bluuebunny/crossref_metadata_2025 huggingface dataset:
Nomenclature of the Micas
Authors: Rieder Milan , Cavazzini Giancarlo , D'yakonov Yurii S. , Frank-Kamenetskii Viktor A. , Gottardi Glauco , Guggenheim Stephen , Koval’ Pavel W. , Müller Georg , Neiva Ana M. R. , Radoslovich Edward W. , Robert Jean-Louis , Sassi Francesco P. , Takeda Hiroshi , Weiss Zdeněk , Wones David R.
Published: August 2006

End members and species defined with permissible ranges of composition are presented for the true micas, the brittle micas and the interlayer-cation-deficient micas. The determination of the crystallochemical formula for different available chemical data is outlined, and a system of modifiers and suffixes is given to allow the expression of unusual chemical substitutions or polytypic stacking arrangements. Tables of mica synonyms, varieties, ill-defined materials and a list of names formerly or erroneously used for micas are presented. The Mica Subcommittee was appointed by the Commission on New Minerals and Mineral Names (“Commission”) of the International Mineralogical Association (IMA). The definitions and recommendations presented were approved by the Commission.
Modification of Sepiolite by Treatment with Fluorides: Structural and Textural Changes
Authors: Belzunce María Jesús , Mendioroz Sagrario , Haber Jerzy
Published: August 2006

In the search for new applications of natural silicates, various F− treatments have been applied to sepiolite to increase its acidic properties and for use as a catalyst in reactions occurring via carbonium ions. Two types of treatments including hydrofluoric acid (HF) at different concentrations and 2 N NH4F have been utilized and the physicochemical characteristics of the resulting materials studied using standard techniques. The X-ray diffractogram (XRD) patterns indicate a decrease in crystallinity of the original material as well as the appearance of amorphous silica. SEM micrographs showed a shortening and aggregation of the sepiolitic fibers. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), thermogravimetric analysis/differential thermal analysis (TGA/DTA), N2 adsorption-desorption isotherms and Hg intrusion were used to study the changes occurring in the structure, surface area and pore distribution of samples and acidity was evaluated by IR and thermoprogrammed desorption (TPD) of adsorbed ammonia and pyridine. It was found that acidity increased in most of the samples after anionic and cationic interchange between the activating agents and the surface sites, or extralattice cations. Additionally, structural changes induced by treatments modified the Brönsted and Lewis acidity. Mild treatments with ammonium fluoride are more effective than HF treatments in acidity generation.
Chemical Variations in Chlorite at the Los Humeros Geothermal System, Mexico
Authors: Martínez-Serrano Raymundo G. , Dubois Michel
Published: August 2006

The chemical composition of hydrothermal chlorite was determined by means of more than 200 electron microprobe analyses (EMPA) in almost all of the 70 chlorite-bearing samples taken from 5 boreholes in a study of the active geothermal system of Los Humeros, Mexico. Bulk rock composition of 6 different volcanic lithologies, as well as available in situ temperatures and chemical compositions of chlorite, were analyzed by principal component analysis (PCA) in order to test the dependence of chlorite composition on physicochemical parameters. The results show that chlorite minerals display a wide range of chemical compositions in this hydrothermal system that reflect the particular conditions of crystallization episodes: The Na + K + 2Ca values are low (from 0 to 0.6) and they show no correlation patterns with octahedral vacancies (¤) in chlorite, indicating that compositional variations are not due to the intergrowth of smectite and/or illite. The octahedral occupancy of most chlorite is relatively high (from 11.3 to 11.95), especially that from a high-temperature range, as is the case of metamorphic chlorite. The octahedral occupancy seems not to be related to other chemical variables of chlorite from the G3, G4 and G5 lithologic units, suggesting that the lack of complete occupancy is not dependent on “contamination” by other silicates (such as quartz). Cationic substitution in tetrahedral sites in chlorite is small and via a Tschermak exchange (MgVISiIV ↔ AlVIAlIV). To preserve a charge balance in the structure, an octahedral substitution of R2+ by Al3+ accompanies the Tschermak exchange. The chemical composition of hydrothermal chlorite is very similar to that of metamorphic chlorite but slightly different from equivalent phases found in diagenetic environments. In hydrothermal chlorite the SiVI, AlVI and ¤ decrease, whereas the AlIV and Fe2+ contents increase with the degree of alteration and depth, the same way as in chlorite formed in diagenetic high-temperature environments. The ferrous iron content, in general, increases with depth and temperature; however, whole-rock chemistry affects the iron distribution in chlorite of Los Humeros. Changes in the oxygen fugacity of fluids at depth also affect the iron distribution in chlorite, XFe = Fe/(Fe + Mg), which ranges from 0.30 to 0.38 in oxidizing conditions and from 0.39 to 0.60 in reducing conditions. Finally, the chemical composition of chlorite in Los Humeros appears to change with temperature, but the correlations of ¤ and AlIV with temperature are more variable than in another nearby active geothermal system located in Los Azufres, Mexico. This implies that geothermometers based on chlorite composition and empirically calibrated in some geothermal systems cannot be generalized and it is necessary to consider other physicochemical variables.
Structural Organization of Na- and K-Montmorillonite Suspensions in Response to Osmotic and Thermal Stresses
Authors: Faisandier K. , Pons C. H. , Tchoubar D. , Thomas F.
Published: August 2006

