bluuebunny/crossref_metadata_2025 huggingface dataset:
The colloidal stability of variable-charge mineral suspensions
Authors: Bartoli F. , Philippy R.
Published: December 2006

A method of analysing the colloidal stability of variable-charge mineral suspensions as a function of pH is described, which combines light scattering with soluble element and surface charge measurements. The absorbance of the suspensions closely follows the A = k−m equation, where m = −dlgA/dlgλ is an aggregate light-scattering index which is inversely related to the limiting sedimentation speed v = dA600nm/dt. Usually, suspensions of variable-charge minerals scatter less near their point of zero charge where the aggregation process is a maximum, in contrast to environments where they are charged and well-dispersed. Although the morphology of goethite is that of elongated needles, kaolinite plates, and imogolite tubes, the coalesced sphere approach of the Mie theory allows rapid correlation of the absorbance at 600 nm with aggregate-size distribution, indirectly measured by the light- scattering aggregate-size index m confirmed by electron microscopy experiments. Kaolinite and goethite suspensions obey the diffraction scattering law with a variation in size of 2–20 µm from the dispersed to the aggregated particles. Imogolite and alumina gel suspensions possibly obey the anomalous diffraction scattering law and are present as 0·05–1 µm aggregates of their 50–100 Å structural units. Silica gel and the more dispersed imogolite suspensions possibly obey the anomalous Rayleigh scattering law with a variation of aggregate size from 700–3000 Å.
Marine and supergene alteration processes in a chloritized amphibole-schist, Deux-Sevres, France
Authors: Proust D. , Dudoignon P. , Bouchet A. , Meunier A.
Published: December 2006

Mineralogical examination of a strongly chloritized amphibole-schist indicated that it had been subjected to two alteration episodes of different origin. Structural and petrographic evidence showed that the alteration processes operated per descensum from the bedrock surface down to shallow depth, thus eliminating any hydrothermal episode due to fluid ascension through deep fractures. The rock was first altered into interstratified chlorite-vermiculite minerals with potassic interlayers. These potassic clay minerals occur in an originally K-deficient rock and seem to have been generated by a marine alteration episode; this episode appears to be contemporaneous with the Cenomanian transgression which covered the amphibole-schist with sandy-clayey deposits. The potassic clay minerals were replaced during a later meteoric alteration episode by kaolinites, iron oxides, and smectites with Mg, Ca interlayer cations.
Neoformation of halloysite on volcanic glass in a marine environment
Authors: Imbert T. , Desprairies A.
Published: December 2006

Transmission electron microscopy of ultramicrotomed thin-sections of Pleistocene and Eocene glass shards revealed the neoformation of (i) illite and (ii) halloysite at the glass periphery. According to previous experimental studies, halloysite neoformation in marine environments can occur on glass shards deposited in Si-rich sediments; an excess of Ca tends to inhibit the reaction.
Natural and monoionic aliettite: hydration and dehydration states
Authors: Brigatti M. F. , Poppi L.
Published: December 2006

The dehydration of an interstratified talc-trioctahedral smectite mineral (aliettite) from Monte Chiaro, Taro Valley, Italy, saturated by Na, K, Rb, Cs, Mg, Ca, Sr, Ba and NH4 cations, was studied by X-ray powder diffraction and thermal analysis, under different conditions of temperature and relative humidity. Both in the natural and exchanged states the mineral exhibited several orders of basal reflections and, to varying relative humidity (p/po) and temperature (T) conditions, behaved like a smectite except that: (i) the c-dimension was not very sensitive to relative humidity increase; (ii) the closest packing was for T > 400°C, the collapsed state being reached gradually as T increased and an inverse trend was apparent between 20° and 300°C; (iii) the endothermic reactions at T = 400°C and T = 600°C appeared to be affected by the exchange treatment. The experimental data are consistent with a structural model in which it is possible to distinguish layers containing a patchwork of talc and smectite domains: the patchworks are superposed to make a regular alternation of the two domains.
The reductive dissolution of synthetic goethite and hematite in dithionite
Authors: Torrent J. , Schwertmann U. , Barron V.
Published: December 2006

The reductive dissolution by Na-dithionite of 28 synthetic goethites and 26 hematites having widely different crystal morphologies, specific surfaces and aluminium substitution levels has been investigated. For both minerals the initial dissolution rate per unit of surface area decreased with aluminium substitution. At similar aluminium substitution and specific surface, goethites and hematites showed similar dissolution rates. These results suggest that preferential, reductive dissolution of hematite in some natural environments, such as soils or sediments, might be due to the generally lower aluminium substitution of this mineral compared to goethite.
Volatile products of clay mineral pyrolysis revealed by their effect on calcite
Authors: Heller-Kallai L. , Miloslavski I. , Aizenshtat Z.
Published: December 2006

