The conversion of smectite to illite has been studied in buried bentonites and shales of the East Slovak Neogene Basin, using X-ray diffraction analysis and transmission electron microscopy. A good correlation was observed in both rock types between the content of expandable layers in interstratified illite-smectite (I-S) minerals and burial depth (temperature), with shales from a given depth being markedly more illitic than bentonties. This difference disappeared at a depth of ~3 km, which represents a temperature of ~150°C The diameter of fundamental illite particles increased with decreasing expandability. Potassium fixation together with neoformation appear to be the mechanisms of conversion of smectite to illite.

Modal and bulk chemical compositions, illite and chlorite "crystallinity" indices (IC and ChC), white mica bo and vitrinite reflectance values of a Palaeozoic variegated clastic sequence have been determined. The strongly varying IC values are inadequate for the determination of metamorphic zones. Based on statistical analyses of the factors which might affect IC, the presence of paragonite, even in very small quantities as a discrete phase and/or as mixed-layers with illitemuscovite, proved to be the decisive factor. In contrast, no significant correlations were found between the modal composition of the main phases, bulk chemical composition (including Fe3+/Fe2+ ratio) and IC, ChC, or white mica bo values. Thus, neither lithofacies (granulometric), nor redox conditions had any effect on "crystallinity" and bo parameters. Chlorite crystallinity indices and vitrinite reflectance values, together with IC values of selected samples, indicate "anchizonal" conditions. The distribution of white mica bo values indicates that this Hercynian metamorphism was of low-pressure type.

The effect of gypsum additions on the physical performance of lime-stabilized kaolinite has been determined. Kaolinite containing different amounts of lime (i.e. 6 and 14 wt%) and gypsum (i.e. 2,4,6 and 8 wt%) was compacted into cylinders and moist cured at 30°C and 100% r.h. for periods from 2 days up to 20 weeks. Unconfined compressive strength, expansion during curing and subsequent soaking, and water absorption and swelling pressure were determined. The addition of lime and subsequent moist curing was found to reduce substantially the water absorption, linear expansion and swelling pressure of the kaolinite. Although small amounts of gypsum further reduced these parameters, higher gypsum levels (up to 8 wt%) produced substantial water absorption, extreme expansion and high swelling pressures. This excessive volume instability when in contact with water was found, for a particular lime content, to be very sensitive to both the initial moist curing time and the gypsum content. The results indicate that the overriding expansion mechanism operating is imbibition of water or transfer of water by osmosis. The question of what drives this process is the subject of Part II of this paper.

It is well known that illite-smectite can form from smectite at elevated temperatures in natural and experimental systems. However, the conversion of smectite to illite-smectite is also found in some natural systems that have never been heated. The present experiments show that illite layers can form from smectite by chemical reaction at 35° and 60°C at high solution pH. The rate of this reaction is accelerated by wetting and drying.

The distribution of clay minerals from the N and S Atlantic Cretaceous deep-sea sediments is related to rifting, sea-floor spreading, sea-level variations and paleoceanography. Four main clay mineral suites were identified: two are inherited and indicative of ocean geodynamics, whereas the others result from transformation and authigenesis and are diagnostic of Cretaceous oceanic depositional environments. Illite and chlorite, together with interstratified illite-smectite and smectite occur above the sea-floor basalts and illustrate the contribution of volcanoclastic materials of basaltic origin to the sediments. Kaolinite, with variable amounts of illite, chlorite, smectite and interstratified minerals, indicates detrital inputs from continents near the platform margins. Kaolinite decreases upward in the series due to open marine environments and basin deepening. It may increase in volume during specific time intervals corresponding to periods of falling sea-level during which overall facies regression and erosion of the surrounding platforms occurred. Smectite is the most abundant clay mineral in the Cretaceous deep-sea sediments. Smectite-rich deposits correlate with periods of relatively low sedimentation rates. As paleoweathering profiles and basal deposits at the bottom of Cretaceous transgressive formations are mostly kaolinitic, smectite cannot have been inherited from the continents. Smectite is therefore believed to have formed in the ocean by transformation and recrystallization of detrital materials during early diagenesis. Because of the slow rate of silicate reactions, transformation of clay minerals requires a long residence time of the particles at the water/sediment interface; this explains the relationships between the observed increases in smectite with long-term sea-level rises that tend to starve the basinal settings of sedimentation. Palygorskite, along with dolomite, is relatively common in the N and S Atlantic Cretaceous sediments. It is not detrital because correlative shelf deposits are devoid of palygorskite. Palygorskite is diagnostic of Mg-rich environments and is indicative of the warm and hypersaline bottom waters of the Cretaceous Atlantic ocean.