In order to understand the influence of salt concentration and temperature on the behavior and properties of clays used in drilling muds, we studied montmorillonite supensions (4 g clay/100 g solution) in 0.1, 0.5 and 1 M NaCl and KCl solutions. A fraction of each sample was heated to 200 °C in a closed vessel for 7 d, then cooled at room temperature (RT, 25 °C). Small-angle X-ray scattering (SAXS) spectra were recorded, for all the samples, at RT. The structure of the clay particles was determined by comparing the experimental intensity with the theoretical intensity computed from a model that took into account the number of layers per particle, the hydration state of the layers (0, l, 2, 3 or 4 water layers) and the order in the succession of these states. With this set of parameters, we can compute the mean statistical parameters M¯ (mean number of layers per particle), d¯ (mean interlayer distance) and δ¯2/d¯2 (parameter describing the disorder of the distribution of interlayer distances). The evolution of these parameters shows that:

1)

At low concentration (0.1 M NaCl or KCl), the samples do not consist of particles but of isolated layers (M = 1). The suspensions form gel-like structures. The difference between Na and K suspensions, or between heated and nonheated samples, is unnoticeable at the studied scale (5–500 Å).

2)

An increase in salt concentration (from 0.1 to 0.5 M) brings the sample in a granular state: we notice the appearance of particles at 0.5 M (M¯ ≥ 25). Differences appear between NaCl and KCl suspensions, and the temperature effect becomes visible. Thus, we noticed that in NaCl suspensions, particles are composed of hydrated layers (1, 2, 3 or 4 water layers) and internal porosity (d > 30 Å), whereas suspensions in KCl are characterized by the presence of interlayer distances of 10 Å, that is, of collapsed layers. Particles in the KCl suspensions are much thicker than in the NaCl corresponding ones, and also less hydrated at the interlayer level as well as at the internal porosity level. Further increase in salt concentration (0.5 to 1 M) amplifies this effect. As far as temperature is concerned, its effect is to promote the clay dispersion by breaking up the particles, dehydrating and disordering them. This effect is more important for low salt concentration, that is, when the system is less stressed.
The Formation of Sulfides During Alteration of Biotite to Chlorite-Corrensite
Authors: Li Gejing , Peacor Donald R. , Essene Eric J.
Published: August 2006

Transmission electron microscopy/analytical electron microscopy (TEM/AEM) were utilized to study pyrite and sphalerite inclusions in chlorite or mixed-layer chlorite-corrensite from an analcimized ash bed in the Etalian stage (Middle Triassic), South Otago, New Zealand. These sulfide inclusions occur as elongated crystals up to 1 × 15 µm in size, within lens-shaped voids between separated, deformed (001) layers of (primarily) chlorite and mixed-layer chlorite-corrensite grains of typical detrital shape or chlorite packets in chlorite-mica stacks (intergrowths of chlorite and phengite packets) up to 40 × 150 µm in size. Relict biotite layers within chlorite, mixed-layer chlorite-corrensite and berthierine have textures implying replacement of the former by the latter, whereas in other unaltered samples only fresh biotite was observed. Anatase occurs in otherwise Ti-free chlorite, whereas relict biotite contains significant Ti (0.3 moles per 22 oxygen atoms). No sulfide minerals have been found in fresh biotite and phengite.

Mass balance considerations indicate that S and Zn were introduced via pore fluids and that the Fe was provided by the decomposition of biotite to secondary phyllosilicates. The alteration of biotite and the reaction of biotite to form chlorite and pyrite is controlled by aH+/aK+ as well as oxidation of reduced S species or reduction of oxidized S species from solution. Simple calculations with the observed compositions of chlorite and biotite suggest that some of the Fe in biotite was actually removed in solution rather than precipitated in pyrite and chlorite. Similar textures are abundant in ferroan phyllosilicates elsewhere, implying that the mechanism may apply widely to precipitation of sulfides in phyllosilicates during early diagenesis of sediments.
Burial Diagenetic Processes and Clay Mineral Formation in the Molasse Zone of Upper Austria
Authors: Gier Susanne
Published: August 2006

Cores of pelitic sediments (Eocene-Miocene) of the drillings Puchkirchen 1 and Geretsberg 1 (Molasse Basin, Upper Austria) have been studied to determine the mineralogical and chemical changes taking place during burial diagenesis. Mineralogical and chemical investigations of the bulk samples show that the deepest samples of the profiles are derived from a different source area. In particular, there is an increase in kaolinite and chlorite with depth and a decrease in quartz related to the initial sedimentology and provenance.

Investigations of the <2 µm and <0.2 µm fractions of the profiles Puchkirchen 1 and Geretsberg 1 reveal the diagenetic overprint of the mineral constituents: The gradual illitization of mixed-layer illite-smectite, also reflected in an increase of K2O and Al2O3, is displayed most prominently in the <0.2 µm fraction. The source for the Al and K is the dissolution of K-feldspar (<2 µm fraction), as indicated in many previous studies.

The I-S mixed-layer phases are randomly interlayered to a depth of 1600 m; from there on a regular interstratified I-S phase appears in coexistence with the randomly interlayered I-S mixed layer. The randomly oriented phase is still present in major amounts to depths of 2500 m, presumably as a result of the low geothermal gradient (2.9 °C/100 m) in the Molasse Basin.

