Showing papers in "Clay Minerals in 2002"
TL;DR: The diagenetic evolution of kaolin and illitic minerals in sandstones is described in this article, where the structural characterization of these minerals, the possible reaction pathways leading to their crystallization, and the origin of the fluids involved are discussed specifically.
Abstract: The diagenetic evolution of kaolin and illitic minerals in sandstones is described here. The structural characterization of these minerals, the possible reaction pathways leading to their crystallization, and the origin of the fluids involved are discussed specifically.
While early precipitation of kaolinite is in general related to flushing by meteoric waters, subsequent diagenetic kaolinite-to-dickite transformation probably results from invasion by acidic fluids of organic origin. Dickite is the stable polytype in most sandstone formations and the kaolinite-to-dickite conversion is kinetically controlled.
The conventional model of kaolin illitization, assuming a thermodynamic control in a closed system, is discussed and compared to an alternative model in which illitization of kaolin is not coupled to dissolution of K-feldspar (Berger et al. , 1997). In the latter model, illite crystallization at the expense of kaolin implies that an energy barrier is overcome either by an increased K+/H+ activity ratio in solution or by a considerable temperature increase.
292 citations
TL;DR: In this article, the structural vibration analysis of dioctahedral smectites is performed by comparing the NIR combination and overtone bands with fundamental stretching and bending absorption features in the mid-IR region.
Abstract: Visible to near-infrared (NIR) reflectance spectra and mid-IR transmittance spectra are presented here for a collection of dioctahedral smectites. Analysis of the structural OH vibrations is performed by comparing the NIR combination and overtone bands with fundamental stretching and bending absorption features in the mid-IR region. Second derivatives are used to determine the actual band centres, which are often shifted slightly by a spectral continuum in the reflectance or transmittance spectra. New bands have been identified near 4170 and 4000 cm–1 in the NIR spectra of nontronite with tetrahedral substitution. A related band is observed near 4100 cm–1 for montmorillonites with substantial tetrahedral and/or octahedral substitution. These bands are correlated with the mid-IR bands near 680 cm–1 for nontronite and near 630 cm–1 for montmorillonite. Comparison of the OH overtone and combination bands with the fundamental stretching and bending vibrations gives consistent results.
185 citations
TL;DR: In this paper, an analysis of the near-infrared (NIR) spectral bands of phyllosilicates, together with the midinfrared bands, enables testing and confirmation of band assignments for the structural OH vibrations.
Abstract: Analysis of the near-infrared (NIR) spectral bands of phyllosilicates, together with the mid-infrared bands, enables testing and confirmation of band assignments for the structural OH vibrations. Spectral analyses of selected smectites and serpentine-kaolin minerals are presented here. The results of this study indicate that dioctahedral smectites may contain both in-plane and out-of-plane OH-bending vibrations, as suggested by Farmer (1974). In-plane bands occur near 800–915 cm −1 , while the weaker out-of-plane vibrations occur near 600–700 cm −1 and are enhanced in dioctahedral smectites when the structure is disrupted by substitutions. Analysis of the OH-stretching vibrations and their NIR overtone bands is also presented for both smectites and serpentine-kaolin minerals. These overtones are more straightforward for serpentines than for kaolinite, and a strong overtone associated with the kaolinite OH-stretching band at 3620 cm −1 is found that supports its assignment as an OH-stretching band.
135 citations
TL;DR: In this article, the adsorption of As(V) by some natural Fe oxyhydroxides and clay minerals and synthetic Al(OH)3 and FeOOH has been studied.
Abstract: 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.
117 citations
TL;DR: In this article, the authors discuss the nature of order, disorder and crystallinity in phyllosilicates and discuss why the use of a "crystallinity index" should be avoided.
Abstract: 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 ‘Kubler index’, and the ‘Arkai 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 ‘Kubler index’, or in honour of a researcher who investigated the importance of the parameter extensively, as in ‘Arkai index’.
