Showing papers in "Clays and Clay Minerals in 2007"

Soil hydroxy-interlayered minerals: a re-interpretation of their crystallochemical properties

Abstract: Hydroxy-interlayered minerals (HIMs) are typical of moderately acidic soils. Barnhisel and Bertsch (1989) defined the hydroxy-interlayered clay minerals as a solid-solution series between smectite, vermiculite and pedogenic or aluminous chlorite end-members. Their experimental data for the relationship between the decrease in cation exchange capacity (CEC) and the amount of Al fixed in the interlayers of smectites and vermiculites is reinterpreted using calculated structural, chemical and X-ray diffraction (XRD) evidence. The adsorbed Al ions are in a 6-fold coordination state: [Al(OH)x(H2O)y](3−x)+ with x + y = 6. The polymerization process occurs before saturation of the exchange sites by Al ions. Some of the adsorbed Al ions form polynuclear cations keeping a constant positive charge. X-ray diffraction patterns of oriented preparations in the ethylene glycol-solvated state suggest that HIMs consist of randomly interstratified expandable and chlorite-like layers (17 and 14.2 A). Chlorite-like layers result from the selective adsorption of Al complex ions in specific interlayer zones that behave similarly to Al-chlorite (donbassite-like) with incomplete (60%) ‘gibbsite-like’ sheets (chlorite60). Using this framework, HIM XRD patterns can be interpreted by comparison with calculated chlorite60-dismectite mixed-layer mineral patternss using the NEWMOD software.

Fougerite, a new mineral of the pyroaurite-iowaite group: Description and crystal structure

Abstract: Fougerite (IMA 2003-057) is a mixed M(II)-M(III) hydroxysalt of the green rust group, where M(II) can be Fe or Mg, and M(III) is Fe. The general structural formula is: ${[{\rm{Fe}}_{1 - }^{2 + }x{\rm{Fe}}_x^{3 + }{\rm{M}}{{\rm{g}}_y}{({\rm{OH}})_{2 + 2y}}]^{ + x}}{[x{\rm{/}}n{A^{ - n}}.m{{\rm{H}}_2}{\rm{O}}]^{ - x}}$ where A is the interlayer anion and n its valency, with 1/4 ≼ x/(1+y) ≼ 1/3 and m ≼ (1−x+y). The structure of green rusts and parent minerals can accommodate a variety of anions, such as OH−, Cl−, ${\rm{CO}}_3^{2 - },\;{\rm{SO}}_4^{2 - }$ . The structure of the mineral was studied by Mossbauer, Raman and X-ray absorption spectroscopies (XAS) at the FeK edge. Mossbauer spectra of the mineral obtained at 78 K are best fitted with four doublets: D1 and D2 due to Fe2+ (isomer shift δ ≈ 1.27 and 1.25 mm s−1, quadrupole splitting ΔEQ ≈ 2.86 and 2.48 mm s−1, respectively) and D3 and D4 due to Fe3+ (δ ≈ 0.46 mm s−1, ΔEQ ≈ 0.48 and 0.97 mm s−1, respectively). Microprobe Raman spectra obtained with a laser at 514.53 nm show the characteristic bands of synthetic green rusts at 427 and 518 cm−1. X-ray absorption spectroscopy shows that Mg is present in the mineral in addition to Fe, that the space group is and the lattice parameter a ≈ 0.30–0.32 nm. The mineral forms by partial oxidation and hydrolysis of aqueous Fe2+, to give small crystals (400–500 nm) in the form of hexagonal plates. The mineral is unstable in air and transforms to lepidocrocite or goethite. The name is for the locality of the occurrence, a forested Gleysol near Fougeres, Brittany, France. Its characteristic blue-green color (5BG6/1 in the Munsell system) has long been used as a universal criterion in soil classification to identify Gleysols. From a thermodynamic model of soil-solution equilibria, it was proposed that for the eponymous mineral, Fougeres-fougerite, OH− may be the interlayer anion. In other environments, the interlayer anion may be different, and other varieties of fougerite may exist. Fougerite plays a key role in the pathways of formation of Fe oxides.

The nature of structure-bonded h2o in illite and leucophyllite from dehydration and dehydroxylation experiments

Abstract: Thermogravimetric analysis combined with mass spectrometry was used to study H2O bound to samples of illite-1 M , illite-2 M 2 and leucophyllite-1 M. Samples were heated in a helium atmosphere at different temperatures and after heating at each given temperature were cooled to 35°C. Each cycle in the mass 18 spectrum of each illite sample contains a low-temperature peak at 60–80°C, a medium-temperature peak at 340–360°C, and a high-temperature peak at a temperature that is very close to the maximum temperature of sample heating of a given cycle. Within each heating-cooling cycle, the sample weight at the beginning of cooling is lower than that at the end of the same cooling stage because of H2O resorption. However, the number of H2O molecules released during each medium-temperature heating cycle is equal to the number of H2O molecules resorbed during the corresponding cooling stages. The weight losses, under medium-temperature heating, of the illite samples are related to dehydration when H2O molecules located in K-free sites of the illite interlayers are removed. The medium-temperature peak is reproducible for each cycle because during each cooling stage the illite interlayers resorb the same number of H2O molecules that were lost during the preceding dehydration. Two distinct features are characteristic of leucophyllite during heating-cooling treatments. First, the number of H2O molecules resorbed during cooling is significantly greater than the number of H2O molecules lost during dehydration. Second, the medium-temperature peaks in the spectrum appear only in the last five cycles and the maximum-peak temperature is 450–460°C. These data indicate that the heating-cooling treatments are accompanied by partial rehydroxylation. This rehydroxylation occurs during each cooling stage when a small number of resorbed H2O molecules are trapped in the interlayers, although most migrate into the octahedral sheet of the 2:1 layers and reform as OH groups. The crystal chemical factors responsible for the dehydration and rehydration as well as for the rehydroxylation reactions are discussed and speculation about the origin of the low- and medium-temperature H2O losses is presented.