The calculation of the structural formula of the end members illite and smectite from this series of I-S mixed-layer phases gave the following results: Smectite: $${K_{0.14}}{X^ + }_{0.44}\left( {A{l_{1.10}}M{g_{0.46}}F{e_{0.36}}T{i_{0.01}}} \right)S{i_{4.03}}{O_{10}}{\left( {OH} \right)_2}$$

Illite: $${K_{0.44}}{X^ + }_{0.19}\left( {A{l_{1.26}}M{g_{0.42}}F{e_{0.38}}T{i_{0.01}}} \right)\left( {S{i_{3.52}}A{l_{0.48}}} \right){O_{10}}{\left( {OH} \right)_2}$$

The end-member interlayer charge for the smectite component (+0.58) is higher than reported for typical smectites (+0.32 to +0.47). It is suggested that the I-S phases of the Molasse Basin are probably intergrowths of 3 layer-silicate members: illite, low-charged smectite and high-charged smectite. The determined smectite end-member composition represents, therefore, an average for a variable 2-component smectite system. The charge-differences of the 2 smectites would likely reflect the differences in source material, which in turn would have led to the formation of different early, highly smectitic I-S phases in the sedimentary basin.
Layer-Charge Heterogeneity in Smectites of I-S Phases in Pelitic Sediments from the Molasse Basin, Austria
Authors: Gier Susanne , Ottner F. , Johns W. D.
Published: August 2006

The purpose of this study was to characterize more fully the surface charge characteristics of the end-member smectite in illite-smectite (I-S) mixed-layer phases found previously in pelitic sediments of the Molasse Basin in Austria. The smectite end member was shown to have an unusually high interlayer charge (0.58). Based on earlier work on pure smectites, it was hypothesized that this high charge represents the mean of a mixture of a higher- and lower-charged smectite component intermixed with illite. To test this hypothesis, the magnitude of the interlayer charge of the smectites was evaluated using 2 different methods: alkylammonium ion orientation and K-fixation by wetting and drying.

Using 2 I-S samples of different I-S ratios, saturated with alkyammonium ions of chain lengths nc = 5–18, X-ray diffraction patterns (XRD) could be interpreted as representing a 3-component system, consisting of randomly interlayered high- and low-charged smectite and illite.

K-fixation, carried out by K-treatment and followed by 100 wetting and drying (WD) cycles, confirmed the presence of a high-charged smectite component admixed with low-charged smectite, both interlayered with illite. The wetting and drying of the K-treated samples led to interlayer collapse of the high-charged smectite component and to the production of illite layers stable against exchange with 0.1 N SrCl2. The 2 smectites occur in the ratio of about 1:1 and consist of 1 phase with an interlayer charge of about 0.76 and another phase with a normal charge of about 0.40. During diagenesis, the 2 kinds of smectite are altering simultaneously to the same end-member illite along 2 different reaction paths.
X-Ray Diffraction Intensity Ratios I(111)/I(3¯11) of Natural Heulandites and Clinoptilolites
Authors: Esenli Fahri , Kumbasar Isik
Published: August 2006

Heulandite-group zeolites are abundant in the Miocene pyroclastics from Western Anatolia, Turkey. We investigated the relation between the I(111)/I(3¯11) intensity ratios measured by X-ray diffraction (XRD) and the content of exchangeable cations for 15 samples of natural heulandite-group minerals gathered from the Gördes and Bigadiç regions of Western Anatolia. The intensity ratios range from 0.77 to 0.94 in natural heulandites and from 1.38 to 1.80 in natural clinoptilolites. The data obtained from Na-, K- and Ca-exchanged forms of a heulandite and clinoptilolite show that the intensity ratio increases with Na-, K- and Ca-exchange in heulandite and also with Na- and K-exchange in clinoptilolite, whereas it decreases with Ca-exchange in clinoptilolite. The intensity ratios were calculated using the known structural data of clinoptilolites to understand the effect of positions, amounts and kinds of exchangeable cations and water molecules. An increase in Na and Ca may increase or decrease the intensity ratio, depending on their sites and occupancies. Potassium causes a significant increase in the intensity ratio and an increase in Mg decreases the intensity ratio. There is a strong correlation between the intensity ratio I(111)/I(3¯11) and (Na + K)/(Ca + Mg) ratio and thermal stability, both of which have been used to characterize heulandite-group minerals.
Solid State NMR Characterization of the Thermal Transformation of an Illite-Rich Clay
Authors: Roch G. E. , Smith M. E. , Drachman S. R.
Published: August 2006

Lode, a dioctahedral illite-rich clay from Latvia belonging to the mica group of clay minerals, undergoes thermal transformation via a series of structurally disordered intermediate phases. Despite containing high levels of paramagnetic Fe substituted into the octahedral sites, 29Si and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectra of sufficient quality are obtained to resolve different structural units, showing clearly defined structural changes which occur in the sample during calcination to 1200 °C. However, Fe plays a significant role in broadening the Al signal, with integrated peak intensities decreasing as temperature increases. Significant differences are revealed in the thermal decomposition process by NMR spectra between pyrophyllite, Ca-montmorillonite and illite clays, possibly due to the different cations present in the interlayer. It has also been shown for illite that no structural differences at the atomic level occur when the dwell time at a particular temperature is varied and no difference is observed between samples that have different thermal histories; however, a minor effect of particle size and surface area is visible in the NMR data.
Destinezite (“Diadochite”), Fe2(PO4)(SO4)(OH)·6H2O: Its Crystal Structure and Role as a Soil Mineral at Alum Cave Bluff, Tennessee
Authors: Peacor Donald R. , Rouse Roland C. , Coskren T. Dennis , Essene Eric J.
Published: August 2006