The volatiles produced when various clay minerals were pyrolysed under a stream of He or in vacuo were condensed and analysed. They contain a wide range of cations and anions in concentrations ranging from ppm to hundreds of ppm. The reactivity of these volatiles was demonstrated by their reaction with calcite. It is suggested that the water liberated on heating acts as a scavenger of various impurities present in the clay.
Cation ordering in lepidolite and biotite studied by X-ray photoelectron diffraction
Authors: Ash L. A. , Evans S. , Hiorns A. G.
Published: December 2006

Comprehensive X-ray photoelectron diffraction (XPD) studies have revealed octahedral cation ordering in a 1M lepidolite and in a 1M biotite. In the lepidolite (from Høydaler, Telemark, Norway), all three octahedral sites are differentiated, with Li and Mn concentrated in the trans M(1) site and Al in cis M(3); M(2) contains all three cations. In the biotite, the major cations do not order but Ti, present at only 1·2% concentration, preferentially occupies the two cis sites, information which is available uniquely from XPD. Long-range tetrahedral ordering should be detectable by XPD, but was not found in either mica.
Structural studies of montmorillonites by 57Fe Mössbauer spectroscopy
Authors: Cardile C. M.
Published: December 2006

Five montmorillonites were analysed by 57Fe Mössbauer spectroscopy and their Fe3+ occupation in tetrahedral and octahedral sites assigned. The montmorillonites, with a range of IVFe3+ contents, were used in an attempt to correlate IVFe3+ content with VIFe3+cis- and trans-OH site occupation to verify the assertion that increasing IVFe3+ content directs VIFe3+ to cis-OH sites. However, VIFe3+ in montmorillonite appears to be located essentially in the trans-OH sites. The two doublets computer-fitted to the VIFe3+ Mössbauer resonance for montmorillonite appear to represent a distribution of a continuum of slightly different Fe3+ resonances, which arise from the variable atomic environment surrounding the VIFe3+ sites, rather than discrete cis- and trans-OH sites. Therefore Mössbauer spectroscopy cannot be used to demonstrate whether an increasing IVFe3+ content directs VIFe3+ substitution into particular sites for montmorillonites.
Mineralogy and genesis of the Pugu Hill kaolin deposit, Tanzania
Authors: Schwaighofer B. , Müller H. W.
Published: December 2006

According to field studies of the Pugu Hill kaolin deposit and mineralogical investigations (X-ray, SEM), two main types of Miocene sandstones are distinguished: (i) clayey-silty kaolinitic sandstones with stacks of idiomorphic pseudohexagonal kaolinite crystals; (ii) massive clayey-silty kaolinitic sandstones with irregular fabric of isolated kaolinite plates. The Precambrian metamorphic rocks of the Uluguru Mountains are a probable source for the kaolinitic sediments of the Pugu Hill Formation. Decomposition products of weathering profiles on meta-anorthosites are mainly 7Å- and 10Å-halloysite and gibbsite. It is suggested that the kaolinitic sandstones were deposited in a former delta. The first sandstone type is considered to have developed in situ from weathered arkosic sandstone, and the second represents channel deposits in an old river system (probably a Miocene predecessor of the Ruvu River) with kaolin transported from a hinterland and redeposited. The variable formation and fabric of the kaolinites in the Pugu Hill Formation are due to in situ weathering of transported primary minerals (fedspar), and to transported weathered material (with secondary halloysite).
Catalytic activity of modified silicates: I. Dehydration of ethanol catalysed by acidic sepiolite
Authors: Corma A. , Perez-Pariente J.
Published: December 2006

The kinetics of the dehydration of ethanol on acidic Al3+-exchanged sepiolite has been studied. The product distribution indicates that the formation of diethylether and ethylene takes place by a series of consecutive and parallel reactions. A mechanism for the formation of both products has been derived by studying the influence of different operational variables on the reaction rates.
The kinetics of dehydroxylation of kaolinite
Authors: Redfern S. A. T.
Published: December 2006

