10) of Fe2+ to the cation-exchange capacity of a natural zeolite from Niki town (Hokkaido, Japan). X-ray diffraction (XRD) patterns and X-ray photoelectron spectroscopy (XPS) spectra showed that the Fe(II) that was originally loaded into the cation-exchange sites in the zeolite became oxidized to a Fe(III) ionic species during the preparation. The catalytic activities of each zeolite were evaluated, based on the degree of darkening for reaction mixtures containing catechol, glycine and glucose as model humic precursors. The catalytic activities of Fe-Z-1 and Fe-Z-10 were higher than that for an untreated zeolite, and increased with the amount of Fe in the zeolite.

The colloidal state of aqueous Ca2+-montmorillonite dispersions was modified with three types of cationic end-capped poly(ethylene oxides). The macromolecules were not only adsorbed at the external surfaces but were also intercalated into the dispersed montmorillonite particles. The amounts adsorbed and the basal spacings (~1.7 nm) were comparable to the corresponding Na+-montmorillonite dispersions. The poly(ethylene oxides) protruding out of the interlayer spaces or adsorbed at the external surface determined the colloidal behaviour of the dispersions. The phase diagrams (sol-gel diagrams) of the Ca2+-montmorillonite dispersions differed from those of the corresponding Na+-montmorillonite because of the different colloidal states of both dispersions (Ca2+-montmorillonite particles vs. delaminated Na+-montmorillonite). The phase diagrams of the poly(ethylene oxide) containing Ca2+-montmorillonite dispersions showed fields of sol and flocs. Attractive gels were formed in a few cases only (TMA+-PEO 1500 and 4000, THA2+-PEO 1500, 4000 and 20,000) and with distinctly lower gel strength than in the presence of Na+ ions. On the basis of the sol-gel diagrams, conditions (type and concentration of poly(ethylene oxides), montmorillonite content) can be selected which lead to peptization of the Ca2+-montmorillonite particles into stable colloidal dispersions (sols). Addition of cationic poly(ethylene oxides) can enhance the salt tolerance up to 1000 mmol/l NaCl.

The clay mineralogy of a set of Tertiary marine sediments from the Internal Subbetic of the Betic External Zone was examined. Two types of sedimentary environment were distinguished: a platform environment consisting of limestones, marls, organogenic limestones, conglomerates and silexites distributed heterogeneously in time and space; and deep environments, where the sedimentation consisted of marls, marly limestones, marly clays and silexites, with no sedimentary gap. A third group of sediments studied belongs to the Águila Complex, with mineralogical and stratigraphic characteristics very similar to the platform sediments. This third type of sediment is found in the sediments of the Campo de Gibraltar Complex as large, disperse blocks resulting from tectonic activity. A very similar mineral association was observed in all three domains, consisting of smectite, illite, mixed-layer I-S, kaolinite and lesser amounts of palygorskite and chlorite. Materials mainly derive from the erosion of Mesozoic sediments, and sedimentation was controlled by the compressive tectonics of the region.

It is well established that palygorskite has an amphibole-like, double-chain structure. The linked tetrahedral groups forming continuous sheets are divided into ribbons of various widths due to alternation of the direction of tetrahedra which run parallel to the fibre axis (Brindley, 1980). This alternation of the chains leaves a series of holes of well-defined size which are filled with water molecules (channel water). Based on microscopic observations of cleavage surfaces (Bailey, 1980), the mineral appears to be built up of regular stacking of planes parallel to (h00) and (hk0) which form predominantly the surface of the laths parallel to the c-axis. This is further supported by the enhanced X-ray reflections from these planes. Some degree of structural disorder might be expected to result from the progressive elimination of the channel water on heating. In addition, the weak interchain bonding in palygorskite is likely to result in a shift of the layers parallel to the fibre axis.

An X-ray diffraction method for the estimation of quartz is described using rock powder pellets originally prepared for X-ray spectrometry, correcting the X-ray intensities for mass absorption. A coefficient of variation of 3·8% is claimed; 95% of all estimates fall within ± 5·5%.