The chemistry of smectites from some bentonite deposits derived from intermediate rocks has been examined by electron microprobe methods. A large variation in chemical composition within very short distances, principally controlled by a well-defined negative relationship between Si and A1, and between A1VI and Fe 3+ and A1VI and Mg has been observed. On the other hand, Mg does not vary systematically with either Si or Fe3+. In several bentonites beidellite coexists with montmorillonite and there is a compositional transition between the two smectite minerals, implying the existence of a possible solid-solution series. This transition occurs only when Cheto-type montmorillonites are present, being absent for Wyoming-type montmorillonites. No compositional transition between Wyoming-and Cheto-type montmorillonite was observed. It is believed that the compositional variations reflect initial chemical gradients originated during the devitrification of the volcanic glass, due to the migration of chemical components.

The results of detailed analyses of the samples discussed in part I are reported. The chemical, morphological and microstructural changes which occurred during moist curing and soaking have been determined using thermal analysis, X-ray powder diffraction analysis, and scanning and transmission electron microscopy combined with EDAX. The analytical results together with the physical observations have shown that the period of volume instability and swelling coincides with the period of gypsum consumption and ettringite formation. However, swelling is not caused by growth of crystalline ettringite but is the result of water absorption. An osmotic mechanism is proposed in which concentration gradients are generated within a surface colloidal layer on the clay particles. Ettringite rods nucleate and grow within this layer and C-A-S-H gel is produced in the areas between the rods. This results in concentration gradients at the clay particle surfaces which provide the driving force for osmosis. The implications of these findings are discussed in relation to lime- stabilization of soils.

A K+-saturated and an NH4+ -saturated smectite from Jelgov 37 Potok (Slovakia) was analysed by X-ray diffraction (XRD) after a series of I to 150 wetting and drying (WD) cycles, and the corresponding distribution functions were calculated using the Dyakonov method. From these data the thicknesses and proportions of different layers were determined. Three kinds of layers (A- 1-00 nm, B-1.26 nm and C-1-52 nm) were detected in the original samples. After 15 WD cycles only A and B type layers were identified in the K-smectite, whereas all three varieties were present during the whole WD treatment in the NH4-smectite. After initial changes the mutual proportion of layers seems to be stable. The 1.00 nm layer is the major layer type in the K-smectite and the 1.26 nm layer is the major layer type in the NH4-smectite. The layer thicknesses evolved during the WD experiments. The systematic changes observed for the NH4-smectite were greater than those for the K-smectite.

Les traitements classiques appliqués pour disperser les argiles et les séparer des carbonates, des phosphates et des sulfates, sont souvent agressifs vis a vis de celles-ci. Une méthode de traitement utilisant les résines échangeuses de cations (REC) a été mise au point. La résine utilisee est l’amberlite IRC-50H. Elle a été éluée ã HCl 1·5 N et utilisée a une température de 60°C. Ce traitement a permis une très bonne dispersion des suspensions de matière d’argile, et l’élimination complete des carbonates, des sulfates et des phosphates. En raison de leur structure silicatée et de leur composition chimique, les argiles sont peu attaquees par les REC, de plus elles sont protegees par les minéraux susceptibles d’être dissous par les REC (carbonates, phosphates et sulfates).