In contrast to a crystalline solid, an ‘amorphous’ solid is one in which the constituent components are arranged randomly. However, many variations occur between the two extremes of crystalline vs. amorphous. For example, one type of amorphous material might consist simply of atoms showing no order and no periodicity. Alternatively, another amorphous material may consist of atoms arranged, for example, as groups of tetrahedra (i.e. limited order) with each group displaced or rotated (e.g. without periodicity) relative to another. Thus, this latter material is nearly entirely amorphous, but differs from the first. Likewise, disturbance of order and periodicity may occur in crystalline materials. The terms ‘order’ and ‘disorder’ refer to the collective nature or degree of such disturbances. Although seemingly simple notions, ‘crystalline’ and ‘amorphous’ are complex concepts.
Crystalline substances may show a periodic internal structure based on direction. For example, two-dimensional periodicity is common in phyllosilicates where two adjacent sheets or layers must mesh. For example, …
112 citations
TL;DR: In this article, the authors evaluated the competitive adsorption of glyphosate and phosphate on goethite and gibbsite and on illite, montmorillonite and two kaolinites differing in surface area.
Abstract: Competitive adsorption of glyphosate and phosphate on goethite and gibbsite and on illite, montmorillonite and two kaolinites differing in surface area was evaluated The results show that glyphosate and phosphate are competing for the adsorption sites, but the degree of competition depends on the adsorbent On goethite the competition is very much in favour of phosphate, on gibbsite the competition is closer, but still phosphate is favoured, while on illite, montmorillonite and kaolinite the competition is almost equal The amounts of glyphosate and phosphate, which can be adsorbed also depends on the adsorbent: the oxides adsorb more than the clay silicates The amount adsorbed on kaolinite was dependent on the specific surface area Changes in the surface area did not affect the competition between glyphosate and phosphate for adsorption sites The results indicate that differences among soils of different mineralogical composition regarding the adsorption of glyphosate and phosphate can be expected
107 citations
TL;DR: In this article, the authors analyzed the optical properties of cationic dyes adsorbed on clay surfaces using VIS spectroscopy and showed that the effects of the dye/ clay ratio and of the swelling properties of the montmorillonite substrate on dye aggregation were compared in terms of the effect of clay layer charge.
Abstract: Theories concerning the optical properties of cationic dyes adsorbed on clay surfaces are analysed in detail. An investigation of the aggregation of methylene blue (MB) in montmorillonite dispersions is conducted using visible (VIS) spectroscopy. The effects of the dye/ clay ratio and of the swelling properties of the montmorillonite substrate on dye aggregation are compared in terms of the effect of clay layer charge. The observed influence on dye aggregation was almost negligible for both swelling and dye loading. The layer charge of the silicate determines the extent and the type of dye aggregation in freshly prepared MB/montmorillonite dispersions. Observed spectral changes with time indicate a rearrangement and redistribution of dye H-aggregates (band close to 570 nm) to monomers (660 nm), dimers (605 nm) and J-aggregates (760 nm). Dye aggregates are probably already formed during dye cation migration in the vicinity of clay colloid particles. The extent and the type of initially formed species are probably affected by the electric double layer of clay layers. After reaching the clay surface, dye cation assemblies are rearranged and decompose as described above. Reaching chemical equilibrium, dye cations adjust the distribution of the layer charge, in order that each cation could balance the charge due to one unequivalent substitution.
103 citations
TL;DR: In this paper, the local coordination environment of Cr, Mn and Ni in synthetic goethite using EXAFS spectroscopy was investigated and it was shown that the perturbations are likely to be responsible for limiting the accommodation of Cr3+, Mn3+, or Ni2+ in the FeOOH structure.
Abstract: The crystal-chemical mechanisms by which transition metals are associated with goethite are fundamental to our understanding of the solubility and bioavailability of micronutrients and heavy metals in soils, and in the formation of laterite ore deposits. Transition metals such as Cr, Mn and Ni may sorb onto goethite by forming surface precipitates, surface complexes or by replacing Fe3+ in the goethite structure. In the work reported here, we investigated the local coordination environment of Cr, Mn and Ni in synthetic goethite using EXAFS spectroscopy. We demonstrate the isomorphous substitution for Fe3+ by Cr3+ (up to 8 mol.%), Mn3+ (up to 15 mol.%) and Ni2+ (up to 5 mol.%). We find, however, that the next-nearest-neighbour coordination environment changes with composition. The perturbations are likely to be responsible for limiting the accommodation of Cr3+, Mn3+ or Ni2+ in the FeOOH structure.
