Showing papers in "Clay Minerals in 1990"
TL;DR: In this article, a unified projection system of chemical composition has been proposed for chlorites, in which for the first time all trioctahedral, di-trioctahedrahedral and dioctalithmous species are included and the chemical composition of chlorites is controlled by the general crystallo-chemical formula.
Abstract: The classification and nomenclature of chlorites have been critically reviewed. A new classification based on the unified projection system of chemical composition has been proposed in which for the first time all trioctahedral, di-trioctahedral and dioctahedral species are included. The chemical composition of chlorites is controlled by the general crystallo-chemical formula: This is superior to the known formulae for the trioctahedral and dioctahedral chlorites. It has been shown that the chlorite end-member compositions of Bayliss (1975) project in one point of the projection field leaving many end-member compositions unnamed. As they correspond to the names used previously, a proposal is made to restore these names.
174 citations
TL;DR: In this article, an empirical method to estimate rapidly both mean total layer charge and location of charge in smectites and vermiculites is presented, involving exchange with a long-chain alkylammonium ion before and after the Greene-Kelly test.
Abstract: An empirical method to estimate rapidly both mean total layer charge and location of charge in smectites and vermiculites is presented, involving exchange with a long-chain alkylammonium ion before and after the Greene-Kelly test. The method utilizes an empirically determined relationship between XRD basal spacings and the mean layer charges calculated from the conventional n-alkylammonium ion-exchange technique using simple linear regression models to describe the relationships for both monolayer-bilayer and bilayer-pseudotrimolecular layer transitions. The method provides a rapid estimation of these charge parameters and facilitates the proper identification of both smectites and vermiculites consistent with the AIPEA criteria for classification based on total layer charge. It is considered superior to conventional methods of differentiation based mainly on expansion and collapse behaviour.
100 citations
TL;DR: In this article, Fe-kaolinites were synthesized at 200°C from glasses (Si/(Al + Fe) = 1) with varying Fe content, and the effect of Fe3+ content is evident on growth kinetics and particle size of kaolinites, both decreasing with % Fe2O3.
Abstract: In order to study Al-Fe substitution, Fe-kaolinites were synthesized at 200°C from glasses (Si/(Al + Fe) = 1) with varying Fe content. XRD and IR spectroscopy showed that kaolinites with increasing Fe contents could be synthesized, and Mossbauer spectroscopy indicated that the iron is strictly ferric. Chemical analyses (STEM) of kaolinite particles determined up to almost 7% Fe2O3, which probably does not represent a structural limit. The effect of Fe3+ content is evident on growth kinetics and particle size of kaolinites, both decreasing with % Fe2O3. However, it is not possible to establish a general correlation between Fe content and percentage of structural defects. Acccording to IR spectroscopy, some synthesized Fe-rich kaolinites can have relatively good crystallinity.
87 citations
TL;DR: In this article, an expert system was proposed to accurately describe the defect structure of kaolinites based on a few measurements taken from a normal powder diffraction profile, which was verified for nine kaolinite samples for which the defect structures was previously determined by comparison of calculated and observed diffraction profiles.
Abstract: Until recently, the determination of the defect structures (previously referred to incorrectly as “crystallinity”) of kaolinites has been obtained in one of two ways: (1) measurement of the Hinckley index, or (2) by comparing calculated X-ray diffraction patterns based on a model of the defect structure (including types of defects and abundances) with experimental diffraction profiles. The Hinckley method is simple and easy to perform but contains no real information about the defect structure. Calculated XRD patterns are based on real defects but these calculations are time consuming and require some skill in application. Another approach is proposed: an expert system which will accurately describe the defect structure of kaolinites based on a few measurements taken from a normal powder diffraction profile. This system has been verified for nine kaolinite samples for which the defect structure was previously determined by comparison of calculated and observed diffraction profiles. The expert system reproduced the correct defect structure for each of the samples.
85 citations
TL;DR: In this article, the authors investigated the influence of carbonate on the formation of goethite and lepidocrocite, synthesizing 200 samples by oxidizing FeC12 solutions with air/CO2 gas mixtures at ambient temperature and pH 6 and 7.
Abstract: To investigate the influence of carbonate on the formation of goethite and lepidocrocite, ~200 samples were synthesized by oxidizing FeC12 solutions with air/CO2 gas mixtures at ambient temperature and pH 6 and 7. The proportion of lepidocrocite in the lepidocrocite/goethite mixtures (Lp/(Lp+ GO) decreased from 100 to 0% with increasing (HCO~) in solution and with decreasing average oxidation rate (AOR). These two parameters explained 81% of the variation of Lp/(Lp + Gt). At a given (HCO~), more goethite was formed at pH 6 than at pH 7. The Lp + Gt mixtures contained 0-8 mg g-i carbon (CO which could not be removed by washing. Ct reached apparent saturation at a (HCO~) equilibrium concentration of ~ 6-8 and 60-80 mmol 1 -~ at pH 6 and pH 7, respectively. In a plot of Ct vs. Lp/(Lp + GO all data fell on the same line irrespective of oxidation parameters (pH, AOR). IR spectra showed two broad bands at ~ 1300 and 1500 cm -I which can be assigned to distorted carbonate adsorbed at the goethite surface. Identical bands were also found in a young, poorly crystalline goethite formed from coal mine drainage in Ohio. It is suggested that carbonate anions direct the polymerization of the double bands of FeO 3 (OH) 3 octahedra common to both minerals toward a comer sharing arrangement, and thereby to goethite, whereas chloride permits edge-sharing as in lepidocrocite.