The INTERSTRAT program has been specifically designed to aid the geologist in the identification of the phyllosilicates from powder XRD data. The program achieves this by comparing the experimental 00ld-spacings with a knowledge base of diffraction parameters; a set of likely solutions is then displayed. The method employed by INTERSTRAT is analogous to that used by the clay mineralogist whereby the clays are initially identified down to the group level from the d(OOl) data alone. This procedure also utilises the d-spacings collected from clays that have been subjected to standard clay mineral treatments, i.e. glycolation and heating to 300~ and 500~ One of the most important features of INTERSTRAT is its knowledge base of d-spacings for the interstratified clay minerals in which calculated d(00l) spacings for an individual mixed-layer clay are recorded with respect to its Reichweite, the state under which the d-spacings were collected and the percentage of the mixed-layer components.

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.

The laser Raman microprobe spectrum of gibbsite displays four intense v (OH)- stretching bands at ~3365, 3435, 3525 and 3618 cm-1, bayerite shows three near 3425, 3545 and 3564 cm-1, nordstrandite has three near 3492, 3566 and 3623 cm-1, and doyleite one broad band centred at -3545 cm-1 with sometimes a prominent shoulder near 3615 cm-1. The four polymorphs also possess distinctly different Raman signatures of medium to strong bands in the region 100–1200 cm-1. These differences provide a non-destructive routine determinative procedure by direct microsampling of untreated crystals, fragments, and microcrystalline powders. Sample preparation is minimal. Excessive noise and non-quenchable fluorescence are the principle limitations of the technique.

Regression analysis of high-precision structural and chemical data on trioctahedral and dioctahedral micas yielded interrelationships between unit-cell parameters, chemical composition and structural details. Regression equations relating b and csinβ parameters of micas to composition were used for estimating composition from cell data in order to analyse P-T conditions of rock formation. Algorithms for computing atomic coordinates for 2M1 37' and 1M dioctahedral micas having either centrosymmetric or non-centrosymmetric layers and 1M trioctahedral micas are presented. Deviations of computed atomic coordinates from experimental values are, on average, 0·002 Å for octahedral cations and 0·005-0·010 Å for other atoms. Discrepancies between calculated and experimental individual interatomic distances seldom exceed 0·01 Å. Computed atomic coordinates were used to calculate X-ray diffraction patterns for glauconite and illite. Results indicate a close fit between the calculated and experimental patterns. The local structure around an octahedral cation of interest can be determined.

Initial and de-intercalated (by washing with water from formamide molecules) kaolinite was investigated by X-ray and IR spectroscopic methods. As a result of de-intercalation by water washing, changes in structural characteristics and in some physical-chemical properties of kaolinites take place: (1) the content of low-defect phase (%ldp) evaluated by the expert system of Plançon & Zacharie (1990) decreases; (2) the degree of order of the structure as determined by the Hinckley index decreases; (3) the size of coherent scattering regions (CSR) determined by the method of fourth moments decrease; (4) the rate of repeated introduction of the formamide molecules to the interlayer increases. The cause of these changes are water molecules introduced into the kaolinite interlayer as a result of de-intercalation. These water molecules have IR absorption bands at 3646 (vas), 3550 (vs) and 1650 (vα) cm-1. The results obtained are discussed in relation to modern ideas on disorder models of kaolinite crystals.

Silica-indurated subsurface horizons of an in situ lateritic profile in semi-arid western Australia were investigated using a range of electron-optical and X-ray diffraction (XRD) techniques. These indurated materials were compared with underlying non-indurated pallid zone material. The secondary silica content of the indurated horizons, as determined by electron microprobe analysis, varied from 8 to 33%. Quantitative digital images for secondary silica, generated by mathematical manipulation of digital Si and AI-Kα: images, showed that kaolinite pseudomorphs after mica contained the lowest amounts of secondary silica, with the highest amounts being present in the inter-pseudomorph clay matrix. Variations in the amount of silica in the matrix are considered to reflect variations in the initial porosity of the clay matrix. Such variations may arise from differences in the Al/Si ratio of parent minerals. Transmission electron microscopy (TEM) showed that amorphous silica adhered to the (001) face of kaolinite crystals. The secondary silica could not be detected by either standard or differential XRD procedures.