The dehydroxylation of kaolinite has been investigated by isothermal thermogravimetry. Kinetic analysis using the Avrami equation shows that a combination of atomic mechanisms operates throughout the temperature range 734 K to 890 K. An empirical activation energy of 222 kJ mol-1 was calculated from the Arrhenius relationship using rate constants based on diffusion and homogeneous models. The activation energy (Ea) was calculated for a series of degrees of dehydroxylation by the time to a given fraction method, showing an increase in Ea during the early stages of the reaction. The isothermal plots indicate that OH is retained in the final stages of the reaction. The observations are explained in terms of a reaction mechanism in which kaolinite grains dehydroxylate from the edges inwards, parallel to (001).
The rapid estimation of the layer charges of 2:1 expanding clays from a single alkylammonium ion expansion
Authors: Olis A. C. , Malla P. B. , Douglas L. A.
Published: December 2006

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 conventionaln-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.
The effect of CO2 and oxidation rate on the formation of goethite versus lepidocrocite from an Fe(II) system at pH 6 and 7
Authors: Carlson L. , Schwertmann U.
Published: December 2006

To investigate the influence of carbonate on the formation of goethite and lepidocrocite, ∼200 samples were synthesized by oxidizing FeCl2 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 + Gt)) decreased from 100 to 0% with increasing in solution and with decreasing average oxidation rate (AOR). These two parameters explained 81% of the variation of Lp/(Lp + Gt)). At a given , more goethite was formed at pH 6 than at pH 7. The Lp + Gt mixtures contained 0–8 mg g−1 carbon (Ct) which could not be removed by washing. Ct reached apparent saturation at a equilibrium concentration of ∼6–8 and 60–80 mmol l−1 at pH 6 and pH 7, respectively. In a plot of Ct vs. Lp/(Lp + Gt) all data fell on the same line irrespective of oxidation parameters (pH, AOR). IR spectra showed two broad bands at ∼1300 and 1500 cm−1 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 FeO3(OH)3 octahedra common to both minerals toward a corner sharing arrangement, and thereby to goethite, whereas chloride permits edge-sharing as in lepidocrocite.
Crystallochemical classifications of phyllosilicates based on the unified system of projection of chemical composition: II. The chlorite group
Authors: Wiewióra A. , Weiss Z.
Published: December 2006

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.
Pore size distribution and adsorption selectivity of sepiolite
Authors: Inagaki S. , Fukushima Y. , Doi H. , Kamigaito O.
Published: December 2006

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 N2 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.
Thermal analysis of sepiolite and palygorskite treated with butylamine
Authors: Shuali U. , Steinberg M. , Yariv S. , Muller-Vonmoos M. , Kahr G. , Rub A.
Published: December 2006

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 N2 the thermal desorption of the amine from sepiolite was observed at 175, 275 and 525°C, and from palygorskite at 170 and 270°C. In addition to desorption, reactions of pyrolysis and condensation to charcoal were detected by the evolution of NH3, CH4 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.
Surface properties and clay mineralogy of hydrated halloysitic soil clays. II: Evidence for the presence of halloysite/smectite (H/Sm) mixed-layer clays
Authors: Delvaux B. , Herbillon A. J. , Vielvoye L. , Mestdagh M. M.
Published: December 2006

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.
Kinetics of the acid leaching of palygorskite: Influence of the octahedral sheet composition
Authors: Corma A. , Mifsud A. , Sanz E.
Published: December 2006

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.
Effects of tetrahedral isomorphic substitution on the IR spectra of synthetic fluorine micas
Authors: Kitajima K. , Takusagawa N.
Published: December 2006

Effects of tetrahedral isomorphic substitution on the IR spectra of fluorine micas were demonstrated by comparing the spectrum of taeniolite KMg2Li(Si4O10)F2 with those of the substituted analogues, in which Ga, Al, B or Ge substituted for Si in tetrahedral sites. The e11 bands move towards lower frequencies as the content of substituted cation in tetrahedral site increases, whereas The a11 and a12 bands moves towards higher frequencies. Linear relationships were found between a12 the band frequency and the extent of tetrahedral substitutions. The magnitude of shifts per molar substitution for the a12 bands is dependent on the species of substituted cation and decreases in the order Ga > Al > Ge > B, showing an intimate correlation with the field strength z1·z2/r2M–O of the substituted cations. This implies that the polarizing power of the substituted cations has a pronounced effect on the Si-O stretching vibrations.
An ESR and calorimetric study of iron oolitic samples from the Northampton ironstone
Authors: Gehring A. U. , Karthein R.
Published: December 2006