84 citations
TL;DR: In this article, a peaty podzol, regularly interstratified mica-vermiculite clearly develops at the expense of mica and is the dominant mineral in the horizon.
Abstract: A B S T R A C T: Vermiculitization of mica is one of the main weathering processes in soils from three upland catchments receiving various levels of acid deposition. Usually this process is manifested by the presence of interstratified mica-vermiculite with the interlayer space in the vermiculite often partially filled with polymeric hydroxyaluminium species. In one peaty podzol, regularly interstratified mica-vermiculite clearly develops at the expense of mica and is the dominant mineral in the Eh horizon. It was concentrated by chemical treatments to remove organic matter, free iron oxides, and any AI species in the interlayer, and the structural formula calculated from chemical analysis confirmed the dioctahedral character of both vermiculite and mica components, and indicated that the vermiculitic weathering product was formed from a dioctahedral mica. The degree of interlayering in the interstratified phases seemed to he pH-dependent with resultant implications for soil and freshwater acidification.
76 citations
TL;DR: In this paper, the authors used low-angle X-ray scattering experiments to quantify the microstructure of Mg-smectites and found that the contribution of interlayer space to the total water content is small.
Abstract: Powdered 2:1 Mg-clay samples were rehydrated up to the maximum hydration. Both scanning and transmission electron microscopy were used to characterize their structural organization i.e. particle arrangement, texture and crystal structure. Low-angle X-ray scattering experiments were carried out to quantify the microstructure of the system. The results showed that sample water contents reached at saturation are not directly related to changes in layer distance. The hydration mechanism is rather correlated to particle size and particle aggregate size. It is also shown that the a, b plane extension of the layers influences particle size and shape. Finally, it appears that for a better understanding of clay swelling mechanisms, at high water contents, it is necessary to take into account all organization levels and that the contribution of interlayer space to the total water content, for Mg-smectites, is small.
66 citations
TL;DR: The verdine facies, previously confused with components of ancient ironstones, have been studied in relation to its distribution, mineralogy, genesis, environment, and geological significance.
Abstract: The verdine facies, previously confused with components of ancient ironstones, has been studied in relation to its distribution, mineralogy, genesis, environment, and geological significance. Several chemically specific components are present including (i) a ferric and magnesian dioctahedral-trioctahedral 1 : 1 clay mineral, (ii) a chemically equivalent chlorite, (iii) a component intermediate between smectite and swelling chlorite, and (iv) a problematic low-temperature pyrophyllite-like clay mineral. The genetic mechanism is a series of crystallogenetic reactions using cations from the previous phase; this model, where a mineral phase is shown to be a temporary state of arrangement of cations, suggests that authigenic “marine” minerals may reflect diagenetic geochemical factors different from those in the original sea.
62 citations
TL;DR: In this paper, a number of thermodynamic properties were obtained from the determination of adsorption isotherms and enthatpies of immersion for systems with water and Na- and Ca-bentonites.
Abstract: A B S T R A C T: A number of thermodynamic properties were obtained from the determination of adsorption isotherms and enthatpies of immersion for systems with water and Na- and Ca-bentonites. Entropy differences were calculated by combining the enthalpies of immersion and the changes in free energy derived from the adsorption isotherms. The swelling pressures, also calculated from the water adsorption isotherms, are in satisfactory agreement with the experimental data. In the second part of this study of the water-bentonite system for well characterized natural Na- and Ca-bentonites, the changes in the adsorption entropy, the enthalpy of immersion and the swelling pressure are examined as the amount of water increases (for the first part of the study see Kraehenbuehl et al., 1987). The transport of water in unsaturated clays and in soils depends on various potentials and on transport coefficients (diffusion coefficients, permeabilities, etc.). The potentials are thermodynamic quantities which can be derived from measurements performed at equilibrium, and they are usually defined in terms of partial specific potentials, for example g,w = ( 6Gw/bmw)T,p and
61 citations
TL;DR: In this article, XRD data showed that the hydrated 1 : 1 layer-silicates in these clays combine with smectite to form interstratified H/Sm clay minerals.
Abstract: A B S TRACT: Six clays from volcanic ash soils at different stages of weathering differ in their relative halloysite content with respect to kaolinite and several surface properties, namely CEC, and exchange selectivity for K +. These three parameters are related to each other in that they all decrease with increasing soil weathering stage. XRD data show that the hydrated 1 : 1 layer-silicates in these clays combine with smectite to form interstratified H/Sm clay minerals. In these mixed-layers, the content and layer charge of smectitic units decrease as the relative halloysite content in the clay decreases. These clays thus depict a weathering sequence that is parallel to the weathering sequence of the soils from which they originate. It is also shown that the smectites in the H/Sm minerals have the distinctive composition and ESR spectrum of Fe-rich 2:1 clay minerals belonging to the beidellite-nontronite series. The information obtained explains why these clays have high CEC and distinct affinities for K + . It is hoped that this study will help to clarify the controversy concerning the CEC and related surface properties attributed to hydrated halloysite.