97 citations
TL;DR: In this paper, two dioctahedral smectites with two kaolinites (with different amounts of structural defects) were studied by IR spectroscopy to verify the ability of IR spectra to detect small amounts of individual components in the mixtures, and the same samples were analysed by X-ray diffraction in transmission and reflection geometries to compare the sensitivities of these techniques.
Abstract: 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.
97 citations
TL;DR: In this paper, high-resolution gas adsorption techniques were used to analyse the evolution of the aspect ratio and adaption energy distribution on synthetic saponite samples with increasing layer charge.
Abstract: High-resolution gas adsorption techniques were used to analyse the evolution of the aspect ratio and adsorption energy distribution on synthetic saponite samples with increasing layer charge. Using Ar as a gaseous probe, the aspect ratio of the saponite particles can be determined easily by decomposing the derivative adsorption isotherms and taking into account high-energy sites which can be assigned to talc-like ditrigonal cavities. Changes in the shape of the elementary particles are observed for layer charges above 1.30, i.e. when all the ditrigonal cavities contain at least one Al atom substituting for Si. When N 2 is used as a probe, high-energy sites that could be wrongly interpreted as micropores on the basis of classical t-plot treatments are observed whatever the layer charge. Using the information obtained from both Ar and N 2 , schemes for describing adsorption can be proposed for all layer charges and suggest complex adsorption mechanisms for charged clay minerals.
69 citations
TL;DR: The amorphous aluminosilicate allophane was synthesized by rapid mixing of inorganic solutions with high initial concentrations (10−100 mmol/l) followed by hydrothermal treatment.
Abstract: The amorphous aluminosilicate allophane was synthesized by rapid mixing of inorganic solutions with high initial concentrations (10–100 mmol/l) followed by hydrothermal treatment. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed homogeneous products having a hollow spherical amorphous structure with a particle diameter of 3–5 nm. The amorphous products had a high BET specific surface area (490–552 m 2 /g) in comparison with natural allophane and had a narrow pore-size distribution (2–5 nm in diameter). The results of water vapour adsorption isotherm studies showed a gradual increase over the range of relative water vapour pressure of 0.6–0.9 and reached a maximum of ~85 wt.%. The synthetic allophane shows promise as an adsorbent material because of its high adsorption-desorption capacity and its unique structure.
TL;DR: In this paper, the detailed structure and diagenetic clay transformation was investigated using X-ray diffraction (XRD) including simulation with a multicomponent program, and the structural formulae were determined from chemical analysis, infrared (IR) and 27 Al NMR spectroscopy and XRD, and particle shape by atomic force microscopy (AFM).
Abstract: Illite-smectite (I-S) mixed-layer minerals from North Sea oil fields and a Danish outcrop were investigated to determine the detailed structure and the diagenetic clay transformation. Clay layers in the chalk and residues obtained by dissolution of the chalk matrix at pH 5 were investigated. The phase compositions and layer sequences were determined by X-ray diffraction (XRD) including simulation with a multicomponent program. The structural formulae were determined from chemical analysis, infrared (IR) and 27 Al NMR spectroscopies and XRD, and the particle shape by atomic force microscopy (AFM). A high-smectitic (HS) I-S phase and a low-smectitic (LS) illite-smectite-chlorite (I-S-Ch) phase, both dioctahedral, together constitute 80-90% of each sample. However, two samples contain significant amounts of tosudite and of Ch-Serpentine (Sr), respectively. Most of the clay layers have probably formed by dissolution of the chalk, but one Campanian and one Santonian clay layer in well Baron 2 may have a sedimentary origin. The HS and LS minerals are probably of detrital origin. Early diagenesis has taken place through a fixation of Mg in brucite interlayers in the LS phase, this solid-state process forming di-trioctahedral chlorite layers. During later diagenesis involving dissolution of the HS phase, neoformation of a tosudite or of a random mixed-layer trioctahedral chlorite-berthierine took place. In the tosudite, brucite-like sheets are regularly interstratified with smectite interlayers between dioctahedral 2:1 layers, resulting in di-trioctahedral chlorite layers.