A new occurrence of destinezite (diadochite), ideally Fe2(PO4)(SO4)(OH)·6H2O, is described from Alum Cave Bluff, Great Smoky Mountains National Park, Tennessee, where it occurs in soil and in a weathered Precambrian phyllite in unusually large crystals associated with other hydrated sulfates such as pickeringite-apjohnite. Destinezite is triclinic, P1̄, with a = 9.570(1), b = 9.716(1), c = 7.313(1) Å, α = 98.74(1)°, β = 107.90(1)°, γ = 63.86(1)° and Z = 2. Its crystal structure consists of infinite chains of Fe(O,OH,H2O)6 octahedra, sulfate tetrahedra and phosphate tetrahedra linked by a unique system of vertex sharing. The chains are weakly bonded into slabs by hydrogen bonding between OH and H2O of the Fe(III) octahedra and oxygen ions of the sulfate tetrahedra. Slabs of tetrahedral/octahedral chains alternate with sheets of H2O molecules. The structure thus somewhat resembles hydrated clay minerals, with H2O molecules that act as hydrogen bond donors and acceptors to oxygen atoms of adjacent slabs. Destinezite and diadochite occur at numerous localities worldwide and have been assumed to be identical, but this identity has never been proven. It is proposed that the name “destinezite” be applied to visibly crystalline, triclinic Fe2(PO4)(SO4)(OH)·6H2O and “diadochite” to massive to earthy, poorly ordered, X-ray amorphous materials that approximate destinezite in composition. Diadochite/destinezite may be an unrecognized component of soils where weathering of pyrite and apatite has occurred and pH is low. It may thus be a significant sink for phosphorus and sulfur in such soils.
Mineralogical Interference on Kaolinite Crystallinity Index Measurements
Authors: Aparicio Patricia , Galán Emilio
Published: August 2006

This study examines the influence of minerals and amorphous phases associated with kaolin and kaolinitic rocks on kaolinite crystallinity indices (KCI) derived from X-ray diffraction (XRD) data in order to select the best index for systematic studies of commercial kaolins or geological sequences. For this purpose, 8 kaolins of differing structural order were chosen and used to prepare mixtures containing different weight fractions of quartz, feldspar, illite, smectite, chlorite, halloysite and iron hydroxide and silica gels. An additional 17 samples of kaolin were also studied to test the results and evaluate the restrictions. KCIs used included Hinckley (HI), Range and Weiss (QF), Liètard (R2), Stoch (IK), Hughes and Brown (H&B) and Amigó et al. (full width at half maximum, FWHM), and the “expert system” of Plançon and Zacharie.

Based on more than 15,000 KCI determinations, the HI and QF are influenced by quartz, feldspar, iron hydroxide gels, illite, smectite and halloysite. IK can be used in the presence of quartz, feldspar and iron hydroxide and silica gels. Also, R2 is the only KCI that could be measured in the presence of halloysite; FWHM indices should not be used in the presence of chlorite and/or halloysite; and H&B should only be used with pure kaolinite samples. The “expert system” of Plançon and Zacharie is strongly affected by the presence of other mineral phases, particularly with more than 25% of well-ordered kaolinite. Their system is less sensitive to other mineral phases when only disordered kaolinite is present, and it should not be used with kaolinite of medium order-disorder because the well-ordered phase is present in an inappreciable proportion (<10%). KCI is only measurable in kaolinitic rocks if kaolinite is >20 wt% and the precision increases with an increase in the quantity of kaolinite. In all cases, the reliability will depend on the other minerals present. When a KCI can be measured accurately, the others can be obtained by using the empirical relationships reported in this paper.
Colloid Chemical Control of Kaolinite Properties Related to Ceramic Processing
Authors: Pavlova Lyudmyla A. , Wilson Michael J.
Published: August 2006

Experimental data on structure formation in highly concentrated aqueous dispersions of kaolinite were analyzed using rheological models. The physicochemical properties of the clay mineral surface were studied during heating at a range of temperatures, and correlation of acid-base properties with physicomechanical characteristics of the spatial structures formed during heating was obtained. It was shown that interparticle interactions and plastic yield mechanisms under load are dependent upon interfacial phenomena. A method for estimating optimal structural parameters was developed for semidry dispersions, enabling regulation of physicochemical and mechanical properties of ceramic mixtures during processing.
Sorption of Selected Cationic and Neutral Organic Molecules on Palygorskite and Sepiolite
Authors: Shariatmadari H. , Mermut A. R. , Benke M. B.
Published: August 2006

Palygorskite and sepiolite show a high sorption capacity for organic molecules. Adsorption of 2 organic cations, methylene blue (MB) and crystal violet (CV), by palygorskite and sepiolite were examined. The maximum sorption of MB and CV far exceeded the cation exchange capacity (CEC) of these minerals. This shows that, besides the contribution of free negative sorption sites (P-), the sites satisfied with sorption of single cations (PXi0) and neutral sorption sites (N) on clay surfaces may contribute to the sorption of organic cations. The number of neutral sites was determined by examining the sorption of 2 neutral organic molecules, triton-X 100 (TX100) and 15 crown ether 5 (15C5), and by application of the Langmuir isotherm.

To determine the contribution of different sites, an adsorption model that applies the Gouy-Chapman equation and takes into account the formation of different clay-organic complexes in a closed system was employed. Application of this model to sorption data provided the calculation of binding coefficients for neutral sites, as well as the surface potential of the minerals at different sorbate concentrations.