57 citations
TL;DR: In this article, changes which occur during the natural weathering of biotite in granite gneiss and associated soils are measured by microanalysis and illustrated by SEM, and their formation in different parts of Biotite flakes taken from different locations within the soil profile is described.
Abstract: A B S T R A C T : Changes which occur during the natural weathering of biotite in granite gneiss and associated soils are measured by microanalysis and illustrated by SEM. Biotite weathers through a series of interstratified minerals to vermiculite and/or smectite phases which decompose rapidly to kaolinite. Both vermiculite and smectite phases appear to be dioctahedral, on the basis of chemical compositions derived from microprobe data. Weathering products are first apparent on the edges of laminae, where interstratified minerals are formed at right angles to both the edge face and the cleavage. Weathering soon develops along cleavage planes, initially most strongly near the edges of flakes, but then permeating extensively into the body of flakes and subdivided segments. The orientation of interstratified minerals and kaolinite within cleavages is parallel to the cleavage. Oxidation of Fe in biotite causes internal stresses which are relieved by physical deformation of the crystals. This accelerates chemical decomposition, particularly along cleavage planes. At an advanced stage of weathering when decomposition is active at many cleavages, biotite deteriorates to very finely divided, wafery remnants consisting of thin laminae separated by more open layers of particulate clay. Parts of the thin laminae remain relatively unweathered and have the same chemical composition as the original biotite immediately after oxidation. These relatively unweathered layers within the laminae have X-ray diffraction (XRD) characteristics of trioctahedral illite and they persist when the biotite remnants are broken up into clay (Fordham, 1989b). Other decomposition products are also formed. Some occur in sufficient bulk (at the microanalytical scale) to be identified directly by microprobe, but the chemical composition of others must be estimated by graphical procedures (Fordham, 1989a). These additional decomposition products of biotite are the subject of the present paper. Their formation in different parts of biotite flakes taken from different locations within the soil profile is described, and the weathering sequence as a whole is discussed. Microanalyses were performed on both thin sections and whole specimens, and the products are illustrated by scanning electron microscopy (SEM).
TL;DR: In this paper, the authors measured the micropore distribution and effective size of the channels of natural sepiolite from Turkey by the BET method, and the results showed that molecules larger than benzene could not migrate into the channels.
Abstract: Micropore distribution and effective size of the channels of natural sepiolite from Turkey were measured by the BET method. Before the BET measurement, the samples were treated under a water vapour atmosphere at various pressures to fill progressively the sepiolite micropores with water. The surface areas measured by means of N 2 adsorption decreased with increased vapour pressures of water. The outer surface area was estimated by comparison of the surface area of the vacuum-dried sepiolite with that filled with adsorbed water. The total surface area was ~290 m2/g, and the outer surface area was 170 m2/g, the difference being attributed to the structural micropores of the sepiolite. The ratio of the surface areas possessed by the channels and that of the outer surface suggest that the mean thickness of the sepiolite fibre was ~ 12 nm. The effective size of the channels was estimated from the number of various-sized molecules sorbed by the sepiolite, the results showing that molecules larger than benzene could not migrate into the channels.
TL;DR: In this article, a study has been carried out on the influence of acid concentration, time and temperature of reaction, liquid to solid ratio and chemical composition of the mineral on the extension and selectivity of the octahedral cations extracted during acid leaching of palygorskite.
Abstract: A study has been carried out on the influence of acid concentration, time and temperature of reaction, liquid to solid ratio and chemical composition of the mineral on the extension and selectivity of the octahedral cations extracted during acid leaching of palygorskite. The mechanism of the extraction of Mg2+, Al3+, and Fe3+ is discussed on the basis of kinetic models fitted for a reacting-shell model, taking into account particle shape and the rate controlling step. A model is given from which kinetics parameters and the activation energy of the process are calculated. The different behaviour observed for the two palygorskites could be explained on the basis of their differences in surface areas.
TL;DR: In this paper, the best fit between experimental and theoretical XRD patterns was obtained using the same model for each glauconite studied the best fitting between XRD pattern and the theoretical model.
Abstract: Glauconites are dioctahedral, microdivided, Fe-containing silicates whose idealized structure may be described as a stacking of 2 : 1 layers with the same azimuthal orientation. The diffractometric and crystallochemical data do not coincide with this idealized structural model. For each glauconite studied the best fit between experimental and theoretical XRD patterns was obtained using the same model. It was possible to describe the stacking by an equally probable occurrence of layers rotated by multiples of 60°. The layer types alternate with a definite tendency to segregation. The model is characteristic for all glauconites, irrespective of composition, age and type of host rock. The alternation of layers rotated by 60° in the structure leads to both octahedral and prismatic coordination for the interlayer K+ cation.