TL;DR: In this paper, the Hofmann and Klemen effect was used to reduce the octahedral charge of a smectite from Olberg (Germany) using X-ray diffraction, infrared spectroscopy and analytical electron microscopy.
Abstract: An Fe-rich smectite from Olberg (Germany) was characterized using X-ray diffraction, infrared spectroscopy and analytical electron microscopy. Progressive reduction of the octahedral charge was performed through the Hofmann & Klemen effect at increasing temperatures. The sample was heterogeneous, consisting of two smectite populations. One population, which comprises a minor portion of the sample, is an ‘Fe 3+ -montmorillonite’ with little or no tetrahedral charge and Fe 3+ as the major octahedral cation. The other population, a major constituent of the sample, contains less Mg and more Al than the first one and exhibits some tetrahedral charge. This fraction may be considered as an inter-grade between nontronite (dominant tetrahedral charge) and Fe 3+ -montmorillonite (dominant octahedral charge). These two populations may occur as separate particles but also as interstratified layers.
TL;DR: In this article, the authors studied a soil sequence from the Brazilian western Amazon consisting of two Typic Udifluvents on the levee of the Javari River, one Aeric Endoaquent in the backswamp, and two Typeic Hapludults on an adjacent terrace.
Abstract: Some soils from the western Amazon region contain KCl-extractable Al contents 5 to 10 times greater than is typical for highly weathered soils containing predominantly kaolinite and gibbsite. We studied a soil sequence from the Brazilian western Amazon consisting of two Typic Udifluvents on the levee of the Javari River, one Aeric Endoaquent in the backswamp, and two Typic Hapludults on an adjacent terrace. We used wet chemical and X-ray diffraction (XRD) analysis to characterize several size fractions of the 0 to 0.2 m layer of the soils. The exchangeable Al content was very high in the Aquent and Udults (up to 180 mmol c kg -1 ), but the 'total' Fe content was low in all samples (<60 g kg -1 ). Smectite, vermiculite, hydroxy-interlayered smectite and kaolinite dominate the fine silt and clay fractions of all soils. The Fluvents contain illite in all size fractions and chlorite in the coarse clay and fine silt fractions. The Aquent and Udults have no chlorite, and small amounts of illite occur only in the coarse clay and fine silt fractions. Lepidocrocite was identified in the Aquent. Chlorite, which occurs in the sand, fine silt, and coarse clay fractions of the Fluvents, and pyrophyllite, which occurs in the fine silt fractions of all soils and in the coarse clay of the two Ultisols, appears to be inherited from the parent sediments. The hydroxy-interlayered 2:1 phyllosilicates that form as a result of weathering are the cause of the very high exchangeable Al contents.
TL;DR: The MacEwan effect of Halloysite interstratification was first noted in the classic work of MacEwen as discussed by the authors, which was used in the unequivocal identification of halloysite (7 A ).
Abstract: X-ray powder diffraction patterns of halloysite (7 A) are characteristically altered following solvation with ethylene glycol. Some effect was first noted in the classic work of MacEwan but its value in the unequivocal identification of halloysite (7 A ) seems to have been overlooked subsequently. The response to ethylene glycol solvation involves a decrease in the intensity (peak height) of the peak at ∼7.2 A and an increase in the intensity (peak height) of the peak at ∼3.58 A thus narrowing the 7.2 A /3.58 A peak height intensity ratio. For pure samples of halloysite, this ratio is narrowed by an average of ∼50%. This distinctive change is related to the interstratified nature of halloysite (7 A), specifically the presence of ‘residual’ interlayer water, i.e. halloysite (10 A), which can be replaced with ethylene glycol so forming 10.9 A layers, a spacing that is almost exactly one and a half times the thickness of dehydrated (7.2 A) layers which do not imbibe ethylene glycol. Thus the separation between the 001 peaks in the 7.2 A /10.9 A interstratification is increased and the 0027.2 (3.58 A) and 00310.9 (3.63 A) peaks become more or less coincident, compared to the 7.2 A /10 A interstratification, i.e. the partially hydrated state. The widespread use of ethylene glycol solvation in clay mineral studies makes it a particularly useful and simple test to determine the presence of halloysite. Pure halloysites should be readily identifiable and experiments indicate a ‘routine’ sensitivity of ∼20% halloysite in mixtures with kaolinite, although this will depend on factors such as ‘crystallinity’ and could be improved with careful attention to intensity measurements. It is proposed to call this phenomenon the ‘MacEwan effect’ in honour of its discoverer Douglas Maclean Clark MacEwan.