Water retention of two natural compacted bentonites

Abstract: This work presents the water retention curves obtained for two natural bentonites compacted at different dry densities The density of the bentonite was kept constant during the determination, for which specific methodologies were developed The materials tested are the FEBEX and the MX-80 bentonites, in the first of which divalent cations (Ca and Mg) predominate in the exchange complex; MX-80 is mainly sodic The water retention capacity of the FEBEX bentonite is greater, although the difference between both bentonites becomes smaller towards low suctions The effect of dry density on the water retention curve is very small or imperceptible for suctions >10 MPa, and below this value the lower the density of the bentonite, the greater its water content The basal spacing of the samples equilibrated at different suctions has been measured and found to be in the order of those measured by other authors in powder samples equilibrated to the same suctions The study was performed in the framework of projects concerning the engineered bentonite barrier of high-level radioactive waste repositories

Phosphate and glyphosate adsorption by hematite and ferrihydrite and comparison with other variable-charge minerals

Abstract: Adsorption by synthetic 2-line ferrihydrite and hematite of glyphosate and phosphate, separately and together, was compared with adsorption results for goethite, gibbsite and two kaolinites in order to determine adsorption differences and similarities, in particular competition and phosphate preference, of these variable-charge minerals. Hematite rapidly adsorbed both compounds, while adsorption by ferrihydrite was slow, in particular of glyphosate, probably because of very slow diffusion of the bulky glyphosate molecules into interior sites in ferrihydrite particles. Accordingly, the Langmuir adsorption capacity of glyphosate (GAC) was considerably smaller (1.85 µmol m−2)than GAC for hematite (2.61 µmol m−2). The phosphate adsorption capacities (PAC) for ferrihydrite and hematite were more alike, 2.91 µmol m−2 and 2.85 µmol m−2, respectively. Differences between surface coordination (mono- or bidentate) may also contribute to the observed differences but conflicting information about the nature of the surface complexes makes this a difficult contributary factor to assess. The minerals were found to exhibit great variation in extent of competition and phosphate preference. Little competition and phosphate preference characterized hematite adsorption, while phosphate almost completely outcompeted glyphosate on goethite; ferrihydrite adsorption fell between these extremes. These differences may be attributed to different numbers of common (competitive) and specific (selective) adsorption sites on the three Fe oxides with a decreasing number of common sites in the order: goethite>>ferrihydrite>hematite, i.e. almost all goethite sites are common but with strong phosphate preference, while most hematite sites are specific for either glyphosate or phosphate. Alternatively, the result may be explained by adsorption in more planes, e.g. glyphosate adsorption onto the inner-Helmholtz-plane-adsorbed phosphate. For all six minerals compared, desorption of glyphosate following phosphate addition was found to be significantly correlated with the difference between the amounts of phosphate and glyphosate adsorbed indicating that this difference may be used as a competition index for predicting the influence of phosphate on glyphosate adsorption.

Clay mineralogy and chemistry of halloysite and alunite deposits in the turplu area, balikesir, turkey

Abstract: A field-mapping and crystal-chemical study of two alunite- and halloysite-rich deposits in the Turplu area, situated northwest of Balikesir on the Biga Peninsula of northwest Turkey reveals a mineralogically diverse and a potentially economic clay deposit. The mineral assemblage along fault zones is dominated by halloysite and sometimes alunite. The alunite is nearly end-member in composition (a = 6.995 A, c = 17.195 A) often occurring with a minor Ca phosphate phase. Of the two deposits studied, the more northerly mine contains more alunite relative to halloysite. Geochemical alteration indices suggest that the northern mine has experienced a slightly greater degree of hydrothermal modification. Halloysite is found in both hydrated and dehydrated states and assumes a tubular morphology. Observations by transmission and scanning electron microscopy are consistent with a model of halloysite dehydration, where the shapes transform from an open-hole tubular morphology to a closed-hole unfurled morphology. Mineral paragenesis includes the effects of initial deposition of volcanic tuffs and andesite on top of karstic terrain. The contact between altered volcanics and underlying limestones is irregular and appears to have provided a mechanism to flush both hydrothermal and meteoric waters through the volcanics. Periods of hydrothermal alteration (hypogene) contemporaneous with extensional and strike-slip faulting have resulted in alunite and halloysite deposits. Hydrothermal alteration is concentrated near the fault zones. Because of subsequent weathering (supergene) away from the fault zones, much of the andesitic volcanic rocks have been altered to a more smectite-rich and kaolinite-bearing assemblage. The deposits continue to be both plastically deformed in the alunite/halloysite regions and to undergo brittle deformation in the saprolitized volcanics. Tectonic deformation has mixed the contacts, such that limestone blocks are entrained into parts of the alteration zones. Gibbsite and gypsum are common weathering products associated with limestone block inclusions. Genetic models for the origins of alunite-halloysite deposits in NW Turkey should consider as possible influencing factors the underlying lithologies, the extent of hydrothermal alteration, and recent weathering by meteoric fluids. In the case of the Turplu deposits, karstic limestones, hydrothermal circulation of sulfate-rich waters, and a post-alteration history of meteoric weathering were all important factors in their formation.

Interlayer structure and dynamics of alkylammonium-intercalated smectites with and without water: A molecular dynamics study

Abstract: The structure and dynamics of alkylammonium-intercalated smectites were simulated using molecular dynamics employing the clayff-CVFF force field, the reliability of which was firstly validated for these systems. The layering behaviors of alkyl chains confirm the scenarios of the monolayer, transition and bilayer configurations for short, medium-length and long carbon tails, respectively. In the systems without water, the alkylammonium groups are all anchored firmly above the surface six-member rings through H bonds between ammonium hydrogen and surface oxygen, and the alkyl tails are a little more mobile. With water involved, some ammoniums are dragged out of the potential barriers of the six-member rings by water molecules through the strong H bonds between water oxygen and ammonium hydrogen. The intercalated water scarcely affects the basal spacing, alkyl chain layering or alkylammonium dynamics. It is also found that the systems with alkyl chains of 11 to 14 exhibit the greatest density, resulting in the extremely limited mobility of the intercalated species.