Electron spin resonance (ESR) spectroscopy and calorimetric methods were used to characterize conversion processes in multimineral samples from the Northampton ironstone (NIS) at temperatures between 25°C and 800°C. The beginning of the thermal conversion processes can be determined by the formation of asymmetric ESR spectra with g ≈ 2 at 250°C. The breakdown of the berthierine structure between 250°C and 520°C is indicated by the disappearance of the hyperfine splitting in the Mn2+ spectrum and the formation of magnetite. The decomposition of siderite and calcite was found by calorimetric methods at 580°C and 700°C, respectively. The hematite formation between 550°C and 800°C is explained by the decomposition of siderite but also by the oxidation of previously formed magnetite. The occurrence of hematite as the dominant ferric oxide at 800°C signifies the end of the conversion process of the major mineral phases in the NIS samples.
Structural studies of Silica Springs allophane
Authors: Childs C.W. , Parfitt R.L. , Newman R.H.
Published: December 2006

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.
Thermogravimetric analysis of the iso-butene oligomerization activity of various forms of synthetic mica-montmorillonite
Authors: Vogel A. P. , O'Connor C. T. , Kojima M.
Published: December 2006

The iso-butene oligomerization activity of pure and metal-substituted synthetic mica-montmorillonite (SMM) was studied by simultaneous thermogravimetric-differential thermal analysis (TG-DTA). The incorporation of matrix Ni and ion-exchanged Co, Ni and Zn into SMM increased its iso-butene oligomerization activity while the presence of water in the olefinic feed reduced activity. These findings corresponded to trends found in previous work on high pressure (50 MPa) propene oligomerization over SMM and metal-substituted SMM.
Quantification des teneurs en opale biogene des sediments de l'Ocean Austral par diffractometrie X
Authors: Bareille G. , Labracherie M. , Maillet N. , Latouche C.
Published: December 2006

Le dosage de l'opale biogène dans les sédiments marins peut être effectué par diffractométrie X par la mesure des surfaces des bandes de diffusion et par la mesure des surfaces des pics de cristobalite. La surface de la bande de diffusion, observée sur les diagrammes X de sédiments non chauffés, caractérise la concentration en composés amorphes (organiques et inorganiques). Elle permet de quantifier l'opale biogène de sédiments ne contenant que peu ou pas d'amorphes non biogènes. La surface du pic de cristobalite, obtenu par transformation de l'opale biogène par chauffage à 1050–1100°C pendant 12 h, permet de doser la silice biogène de divers sédiments. Ces deux approches méthodologiques ont été appliquées aux sédiments d'une carotte (MD 84–527) prélevée dans le secteur ouest-Indien de l'Océan Austral. Ce matériel, qui a enregistré la sédimentation des 40,000 dernières années, ne renferme qu'accessoirement des constituants amorphes volcaniques. Les concentrations en silice biogène sont obtenues avec une précision de ±10%. Le comptage des diatomées par observation au microscope a été également réalisé sur les mêmes sédiments. Les courbes des teneurs en opale biogène obtenues par les deux méthodes sont comparables et se corrèlent bien à l'abondance totale des diatomées.
X-ray study of the nature of stacking faults in the structure of glauconites
Authors: Sakharov B. A. , Besson G. , Drits V. A. , Kameneva M. Yu. , Salyn A. L. , Smoliar B. B.
Published: December 2006

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.
Nature and origin of an aluminous vermiculitic weathering product in acid soils from upland catchments in Scotland
Authors: Bain D. C. , Mellor A. , Wilson M. J.
Published: December 2006

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 Al 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 be pH-dependent with resultant implications for soil and freshwater acidification.
Clay mineral formation at the continent-ocean boundary: the verdine facies
Authors: Odin G. S.
Published: December 2006

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.
The influence of pH on the synthesis of mixed Fe-Mn oxide minerals
Authors: Ebinger M. H. , Schulze D. G.
Published: December 2006

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°C for 40 days. The Mn mole fraction in goethite was <0·07 at pH 4 but increased to ∼0.47 at pH 6. Goethite and/or hematite formed in Fe and Fe + Mn syntheses at pH 4 and pH 6 at Mn mole fractions ≤0·8, and at Mn mole fractions ≤0·2 at pH 8 and pH 10. Hausmannite and jacobsite formed at pH 8 and pH 10 at Mn mole fractions ≥0·4. In the pure Mn syntheses, manganite (γ-MnOOH) formed at pH 4 and pH 6, whereas hausmannite (Mn3O4) 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 Mössbauer Spectrum of Illite
Authors: Murad E. , Wagner U.
Published: December 2006