TL;DR: In this paper, the illite and smectitic-smectitic clays were matured with a ferruginous, bicarbonate-rich and sulphate rich water for different periods of time (7, 15, 30, 60 and 90 days) and subjected to discontinuous stirring, to test their use in pelotherapy.
Abstract: Illitic-smectitic clays were matured with a ferruginous, bicarbonate-rich and sulphate-rich water for different periods of time (7, 15, 30, 60 and 90 days), and subjected to discontinuous stirring, to test their use in pelotherapy. A progressive degradation of the clay minerals was observed during the maturation process, with a reduction in the illite and smectite crystallinity, in the percentage of smectites and in the phyllosilicate content. The percentage of <2 μm particles also decreased. These modifications caused changes in the clays' physicochemical properties, which are evident in an increase in their plasticity index and in slower cooling of the peloid, both of which improved the clays' effect in pelotherapy.
TL;DR: The opaline silica of silica residues enjoys a reaction relationship with both kaolinite and aluminium sulphates, including alunite and alunogen, as pH, pH, Eh and available moisture fluctuate across the field surface as discussed by the authors.
Abstract: Opaline silica residue accumulates on the surface and in the near surface of the Te Kopia, Tikitere and Rotokawa geothermal fields, where rhyolitic tuffs are attacked by steam condensate, made acid (pH 2–3) by sulphuric acid produced by oxidation of H2S that accompanies steam discharge. Silica residue is one product of this alteration process that also yields kaolinite, sulphur, sulphide and aluminous sulphates, including alunite and alunogen, as pH, Eh and available moisture fluctuate across the field surface. Coagulation of colloidal polymeric silica or, possibly, direct deposition of monomeric silica can occur from the acid solutions of the digested country rock, depending on pH, concentration, temperature and the presence and concentration of other species. As with silica sinter, the first-formed silica phase consists of disordered opal-A microspheroids, commonly 0.1–5 μm in diameter. These coalesce and become overgrown by further opaline silica to yield a mass resembling gelatinous ‘frog spawn’ that lines cavities and envelops surfaces. This mass is the principle component of botryoidal, transparent to translucent hyalite that comprises much residue. Following deposition, this juvenile residue may crystallize to opal-CT lepispheres, 1–3 μm across and, subsequently, to chalcedonic quartz. Both the opal-A and opal-CT of the New Zealand residues are more disordered than those occurring in typical moderate- to low-temperature sinters. The opaline silica of silica residues enjoys a reaction relationship with both kaolinite and aluminium sulphates, including alunite and alunogen. These phases and the silica precipitate continuously and undergo dissolution at the surface of all three localities. The precise pathway followed depends upon the prevailing surface conditions, including humidity, pH, Eh, and Al and K activities. As Al is flushed from the system, the ultimate stage of alteration that may result is the dissolution of the silica itself in acidified rainwater, fogdrip or further steam condensate.
TL;DR: In this paper, the microstructure of activated montmorillonites was investigated using XRD, 29Si and 27Al MAS NMR to investigate the micro-structure.
Abstract: Bentonite samples from Choushan treated at various acid concentrations were studied using chemical analysis, XRD, 29Si and 27Al MAS NMR to investigate the microstructure of the activated montmorillonites. Two types of structural units were formed during the activation: (1) (SiO)3SiOH, in which up to 15% of Si is bound; (2) Q4(0Al), a major building unit when the acid concentration is >10%. A significant 27Al signal at 55.0 ppm was recorded for both untreated montmorillonite and (to a much greater extent) in acid- reated montmorillonites. This was interpreted as arising from four-fold coordinated Al located in the ‘bulk’ octahedral sheet of montmorillonite. In the course of activation, the removal of one of a pair of octahedral Al ions from montmorillonite removes two hydroxyl groups and leaves the other Al of the pair in four-fold coordination.