Weathering sequences of clay minerals in soils along a serpentinitic toposequence

Abstract: There has been limited research on clay mineral transformation in serpentinitic soils under humid tropical conditions. In this study, four soil pedons were selected along a toposequence from the summit (Entisol), shoulder (Vertisol), backslope (Alfisol) to footslope (Ultisol) positions to explore the contributions and the significance of landscape and weathering status of serpentinitic rock with regard to clay mineral transformations in eastern Taiwan. Experimental results indicated that the large amount of dithionite-citrate-bicarbonate-extractable Fe (Fed) and clay in the subsurface horizon were mainly caused by the strong leaching potential from intensive rainfall and weathering of the fine-grained parent rocks. The clay mineralogy reflected the clear weathering trend of the soils along the toposequence: (1) the soils on the summit and shoulder contained smectite and serpentine, which are predominant in the young soils derived from serpentinitic rocks; and (2) vermiculite gradually increased in the relatively old soils on backslope and footslope. The mineralogical transformations observed along the toposequence indicated that chlorite and serpentine, initially present in the Entisol on the summit, weather into smectite and interstratified chlorite-vermiculite in the intermediate soil on the shoulder under strong leaching and oxidizing conditions. Furthermore, vermiculite formed as the major weathering product of chlorite and smectite in the soil developed on the backslope. In addition to vermiculite, kaolinite and quartz formed in the soils on the footslope with the greatest concentration of Fed along the toposequence.

NONTRONITE PARTICLE AGGREGATION INDUCED BY MICROBIAL Fe(III) REDUCTION AND EXOPOLYSACCHARIDE PRODUCTION

Abstract: Clay particle aggregation affects a number of environmental processes, such as contaminant sorption/desorption, particle movement/deposition, and sediment structure and stability, yet factors that control clay aggregation are not well understood. This study was designed to investigate how microbial reduction of Fe(III) in clay structure, a common process in soils and sediments, affects clay-particle aggregation. Microbial Fe(III) reduction experiments were conducted with Shewanella putrefaciens CN32 in bicarbonate buffer with structural Fe (III) in nontronite as the sole electron acceptor, lactate as the sole electron donor, and AQDS as an electron shuttle. Four size fractions of nontronite (D5–D95 of 0.12–0.22 µm, 0.41–0.69 µm, 0.73–0.96 µm and 1.42–1.78 µm) were used to evaluate size-dependent aggregation kinetics. The extent of Fe(III) bioreduction and the amount of exopolysaccharide (EPS), a major biopolymer secreted by CN32 cells during Fe(III) bioreduction, were measured with chemical methods. Nontronite particle aggregation was determined by photon correlation spectroscopy and scanning electron microscopy. The maximum extent of Fe(III) bioreduction reached 36% and 24% for the smallest and the largest size fractions, respectively. Within the same time duration, the effective diameter, measured at 95% percentile (D95), increased by a factor of 43.7 and 7.7 for these two fractions, respectively. Because there was production of EPS by CN32 cells during Fe(III) reduction, it was difficult to assess the relative role of Fe(III) bioreduction and EPS bridging in particle aggregation. Thus, additional experiments were performed. Reduction of Fe(III) by dithionite was designed to examine the effect of Fe(III) reduction, and pure EPS isolated from CN32 cells was used to examine the effect of EPS. The data showed that both Fe(III) reduction and EPS were important in promoting clay mineral aggregation. In natural environments, the relative importance of these two factors may be dependent on local conditions. These results have important implications for understanding factors in controlling clay particle aggregation in natural environments.

Oligocene clay mineralogy of the linxia basin: evidence of paleoclimatic evolution subsequent to the initial-stage uplift of the tibetan plateau

Abstract: The clay mineral content of the Oligocene sediments in the Linxia Basin has been investigated using X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The clay mineral assemblages are mainly mixed-layer illite-smectite (I-S), illite, kaolinite and minor palygorskite in the early-Middle Oligocene deposits, mixed-layer I-S, illite and kaolinite in the Middle Oligocene deposits, mainly illite and chlorite (usually >50–70 vol.%), mixed-layer I-S, and trace to minor palygorskite in the late Oligocene sediments, respectively. The mineral assemblage indicates a warm and seasonally humid climate in the Middle Oligocene, with an episode of warm and dry conditions in the early stage of the Middle Oligocene, and a trend of temperature decrease and more arid conditions in the late Oligocene. Climate evolution in the Oligocene corresponds with the significant elevation change in central Tibet since late Oligocene, and therefore, suggests that tectonic-forced cooling of climate took place in Linxia in the northeast margin of the Tibetan Plateau. The ubiquitous mixed-layer I-S and carbonates throughout the Oligocene sediments reflect relatively small fluctuations in climate conditions during the epoch. The changes in clay mineral components and feldspars in the late Oligocene suggest a variation in the source of clastic materials, which probably reflects an increase in erosion of soils and poorly weathered parent rock in more elevated or high-relief source areas during this period of tectonic uplift.