At sorption maxima, for both palygorskite and sepiolite, the contribution of neutral sites for sorption of organic cations was the highest, followed by the PXi0 sites in case of CV sorption, while in sorption of MB the contribution of P- sites was the second highest. The Fourier transform infrared (FTIR) patterns of clay-organic cation complexes compared with pure clays confirm that the sorption of organic cations is by silanol groups located at the edge of fibrous crystals, which account for neutral sorption sites.
Applying X-Ray Geothermometer Diffraction to a Chlorite
Authors: Battaglia Stefano
Published: August 2006

A new method is proposed for applying the chlorite geothermometer using X-ray diffraction (XRD) data. A linear correlation has been found between the (001) basal spacing of chlorite and its “crystallization” temperature. The basal spacing values were corrected for an increase of Al(IV) with Fe enrichment (Fe/Fe + Mg), when the Fe(II) value of chlorite is >2.6 in the formula unit. The regression coefficient of the best fit is r = 0.95. Only 2 Bragg lines need to be measured for application of the proposed technique: the (001) and (060) X-ray spacing. The proposed method is applied to 19 chlorite samples from 4 different geothermal fields. The temperatures of chlorite formation obtained with the present method and those calculated by the expressions formulated by Cathelineau (1988) and Kranidiotis and MacLean (1987) are presented. The method's validity was also tested on geothermal chlorites from the literature, and the results show good agreement with previous experimental trials.
Eocene and Oligocene Otay-Type Waxy Bentonites of San Diego County and Baja California: Chemistry, Mineralogy, Petrology and Plate Tectonic Implications
Authors: Berry Richard W.
Published: August 2006

Otay-type waxy bentonites of San Diego County are illite-smectite (I-S) with 85% dioctahedral smectite mixed with dioctahedral illite showing a Reichweite of 0. Primary or secondary waxy bentonite exposures are found in all Eocene and Oligocene formations of southwest San Diego County and western Baja California north of Ensenada. Primary waxy bentonites formed when hot volcanic ash fell into quiet marine or brackish coastal water. The transformation from glass to bentonite occurred within hours or days but consolidation of the bentonite into its waxy consistency took longer. Primary waxy bentonite consists of 95 wt% I-S with the remainder consisting of volcanic glass shards, sanidine fourling twins, hexagonal biotite crystals and amorphous manganese oxides and hydroxides. Secondary waxy bentonite is primary waxy bentonite that was mixed with nonvolcanic detritus either before consolidation or after consolidation and subsequent erosion. The hydrophobic character of primary waxy bentonite allows it to reflect, accurately, the chemistry and petrology of the original volcanic material. Chemical analysis of primary waxy bentonites shows that the original lava was subduction-related and exhibited petrologic variations nearly identical to those of the modern Cascades of the northern Pacific coast of the lower United States. Primary and secondary waxy bentonites as well as smectites derived from the weathering of volcanic ash that fell outside the waxy bentonite-producing environments are the previously unrecognized products of extensive Eocene and Oligocene subduction-related volcanic activity. Baja California exposures of waxy bentonite demonstrate pre-Pliocene subduction tectonics that gave way to rifting tectonics.
Stable Isotope Evolution of Volcanic Ash Layers During Diagenesis of the Miocene Monterey Formation, California
Authors: Compton J. S. , Conrad M. E. , Vennemann T. W.
Published: August 2006

The oxygen and hydrogen isotope compositions of volcanic ash layers from coastal outcrops of the Miocene Monterey Formation elucidate the progressive burial diagenesis of glass to bentonite and metabentonite. Volcanic glass that texturally appears unaltered is found to have δl8O and δD values that are significantly higher than fresh volcanic glasses. The positive shift in δ18O and δD values is proportional to the amount of hydration and chemical alteration of the glass samples. Initial hydration of the glass results in the exchange of Na for H; later hydration results in the loss of K and Fe in exchange for H and Na. The δ18O values of the most hydrated glass, and clay minerals from bentonite and metabentonite layers are approximately in equilibrium with slightly modified seawater. The δD values of the hydrated glass, and clay minerals from bentonite and metabentonite layers, are significantly depleted in D relative to seawater and suggest meteoric exchange associated with tectonic uplift and erosion in the Pliocene and Pleistocene. Smectite from bentonite layers has δ18O and δD values similar to the most hydrated glass samples, suggesting similar glass-water and smectite-water fractionation factors. Kaolinite and mixed-layered illite-smectite (I-S) altered from smectite have lower δ18O and higher δD values than their precursor. The δ18O and δD of nonvolcanic siliceous mudstones from the Pt. Arguello oil field show an unusual decrease in δD with increasing burial depth that probably reflects the presence of organic hydrogen in the analyzed samples as well as possible D-depleted formation waters from detrital illite-water and hydrocarbon-water exchange.
K-Ar Dating of Illitic Fractions of Estonian “Blue Clay” Treated With Alkylammonium Cations
Authors: Chaudhuri Sam , Środoń Jan , Clauer Norbert
Published: August 2006

Two clay fractions of a Cambrian claystone from Estonia, consisting essentially of illite and 20% expandable illite-smectite, (I-S) were treated with C12 and C18 alkylammonium cations for K-exchange. Both the untreated and treated samples were dated by the K-Ar method. The treated clays lost several percent of their original K2O, with greater losses for longer-chain cations and for longer reaction time, in accordance with previously published studies. The dates of the treated clay fractions were 20–30 Ma lower than those of the untreated clays. The decrease in the dates suggests preferential opening of older, detrital clays. The K-Ar dates of the illite layers susceptible to K extraction by the various treatments were calculated by subtracting K2O and radiogenic 40Ar values of the consecutive step products, and they were plotted against the total % K2O removed, used as an indicator of the reaction progress. Extrapolation of the plot revealed a detrital (1550 Ma) and a diagenetic (380 Ma) age for the 2 illitic minerals present in the investigated shale sample. The inferred Devonian age of diagenesis of the Estonian clay corresponds to the period of massive dolomitization in the area. Both alteration processes can be related to a Devonian incursion of hot or alkaline fluids, which helps to explain the occurrence of 20% expandable I-S in claystones that have never been buried more than 1000 m.