TL;DR: In this article, the authors found that in British Lower Palaeozoic slate belts formed during Caledonian terrane amalgamation, a greater diversity of species in clay mineral assemblages was found in the convergent basins.
Abstract: Regional differences in clay mineralogy are found in British Lower Palaeozoic slate belts formed during Caledonian terrane amalgamation. Extensional basins in Wales, the northern Lake District and the Isle of Man are characterized by a greater diversity of species in clay mineral assemblages. Slates that evolved in these basins contain both the K- and Na-rich products of the 2:1 dioctahedral reaction series. Pyrophyllite, rectorite and corrensite are sporadically distributed but kaolinite is rarely recorded even in lowest-grade mudstones. In contrast, clay assemblages that evolved in the convergent basins of the Scottish Southern Uplands and northern England generally contain fewer mineral species, and Na-micas and pyrophyllite are rare or absent. Na-bearing clays may have been generated from low-temperature mixing of hydrothermal fluids and seawater in the extensional basins. Such fluids appear to have been unavailable in the convergent basins through lack of volcanic activity in the early stages of basin development.
TL;DR: In this paper, the authors 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.
Abstract: Vivianite [Fe 3 (PO 4 ) 2 ·8H 2 O] 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 CO 2 -free O 2 . Experiments were finished when oxidation rate and P removal by the AER became slow, which was at 53 days (air system) or 28 days (CO 2 free O 2 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}.
TL;DR: Chlorites from Cambrian basaltic vesicular lavas, characterized by relatively high Xc (081 098), gave temperatures of formation of 285 to 3508C (Cathelineau's empirical geothermometer) Both the Xc and temperature calculations gave results which were too high for the diagenetic conditions indicated by the interbedded shale mineralogy as discussed by the authors.
Abstract: Chlorites from Cambrian basaltic vesicular lavas, characterized by relatively high Xc (081 098), gave temperatures of formation of 285 to 3508C (Cathelineau's empirical geothermometer) Both the Xc and temperature calculations gave results which were too high for the diagenetic conditions indicated by the interbedded shale mineralogy The HRTEM and XRD studies indicate the absence of smectite layers in these chlorites; ie according to lattice images, the actual value of Xc is 1 The chlorite composition in these basaltic lavas must, therefore, be explained in relation to their whole-rock geochemistry, with which a good correlation has been found The basaltic lavas are characterized by relatively high FeO/MgO ratios (328±166) and must be considered as an Fe-rich system, with similar chemical behaviour to pelitic rocks In these cases, direct chlorite formation, without a previous smectite precursor, is a normal occurrence and the Xc calculation and empirical geothermometric calculations are inadequate
TL;DR: In this paper, the ideal b dimensions of tetrahedral and octahedral sheets were calculated for the samples used in this work and for others from the literature, using the tetrasmectites of various tetrahedrahedral compositions (SAz-1, Chambers, Belle Fourche, two subsamples of nontronite 33B and SWy-1) submitted to 70 wetting and drying cycles.
Abstract: Six smectites of different tetrahedral and octahedral compositions (SAz-1, Chambers, Belle Fourche, two subsamples of nontronite 33B and SWy-1) were Cs-exchanged and submitted to 70 wetting-and-drying cycles. X-ray diffraction (XRD) of oriented and glycolated mounts of the resultant material showed non-expandable layer proportions ranging from 15 to 60%. They were also analysed by powder XRD at 200°C in vacuum. These patterns showed that 15–40% of the layers were not rotated relative to each other and the rest were randomly rotated (no rotations of the 60° and 120° types). All layers had a d -spacing of 11 A, corresponding to collapsed layers with Cs in the cavities created by the hexagonal rings of the tetrahedral sheets. Analysis of the number of cavities available in relation to the layer rotation shows that the rotation angle must be close to 30° or its multiples 90, 150, 210, 270 and 330°. X-ray diffraction and thermal analysis detected the same proportion of cis - and trans -vacant sites in the smectites. The ideal b dimensions of the tetrahedral and octahedral sheets (the sheets are considered independently, without deformation) were calculated for the samples used in this work and for others from the literature, using the tetrahedral and octahedral compositions. These ideal b dimensions have a strong positive correlation. The cis/trans -vacant character of the smectites is related to the relative lateral dimensions of the ideal tetrahedral and octahedral sheets. A possible explanation of this fact is offered, in which the different configurations of hydroxyls and oxide ions in cis - and trans -vacant structures can affect octahedral-sheet dimension.