Correlation between surface area and Atterberg limits of fine-grained soils

Abstract: As the water content is increased, the consistency of a fine-grained soil changes from a semi-solid state to a plastic state and finally to a liquid state The plastic limit (PL) is the point at which the consistency, caused by the soil water content, is transformed from a semi-solid state to a plastic state The liquid limit (LL) is the point at which the consistency is transformed from a plastic state to a liquid state The plastic limit and liquid limit are often collectively referred to as the Atterberg (or consistency) Limits Although the liquid and plastic limits are easily determined, fundamental interpretations of the limits and quantitative relationships between their values and compositional factors are more complex Previous studies examined artificially-prepared soil samples that contained monomineralic clays and a non-clay substance(quartz sand) These studies have shown that in soils without expandable clays the PL and LL water contents were mostly related to surface area and clay content For soils that contain expandable clays, the PL and LL values are also dependent on interlayer water content Hence, expandable clay mineral contents are needed to calculate PL and LL values These relationships have been presented in a general analytical form The aim of these investigations was to identify practical applications Mineral compositions and surface areas of five randomly selected natural soil samples were used to estimate PL and LL values The estimated values were compared to experimentally measured liquid limits (by the ‘fall-cone’ test) and plastic limit (by the ‘rolling thread’ test) values The measured PL values ranged from 1877 to 4492% and the LL values from 3119 to 8210% The differences between estimated and measured Atterberg Limits were 30–71% for thePL and 27–78% for the LL Minor differences in measured and estimated Atterberg Limits were probably due to soil organic matter (12–27%)

Adenine, adenosine, ribose and 5'-amp adsorption to allophane

Abstract: We have investigated the adsorption of adenine, adenosine, ribose, and adenosine-5′-phosphate (5′-AMP) by allophane at pH 4, 6 and 8. Adenine, adenosine and ribose gave similar isotherms, i.e. adsorption increased regularly with solution concentration and decreased in the order: pH 8 > pH 6 > pH 4. Allophane had a greater affinity for 5′-AMP than for adenine, adenosine or ribose. Further, the extent of adsorption for 5′-AMP increased in the order: pH 8 ≪ pH 6 ≈ pH 4. The adsorption of 5′-AMP at pH 4 and pH 6 was about 60 times greater than at pH 8. The strong adsorption of 5′-AMP accords with the well known high phosphate-retention capacity of allophane and allophane-rich soils. The experimental data may be rationalized in terms of the pH-dependent charge characteristics of the organic solutes and allophane. The large propensity of allophane to retain 5′-AMP is ascribed to ligand exchange between the phosphate of 5′-AMP and the hydroxyl of (HO)Al(OH2) groups, exposed at perforations on the wall of allophane spherules, giving rise to a surface (chelation) complex. The high affinity of nucleotides for allophane has implications for the possible role of allophane in the abiotic formation of RNA-type polynucleotides although nucleotide ‘immobilization’ by surface complexation might hinder RNA oligomerization.

Combined near-infrared and x-ray diffraction investigation of the octahedral sheet composition of palygorskite

Abstract: The octahedral composition of palygorskite in more than 300 samples from the Pefkaki deposit, W. Macedonia, Greece, has been studied by near-infrared (NIR) and X-ray diffraction (XRD), and evaluated according to the formula $y{\rm{M}}{{\rm{g}}_5}{\rm{S}}{{\rm{i}}_8}{{\rm{O}}_{20}}{\left( {{\rm{OH}}} \right)_2} \cdot x{\rm{M}}{{\rm{g}}_2}{\rm{Fe}}_{\rm{2}}^{{\rm{III}}}{\rm{S}}{{\rm{i}}_8}{{\rm{O}}_{20}}{\left( {{\rm{OH}}} \right)_2} \cdot \left( {1 - x - y} \right)$ Mg2Al2Si8O20(OH)2. Included in the study were PFl-1 and several commercial palygorskites. Our analysis of 2nd derivative NIR spectra shows that the dioctahedral composition is adequately described by three sharp overtone bands representing AlAlOH, AlFeIIIOH and FeIIIFeIIIOH in M2 dioctahedral sites, and that the summed intensity of these bands is proportional to the amount of dioctahedral component present (1−y). The samples show large variations in the degree of dioctahedral FeIII-for-Al substitution with FeIII occupying up to 70% of the dioctahedral M2 sites. Ternary analysis shows that the distribution of dioctahedral Al and FeIII is not random, but displays a tendency towards homoionic pairing. An overtone band at 7214 cm−1 and several combination bands are indicative of a trioctahedral Mg3OH component (y), and their appearance correlates with a distinct palygorskite signature in thermogravimetric analysis. Nevertheless, these bands cannot be used reliably for the quantification of a trioctahedral palygorskite component due to their close similarity to those of sepiolite. To circumvent this problem, we have evaluated y indirectly by calculating the difference between 1−y and the total concentration of palygorskite determined by the normalized intensity of the d110 XRD peak of palygorskite at 10.4 A. Using this methodology, we have found that the samples conform to a trioctahedral limit of y ≈ 0.55, although within this limit they display large variations in octahedral character. Finally, we extend the above methodology to PLS chemometrics and show how NIR can be used to determine palygorskite content routinely in multimineralic geological samples.

Crystallochemical characterization of the palygorskite and sepiolite from the allou kagne deposit, senegal

Abstract: The Allou Kagne (Senegal) deposit consists of different proportions of palygorskite and sepiolite, and these are associated with small quantities of quartz and X-ray amorphous silica as impurities. No pure palygorskite or sepiolite has been recognized by X-ray diffraction. Textural and microtextural features indicate that fibrous clay minerals of the Allou Kagne deposit were formed by direct precipitation from solution. Crystal-chemistry data obtained by analytical/transmission electron microscopy (AEM/ TEM) analyses of isolated fibers show that the chemical composition of the particles varies over a wide range, from a composition corresponding to palygorskite to a composition intermediate between that of sepiolite and palygorskite, but particles with a composition corresponding to sepiolite have not been found. Taking into account the results from selected area electron diffraction and AEM-TEM, fibers of pure palygorskite and sepiolite have been found but it cannot be confirmed that all of the particles analyzed correspond to pure palygorskite or pure sepiolite because both minerals can occur together at the crystallite scale. In addition, the presence of Mg-rich palygorskite and very Al-rich sepiolite can be deduced. It is infrequent in nature that palygorskite and sepiolite appear together because the conditions for simultaneous formation of the two minerals are very restricted. The chemical composition of the solution controls the formation of the Allou Kagne sepiolite and palygorskite. The wide compositional variation appears as a consequence of temporary variations of the chemical composition of the solution.