TL;DR: The structure of Silica Springs allophane from New Zealand has been studied by high-resolution 27A1 and 29Si NMR spectroscopy, IR and electron microscopy as mentioned in this paper.
Abstract: The structure of Silica Springs allophane from New Zealand has been studied by high-resolution 27A1 and 29Si NMR spectroscopy, IR spectroscopy and electron microscopy. Experimental NMR conditions were chosen to give a quantitative relationship between signal strength and Al content. Aluminium is present in both octahedral (Alvi) and tetrahedral (Aliv) coordination, and the ratio Alvi:Aliv was obtained for three samples with different total Al:Si ratios. In all cases the Aliv:Si ratio was 1 : 3, consistent with the ratio in ideal muscovite. The negative charge arising from Aliv was apparently balanced by positive charge at adjacent Alvi sites. Both NMR and IR spectra indicate that Si exists in a condensed network, probably a sheet, with Si atoms linked (through oxygen) to one, two and, possibly, three other Si atoms, but not four. The spectra are consistent with a mixture of Si-O-Si, Si-O-Al, and Si-OH linkages. A structure based on fragments of single curved 1 : 1 aluminosilicate layers, with the tetrahedral sheet on the outer surfaces, is suggested, the diameter of curvature being 2–3 nm. The tetrahedral sheet is more or less complete and has a Aliv : Si ratio of 1 : 3; the octahedral Alvi sheet is incomplete. Electron micrographs suggest that, at least in some cases, the fragments form more or less complete spherules. This proposal seems to accord with Farmer's concept of “aluminous hydrous feldspathoids”. The minimum pH at which Silica Springs allophane has precipitated corresponds to the initial presence of tetrahedrally coordinated Al species in solution.
TL;DR: In this paper, a combination of parabolic and linear kinetics was proposed to explain the formation of allophane from volcanic glass, which is a more advanced form of weathering.
Abstract: A B S T R A C T: The kinetics of clay formation in buried paleosols developed from late Quaternary rhyolitic tephra layers near Rotorua, New Zealand, can be described in terms of a combination of parabolic and linear kinetics, reflecting the hydration of glass, and the formation of clay minerals, respectively. Such a model is consistent with the formation of clay minerals showing an Arrhenian temperature dependence and suggests, on the basis of calculated activation energies, that the process of formation of Al-rich allophane (imogolite) is diffusion controlled, whereas the rate of formation of Si-rich allophane is controlled by the chemical processes at the site of reaction. The weathering behaviour of glass in the natural environment has been of interest to archaeologists because of their concern with dating obsidian artefacts and, in an attempt to define the kinetics of the process, short-term dissolution experiments undertaken in laboratories by geochemists have been useful. Our study has been concerned with a more advanced form of weathering: the formation of clay minerals from volcanic glass. The starting materials for our investigation were glass shards and derived clay minerals in buried paleosols developed on rhyolitic tephra deposits of known age and time for weathering (Fig. 1). From the proportions of clay minerals and glass, kinetic models have been developed to help explain the occurrence and neoformation of allophane in tephra deposits. Laboratory investigations of the weathering of glass have consistently shown that, at least in the early stages, cations are released into solution, and the glass hydrates according to socalled parabolic kinetics (e.g. White & Claassen, 1980). This can be represented: C = kpt 112
TL;DR: The first reported occurrence of berthierine in non-marine Wealden sediments in England, and suggests a possible genesis as discussed by the authors, was reported by Worssam et al. in 1970.
Abstract: A B S T R A C T: A thin (15-20 cm) Fe-rich intraformational conglomerate in the fresh- to brackishwater Early Cretaceous succession of south-east England contains pisoids and pseudo-ooids of a green clay mineral which has been identified as berthierine. The pisoids (up to 0-5 cm in size) are concentrically laminated, have complex structure, and are frequently nucleated around a sandstone fragment. They show evidence of weathering due to a change in their environment after formation. The ooids have well to moderately well developed concentric lamination, are very often multinucleated and do not always completely cover the nucleus. They suggest formation as a result of mineral precipitation as opposed to agitation and accretion. The climate and environment during the Wealden were suited to the formation of Fe-rich soils and it is likely that the pisoids and ooids were originally composed of iron oxyhydroxide and kaolinite, having formed in soil in the Weald Basin. They were then eroded and deposited in the base of a large scour structure as part of the conglomerate. On burial, and the attainment of low Eh conditions, berthierine formed by diagenetic transformation of the pre-existing minerals. Berthierine is a trioctahedral Fe-rich clay mineral with the general formula X3Y205(OH)4 , where X = Fe, Mg or ALl, and Y = Si or A1. It has a 1 : 1 type structure and a basal spacing of 7 A, and is related to the kaolinite-serpentine subgroup of clay minerals. It is a common mineral in marine oolitic ironstones (see Van Houten & Purucker, 1984 for a review), but reports of berthierine in non-marine sediments are very few. Thurrel etal. (1970) described an example of berthierine (which they named chamosite, but this term is now properly restricted to an Fe-rich chlorite with a basal spacing of 14 A) in the brackish-water sediments of the Early Cretaceous Weald Clay of south-east England. Worssam & Ivimey-Cook (1971) reported "chamosite" ooids from the Wealden sediments of the Wartingham Bore, but these were identified purely on petrographic observations. Nikitina & Zvyagin (1972) described berthierine from a Carboniferous laterite, and Kodama & Foscolos (1981) reported it in a Canadian arctic soil. These reports suggest that berthierine may form in a wide range of environments. This paper describes an occurrence of berthierine in non-marine Wealden sediments in England, and suggests a possible genesis.