TL;DR: In this paper, the structural and magnetic properties of Al-substituted small-particle soil-related oxides are investigated using Mossbauer spectroscopy, showing that up to ∼10 at.% Al can be incorporated in the structure of lepidocrocites.
Abstract: This paper presents various aspects, revealed by Mossbauer spectroscopy, of structural and magnetic properties of Al-substituted small-particle soil-related oxides. For goethite we focus on the relations between the hyperfine fields on the one hand, and crystallinity and Al content on the other. It is argued that these relations only provide a rough estimate of the Al content in natural samples. The ferrimagnetic-like behaviour reflected in the external-field Mossbauer spectra (4.2 K, 60 kOe) of certain Al goethites is presented. The spectra obtained for lepidocrocites are not spectacular, but confirmed that up to ∼10 at.% Al can be incorporated in the structure. Three differently-made series of hematites are considered. The Morin transition and spin structures in hematite are very sensitive to crystallinity and Al content, and probably to the presence of structural OH–. Integral low-energy electron Mossbauer spectroscopy on non-substituted samples indicates that the Morin-transition temperature in the surface layers (2 to 5 nm) is not significantly shifted from the bulk value. Measurements in extremely high magnetic fields (140 kOe) have shown that a spin-flip transition is induced in highly-substituted samples which exhibit no Morin transition in zero field. The use of external fields is crucial for the characterization and precise determination of the hyperfine parameters and site occupancies for maghemites, and for phase analyses of magnetic soils.
TL;DR: In this paper, the adsorption of D- and L-alanine, and their respective dimers, by three allophanes with different Al/Si ratios was investigated.
Abstract: 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 D-enantiomer. The size, intra-molecular charge separation, and surface orientation, of L-alanyl-L-alanine 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.
TL;DR: In this paper, a natural phengite-2 M 1 of composition (K 0.95 Na 0.05 )(Al 0.76 Fe 0.14 Mg 0.10 ) 2 (Si 3.25 Al 0.75 )O 10 (OH 1.96 F 0.04 ) [a = 5.2173 A, b = 9.0493 A, c = 19.989 A and β = 95.734(4)°] was studied using in situ high-temperature FTIR.
Abstract: A natural phengite-2 M 1 of composition (K 0.95 Na 0.05 )(Al 0.76 Fe 0.14 Mg 0.10 ) 2 (Si 3.25 Al 0.75 )O 10 (OH 1.96 F 0.04 ) [ a = 5.2173(1) A, b = 9.0493(2) A, c = 19.989 (1) A and β = 95.734(4)°] was studied using in situ high-temperature FTIR. Correlations to structural changes were made using previously-reported neutron diffraction data from the same sample. Correlations have been made between the microscopic atomic displacements (arising from thermal effects) and analogous macroscopic properties, such as bond strain and ditrigonal distortions. Spectra were collected in the far-infrared region to study the behaviour of the interlayer (K + ) cation and also in the mid-infrared region to distinguish the Si–O stretching modes. We found anisotropic thermal expansion of the interlayer site. The K–O bond length is divided into K–O outer and K–O inner , and the K–O inner bond length is correlated with the far-infrared spectra. The thermal dependence of the correlation between K–O bond length and corresponding far-infrared stretching frequency is different from the effect of the chemical composition. We also found that the K–O bond strain could be successfully resolved into the sum of inner strain and lattice strain. The Si–O stretching mode, obtained from the mid-infrared measurements, showed only weak changes. However, the neutron refinement data showed different thermal behaviour for distinct crystallographic T -sites.
TL;DR: In this article, 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.
Abstract: 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.
TL;DR: In this article, the authors focus on the newly formed, metastable, hydrothermal phases that eventually transform into clays or Fe oxides in the sedimentary column of the Atlantis II Deep.