Characterization of alteration products in tephra from haleakala, maui: a visible-infrared spectroscopy, mössbauer spectroscopy, xrd, empa and tem study

Abstract: Altered basaltic tephra from Haleakala, Maui, are characterized using multiple techniques in order to identify the minerals formed under a variety of conditions and to understand the soil formation processes here. We collected samples that are representative of typical bulk weathered material in the crater, as well as solfataric alteration in a hydrothermal environment. For this study X-ray diffraction, electron probe microanalysis, scanning electron microscopy and transmission electron microscopy are coupled with spectroscopic techniques including Mossbauer, visible-infrared reflectance, transmission infrared, and thermal infrared emission spectroscopies to analyze these samples. The unaltered tephra are composed of feldspar, glass, pyroxene and olivine. Observed alteration products include Fe oxides, phyllosilicates and sulfates, as well as SAED amorphous Al-Si-bearing material. These samples are potential analogs for altered volcanic material on Mars as the pedogenic influences and contact with plants and animals are minimal. Results from this study may help to determine spectral signatures of these samples that could be used for identification on Mars of the minerals observed here.

Fe(III)-modified montmorillonite and bentonite: Synthesis, chemical and UV-VIs spectral characterization, arsenic sorption, and catalysis of oxidative dehydrogenation of propane

Abstract: Two major species were identified in Fe-treated montmorillonite: monomeric or dimeric hydroxoaqua cations ${\rm{Fe}}({\rm{OH}})_x^{(3 - x) + }$ (form I), and polymeric structures with edge-shared Fe(O,OH)6 (form II). These species have different electron spectra (absorption maximum is 29,600 cm−1 in form I, and 26,000 and 28,000 cm−1 in form II), chemical and thermal stability, and electrochemical behavior. Form I behaves as a partly exchangeable cation in interaction with Cu2+ from Cu-trien solution and Ni2+ from Ni-EDTA, that can be used for selective quantitative analysis. On heating above the dehydration temperature (∼100–150°C) montmorillonite with Fe3+ in form I is converted to a mica-like structure and Fe3+ ions are fixed more strongly in the montmorillonite structure. Form II behaves similarly to hydrous ferric oxides, but its thermal crystallization to hematite is postponed to ∼500–600°C. The Fe3+ cations in the interlayer space are much less thermally stable than Al pillars in pillared interlayered clays (PILCs). Form I is more active in oxidative dehydrogenation of propane, while form II is the active species in sorption of As and the non-specific combustion of propane. To produce only form II by the treatment of montmorillonite with Fe3+, its load must be kept below ∼20 wt.%; otherwise the usual hydrous ferric oxides are formed.

Altered volcanic ash as an indicator of marine environment, reflecting pH and sedimentation rate : Example from the ordovician kinnekulle bed of baltoscandia

Abstract: The composition of altered volcanic ash of the Late Ordovician Kinnekulle bed was studied in geological sections of the Baltic Paleobasin. The composition of altered ash varies with paleosea depth from northern Estonia to Lithuania. The ash bed in shallow shelf limestones contains an association of illite-smectite (I-S) and K-feldspar, with the K2O content ranging from 7.5 to 15.3%. The limestone in the transition zone between shallow- and deep-shelf environments contains I-S-dominated ash with K2O content from 6.0 to 7.5%. In the deep-shelf marlstone and shale, the volcanic ash bed consists of I-S and kaolinite with a K2O content ranging from 4.1 to 6.0%. This shows that authigenic silicates from volcanic ash were formed during the early sedimentary-diagenetic processes. The composition of the altered volcanic ash can be used as a paleoenvironmental indicator showing the pH of the seawater or porewater in sediments as well as the sedimentation rate.

Clay mineral assemblages and vitrinite reflectance in the Laga Basin (Central Apennines, Italy): what do they record?

Abstract: Temperature-dependent clay mineral assemblages and vitrinite reflectance data have been used to investigate levels of diagenesis from the Messinian Laga Basin in the Central Apennines developed at the footwall of the Sibillini Mts. and the Gran Sasso Massif. Data are from stratigraphic units forming the main siliciclastic basin fill up to Middle Messinian gypsum-arenites and its pre-orogenic substratum. Specifically, the largest Rom% values and percentages of illite layers in illite-smectie (I-S) are found in the basin depocenter and at the footwall of the main carbonate thrust sheets. Smaller Rom% values, and percentage of illite layers in I-S characterize less subsided sectors surrounding the depocenter. The X-ray diffraction data were treated using decomposition methods and the peaks identified were rationalized in terms of discrete and/or mixed-layer phases. Complex clay mineral assemblages were found in the Laga Fm. including three sub-populations of illitic material corresponding to authigenic and detrital components. I-S mixed layers record the maximum paleotemperature the Laga Fm. experienced, which is directly related to its burial history. Kubler index (KI) data, however, suggest higher temperatures related to detrital K-micas inherited from the uplift of the Alpine-Apennines chain. A tentative calculation of paleotemperatures from selected data of organic and inorganic parameters is also proposed and compared with recent sedimentological, stratigraphic and structural data. We conclude that the Laga Basin fill never experienced temperatures of >100–110°C, generally due to variable sedimentary loading, whereas localized anomalous heating is due to the effect of the tectonic emplacement and subsequent local erosion of the Sibillini and Gran Sasso thrust sheets.