TL;DR: In this paper, the dissolution kinetics of Spanish sepiolite from Eskisehir (Turkey) have been investigated at various temperatures and particle sizes using dilute hydrochloric and nitric acids, and the reaction rate constants were calculated and apparent activation energies were dependent on acid concentration.
Abstract: A B S T R A C T: Dissolution kinetics of sepiolite from Eskisehir (Turkey) have been investigated at various temperatures and particle sizes using dilute hydrochloric and nitric acids. Dissolution reaction rate constants were calculated and apparent activation energies were dependent on acid concentration. For both acids, apparent activation energy values reached a minimum of ~11 kcal/mol at an acid concentration of 0.75 u. For the second-order reaction which is independent of the acid concentration, the activation energy was 14.5 kcal/mol for both acids. The reaction rate constants were proportional to the acid concentrations, and inversely proportional to the square-root of the initial particle radii of the sepiolite. The activation of natural clay surfaces by acid treatment has been studied extensively. Dissolution of Mg from sepiolite mined at Eskisehir (Turkey) using dilute acids was first attempted by Abdul-Latif & Weaver (1969) who found that dissolution of palygorskite and sepiolite in excess hydrochloric acid was a first order reaction in terms of concentrations of A1, Fe and Mg. They also noticed that the dissolution reaction rate constant of Mg in sepiolite was 240 times that for Mgin palygorskite. Several studies of the acid activation of Spanish sepiolite have been carried out to
TL;DR: In this paper, the authors provided a historical perspective on detrital clay input and depositional environment, followed by a review of the main modes of clay mineral formation likely to be of importance in the North Sea context.
Abstract: A B S TRACT: Clay mineral abundances in Mesozoic and Tertiary argillaceous strata from 15 exploration wells in the Inner and Outer Moray Firth, Viking Graben and East Shetland Basins of the northern North Sea have been determined in <0.2 ~m fractions of cuttings samples. The clay assemblages of more deeply-buried samples cannot be unambiguously related to sedimentary input because of the diagenetic overprint which may account for much c)f the chlorite and related interstratified minerals. Other sediments, discussed on a regional basis and related to the geological history of the basins, are interpreted in terms of clay mineral provenance and control by climate, tectonic and volcanic activity. The distribution of illite-smectite can often be related to volcanic activity both in the Forties area during tbe M. Jurassic, and on the NE Atlantic continental margin during the U. Cretaceous-Early Tertiary which affected the North Sea more widely and left a prominent record in the Viking Graben and East Shetland Basin. Kaolinite associated with lignitebearing sediments in the Outer Moray Firth Basin was probably derived by alteration of volcanic material in lagoonal or deltaic environments. Some U. Jurassic and L. Cretaceous sediments of the Inner Moray Basin are rich in illite-smectite, the origin of which is not clear. Petroleum exploration in the North Sea has provided access in the offshore basins to sedimentary rocks ranging in age from Carboniferous to Recent. Although the geology and structural development of the North Sea are now well established (Glennie, 1986b) and much has been published on the petrography and diagenesis of the reservoir sandstones, so far, relatively few data exist in the literature concerning the distribution of clay minerals in the argillaceous facies. Hurst (1985b) reported detrital chlorite in Mesozoic strata from wells in the Sleipner area, while Karlsson et al. (1979) discussed data for a Tertiary sequence from well 2/11-1 in the Central North Sea. Hurst (1985a) has given a detailed account of clay distributions in the inshore Jurassic exposures of the Sutherland coast, N, Scotland. Data obtained by the author and coworkers during studies of clay diagenesis (Pearson & Small, 1988; Kendall, 1988; Small, 1983) provide a basis for the discussion of clay distributions in the Moray Firth, Viking Graben and East Shetland Basins (Figs. 1 & 2) through strata ranging in age from Permian to Miocene. Discussion of such data necessarily presents problems since sediment sources, drainage areas and patterns, basin geometries and sizes and the prevailing climate all varied greatly through such a long period. This paper is therefore structured so that a historical perspective is first provided of the main controls on detrital clay input and depositional environment, followed by a review of the main modes of clay mineral formation likely to be of importance in the North Sea context. Features of significance in the stratigraphical distributions are then dealt with and interpreted on a regional basis in terms of provenance, climate and tectonic activity. The three regional groupings of the East Shetland Basin with most of the Viking Graben, the South Viking
TL;DR: In this paper, the preparation of green rusts from sulphate solutions and representative M6ssbauer spectra are described, where the authors focus on the M6sbauer parameters at liquid nitrogen and helium temperatures and show that the linewidth of the site at 77 K is slightly larger than that for iron metal and could be explained by a variation in the number of near Fe 3+ neighbours at different Fe e+ sites, consistent with the assumption that the ferrous iron site is in the hydroxide sheet.
