Three raw samples of Fe-rich smectites from Gafsa (Jebels Shemsi and Hammadi, Tunisia) have been characterized by different techniques which indicate that they contain (15 – 20%) illite, probably interstratified and to a lesser extent they also contain kaolinite, calcite, quartz and Fe oxides. These samples present a relatively high Fe content (∼9%) in the <2 μm fraction. From EPR and Mössbauer spectroscopy it is deduced that Fe is mainly present as Fe(III) in the octahedral environment of smectites and also in Fe-oxyhydroxides associated with the clays. Aluminium-pillared clays have been prepared from the Na+-purified samples, and their thermal stability and acidity have been studied.

Soil kaolins from Indonesia and Western Australia and a range of reference kaolins were studied using Mössbauer spectroscopy, electron paramagnetic resonance (EPR) spectroscopy and SQUID magnetometry. Mössbauer spectra indicate that the Fe within the kaolins is in the highspin Fe3+ oxidation state and that a large fraction of the Fe is present as dispersed atoms residing within the octahedral sites of the kaolinite crystal structure. The EPR spectra are typical for soil kaolins except for the absence of radiation-induced defects for the Indonesian kaolins. The Fe(I) spectra are dominant with a strong symmetric peak at g= 4.3, the presence of Fe(II) spectra is shown by a shoulder on this peak at g= 4.9 and a small phase up peak at g= 9.2.

Low-temperature (5 K) magnetization (M) measurements over large field (H) sweeps (±70 kOe) yielded M(H) curves which are fitted well with Brillouin functions indicating the paramagnetic nature of the kaolins at temperatures down to 5 K. A very small remanent magnetization was detectable in the kaolins. Remanent magnetization to saturation magnetization ratios ranged from 10–4 to 10–3 for the Indonesian kaolins and were all ∼10–3 for the Western Australian kaolins, indicating that at high fields the vast majority of the magnetization of the kaolins is due to paramagnetic ions.

Zero-field-cooled and field-cooled magnetization measurements in small fields (500 Oe) indicate that the Indonesian kaolins are generally free from magnetically-blocked material down to a temperature of 5 K. The magnetic susceptibility of the Indonesian kaolins shows Curie Law behaviour indicating paramagnetic behaviour over all temperatures down to 5 K. Measurements on the Western Australian kaolins indicated the presence of some magnetic material that is magnetically blocked at temperatures below ∼200 ­ 250 K. As a consequence, the magnetic susceptibility showed large deviations from Curie Law behaviour.

This study focuses on the mineralogical and chemical analysis of sediments overlying basaltic basement through which seawater circulates (ODP Leg 168, flank of the Juan de Fuca Ridge). A SEM and TEM-EDX study of the authigenic clays and zeolites allowed the characterization of the hydrothermal phases and the determination of their mechanism of formation. Silicate authigenesis related to hydrothermal alteration of sediment was observed in the sediment layer just above basement at sites located >30 km from the ridge axis. This sediment alteration is particularly intense at Site 1031 where authigenic formation of Fe-Mg- rich smectites (montmorillonite and saponite) and zeolites occur, linked to the dissolution of biogenic calcite. Vertical advection of basement fluid through the sediment column is required to produce this alteration. This process is still active at Site 1031, based on systematic variations in porewater profiles and temperatures obtained from stable isotopic data on calcium carbonates, and the nature of authigenic minerals.

Hand-made bricks were manufactured from natural sediments by firing at 700°C and 800°C after which they were hydrothermally altered at 150°C in a high-pressure reactor for 1200 h. Sediments and fired pieces were studied by X-ray diffraction. The <2 μm size-fraction of fired and hydrolysed samples were also studied by X-ray diffraction and oxygen isotope analysis. The oxygen isotope composition of the samples became depleted in 18O by alteration. Our results are consistent with a process of hydration and hydroxylation of the partially destroyed clay minerals in the fired bricks. The work is relevant to understanding the origins and alteration processes in old ceramic materials.