Clay mineral formation during podzolization in an alpine environment of the Tatra Mountains, Poland

Abstract: The processes of clay mineral formation were studied in seven podzol profiles developed on granitic regoliths in the Polish part of the Tatra Mountains. The selected profiles have similar parent material and macroscopically represent different stages of soil development (from initial to advanced). Bulk soil material (<2 mm fraction) and separated clay fractions (<2 µm) were studied using a petrographic microscope, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy-energy-dispersive spectrometry methods. The mineral compositions of the bulk soil samples are more or less the same (quartz, feldspars, mica and minor amounts of other phyllosilicates). The clay fractions are composed of mica and mixed-layer minerals which contain hydrated interlayers of vermiculitic and/or smectitic type, and kaolinite. Smaller amounts of chlorite, feldspars and quartz were also identified. Chlorite is present almost exclusively (except for one profile) in lower soil horizons (C, B/C, B). The amount of minerals with hydrated interlayers increases up the profiles. Kaolinite is present in all the samples except for the lowermost soil horizons (C) of two of the profiles. In some of the B horizons, the formation of hydroxy interlayers within hydrated interlayers is observed. The main processes of clay mineral formation recognized in the soils studied are: inheritance from the parent rocks; crystallization of kaolinite from soil solutions; the formation of dioctahedral vermiculite at the expense of inherited dioctahedral mica, and the formation of dioctahedral smectite at the expense of vermiculite. The recognized sequence of transformation is as follows: M → R0 M-V (12 A or 14 A) → R0 M-12 A V → R1 M-12 A V → 12 A V → V-S → S. Observed formation of hydroxy interlayers seems to be pH dependent, starting when the pH ⩾ 4.4. The process of dissolution of primary silicates occurring simultaneously with the transformation is also documented.

ADSORPTION OF Eu3+ TO SMECTITES AND FLUORO-TETRASILICIC MICA

Abstract: The adsorption of Eu 3+ from aqueous solution to natural Na + -montmorillonite (Kunipia F), synthetic saponite (Sumecton SA) and synthetic fluoro-tetrasilicic mica (Na + -TSM) clay samples was investigated. Adsorption capacities derived from the isotherms were 1.02, 0.71 and 1.00 meq/g of clay, respectively, for Kunipia F, Sumecton SA and Na + -TSM. The adsorption capacities were comparable to the cation exchange capacities of the clays, which were 1.19, 0.71 and 0.94 meq/g of clay, respectively. The greater slope of the TSM adsorption isotherm relative to the montmorillonite and saponite isotherms indicates a high affinity of Eu 3+ for Na + -TSM. The high affinity of TSM for Eu 3+ was thought to be related to the large electronegativity of the octahedral fluorine groups in TSM. Photoluminescence of adsorbed Eu 3+ was observed for saponite and TSM, but not for montmorillonite. Quenching of Eu 3+ luminescence by Fe in the montmorillonite structure is the probable reason for this phenomenon. The luminescence intensity varied with the amount of adsorbed Eu 3+ for saponite and TSM as a result of self-quenching.

Inheritance vs. neoformation of kaolinite during lateritic soil formation : A case study in the middle Amazon basin

Abstract: The tropical weathering of sedimentary kaolin deposits from the plateaux surrounding Manaus (Alter do Chao formation, Amazon basin, Brazil) leads to the in situ formation of thick kaolinitic soils. The structural changes of kaolinite have been investigated quantitatively by infrared spectroscopy and electron paramagnetic resonance. Both techniques consistently show that each sample contains two types of kaolinite in various proportions. The progressive decrease in kaolinite order from the bottom to the top of the profile results from the gradual replacement of an old population of well-ordered kaolinite, typical of the underlying sedimentary kaolin, by a more recent generation of poorly ordered soil kaolinite. The vertical pattern of kaolinite replacement differs from that of the transformation of Fe oxides and oxyhydroxides previously observed in the same profile. The inherited fraction of well-ordered kaolinite ranges from 60% at a depth of 9 m to 30% in the upper levels of the soil. The persistence of sedimentary kaolinite in the upper horizons suggests that the rate of kaolinite transformation is relatively slow at the time scale of lateritic soil formation. Kaolinite inheritance unlocks the lateritic record of past weathering conditions.

Silicic acid magadiite as a host for n-alkyldiamine guest molecules and features related to the thermodynamics of intercalation

Abstract: Somen-alkyldiamines with thegeneral formulae H2N(CH2)nNH2 (n = 2–5) were intercalated into the layered silicic acid magadiite, from aqueous solution, causing an increase in the original interlayer distance of 1172 pm. The synthetic magadiite and all intercalated compounds were characterized by elemental analysis, infrared vibrational spectroscopy, X-ray diffractometry, 29Si nuclear magnetic resonance in the solid state, thermogravimetry, scanning electron microscopy, surface area and porosity. The intercalation was followed through a batch-wise method at 298±1 K and gave the maximum amounts 3.70, 2.80, 1.75 and 1.18 mmol g−1, for n varying from 2 to 5, respectively. The well characterized magadiite was calorimetrically titrated in a heterogeneous medium, to obtain the thermodynamic data of intercalation at the solid/liquid interface. Linear correlations were obtained for the number of moles intercalated (Nf), th einterlamellar distance (d) and the specific enthalpy (Δinth) values of the interactive process as a function of the number of C atoms of the aliphatic organic chains (nC) for n-alkyldiamine: Nf = (5.36±0.25) − (0.86±0.07)nC, d = (1406.6±1.9) + (20.9±0.5)nC and Δinth = (5.96±0.25) + (0.06±0.01)nC. The basic N guest atom/silanol acidic center interactions inside the host nanospace gallery gave exothermic enthalpies, positive entropies and negative Gibbs free energy values. This set of data suggests the spontaneity of these intercalation reactions.