Eight illites were studied by Mössbauer spectroscopy at room temperature and 4.2 K. On the basis of their Fe contents, these illites can be divided into an Fe-rich (>5 wt% Fe) and an Fe-poor (<1 to ∼3 wt% Fe) group. Mössbauer spectroscopy showed that the Fe-rich illites had lower proportions of divalent Fe than their Fe-poor counterparts. Slow paramagnetic relaxation was observed in the Fe-poor illites and must be accounted for when fitting the spectra. Two samples contained iron oxides that were superparamagnetic and thus, although contributing to the Fe3+ doublets, escaped detection at room temperature. Structural Fe3+ had a temperature-independent quadrupole splitting that was lower for the Fe-rich illites (0.59 mm/s) than that of the Fe-poor illites (0.73 mm/s). The Fe2+ quadrupole splittings were higher at 4.2 K than at room temperature, but the Fe-rich illites again had lower Fe2+ quadrupole splittings both at room temperature (2.69 vs. 2.88 mm/s) and at 4.2 K (2.96 mm/s vs. 3.08 mm/s). Distinction of Fe sites in the illites with cis- and trans-OH coordination was not possible. The presence of tetrahedral Fe3+ was observed only in the most Fe-rich sample (8.4 wt% Fe).
Acid-Treated Montmorillonites—A Study by 29Si and 27Al MAS NMR
Authors: Tkáč I. , Komadel P. , Müller D.
Published: December 2006

The JP (Jelšový Potok, Slovakia) and SWy-1 (Wyoming, USA) montmorillonites were treated in 6 m HCl at 95°C. The rates of dissolution of tetrahedral and octahedral Al (Altet and Aloct) are comparable. Aluminium in the tetrahedral sheets was also identified in both untreated samples by 29Si MAS NMR spectroscopy. About 12% of total Si in SWy-1 was found to be bound in quartz. Traces of undecomposed montmorillonite and a small amount of Altet in the three-dimensional SiO4 framework were found in the reaction product of montmorillonite decomposition. Three different types of structural units were identified in acid-treated samples: Q4(OAl) units of amorphous silica with three-dimensional crosslinked framework; (SiO)3SiOH units, remaining as a result of poor-ordering of the framework without the possibility of cross-linking; and Q4(1A1) units.
Interstrat—An Expert System to Help Identify Interstratified Clay Minerals from Powder XRD Data: II. Testing the Program
Authors: Garvie L. A. J.
Published: December 2006

INTERSTRAT is designed to help clay mineralogists identify clay minerals from powder X-ray diffraction data and is especially useful as an aid in the interpretation of interstratified clay minerals. This paper illustrates the use of the INTERSTRAT program in the identification of a set of interstratified clay minerals. One of the examples has been matched against the PDF and the answers compared with those obtained by INTERSTRAT. The most useful features of the program are the knowledge bases of diffraction parameters for the interstratified clay minerals, the ability of the program to compare the clays identified in more than one state and the hierarchical clay text file.
Expert System for Structural Characterization of Phyllosilicates: I. Description of the Expert System
Authors: Plançon A. , Drits V. A.
Published: December 2006

An expert system has been designed for the structural characterization of disordered phyllosilicates as well as the mixed-layer minerals and the minerals containing stacking faults or isomorphic substitutions. X-ray diffraction being the simplest tool for structural characterization, the expert system uses such data but can account for data provided by any characterization technique (infrared spectroscopy, EXAFS, etc.). The expert system aims to summarize in a unique set the different approaches of the structural characterization using diagrams or tables which have been proposed, avoiding the requirement of the knowledge of their application field and excluding calculations. It runs in an interactive way, to mimic the way a human expert would draw its conclusions.
Potassium Release from Micas and Characterization of the Alteration Products
Authors: Dreher P. , Niederbudde E.-A.
Published: December 2006

Interlayer K from two biotites of different origin was extracted with octadecylammonium chloride (ODA) and sodium chloride/sodium tetraphenylboron (STB) before and after oxidation with saturated bromine water (Br2). Potassium release, Fe oxidation and Fe ejection from octahedra were measured. With ODA and STB the untreated biotites released between 40 and 90% of initial interlayer K, the muscovite less than 5%. After Br2 treatment, substantially less K was extracted from both biotites. Suppression of K release was caused by the formation of octahedral vacancies formerly occupied by Fe. The extent of Fe ejection was not proportional to the extent of octahedral Fe oxidation. During Br2 treatment, the biotites transformed into hydrobiotite. The hydrobiotite sample, high in Fe ejection during preceding Br2 treatment, strongly resisted subsequent K extraction with STB, whereas the sample with minor Fe ejection transformed to vermiculite. Octadecylammonium chloride extracts K more effectively than STB from biotites intermediate between trioctahedral and dioctahedral structure and is considered to be suitable for the distinction between biotite K and muscovite K.
Thermogravimetric, Infrared and Mass Spectroscopic Analysis of the Desorption of Tetrahydropyran, Tetrahydrofuran and 1,4-Dioxan from Montmorillonite
Authors: Breen C.
Published: December 2006