Three terrace soils comprising a hydrosequence were examined to determine how the spatial distribution of lepidocrocite was related to depth and duration of saturation. Vertical relief was 1.0 m with well drained, moderately well drained, and somewhat poorly drained pedons spaced ∼60 m apart. All soils contained brittle, slowly-permeable subsoil horizons and were acidic with <35% base saturation throughout the upper sola. The well drained soil (Fragic Hapludult) had no morphological indicators of wetness within a depth of 180 cm, and water was perched above a brittle horizon at 82 cm for a total of only 41 days during the 3.4 year observation period. Nevertheless, trace amounts of lepidocrocite were detected in the subsoil. The moderately well drained soil (Typic Fragiudult) was saturated at a depth of 180 cm for 6% of the time, and water was perched on top of a fragipan at 74 cm for 13% of the time. Lepidocrocite was most abundant in this pedon and reached maximum concentrations below the fragipan in the capillary fringe of the regional water table (150–183 cm). The somewhat poorly drained member of the hydrosequence (Aeric Fragiaquult) was saturated at a depth of 180 cm for 96% of the observation period and also contained perched water above a fragipan for >90% of the time. Lepidocrocite occurred throughout this pedon but was most concentrated in fragipan horizons (86–135 cm) between the perched and regional zones of saturation. These horizons were saturated from 22 to 48% of the observation period. The results of this study suggest that lepidocrocite formation was favoured in horizons that were saturated for 5–50% of the time when soil temperatures exceeded 5°C.

The interlayer structures in one- and two-layer hydrates of Na-vermiculite are described by presenting the positional parameters of their constituent atoms, including protons.

The revision of these structures has been accomplished by: (1) determining accurate water contents of the two hydrates by thermoanalysis (TG, DSC); (2) using earlier X-ray diffraction data published by Slade et al.(1985) and de la Calle et al. (1984) as a reference; and (3) applying least-squares refinements when considering the constraints for atomic distances and bond angles between interlayer constituents.

In the 1.485 nm hydrate of Na-vermiculite (nH2O/nNa ≈ 4), sharing edges of Na(OH2)6 octahedra cause their chainlike arrangement. The chains are aligned along [100] and are stabilized by H-bonds between interlayer water molecules and oxygens of the silicate layer. The partial loss of these bonds during dehydration forces the stacking order to change from V3 to Vc in the resulting 1.185 nm (nH2O/nNa ≈ 2) hydrate.

This new understanding may help to explain differences in the rotational correlation time of water molecules between one- and two-layer hydrates of vermiculite as observed by quasielastic neutron scattering (Swenson et al., 2000).

The surface properties of various synthetic layered silicates, Na-kanemite, Nakenyaite and magadiite, exchanged with H, K and Ca, were examined using high-resolution nitrogen and argon adsorption and the data were treated using the Derivative Isotherm Summation method. Using argon as an adsorbate, the aspect ratio of platelets can be determined. In the case of magadiite exchanged with various cations, the stacking of particles is influenced by the nature of the exchangeable cations, thicker platelets being observed for ions with low polarizability. Highresolution argon adsorption data also confirm some structural information previously deduced from Raman spectroscopy experiments concerning the existence of rather open six-membered rings at the surfaces of both magadiite and kenyaite. Furthermore, in the low-energy domain of the isotherms, argon forms a very organized film on basal planes, suggesting a commensurate relationship between silica framework and argon atoms for both magadiite and kenyaite, contrary to what is observed for kanemite. Nitrogen adsorption results reveal the presence of polar sites on the surface of all the investigated minerals but does not allow us to propose an unequivocal assignment for such sites.

Two soils, a haplic Podzol and a dystric Cambisol, developed from post-glacial tills, were studied with respect to their soil chemistry and clay mineralogy. Although the state factors (age, geology, topography, climate) of soil formation were almost identical, two different types developed. The E horizon of the Podzol contained more smectite, characterized by a montmorillonite-beidellitemixed phase. The neoformation of smectite could be traced back to the weathering of mica and chlorite. The Podzol had less hydroxy-interlayered smectite (HIS) in the surface horizons than the Cambisol. A larger amount of chelating compounds in the E horizon of the Podzol either transformed HIS into smectites or inhibited the formation of HIS and favoured the formation of smectites. The physical structure of the soil material is believed to be the most important factor in the different modes of soil evolution. The greater abundance of coarse pores in the topsoil at the Podzol site probably led to a faster eluviation of base cations, a different vegetation at ground level, and, consequently, to a faster soil evolution with the formation of spodic horizons.