Nanometer-scale chemical modification of nano-ball allophane

Abstract: Nano-ball allophane is a hydrous Al silicate with a hollow-sphere morphology that contains some defects or pores along the spherule walls. Enlargement of the pore openings by dilute alkali treatment was confirmed by cation exchange capacity determinations using various alkylammonium cations as replacement cations. An allophane sample with a low Si/Al ratio (0.67) was equilibrated with 10 mM CaCl2 (pH = 6.0) and the Ca2+ retained was extracted using aqueous 1 M NH4C1 or alkylammonium chloride salts. The Ca2+ extracted by ${\rm{NH}}_4^ + $ was 15.1 cmolc kg−1, but ${\rm{C}}{{\rm{H}}_3}{\rm{NH}}_3^ + $ (mean diameter = 0.38 nm) only extracted 7.9 cmolc kg−1 of Ca2+. After 10 mM NaOH treatment (0.25 g:100 mL) of the allophane, the Ca2+ extracted by ${\rm{NH}}_4^ + $ was 29.7 cmolc kg−1, 29.6 cmolc kg−1 by ${\rm{C}}{{\rm{H}}_3}{\rm{NH}}_3^ + $ , and 29.4 cmolc kg−1 by ${{\rm{(C}}{{\rm{H}}_3}{\rm{)}}_2}{\rm{NH}}_2^ + $ . The extraction of Ca2+ by the large ${{\rm{C}}_2}{{\rm{H}}_5}{\rm{NH}}_3^ + $ cation (mean diameter = 0.46 nm) only decreased to 26.1 cmolc kg−1, indicating that pore diameters were enlarged from ∼0.35 to 0.45 nm. The significant increase in Ca2+ retention after NaOH treatment was attributed to the dissociation of increased numbers of newly exposed silanol groups in the enlarged pores. The low Si/Al ratio of the NaOH-dissolved material (0.35) and the decreased intensity of the 348 cm−1 IR band also suggested selective dissolution of the pore region. For allophane with a high Si/Al ratio (0.99) and much accessory polymeric Si, dissolution of polymeric Si and of the pore region occurred simultaneously. Alkali treatment produced a smaller increase in pore size and Ca2+ retention for allophanes with large Si/Al ratios than for allophanes with small Si/Al ratios. It was concluded that by altering the dilute alkali treatment conditions and varying the Si/Al ratio of allophane, the extent of structural modification or pore enlargement of the hollow spheres might be controlled.

Thermodynamics of organic cation exchange selectivity in smectites

Abstract: The selectivities of clay minerals for larger organic cations over smaller ones have been attributed to favorable clay-organic interactions in clay interlayers and to hydrophobic effects resulting from (partial) dehydration of organic cations in the clay interlayers, but the magnitudes of these energy components have not been estimated. The objective of this study was to differentiate and quantify the contributions of clay-phase and aqueous-phase energy changes to the overall thermodynamics of cation exchange, and thereby to determine which forces control the general selectivity of smectites for organic cations. We compiled literature measurements and estimates for the free energies of overall cation exchange reactions and also for the free energies of organic cation hydration. Our study suggests that organic cation-exchange thermodynamics can be broken into three classes: (1) For two organic cations with identical head-groups, the difference in their cation exchange selectivities is driven almost quantitatively by the difference in their free energies of hydration. Here, the mechanism for organic cation selectivity is almost pure hydrophobic expulsion of the larger cation from water. The clay interlayer simply behaves like a subaqueous phase into which the least hydrophilic organic cations partition and the essentials of such cation exchange selectivity can be explained without any favorable clay-organic interactions. (2) For two organic cations with rather different head-groups, the difference in their cation exchange selectivities is just a small percentage of the difference in their free energies of hydration. This indicates that the clay phase interacts much more strongly with the cation having the smaller head-group, as might be expected on the basis of simple electrostatics. Here, the clay has an intrinsic strong preference for the cation with smaller head-group yet ‘selects’ for the cation with larger head-group because the aqueous-phase preference for the cation with smaller head-group is even stronger than the clay preference. (3) When the clay is already substantially loaded with organic cations, then van der Waals forces apparently can play a significant role in determining organic cation exchange selectivity differences.

Ab initio calculations of relative stabilities of different structural arrangements in dioctahedral phyllosilicates

Abstract: An ab initio theoretical approach has been used to calculate optimized geometries and the relative energies of various compositional arrangements in structures of dioctahedral smectites based on models consisting of two unit-cells. These calculations indicate that the energy differences between structures having vacancies in sites with cis- or trans-OH coordination are small and that their relative energies vary with the chemical nature of the substitutions. For example, a cis-OH coordination for the vacancy was the most stable when the interlayer charge originated from substitution of Al for Si in the tetrahedral sheet, whereas the trans-coordination was the more stable for most cases of substitution in the octahedral sheet, an exception being Fe(II) for Al where the cis-OH coordination was favored. It seems likely, therefore, that long-range structural disorder will be a common phenomenon in natural phyllosilicate specimens.

Applied Clay Mineralogy. Occurrences, processing and application of kaolins, bentonite, palygorskite-sepiolite, and common clays.Haydn H. Murray. Developments in Clay Science, volume 2, Elsevier Science, Amsterdam, 2007, 180 + viii pp. ISBN-13: 978-0-444-51701-2, ISBN-10: 0-444-51701-4. Price: USD $145, EUR €120, GBP £83.

Abstract: Any article or book written by Professor Haydn Murray is to be welcomed, as he is one of the leading figures in the Industrial Minerals field, particularly with respect to various types of clays. Following a distinguished career in industry he became Professor in the Department of Geological Science in Indiana University in the USA and in his retirement continues to work actively in the field as a consultant. Many of his former PhD students are now in senior positions in industry with some of the major kaolin and clay companies both in the USA and overseas. His book covers a wide range of topics and is just 145 pages of text and figures with 45 pages of Appendices and an Index. The book is clearly aimed as an introduction to clay mineralogy and the occurrences, processing and applications of various clay minerals. For specialists in the field it will be a useful reference point for looking up locations of clay minerals they are not so familiar with. Specialists in particular clay minerals, e.g. kaolin, will view the book as a general summary of world occurrences but for more detail on particular deposits will need to carry out further reading and research. Generally …

Formation and transformation of mixed-layer minerals by tertiary intrusives in cretaceous mudstones, west greenland