The desorption of tetrahydropyran (THP), tetrahydrofuran (THF) and 1,4-dioxan (DIOX) from Na+-, Ca2+-, Al3+- and Cr3+-exchanged montmorillonite has been studied using variable temperature infrared spectroscopy and thermogravimetric analysis. The derivative thermograms for the desorption of each cyclic ether exhibited three maxima but there was little uniformity in the temperatures at which these maxima occurred. Nonetheless, the desorption of both THP and THF occurred at lower temperatures in the Cr3+-exchanged form than in the Al3+-form. The desorption of DIOX showed little cationic dependence. Mass spectroscopic analysis of the thermally evolved vapours indicated that no transformation products were desorbed at temperatures ⩽230°C.
Intracrystalline Swelling of Mixed-Layer Illite-Smectite in K-Bentonites
Authors: Müller-Vonmoos M. , Kahr G. , Madsen F.T.
Published: December 2006

To investigate the long-term stability of bentonite under final disposal conditions of highly radioactive waste, K-bentonites from Kinnekulle (Sweden) and from the Marias River Formation in the Montana disturbed belt (USA) were studied. After separating the mixed-layer illite-smectite (I-S) from the K-bentonite samples, the interlayer charge was calculated from the cation exchange capacity (CEC) and the amount of fixed interlayer K+ ions (Kfix). The interlayer charge was also determined by the alkylammonium method. According to both methods the interlayer charge was in the range for smectite. The results show that the amount of exchangeable cations increased linearly with decreasing Kfix. A small increase in the interlayer charge with increasing Kfix was observed as was a linear correlation between the intracrystalline swelling up to the second water layer, the CEC and the content of Kfix. Divalent exchangeable cations were then found to be surrounded by approximately 24 water molecules per cation. Fixed interlayer K+ ions were unhydrated. Forming the third and fourth water layer, swelling was presumably limited by free silica formed by the vitrification of the volcanic ash.
The Influence of Structure on Ba and K Uptake by a Synthetic Phyllomanganate
Authors: Paterson E. , Swaffield R. , Clark L.
Published: December 2006

The uptake of Ba2+ and K+ by a synthetic Na-phyllomanganate has been studied by chemical analysis, X-ray diffractometry and X-ray photoelectron spectroscopy. The changes in basal spacing arising from cation exchange have been used to monitor the progress of the exchange reaction and confirm the selectivity measured by bulk chemical analysis. However, the selective uptake of Ba2+ over Ca2+ is much greater than that of K+ over Na+ and it is suggested that charge distribution in the interlayer is important. The results are discussed in the light of recent advances in our understanding of the phyllomanganate structure.
Mafic Phyllosilicates in Low-Grade Metabasites. Characterization Using Deconvolution Analysis
Authors: Robinson D. , Bevins R. E.
Published: December 2006

The <2 µm clay fractions from low-grade metabasalts of eastern North Greenland are mixtures of mafic phyllosilicates and celadonite that show complex X-ray diffraction (XRD) patterns. Interpretation of such patterns is difficult and subjective using only visual examination of peak positions and shapes. Deconvolution analysis offers a less subjective means of identifying peak positions for overlapping peaks and is applied to several composite peaks in a pattern; the peaks identified are then rationalized in terms of specific mixed-layer phases. Comparison against NEWMOD patterns of the identified clay mixture provides an additional constraint on the phases identified. Three mafic phyllosilicates, discrete chlorite and two chlorite-smectites with 60:40 and 80:20 proportions are demonstrated in the same XRD pattern. Modelling using NEWMOD of a mechanical mixture between these mineral shows an excellent match to the observed XRD pattern. The recognition in low-grade metabasalts of chlorite and random and different varieties of regular mixed-layer chlorite-smectite offers support for the classical model of a tri-smectite to chlorite transition. This is in contrast to an alternative model proposing smectite and chlorite end-members with corrensite as a discrete phase crystallizing directly without intervening mixed-layer chlorite-smectite.
Parent Material and Pedogenic Processes in South Africa
Authors: Bühmann C.
Published: December 2006