The formation of clay minerals was investigated in Spodosols developed in the subalpine belt, with similar exposure, climate and age, but deriving from different parent materials. All the soils were classified as Haplic Podzols and showed the characteristic eluviation and illuviation features of Fe, Al and organic carbon. However, varying parent material lithology led to different clay mineral assemblages in the soil. Smectite could be found in the E horizons of soils developed from granodiorite and tonalite materials. Its formation was strongly dependent on the presence of chlorite in the parent material. If nearly no other 2:1 mineral components, such as chlorite, are present in the lower soil horizons, then a residual micaceous mineral becomes the dominant clay mineral. The latter derives from a mica-vermiculite interstratified mineral.

Clay mineral evolution in diagenetic and very low-grade metamorphic sedimentary rocks from the Maláguide Complex was studied using the following parameters: illite and chlorite crystallinity, b cell dimension of illite, chemistry of chlorite, and the occurrence and distribution of the following phyllosilicates: I-S mixed-layer minerals, kaolin polytypes, chlorite-bearing mixedlayer minerals (tosudite and mica-chlorite interstratifications), vermiculite-like minerals, paragonite and biotite. The distribution of IC values permits the subdivision of the study area into three zones: diagenetic, anchizone and epizone. On the contrary, the distribution of CC values cannot be used in the study of the metamorphic zonation. The mineralogy and b dimension of illite indicate that the Maláguide samples display a low to low-medium pressure metamorphism, also characterized by steep temperature gradients.

The correlation between IC data and distribution of other significant minerals has permitted the establishment of a zonation within the chlorite zone, which is confirmed by the appearance of some index minerals, such as paragonite, biotite, chloritoid and andalusite.

A series of reduced-charge montmorillonites with cation exchange capacities of 89, 73, 49 and 29% of the starting mineral was prepared from a Li-saturated smectite (Kriva Palanka, Republic of Macedonia) by heating at 110, 130, 160 and 300°C for 24 h (samples KP110 – KP300, respectively). Hydration properties of this series were investigated gravimetrically and by in situ XRD at different relative humidities (RHs). In the gravimetric experiments, higher water contents were observed for desorption than for sorption and hysteresis was present over the whole range of RHs for all the samples. The parent montmorillonite and the samples KP110 and KP130 retained similar amounts of water under the same conditions, thus showing that the decreased negative charge on the layers had minor effect on the water uptake at all investigated RHs. Significantly decreased water content was retained by KP160 while KP300 contained only 8% water at 100% RH. The d001 values of the parent montmorillonite and the samples KP110 and KP130 increased with RH, while those of KP160 and KP300 were independent of RH and remained at ∼10.4 and ∼9.6 Å, respectively.

Five vermiculite samples collected from Béni Bousera, Morocco and four from Palabora, South Africa were investigated by X-ray diffraction, chemical analysis, 57Fe Mössbauer spectroscopy, and 27Al magic angle spinning nuclear magnetic resonance. The X-ray diffraction studies indicate that all vermiculites have very similar crystallographic parameters. The chemical analyses and the NMR spectra indicate that the Béni Bousera vermiculites contain Al3+ cations in both octahedral and tetrahedral sheets and the Palabora vermiculites contain Al3+ in the tetrahedral sheet. The Mössbauer spectra indicate that the Béni Bousera vermiculites contain more Fe2+ cations than the Palabora vermiculites and do not contain tetrahedral Fe3+ cations. The different cation compositions and distribution in the two sets of vermiculites may result from different parent minerals, i.e. chlorite in the case of Béni Bousera and phlogopite in the case of Palabora, and different genetic processes, i.e. weathering in Béni Bousera and hydrothermal alteration in Palabora.