Abstract: The preparation of green rusts from sulphate solutions and representative M6ssbauer spectra are described. As the samples oxidized readily, attention focused on the M6ssbauer parameters at liquid nitrogen and helium temperatures. The spectra recorded at 77 K could be fitted satisfactorily with one ferrous iron quadrupole doublet with a separation of 2.93 mms 1 and one ferric iron quadrupole doublet with a separation of 0.45 rams -1. In some spectra a ferric iron magnetic hyperfine of strength 49.2 T was also apparent. At 4.2 K, the ferrous iron exhibited a hyperfine splitting with a field of 12.4 T whilst the ferric iron exhibited a hyperfine splitting with a field of strength 50-4 T. The ratio of ferrous to ferric ions was 2.25 + 0.25 at 77 K and at 4.2 K, and -1.6 with a large variation at room temperature. The liquid helium spectra did not always give a good chi-squared fit, the main reason being attributed to relaxation. The line-width of the ferrous iron site at 77 K is slightly larger than that for iron metal and could be explained by a variation in the number of near Fe 3+ neighbours at different Fe e+ sites, consistent with the assumption that the ferrous iron site is in the hydroxide sheet. The effect of different numbers of Fe 2+ and Fe 3+ neighbours probably contributed to the increase in line-widths at 4.2 K compared with those at 77 K. The ferrous iron doublet is marginally different to those of chloride and hydroxy- carbonate green rusts and the aluminium analogues. Green rusts are unstable compounds containing a mixture of ferrous and ferric iron and were first described by Keller (1948) who produced a chloride and a sulphate green rust. The ratio of ferrous to ferric iron was found to lie between 0.8 and 4-0. A study by Bernal et al. (1959) of iron oxyhydroxides, which included green rusts, identified two forms of the sulphate species as well as the chloride form. These green rusts were prepared "by the partial oxidation of ferrous iron solutions" but the method was not described in sufficient detail to enable repeat studies to be made. Misawa et al. (1973, 1974) made a study by ultra-violet spectroscopy and chemical analysis of the aerial oxidation of neutral and slightly alkaline ferrous sulphate solutions. An intermediate green complex was observed which was shown to be a precursor of green rust II and on that basis the ferrous to ferric ratio was estimated to be about unity.
TL;DR: In this article, six deferrated clay (<2m) samples from the major B horizons of pedons derived from basaltic pyroclasts (Western Cameroon) were selected, which represent the types of secondary constituents characteristic of different weathering stages in soils derived from such volcanic materials under humid tropical conditions.
Abstract: A B S T R A C T : Six deferrated clay (<2 ~m) samples from the major B horizons of pedons derived from basaltic pyroclasts (Western Cameroon) were selected. These soil clays, which differ mainly in their contents of halloysite and kaolinite, represent the types of secondary constituents characteristic of different weathering stages in soils derived from such volcanic materials under humid tropical conditions. On these clays, Ca2+-K + exchange equilibria were performed at pH 6 and 0.01 N chloride concentration. The amounts of K + specific sites were estimated through a two-site modelling of the exchange isotherm curves. The total and external surface areas of the clays were measured by EGME retention and by the BET treatment of the N 2 adsorption isotherm, respectively. Relative halloysite content was found to be directly related to all measured surface charge properties, i.e. CEC, amount of K + specific sites, and total and internal surface areas. It was also observed that thermal collapse of halloysitic layers reduced both the CEC and the amount of K + specific sites. All the surface properties observed point to the presence of smectite units intimately associated with halloysite in these clays. The results further suggest that the layer charge of these smectite units differs in different samples.
TL;DR: In this paper, the most important weathering processes are the total breakdown of trioctahedral chlorite and biotite, and the transformation of dioctal mica (muscovite-phengite) to a regularly interstratified mineral, and further to Al-vermiculite or smectite.
Abstract: A B S TR ACT: Weathering processes have been studied in a podzol profile developed on sand during a postglacial period of 9400 years. Due to disintegration of rock fragments, the particle-size distribution has changed markedly in the upper part of the profile, and minerals have been transferred from sand fractions to silt and clay fractions. The most important weathering processes are the total breakdown of trioctahedral chlorite and biotite, and the transformation of dioctahedral mica (muscovite-phengite) to a regularly interstratified mineral, and further to Al-vermiculite or smectite. By using quartz as an internal standard, the annual loss due to weathering was found to be 3.2 g/m 2. The release of elements due to silicate weathering was calculated from depletion curves, and the average annual release of Na + K + Mg + Ca for the postglacial period was 19 mEq/m 2. This study is part of the Norwegian Surface Water Acidification Programme (SWAP) and is a continuation of the weathering studies by Nybakken (1984). The purpose is to determine the most important weathering processes and weathering rates during postglacial time. These rates are required when studying the possible effects of acid precipitation on soils and run-off water, as well as in studies of elemental cycling, and retention and loss of nutrients in forest ecosystems. Important cations such as Mg, Ca, K and Na are derived mainly from two sources, precipitation and weathering. STUDY AREA The study area, the field station Nordmoen, is located within the Romerike groundwater reservoir which has an area >100 km 2 (Ostmo, 1976), -40 km NE of Oslo, Norway. The study was performed on several profiles from a flat glaciofluvial sand deposit. The surface has a slope <0-5% showing no signs of postglacial erosion, the sediments are -60 m deep, and the groundwater table fluctuates between 1 and 3 m below the level surface. Due to rapid isostatic uplift, precipitation could have infiltrated the soil and initiated weathering shortly after the ice retreated 9400 BP (S~rensen, 1983). During the postglacial period there have been changes in climate, and the present mean annual precipitation and annual standard air temperature are 850 mm and 4.3~ respectively. Today the dominant overstory vegetation is pure Norway spruce with a few scattered pines, and the understory vegetation is dominated by Vaccinium myrtillus. Iron or iron-humus podzols (Typic Udipsamment, USDA) have developed in the glaciofluvial sand, and the soil profiles show no sign of previous cultivation.