The soils over about half of South Africa are developed from sedimentary rocks of the Karoo Supergroup. Some units within the Karoo strata display variations in their mineralogical composition which correlate with fluctuations in the environment of deposition and with palaeotemperature. The former trends are reflected in the ratio of kaolinite to 2:1 layer-silicates, range from kaolinite-dominated to kaolinite-free, and are particularly evident in rocks of the Vryheid Formation. Geothermal history is preserved in various stages of smectite illitization ranging from R = 0 structures with 25% illite to 100% illite. Compositional trends may be significant on a regional, local or topographic scale down to a distance equal to the depth of a soil profile or even an horizon.
Palygorskite in the Regolith from the Mokau District, North Island, New Zealand
Authors: Kirkman J. H. , Wallace R. C.
Published: December 2006

Corrugated mats of palygorskite occurring in regolith overlying a fissured limestone were examined by X-ray diffraction, infrared spectroscopy, and electron optical techniques after heating at 50°C intervals to 700°C. Palygorskite ‘anhydride’ formed at 400°C and sillimanite formed at 500°C. The palygorskite is believed to have formed in joints in limestone of Upper Oligocene age (Duntroonian) prior to uplift and subsequent weathering. It is highly crystalline, and appears not to have altered or weathered since precipitation.
Calcretes, Palycretes and Silcretes in the Paleogene Detrital Sediments of the Duero and Tajo Basins, Central Spain
Authors: Rodas M. , Luque F.J. , Mas R. , Garzon M.G.
Published: December 2006

Three duricrust types (calcretes, palycretes and silcretes) have been distinguished in the Lower Paleogene arkosic materials from the margins of the Duero and Tajo basins (central Spain). In the calcretes the cements are composed of calcite plus palygorskite, whereas palygorskite is the only cement in the palycretes. In the silcretes, the cement consists chiefly of opal and chalcedony, with minor quartz. The important duricrust development in the Paleogene detrital materials can be correlated with a drastic climatic change towards colder and more arid conditions during this time, as inferred from the sedimentological features and the clay mineral evolution. The origin of calcretes and palycretes is related to the movement of alkaline phreatic waters generated from dolomitic rocks of Cretaceous age cropping out in the near surroundings. Silcretes originated from the vertical transfer of silica from supersaturated groundwaters, from the Hercynian granitic rocks, up to the surface. Silcretes are developed either on unconsolidated arkosic materials or replace previous calcrete or palycrete levels.
Dehydration and rehydration of vermiculites: I. Phlogopitic Mg-vermiculite
Authors: Graf v. Reichenbach H. , Beyer J.
Published: December 2006

Dehydration and rehydration of a phlogopitic Mg-vermiculite were studied by thermo-analysis (TG, DSC) andin situX-ray powder diffractometry. A detailed analysis of the relation between temperature and state of hydration of the vermiculite was rendered possible by use of slow heating rates in combination with a fast-recording position-sensitive detector. The results confirm the existence of a number of definite states of hydration characterized by basal spacings of 1.441,1.429,1.376, 1.165, 1.151,1.002 and 0.926 nm, all of which have already been described in the literature. In addition, so far undetected regular 1 : 1 interstratifications have been found. They formed during those transformations which lead to a change in the number of sheets of interlayer water molecules. These structures exhibit integral series of 00l reflections and d(001) spacings of 2.54 and 2.15 nm for the 2 : 1 and 1 : 0 transitions in the ratio of molecular layers of water, respectively.
Acid activation of a Spanish sepiolite: physico-chemical characterization, free silica content and surface area of products obtained
Authors: Vicente Rodriguez M. A. , DE D. Lopez Gonzalez J. , Bañares Muñoz M. A.
Published: December 2006

A sepiolite from Vallecas (Spain) was treated with solutions of HC1 (1.25, 2.5, 5.0, 10.0 and 20.0 wt%) at 25°C for 2, 6, 24 and 48 h, respectively. The resulting solids were characterized by XRD, FT-IR and thermal analyses, along with SEM, TEM and nitrogen adsorption isotherms at 77 K. The free silica was digested and determined in all samples. Several samples were seen to have specific surface areas up to 450 m2/g, with a maximum value of 549 m2/g in the sample treated with 1.25 wt% HCl for 48 h. A sudden decrease in specific surface areas was observed when free silica was digested.
Mineralogy and geochemistry of Miocene deposits at Alcubierre Sierra, central sector of the Ebro Basin, Spain
Authors: Bauluz Lazaro B. , Arenas Abad C. , Fernandez-Nieto C. , Gonzalez Lopez J. M.
Published: December 2006