Mechanically-prepared binary mixtures of two dioctahedral smectites (of different chemical compositions) with two kaolinites (with different amounts of structural defects) were studied by infrared (IR) spectroscopy to verify the ability of IR spectroscopy to detect small amounts of individual components in the mixtures. The same samples were analysed by X-ray diffraction (XRD) in transmission and reflection geometries to compare the sensitivities of these techniques. Infrared spectroscopy is suitable for detecting small amounts of kaolinite in the smectite-rich samples but is not sensitive to small amounts of smectite in kaolinite-rich samples. The IR spectra of kaolinite/ smectite mixtures have a ‘strongly kaolinitic character’ even with only 30% kaolinite. The most characteristic band of kaolinite, near 3695 cm–1, gradually decreased in intensity with decreasing kaolinite content though the presence of this absorption allowed 0.5 mass % of both kaolinites to be detected in their mixtures with smectites. On the other hand, XRD powder techniques are much more adept at detecting low smectite contents in kaolinite-rich samples.

Vivianite [Fe3(PO4)2·8H2O] is easily oxidized in the presence of air. In this work, we studied the oxidation and incongruent dissolution of vivianite in a calcareous medium containing an anion-exchange resin (AER) that acted as a sink for phosphate. Freshly prepared vivianite suspensions with calcite sand and an AER membrane were oxidized and stirred by bubbling air or CO2-free O2. Experiments were finished when oxidation rate and P removal by the AER became slow, which was at 53 days (air system) or 28 days (CO2free O2 system). At these times, the respective values of the Fe(II)/total Fe ratio were 0.29 and 0.12, and the respective values of the atomic P/Fe ratio were 0.15 and 0.11. The final product of the oxidation was poorly crystalline lepidocrocite in the form of thin (1 ­ 5 nm), irregular lamellae that were soluble in acid oxalate. The unit-cell edge lengths of this lepidocrocite were a= 0.3117, b= 1.2572, and c= 0.3870, vs. a= 0.3071, b= 1.2520 and c= 0.3873 nm for the reference lepidocrocite. The lepidocrocite lamellae contained occluded P (P/Fe atomic ratio = 0.03 ­ 0.04). The results of this and a previous study made us hypothesize that this occluded P is structural and occupies tetrahedral sites adjacent to the empty octahedral sites in the sheets extending on ﹛010﹜.

Among the arsenic species in the environment, arsenate predominates under oxidizing conditions in soils and waters. The adsorption of As(V) by some natural Fe oxyhydroxides and clay minerals and synthetic Al(OH)3 and FeOOH has been studied. The results show a very high As(V) adsorption capacity on both synthetic Al hydroxide (122 mg/g at pH: 5) and Fe oxyhydroxide (76 mg/g at pH 5). This adsorption capacity is pH dependent and shows maximum values at ∼pH 4. The application of these adsorbents to arsenic immobilization in the remediation process of two polluted mining soils with some differences in their physicochemical characteristics has also been studied. The best results were obtained when synthetic Al(OH)3 and FeOOH were used; these materials decreased the water-extractable fraction of As by 55–79% for one soil and by nearly 100% for the other soil, the latter with higher pH and Eh values.

We have investigated the adsorption of D- and L-alanine, and their respective dimers, by three allophanes with different Al/Si ratios. The Kanuma (Al/Si = 1.2) and Kitakami (Al/ Si = 1.5) allophanes were from Japan whereas the Te Kuiti (Al/Si = 1.6) sample came from New Zealand. The three allophanes differed in their capacity for adsorbing alanine but none of the samples showed a clear preference for either the D- or the L-form. In the case of alanyl-alanine both Kanuma and Kitakami allophanes gave a hint of preferring the L- to the D-enantiomer. On the other hand, the allophane sample from Te Kuiti showed a clear preference for L-alanyl-L-alanine. In keeping with this observation, circular dichroic spectrometry indicated that solutions of a racemic mixture of alanyl-alanine, after equilibration with Te Kuiti allophane, became relatively enriched in the Denantiomer. The size, intra-molecular charge separation, and surface orientation, of L-alanyl-Lalanine zwitterions apparently combine to confer ‘structural chirality’ to the complex (adduct) with Te Kuiti allophane. As a result, the mineral-organic complex develops a preference for the L-form of alanyl-alanine. This finding points to a possible role of certain allophanes in the origin of biochirality.