TL;DR: In this article, the thermal behavior of sepiolite and palygorskite treated with butylamine was investigated by DTA, TG and EGA-MS under a flow of air and N2.
Abstract: The thermal behaviour of sepiolite and palygorskite treated with butylamine was investigated by DTA, TG and EGA-MS under a flow of air and N2. It was shown that the amine was adsorbed by the clays, penetrating into the pores and replacing zeolitic and bound water. The presence of amine in the pores shifted the dehydroxylation peak to temperatures higher than for the untreated clays. Under Nz the thermal desorption of the amine from sepiolite was observed at 175, 275 and 525~ and from palygorskite at 170 and 270~ In addition to desorption, reactions of pyrolysis and condensation to charcoal were detected by the evolution of NH3, CH~ or H2, respectively. In air, oxidation of the organic matter led to the appearance of exothermic peaks, the temperatures of the most intense peaks being determined by the rate of C oxidation, but the shape of the DTA curves and the temperatures of exothermic shoulders were determined by the rate at which H from the organic molecules combined with O from the air. Sepiolite and palygorskite are closely related clay minerals differing mainly by their unit-cell values, pore dimensions, and the Mg to A1 ratio in the octahedral sheet (Nagy & Bradley, 1955; Brauner & Preisinger, 1956; Bradley, 1940). The thermal analysis of these minerals has been thoroughly investigated (see e.g. reviews by Martin-Vivaldi & Fenoll Hach-Ali, 1970, and Singer, 1989). It has been found that organo-clay complexes frequently give rise to characteristic DTA curves which are diagnostic for the clay (Yariv, 1985). However, most of the thermal analysis work on clay-organic associations has been carried out on montmorillonites, whereas little work has been performed on sepiolite and palygorskite treated with organic substances. Martin-Vivaldi & Fenoll Hach-Ali (1970) published DTA and TG results of ethylene glycol, hexanol and hexylamine adsorbed on sepiolite, and also of ethylene glycol adsorbed on palygorskite, showing characteristic exothermic peaks in air. Yariv & Heller-Kallai (1984) in a study of the adsorption of stearic acid by hormites, showed that the DTA exothermic peaks can indicate the formation of organo-sepiolite and organo- palygorskite complexes. In the present investigation DTA and TG techniques were used to study the thermal behaviour of sepiolite and palygorskite treated with n-butylamine (BA), both in an air atmosphere and nitrogen. In order to obtain a better understanding of the nature of the DTA curves, DTA was simultaneously supplemented by mass spectrometry (MS) of the evolved gases and vapours. When the heating takes place in an inert atmosphere, the organic material undergoes diagenetic alteration consisting of a pyrolytic degradation (cracking) which occurs simultaneously with condensation. Thermodynamically, the thermal alteration of amines
TL;DR: In this article, a unified system of projection of chemical composition, prepared initially for micas and chlorites, has been applied to minerals of the serpentine-kaolinite group, and it has been shown that the chemical composition in the projection field is controlled by the formula, the unit of which is: (R~u § Ry 3+ %)(Si~2 _ x)Alx)O5 (OH)4, where u + y + z = 3, z = y - x.
Abstract: A B S T R A C T : A unified system of projection of chemical composition, prepared initially for micas and chlorites, has been applied to minerals of the serpentine-kaolinite group. It has been shown that the chemical composition in the projection field is controlled by the formula, the unit of which is: (R~u § Ry 3+ %)(Si~2 _ x)Alx)O5 (OH)4, where u + y + z = 3, z = y - x. Using projection fields for different chemical systems it has been shown that among the most important endmembers are kaolinite minerals, true serpentines, berthierine, brindleyite, amesite, cronstedtite, greenalite, nepouite and their analogues having different substitutions in the octahedral sheets.
TL;DR: In this article, the authors used EXAFS spectroscopy to obtain information on the octahedral or interlamellar position of Cu(II) in natural smectites from Burkina Faso (West Africa).