Abstract: Amorphous silicate sediments comprise most of the upper part of the sedimentary column of the Atlantis II Deep, whereas more crystalline phases are found in the lower part. The objective of this study was to focus on the newly-formed, metastable, hydrothermal phases, that eventually transform into clays or Fe oxides. Short-range ordered Si-Fe phases (Si/Fe = 0.2–0.6) rounded to elliptical in shape, and amorphous Si-Fe platy phases (Si/Fe = 0.09–pure Si) comprise some of the amorphous sediments in Atlantis II Deep. The rounded particles have distinct electron-dense (thicker, relatively ordered) margins and a less crystalline inner core. They have rhombohedral symmetry with unit-cell parameters of a = 0.504 nm and c = 1.08 nm. They presumably transform into crystalline clay minerals in statu nascendi (at the formative stage) in the sediments. Synthesis in NaCl brines designed to simulate crystallization of the rounded particles, was performed successfully. Similar rounded phases (Si/Fe = 0.26) were synthesized under saline, neutral, hydrothermal conditions (40°C, pH 7, 2 m NaCl) with initial Si/Fe = 1.5. We suggest that the metastable rounded particles precipitate from the hot brine created by the encounter between Red Sea Deep Water and the hydrothermal brine underneath. Within a few thousands years they disintegrate and transform into clay minerals, probably nontronite.
TL;DR: In this article, a new method is proposed for modeling complex X-ray diffraction patterns effectively, based on the calculation of the interference function of the onedimensional disordered crystals with finite thickness.
Abstract: A new method is proposed for modelling complex X-ray diffraction patterns effectively. The method is based on the calculation of the interference function of the onedimensional disordered crystals with finite thickness. First, we calculated the diffraction effects from structures of individual mineral phases with different layer defects modelled according to the Reynolds’ algorithm. To fit the theoretical to the observed XRD patterns more accurately, we then used a specially developed optimization procedure. This iterative procedure selects the optimal set of chemical and structural parameters (probability and domain size) and yields consistent solutions. The composition of the clay component in bottom sediments of Lake Baikal relates strongly to glacial/interglacial climate cyclicity. Besides changes in the relative abundance of illite and illite/ smectites between glacial and interglacial periods, significant differences are observed in the crystal chemistries and structures of layered minerals. A change from chlorite during glacial periods to chlorite-smectite during interglacials is probably indicative of the weathering processes in the watershed. Changes in the degree of ordering, in domain size and grain-size distribution of illitesmectites imply differences in genesis of this mineral phase in different palaeoenvironments. These findings further strengthen the case for using clay minerals in the sedimentary record of Lake Baikal as palaeoclimate indicators. One of our findings was that none of the fractions separated by Stokes’ settling is representative of the bulk sample for either the glacial or interglacial intervals. For the interglacial sample, illitesmectite was concentrated in the <2 μm fraction whereas, for the glacial sample, most of illitesmectite is contained in the <1 μm fraction. The selective use of one fraction is yet another potential source of uncontrolled errors that has to be avoided. We suggest using X-ray patterns of bulk samples as a preferred method of analysis of Lake Baikal (and other) sediments.
TL;DR: In this article, the impact-generated material derived from target rocks produced the ejecta layer deposits around Chicxulub crater, which were subsequently diagenetically altered to mainly smectite in marine sections and to kaolinite in continental sections.
Abstract: The proposed impact event at the end of the Cretaceous resulted in mass extinctions and subsequently significant variations in the geochemical and mineralogical composition of the sediments marking the K/T boundary. The impact-generated material derived from target rocks produced the ejecta layer deposits around Chicxulub crater, which were subsequently diagenetically altered to mainly smectite in marine sections and to kaolinite in continental sections. The fireball layer represents the cosmic dust dispersed and deposited globally and contains smectite derived from the alteration of microkrystites and the finest fraction. The lowermost Danian clay layer, recognized in marine sections, resulted from the sudden decrease in ocean productivity and represents a reduced sedimentation deposit. Its clay mineral associations depend on local environmental conditions and diagenetic processes. Overall, the diagenetic alteration of the boundary materials resulted in a significant modification of original signatures. The composition of the clay mineral phases can, however, still be evidence of the nature of the precursor materials providing evidence for an extraterrestrial impact event.
TL;DR: 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 hours as discussed by the authors.
Abstract: 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 d 001 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 A, respectively.