Extrapolated K-Ar ages and K2O contents of the illitic minerals, estimated from the X-ray diffraction (XRD) data, were used to model the experimental data. A good agreement was reached when dilution effects (chlorite and expanded illite) were taken into account.
“Retrograde Diagenesis” of Clay Minerals in the Precambrian Freda Sandstone, Wisconsin
Authors: Zhao Gengmei , Peacor Donald R. , Mcdowell S. Douglas
Published: August 2006

Siltstones from the Precambrian Freda Formation in Wisconsin have been studied by scanning, scanning-transmission and analytical electron microscopy (SEM, STEM and AEM), and X-ray diffraction (XRD). XRD data for drill core samples show a change from smectite-rich Illite-Smectite (I-S) in shallow samples to illite in deeper samples, implying a transition during burial diagenesis.

Transmission electron microscopy (TEM) observations of shallow samples reveal the presence of three clearly distinguishable kinds of dioctahedral clay minerals: (1) detrital grains of micrometer-sized, mature muscovite; (2) small packets in the matrix consisting of dominant (Reichweite) R1 I-S or (3) small packets of illite. The illite and I-S stacks occur separately and have similar textures, with packet thicknesses averaging ∼400 Å, within the range of anchizonal illite. Illite and detrital muscovite commonly display strain features typical of the effects of tectonic stress. Void space within I-S or illite packets is inferred to be a strain feature, and to have served as pathways for fluids. Detrital muscovite shows abundant alteration features including (001) boundaries which are continuous with parallel packets of I-S; individual layers commonly show along-layer transitions of muscovite to smectite or I-S. Trioctahedral clays consist primarily of detrital chlorite which commonly shows direct alteration to R1 I-S and smectite, as with detrital muscovite.

Deep samples contain only unaltered, coarse detrital muscovite, and thin packets of illite forming stacks and comprising most of the matrix. The texture of the illite appears to be identical to that of shallow samples, with characteristics such as packet size typical of anchizonal illite. Trioctahedral clays consist almost entirely of detrital grains of chlorite and corrensite. They occur as separate grains with rather constant composition, without signs of alteration.

The data imply that all of the studied rocks have been subjected to a uniform anchizonal grade of metamorphism in which detrital grains were largely unchanged but matrix clays were transformed to packets of illite. The unusually abrupt transition with depth from highly expandable I-S to illite is inferred to actually be the result of subsequent alteration of authigenic illite and detrital chlorite and muscovite to R1 I-S and smectite in shallow rocks. This late overprinting of the anchimetamorphic clay mineral assemblage is inferred to have been locally caused by fluids with temperatures less than those of peak metamorphism. This process, called “retrograde diagenesis”, gave rise to a sequence of dioctahedral I-S and illite which mimics classic prograde sequences. Interpretations of such sequences as being prograde, especially in cases of ancient rocks, should be interpreted with caution when high-resolution images of textures are not available.
Effect of Permo-Carboniferous Climate on Illite-Smectite, Haushi Group, Sultanate of Oman
Authors: Hartmann Bernhard H. , Bodnár Katalin Juhász , Ramseyer Karl , Matter Albert
Published: August 2006

The Late Westphalian to Artinskian Haushi Group in the Sultanate of Oman consists of the glaciogenic Al Khlata Formation and the Gharif Formation which contains marginal marine, coastal plain, and fluvial sediments. The sequence was deposited during a global-warming event following the Permo-Carboniferous glaciation of Gondwana. Because of a varied subsidence history, these sediments range from the surface in the SE to almost 5000 m in the NW of the basin.

Mixed-layer illite-smectite (I-S) is an important constituent of the <2 µm size fraction of sandstone and shale samples in both formations at all depths. Different starting compositions lead to three distinct trends of illite layers in I-S versus temperature for different sedimentary environments and paleoclimatic conditions. The starting compositions of I-S at the surface range from an ordered I-S in the Al Khlata Formation to smectite-rich in the Upper+Middle Gharif members.

Physical, chemical and environmental factors were investigated as causes for the different starting compositions of I-S. Both formations share an identical burial history, paragenesis, thermal evolution, and source of detrital material. They differ only in environmental conditions during sedimentation. Thus, the variation in starting composition of I-S appears to be best explained by distinct weathering conditions during sedimentation of the three units. In particular, the expected low intensity of chemical weathering during glaciogenic conditions is marked by the presence of higher amounts of unstable volcanic and sedimentary rock fragments in the Al Khlata Formation.
Chemical Changes and Genesis of Secondary Minerals During the Alteration of Biotites from Ignimbrites in the Tazzeka Mountain (Morocco)
Authors: Dejou Jean , De Kimpe Christian , Macaire Jean-Jacques , Perruchot Alain
Published: August 2006