Two profiles in Miocene fluvio-lacustrine deposits consist of sandy, marly, lutitic and carbonatic levels constituted by variable percentages of quartz, calcite and clay minerals as major components, and feldspars, dolomite and occasionally gypsum and anhydrite as minor ones. The clay minerals are inherited and consist mostly of micas, with minor quantities of chlorites, pyrophyllites and kaolinites. The crystallochemical parameters of the micas indicate muscovitic compositions and their uniformity through both the different rocks and their silt and clay fractions suggest the same provenance source area, possibly located northward.

Clay minerals concentrate preferentially Li, Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Cs, Ba, Zr, Hf, Th, U and REE whereas the authigenic carbonates concentrate Mn and Sr. The Sc, Cr, Th, Y, Zr and REE values in clay minerals indicate that the provenance source area of these deposits was similar in composition to the average continental upper crust, probably as a result of sedimentary recycling processes.

Zeolitic levels constituted by different proportions of analcime and smectite as major components outcrop at the top of the profiles. The analcimes show anhedral to euhedral morphologies, with grain-size ranging between 1 and 20 μm, and Si/Al ratios ranging from 2.2 to 2.5. The smectites are dioctahedral and beidellitic in composition. The zeolitic levels present significant chemical differences relative to the other ones, such as higher overall REE contents, more pronounced negative Eu anomalies and higher (La/Yb)n, Th/Sc and La/Sc ratios, suggesting a different provenance source area. Their chondrite-normalized REE patterns reflect the possibility that the starting materials were pyroclastic eruptive rocks originating from intracrustal partial melting. The variable analcime and smectite percentages are attributed to variations in H+/(Na+ + K+) and K+/(Na + Ca2+ + Mg2+) activity ratios and silica and water activities in the pore-waters during diagenetic processes.
Effects of diagenesis on shale nano-pore structure and implications for sealing capacity
Authors: Katsube T. J. , Williamson M. A.
Published: December 2006

The effect of diagenesis on shale petrophysical characteristics is being investigated as part of a study on shale sealing capacity because of its significance for modelling hydrocarbon charge histories of sedimentary basins. Results to date indicate that diagenesis (degree of cementation and dissolution) significantly affects porosity and inter-connectivity of the nano-pores (0.3–60 nm), the pores constituting the main pore-throats for tight shales. Diagenesis causes tight shale permeabilities to vary over a range exceeding an order of magnitude (10−21 − 6 × 10−20m2) and porosities to vary between 1 and 12%. In addition, diagenesis significantly influences shale nano-pore resistance to collapse during compaction and burial, mainly at depth > 2–3 km, affecting hydrocarbon trapping, overpressure and sealing capacities. Dissolution tends to delay the timing of excess pressure pulses, while cementation has a reverse effect. The significance of diagenesis is reduced at shallower depths.
Porosity/depth trends in reservoir sandstones: assessing the quantitative effects of varying pore-pressure, temperature history and mineralogy, Norwegian Shelf data
Authors: Ramm M. , Bjørlykke K.
Published: December 2006

Empirical porosity/depth trends from the Norwegian Continental Shelf are discussed in the light of models on compactional processes during burial. Linear best-fit lines are useful as a first approximation, illustrating the general decline in porosity with depth. Porosity increases non-linearly with pore-pressure, and notably higher than normal porosity is found in very high overpressure reservoirs. Hydrostatic pressure sandstones from the Haltenbanken area are on average more porous than equivalents from the northern Viking Graben. This may be related to the burial history, as generally more subsidence occurred in Late Pliocene and Pleistocene in the Haltenbanken basins. The porosity/depth data show considerable scatter, and this is to a large degree related to the initial mineralogical composition. Correlated with mineralogical analyses, the reservoir sandstones show a trend towards lower porosity with increasing clay content at shallow burial, probably due to more extensive mechanical compaction. At depths >3.0–3.5 km, the porosity loss is highest in sandstones with low clay contents. This may be explained by a lower rate of quartz cementation in sandstones with abundant intergranular clays or clay coatings around quartz grains. These data show that pre-burial mineralogy is a very important factor in porosity prediction of sandstones, in many cases more important than the degree of overpressure.