Goethite, lepidocrocite, magnetite and akaganeite were synthesized in 0.8 M, 2 M and 5 M NaCl solutions at various temperatures (25, 40, 60°C) under slightly acidic to slightly alkaline pH with or without Si additions. Elevated temperatures prevent complete oxidation of initial Fe2+ solutions and magnetite and siderite precipitate, accompanied by goethite and lepidocrocite. At higher salinity, O2 solubility is reduced and its distribution is limited, leading to coprecipitation of lepidocrocite, akaganeite and goethite.

Lepidocrocite morphology changes from plates at pH 5.5 through rods at pH 7 to multi-domainic crystals at pH 8.2, due to enhanced crystal growth along the c axis. Salinity and temperature have opposite effects on lepidocrocite crystallinity.

Goethite crystals are multi-domainic and twinning appears only at elevated temperatures. Increases in temperature and salinity improve goethite crystallinity as observed by IR spectra. Addition of Si up to Si/Fe = 0.1 retards crystal growth and Si-OH-stretching bands appear. At Si/Fe = 1 most of the precipitate is short range ordered.

Platy and rod-shaped lepidocrocite from the Thetis and Atlantis II Deeps, were probably formed under the slightly acidic conditions of the hydrothermal brines. The Si concentration was greater in Atlantis II Deep than in Thetis Deep, leading to larger lepidocrocite and goethite crystals in the latter.

Multi-domainic goethite could have precipitated throughout. Pure phase goethite might have precipitated in the less concentrated brine, whereas mixtures of goethite and lepidocrocite might have precipitated in the more concentrated brine, depending mainly on oxidation rate and oxygen mobility within the brine.

The purpose of this report is to describe the appropriate use of indices relating to crystallinity, such as the ‘crystallinity index’, the ‘Hinckley index’, the ‘Kü bler index’, and the ‘Árkai index’. A ‘crystalline’ solid is defined as a solid consisting of atoms, ions, or molecules packed together in a periodic arrangement. A ‘crystallinity index’ is purported to be a measure of crystallinity, although there is uncertainty about what this means (see below). This report discusses briefly the nature of order, disorder and crystallinity in phyllosilicates and discusses why the use of a ‘crystallinity index’ should be avoided. If possible, it is suggested that indices be referred to using the name of the author who originally described the parameter, as in ‘Hinckley index’ or ‘Kübler index’, or in honour of a researcher who investigated the importance of the parameter extensively, as in ‘Árkai index’.

A series of kaolin-rich mineral samples was treated with hydrofluoric acid (HF) and the residual material characterized using infrared (IR) spectroscopy, supplemented by scanning electron microscope (SEM) observations. By examining the hydroxyl-stretching region of the IR spectra before and after treatment with hydrofluoric acid, it was possible to identify the three kaolin polytypes – kaolinite, dickite and nacrite – with greater certainty. The SEM observations suggested that the rate of dissolution of the kaolin phase was largely dependent on particle size. In general, dickite and nacrite tend to occur in the coarser clay fractions, and for this reason the finer-grained kaolinite is preferentially dissolved by the HF treatment. However, in the Keokuk kaolinite, which occurs in exceptionally large particles, it was still possible to concentrate a dickitic fraction by HF treatment, suggesting that in some cases kaolinite may be more susceptible to HF dissolution for reasons other than particle size. The IR spectra of disordered kaolinite could be interpreted as arising from a mixture of kaolinite and dickite components. However, both components dissolve at the same rate in HF, supporting the idea that disordered kaolinite consists of an intimate association of randomly stacked dickite-like and kaolinite-like components.

This work deals with the formation of humic-like compounds, products of the Maillard reaction between glycine and D-glucose, on clay (K+, Ca2+ and Al3+-saturated montmorillonite and kaolinite) and quartz systems in the presence of the same cations. Natural quartz was used as the control while the effect of cation type, mineral substrate and CEC was evaluated. All the systems form humic-like substances that are probably responsible for the decrease in the pH (H2O) after 30 d. The type of cation does not influence the overall production of humic substances, while the amount of cations controls the formation of humic-like material especially in the presence of clays. A mineral surface is necessary to synthesize molecules with this high degree of complexity.

Fulvic-like compounds are produced in great amounts on natural quartz and their formation is hampered by the presence of ‘free’ cations, regardless of their amount. Humic substances do not penetrate the interlayer of montmorillonite.