The Tazzeka Mountain, located approximately 20 km south of Taza, eastern Morocco, is composed of a Westphalian volcano-sedimentary complex. It contains rhyolitic ignimbrites with the following minerals: quartz, potassium feldspar, oligoclase-andesine, and biotite. The ignimbrites are extensively altered because of a dense network of fractures in the massif. Alteration has resulted in the formation of spheroidal rocks and saprolite, the thickness of which depends on local topography. The evolution of the biotites in the ignimbrites was investigated by microprobe analysis of the mica crystals. This technique provides data that are not accessible through classical analytical methods. Biotites are transformed into secondary clay minerals, mainly chlorites and illites; intermediate stages are related to the degree of alteration of biotite, the latter being expressed by the K2O content which decreases progressively from 7.3 to 1.3%. Next come protochlorites and chlorites sensu stricto, in which the K2O content is 0.3%. Several processes including retrodiagenesis, hydrothermal activity, fumarolic activity, and geochemical weathering contributed to the transformation of the biotites at Tazzeka.
Cation Exchange Capacity of Kaolinite
Authors: Ma Chi , Eggleton Richard A.
Published: August 2006

Experimental cation exchange capacities (CEC) of kaolinites were determined and compared to theoretical calculations of CEC. The comparison reveals that the exchangeable cations occur mostly on the edges and on the basal (OH) surfaces of the mineral. It also shows that permanent negative charge from isomorphous substitution of Al3+ for Si4+ is insignificant. The CEC of kaolinite strongly depends on the particle size (both thickness and diameter in the (00l plane) and pH value. Particle size is more important than crystallinity in affecting kaolinite CEC. This study shows that the hydroxyls on the exposed basal surfaces may be ionizable in aqueous solutions. The amount of negative charge on the edges and the exposed basal hydroxyls depends on pH and other ion concentrations. A higher pH value gives rise to more negative charges, which lead to a higher CEC value. This study indicates that charge from broken edges and exposed OH planes rather than charge from Al/Si substitution determines the kaolinite CEC, even at zero point charge. A high CEC in some kaolinites is found to be due to smectite layers on the surface of the kaolinite crystals.
Monte Carlo Simulation of the Total Radial Distribution Function for Interlayer Water in Sodium and Potassium Montmorillonites
Authors: Sposito Garrison , Park Sung-Ho , Sutton Rebecca
Published: August 2006

Monte Carlo simulations based on tested water-water, cation-water, and water-clay potential functions were applied to calculate radial distribution functions for O-O, O-H and H-H spatial correlations in the interlayer region of the two-layer hydrates of Na- and K-montmorillonite. The simulated radial distribution functions then were used to compute the total radial distribution function for interlayer water, a physical quantity that can be determined experimentally by H/D isotopic-difference neutron diffraction. The simulated total radial distribution functions were compared with that for bulk liquid water, and with a total radial distribution function determined experimentally for the two-layer hydrate of Na-montmorillonite by Powell et al. (1997). This comparison suggested that water molecules in the two-layer hydrate of montmorillonite have nearest-neighbor configurations which differ significantly from the tetrahedral ordering of nearest neighbors that characterizes bulk liquid water.
Supergene Origin of the Lastarria Kaolin Deposit, South-Central Chile, and Paleoclimatic Implications
Authors: Gilg H. A. , Hülmeyer S. , Miller H. , Sheppard S. M. F.
Published: August 2006

The residual kaolin deposits near Lastarria, South-Central Chile, were formed by weathering of subvolcanic quartz porphyry stocks, which intruded the metamorphic basement of the Coastal Cordillera. The clay fractions (<2 µm) consist mainly of poorly-ordered, very fine-grained kaolinite and lath-shaped illite (17–38 wt. %) with minor amounts of quartz, sanidine, and goethite. A sample from the top of the deposit contains major quantities of gibbsite morphologically indistinguishable from kaolinite flakes. The gibbsite-free clays contain 35.5–36.6 wt. % Al2O3, 0.4–2.6 wt. % Fe2O3, 1.3–3.9 wt. % K2O, and have low TiO2 concentrations (<0.02 wt. %). The absence of quartz veining, the abundance of melt inclusions, and the scarcity of secondary fluid inclusions in quartz phenocrysts from altered rocks imply a lack of significant hydrothermal activity in the quartz porphyries. The δ 18O and δD values of the kaolins indicate formation in a weathering environment at significantly higher annual mean air temperatures (∼12°C) than present mean temperatures of ∼9.4°C. Uplift of the region alone probably cannot account for the change in climate. The stable isotope composition of gibbsite is consistent with an origin of desilication of kaolinite at superficial temperatures. Various criteria proposed to distinguish supergene from hypogene kaolins are discussed.
Hydrothermal Synthesis of Corrensite: A Study of the Transformation of Saponite to Corrensite
Authors: Roberson Herman E. , Reynolds R. C. , Jenkins David M.
Published: August 2006

Hydrothermal synthesis experiments were conducted to study the transition from smectite to corrensite. A mixture of oxides with the bulk composition of corrensite—Na0.4(Si6.4Al1.6)(Mg7.8Al1.2)-O20(OH)10—was sealed in platinum capsules with 29–37 wt. % water. One set of samples was treated in cold-seal vessels at 500°C and 2 kbar for durations of 2, 3, 6, 12, and 24 h; the other set was treated at 350°C and 2 kbar for periods of 12 to 89 d. X-ray diffraction patterns (XRD) of oriented aggregates from treated products were obtained from ethylene glycol-solvated and air-dried preparations. Samples were also heated to 350°C either in a calibrated muffle furnace, removed and quickly placed in a nitrogen filled chamber on the diffractometer, or were heated at 350°C by using a calibrated heating stage mounted on the diffractometer.