Abstract: ESR has been used to obtain information on the octahedral or interlamellar position of Cu(II) in natural smectites from Burkina Faso (West Africa). On the basis of 060 XRD reflections and chemical data, these smectites were found to be Al-rich and dioctahedral. After both Mehra & Jackson, and De Endredy deferrification treatments, the Cu contents remained high (4500 and 22000 p.p.m., respectively). The Cu(II) ESR spectra of these deferrated smectites were compared to those of two reference smectites for which the structural position of Cu(II) was precisely known. The interlayer Cu(II) signal was obtained on a Cu-saturated Camp Berteau montmorillonite, while the octahedral Cu(II) signal was obtained on a synthetic Cu-rich smectite. For this latter reference sample, EXAFS spectroscopy provided evidence that Cu was in six-fold coordination in the octahedral sheet only, and was not exchangeable. In agreement with the experiments by Clementz, Pinnavaia and Mortland, a shift in the g⊥ ESR signal was observed when the air-dried Cu-saturated Camp Berteau montmorillonite (g⊥ = 2·05) was soaked in water for 48 h (g⊥ = 2·13). A small shift in the opposite sense was observed for the synthetic Cu smectite (g⊥ = 2·05 for the air-dried sample, g⊥ = 2·02 for the water-soaked sample). For the two natural smectites a small shift similar to that for the synthetic Cu-smectite was observed. These results indicate that up to 10% of the Cu atoms substitute for Al-Mg-Fe atoms in the octahedral sheets of the smectites studied.
TL;DR: Ebinger and Schulze as discussed by the authors showed that large amounts of Mn can substitute for Fe in the goethite structure, but the factors that control the substitution could not be specifically determined.
Abstract: Mn-substituted iron oxides were synthesized at pH 4, 6, 8, and 10 from Fe-Mn systems with Mn mole fractions (Mn/(Mn + Fe)) of 0, 0.2.0.4, 0.6, 0.8, and 1.0, and kept at 50~ for 40 days. The Mn mole fraction in goethite was 0.4. In the pure Mn syntheses, manganite (y-MnOOH) formed at pH 4 and pH 6, whereas hausmannite (Mn304) formed at pH 8 and pH 10. As the Mn substitution increased, the unit-cell dimensions of goethite shifted toward those of groutite, and the mean crystallite dimensions of goethite decreased. The substitution of Mn in the crystal structures of iron oxide minerals, particularly goethite, has been the subject of recent research (Karim, 1984; Stiers & Schwertmann, 1985; Cornell & Giovanoli, 1987; Lim-Nufiez & Gilkes, 1987). Karim's study (1984) was conducted at pH 7, and the other studies were conducted at pH > 8. Ebinger & Schulze (1989) showed that Mn-substituted goethite (ol-FeOOH) and Fe-substituted groutite (ol-MnOOH) can also form at acid pH. The experiment described by Ebinger & Schulze (1989) showed that large amounts of Mn can substitute for Fe in the goethite structure, but the factors that control the substitution could not be specifically determined. First, pH was not controlled during the synthesis, and the influence of pH on the formation of Mn-substituted goethite could not be distinguished from the influence of Mn on the formation of the minerals. Second, MnSO4 was the source of the Mn, and 8042- may have altered the rate or the mechanism of formation of the
TL;DR: The magnetic susceptibilities of seven different nontronites in their natural oxidation states were measured between 5 and 100 K as discussed by the authors, and the magnetic exchange interaction in all samples was anti ferromagnetic, except no clear minimum occurred at the N6el temperature.
Abstract: The magnetic susceptibilities of seven different nontronites in their natural oxidation states were measured between 5 and 100 K. Results revealed that the magnetic exchange interaction in all samples was anti ferromagnetic, except no clear minimum occurred at the N6el temperature. Possible explanations for this phenomenon which are discussed include magnetic dilution due to isomorphous substitution, and antiferromagnetic frustration due to either non-centrosymmetric distribution of octahedral Fe 3+ or tetrahedral Fe 3+ substitution. A computer simulation model was developed to demonstrate the effects of these variables on long- range magnetic ordering. Magnetic dilution and tetrahedral Fe 3+ content could explain the anomalous antiferromagnetic behaviour in some, but not all, samples. The non-centrosymmetric model is the only one which explains the behaviour of all samples. In this model, at least 13~ of the octahedral Fe 3+ would occupy trans-dihydroxide sites, with the balance in cis sites. Magnetic frustration occurs because two Fe 3+ neighbours of a third Fe 3+ ion are also neighbours to each other, making the simultaneous satisfaction of all antiferromagnetic exchange interactions impossible. This study characterizes the magnetic susceptibility of Fe-rich smectites, and discusses the use of this information to deduce site distributions of structural Fe. Iron in the crystal structure of smectites imparts many unique chemical and physical attributes to these layer- lattice silicates (Stucki, 1988), including magnetic exchange due to the interactions of unpaired electrons in the valence shells of nearby constituent Fe atoms. Coey (1984, 1988) reviewed the magnetic properties of a number of different types of layer-silicates, and showed that unaltered nontronite displays antiferromagneti c behaviour, probably by superexchange through the common oxide ligand. A recent study by Lear & Stucki (1987) reported that creation of mixed oxidation states of structural Fe changes the average exchange interaction in nontronite from antiferromagnetic to ferromagnetic, probably due to double exchange.