The composition of fluvial waters can be used to predict the processes of formation and evolution of secondary minerals in Galician soils. These processes are similar in areas with different rocks, from acid to basic, the only exception being strongly serpentinized materials. In general, the nature of the rock has less influence than the characteristics of the alteration system, which is always open, acid and freely draining. Mineral neoformation is always of the monosialitic type, having different degrees of evolution. The incipient phases tend to form gibbsite as a more stable mineral, and halloysite, allophanes and imogolite as metastable forms. With time, a crystalline kaolinite would be the only stable species. These results agree with the mineralogy and the andic or ferralic properties of the soils.

The pillaring of a Laponite by alumina pillars, iron pillars and mixed Al-Fe pillars was obtained by a simple in situ method starting from AlCl3 and/or FeCl3 solutions with different molar ratio Fe/(Fe + Al), and from NaOH solution added simultaneously to the clay suspension. The Al13 pillars were evidenced by XRD and NMR spectra. The density and the charge of these pillars were calculated from the chemical analysis. The Fe pillars (in samples with Fe content >26%) are larger than Al13 pillars and slowly reducible by hydrogen temperature programmed reduction (H2TPR), but we do not have any information on their structure. There is also an excess of non-pillar Fe retained by the pillared clays probably as oxyhydroxides. The isomorphic substitution in the mixed (Al-Fe)13 pillars (in samples with an Fe content >26%) was evidenced by H2TPR results compared to the chemical analyses and by the interpretation of the 27A1 peaks in the NMR spectra.

In Upper Jurassic sandstones of the Magnus Sandstone Member from the Magnus Oilfield in the North Sea, diagenetic kaolinite morphology and isotopic composition vary away from the Late Cimmerian unconformity. Near the unconformity, coarse-grained (15-30 μm) vermiform kaolinite morphology is most common, whereas downdip, 3 km away, fine-grained (∼10 μm) blocky morphology is prevalent. Kaolinite abundances increase downdip, away from the unconformity, and kaolinite near the unconformity has low δ18O (12·5-14·9%o smow) compared to that downdip (15·9−17·5%o). This reflects replacement of marine depositional pore-waters by meteoric water near the erosion surface. However, isotopic temperature estimates suggest that the majority of kaolinite formed at elevated burial temperatures of ~80°C, and not during subaerial exposure of the sandstone. The δD of kaolinite close to the unconformity is also lower than that downdip. Kaolinite morphology and isotopic composition record meteoric water ingress during Late Cimmerian subaerial erosion and retention of meteoric-derived water in the crest of the Magnus structure during burial diagenesis. Kaolinite formation during subaerial exposure is not of significance to the sandstone reservoir quality.

The cation exchange capacity (CEC) of clay minerals has been determined by titration of aqueous suspension of clays with hexadecylpyridinium chloride, monitored using surface tension measurements. In order to make the method suitable for an accurate analysis of the CEC of the clays in drilling fluids or in soils, some parameters affecting the CEC determination (e.g. the presence of carboxymethylcellulose, mixing time and measurement device) have been investigated.

A moderate to high rate of clay sedimentation is characteristic of the Toarcian sequences in the Umbria-Marche basin. The clay mineral assemblages and geochemical characteristics indicate that the Marne di Monte Serrone Formation and the Rosso Ammonitico Umbro-Marchigiano Unit were deposited in a shallow marine environment. In this general palaeogeographic scheme, a reducing subenvironment must have exsisted in which black shale-type facies were deposited resulting in geochemical anomalies in As, Sb, Zn, Co, Cu, Pb, V, Cr, and Ba, among other elements. The high values of both the detrital index and the Ce/Ce* ratio reveal the influence of proximal emerged reliefs. It is suggested that the palaeosoils that developed on the Liassic carbonate Laziale-Abuzzese platform were the source area of these sediments, following a palaeogeographic scheme analogous to that proposed for the Betic Cordilleras (Spain) during the Middle Domerian to Middle Toarcian. The positive and negative Eu anomalies are due to the decisive influence of the weathering process in which sediments with heterogeneous Eu anomaly size were mixed. The final distribution pattern of REE is the result of the different environments to which the clay minerals were subjected and the differences in intensity of weathering.