Initial mineral assemblages at both temperatures contained only saponite and serpentine. In experiments at 500°C, saponite transformed to corrensite within 6 h; in experiments at 350°C, the transformation occurred as early as 22 d. Increased experiment times at both temperatures produced increasing amounts of well-crystallized corrensite, as indicated by several well-defined XRD peaks. No evidence of a randomly interstratified chlorite-smectite (C-S) precursor to corrensite was found. The identification of pure smectite, as opposed to highly-expanded randomly interstratified C-S, was possible only when clays were dehydrated on a heating stage on the diffractometer.

These results call for a new examination of hydrothermally-altered basalt that has been reported to contain randomly interstratified C-S as an intermediate step in the reaction of smectite to corrensite or chlorite. These results also strengthen the view held by increasing numbers of investigators that corrensite should be regarded as a single phase, not as a mixed-layered phyllosilicate.
Clay Mineralogy and Occurrence of Ferrian Smectites Between Serpentinite Saprolites and Basalts in Biga Peninsula, Northwest Turkey
Authors: Ece Ö. Işik , Çoban Fazli , Güngör Nurfer , Suner Fikret
Published: August 2006

The clay mineralogy of an oxisol-saprolite overlying serpentinite and underlying basalt was studied with different techniques to evaluate the clay mineral transformation that occurred and to understand the origin of Fe3+-rich smectite. The saprolite zone of the oxisol, up to 30 m thick, contains smectites of the montmorillonite-beidellite and montmorillonite-nontronite series, as well as illite, chlorite, talc, and goethite or amorphous oxyhydrates. Illite is mainly concentrated in the upper 50 cm thick zone underlying the basalt layer and chlorite-content increases toward altered serpentinite at the base. Minor amounts of nontronite formed mostly toward westward exposures where the hot contact layer between serpentinite and basalt is only 20 cm thick. Greene-Kelly Li-tests revealed that all samples contain montmorillonite, but one sample shows the presence of a minor amount of beidellite.

Parent rocks are a mixture of mainly mica schist (the source of beidellite), and minor serpentinite in different percentages and laterally distributed. These rocks were intensely weathered under humid climatic conditions. Silica was concentrated as amorphous transparent (pure silica) cobbles and milky quartz pebbles, and originated from geothermal solutions rising through the Ovaclk thrust fault. The Mg partly formed chlorite. Ferrian smectites in serpentinites were derived obviously from the Mg-rich minerals but Mg is lost much more rapidly than Si during the formation of the clay deposit. The structural formula of the most Fe-rich smectite samples from the study area is (Si6.60−7.10Al1.40−0.90)(Al2.54−1.22Mg0.32−0.92Fe3+1.18−1.68−Ti0.06−0.04)(Ca0.16−0.10Na0.02K0.02−0.12)O20(OH)4. This composition is within the range recorded for the ferrian montmorillonite-beidellite series, with very little vermiculite forming the oxisol-vertisol horizon.
Mg-Smectite Authigenesis in a Marine Evaporative Environment, Salina Ometepec, Baja California
Authors: Hover Victoria C. , Walter Lynn M. , Peacor Donald R. , Martini Anna M.
Published: August 2006

Formation of authigenic trioctahedral Mg-rich smectite is common in evaporative lake sediments, but was not described previously in modern marine evaporative environments. This study documents formation of authigenic K-rich, Mg-smectite during very early diagenesis in the dominantly siliciclastic Salina Ometepec (Baja California), a large supratidal evaporative sabkha complex near the mouth of the Colorado River. Here, sediment pore waters are exceptionally Mg2+-rich relative to other marine evaporative environments due to suppressed sulfate reduction which limits production of carbonate alkalinity and, hence, carbonate (particularly dolomite) precipitation. Sediment cores were obtained along a five km transect seaward across the hypersaline mud flat to evaluate how these atypical geochemical conditions would affect the clay mineral compositions.

Scanning transmission electron microscopy (STEM) observations show that the smectite from the marine Inlet, near the sediment source, consists of grains of irregular shape that give selected area diffraction (SAED) patterns reflecting dominant turbostratic stacking. Analytical electron microscopy (AEM) analyses indicate that K+ is the dominant interlayer cation; the mean composition is approximately K0.7(Al3.3Fe(III)0.3Mg0.5)(Al0.5Si7.5)O20(OH)4. Such smectite is implied to be detrital in part because it is similar to smectite known to be deposited by the Colorado River.

Smectite from the hypersaline mud flat occurs as aggregates of small subhedral pseudohexagonal plate or lath-shaped crystals ≤250 nm in diameter, with thicknesses varying between three and ten layers. The SAED patterns reflect substantial turbostratic stacking, but with a greater frequency of interlayer coherency as compared with detrital smectite. Crystals from greater sediment depths are larger and more nearly euhedral. This smectite is dominantly trioctahedral, with mean composition approximately K0.7(Al0.7Fe(III)0.5Mg4.45)(Al1.2Si6.8)O20(OH)4 (saponitic). This smectite is inferred to be dominantly authigenic in origin.

The X-ray diffraction (XRD) and STEM/AEM data collectively imply that detrital aluminous dioctahedral smectite reacts to form authigenic Mg-rich trioctahedral smectite, driven in part by the high Mg2+/ Ca2+ ratio of pore waters. Such early-formed Mg-rich smectite may be the precursor for the trioctahedral mixed-layer smectite, corrensite, and chlorite assemblages found in ancient marine evaporative sequences. These results also add to the accumulating evidence that interlayer K+ in marine smectite is fixed during the earliest stages of marine diagenesis near the sediment water interface.