Abstract: In the Nuussuaq Basin, West Greenland, a thick succession of Tertiary dolerites has penetrated Upper Cretaceous mudstone. The mixed-layer minerals of mudstone core samples have been analyzed by X-ray diffraction, solid-state 29Si and 27A1 magic-angle spinning nuclear magnetic resonance, Mossbauer and infrared spectroscopies, thermal analysis, chemical analysis, stable isotopes (18O/16O), and K/Ar dating. The mixed-layer minerals include for each sample two mixed-layer phases consisting of pyrophyllite, margarite, paragonite, tobelite, illite, smectite and vermiculite layers. The main, 80 m thick intrusion resulted in the formation of pyrophyllite, margarite, paragonite and tobelite layers. However, the tobelite layers are absent in samples <21 m from this intrusion. Furthermore, chlorite was formed and kaolinite destroyed in samples adjacent to minor intrusions and at distances <60 m from the large intrusion. For the first time, the detailed, complex mixed-layer structures formed during contact metamorphism of kaolinitic, oil-forming mudstones have been investigated accurately. The formation of tobelite layers reveals that oil formation has taken place during contact metamorphism. Furthermore, K/Ar dating of mixed-layer minerals from shale indicates that the intrusives are of early Eocene age. The 80 m thick intrusive is responsible for the main mixed-layer transformations, whereas two thin (3 m and 0.5 m thick) intrusions contribute little. Thus, the detailed mixed-layer investigation has contributed significantly to the understanding of the regional geology and the contact metamorphic processes.

X-ray diffraction criteria for the identification of trans-and cis-vacant varieties of dioctahedral micas

Abstract: To provide structural and diffraction criteria for the identification of trans-vacant (tv)and cis-vacant (cv) mica varieties with different layer stackings, powder X-ray diffraction (XRD) patterns have been simulated for 1M, 2M1, 2M2, 3T and 2O structural models consisting of either tv or cv layers. The differences in the unit-cell parameters resulting from the specific structural distortions of tv and cv layers lead to the differences in the positions of reflections having the same indices in the XRD patterns for tv and cv 1M, 2M1 and 2M2 mica varieties. The tv 1M, 2M1 and 2M2 varieties of Al-rich micas can therefore be distinguished from the corresponding cv varieties using powder XRD diffraction provided that the d values are measured with high precision and accurately compared with those calculated from the unit-cell parameters for the corresponding hkl indices. The differences in reflection positions for these tv and cv varieties should decrease with increasing Mg and/or Fe contents, thus complicating their identification. The peak positions and intensity distributions in the XRD pattern for the tv 3T variety are similar to those for the cv 3T structure with the vacancy in the right-hand cis site (3T-cv1), and both XRD patterns are similar to that for the 1M-cv mica. The simulated XRD pattern for the cv 3T structure with the vacancy in the left-hand cis site (3T-cv2) is similar to that for the 1M-tv variety. The similarities and dissimilarities in intensity distribution between the XRD patterns simulated for the 1M and 3T varieties in question may be associated with the differences in the mutual arrangement of cations and anions in successive layers. Possible interstratification of tv and cv layers within the same structure should seriously complicate the identification of dioctahedral mica polytypes and polymorphs.

Lamellar nanostructure in ‘somasif’-based organoclays

Abstract: Thermally induced lamellar structure changes due to phase transition and degradation in organoclays based on a synthetic ‘Somasif’ mineral and two organic surfactants, di-methyl dihydro-ditallow ammonia chloride (DMDTA) and tri-butyl-hexadecyl phosphonium bromide (HTBP) were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, in situ simultaneous small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) over the temperature range 30–280°C. Results indicated that the surfactant layer in ‘Somasif’-based organoclays underwent thermally induced melting-like order-disorder transition followed by desorption of surfactant molecules, resulting in drastic changes in the character of the layer periodicity. The transition temperature (Ttr), determined from the endothermic transition in DSC, was found to depend strongly on the type and the content of surfactant incorporated. Temperature-resolved SAXS indicated complex intercalated layered structures, containing multiple lamellar stack populations of two different organic layer thicknesses. A weak scattering peak (s0), located at exactly the half angular position of the strong first scattering maximum s1 (s0 = 0.5s1), was found in all tested ‘Somasif’ clays. The presence of this peak can be attributed to a slight breaking of the translational symmetry in the layered structure, causing the 1D repeat period in real space to be doubled. In other words, some portions of layers are grouped into pairs and a single pair forms the new repeat unit. This arrangement is reminiscent of the Peierls-like distortion.

ALTERATION OF SPODUMENE TO COOKEITE AND ITS PRESSURE AND TEMPERATURE STABILITY CONDITIONS IN Li-BEARING APLITE-PEGMATITES FROM NORTHERN PORTUGAL

Abstract: The alteration of spodumene to cookeite has been identified in a Li-bearing aplite-pegmatite from northern Portugal. Optical microscopy and scanning and transmission electron microscopy (SEM/TEM) were used to characterize the alteration products in both cookeite + quartz and cookeite + kaolinite ± mica assemblages. Mutual relationships between the minerals were assessed using back-scattered electron imaging. The first assemblage occurs along the cleavage planes of spodumene, whereas the second forms as the result of spodumene breakdown. Fine mica grains surrounded the cookeite aggregates in the second assemblage only. Precipitations of cookeite and quartz in open pore spaces and parallel packets of cookeite and kaolinite were identified by TEM. Selected area electron diffraction carried out on cookeite identified a layer-stacking sequence from highly disordered to one-layer order-disorder with a lesser participation of two-layer polytypes. The thickness of one-layer cookeite packets averaged ∼85 −100 nm. Disordered cookeite has a mean thickness of 450 nm. The chemistry of cookeite was analyzed by both electron and ionmicroprobe techniques. The structural formula of cookeite from the first assemblage corresponds to: Al2.0(Si3.23Al0.766)O10(OH)2(Al1.80Li1.166Mg0.004Fe0.09)(OH)6. Two distinct compositional varieties were found: one corresponding to ideal cookeite, whereas the second belongs to the cookeite-donbassite join. The thermodynamic stability field for the observed minerals was calculated using the SUPCRT® programme. Two distinct stages of cookeite crystallization are discussed. The lower pressure and temperature stability of the reaction of spodumene to cookeite + quartz were estimated at ∼2.4 kbar and 240°C. The cookeite + kaolinite ± mica assemblage is still in equilibrium with quartz at ∼2.2 kbar and 220°C. The lower limit for the stability of cookeite was found at 205°C and 2 kbar.