Transformation Of Biotite Research Articles

A multidisciplinary approach to investigate weathering processes affecting gneissic rocks (Calabria, southern Italy)

The paper focuses on the weathering processes affecting gneissic rocks of the western Sila Grande Massif (Calabria, Italy) through the development of an interdisciplinary research based on field studies and investigations, minero-petrographical analyses and geochemical modeling. Both physical and chemical weathering affect gneissic rocks of the study area, where the combination of tectonic and past climatic conditions played an important key role in the development of complex and deep weathering profiles. Field surveys and cut slope analyses highlight articulated and complex geometric relationships between various classes of weathering (i.e., out-of-sequence weathering horizons giving rise to a partial, or even complete inversion of the “normal” weathering profile). The weathering profile has turned out particularly intense, as classes IV, V and VI are widespread. Among the class VI, the colluvial soils are prominent in comparison whit the residual soils. Borehole logs, that confirm the intensity and complexity of weathering profiles in deep, allow to estimate the presence of weathered rocks to be at least 70 m in thicknesses.The main mineralogical modifications linked to weathering processes concern the partial transformation of biotite and the partial destruction of feldspars (mainly plagioclases), associated with the neoformation of secondary mineralogical phases (clay minerals and Fe-oxides). Neoformed clay minerals (such as sericite, illite and mixed layer phases) and ferruginous products replaced feldspars and biotite during the most advanced weathering stage. Results of XRD analyses and geochemical modelling provide a good indication on the secondary mineral assemblage due to the increase of the weathering intensity (form class III to class VI) that reflects the different contributions of chemical elements provided by dissolution of silicate minerals into the surrounding groundwater system. The chemical composition of the studied rock samples and the oxides variations suggest a removal of some alkali (Na and K) and alkaline earth (Ca and Mg) into solution as a consequence of weathering reactions. The chemical analysis and the weathering indices (CIA, PIA, CIW and CIW’) show a marked alteration process, with ferromagnesian minerals and feldspars probably dissolved and leached into the surrounding groundwater system. The CO2-controlled dissolution of plagioclase appears to be the most important reaction during chemical weathering. The progressive dissolution results then dominated by biotite, followed by a minor amounts K-feldspar, chlorite and garnet; whereas the sillimanite shows a neglectable amounts. The secondary solid phases observed during the geochemical modeling (illite, followed by vermiculite, ferrihydrite and saponite) are similar to those found in this natural system. The proposed approach could be used to characterize weathered crystalline rocks and related weathering profiles in similar geological setting, and the obtained results represent a key point for the evaluation of the control exerted by weathering on landscape evolution under current environmental settings in terms of sediment generation, soil erosion rates, and mass movements, and for the mechanical characterization of weathering profiles for engineering geological purposes.

Short-Term Changes of Biotite in Various Particle-Size Fractions of Podzolic Soil in a Model Field Experiment

An experiment on the transformation of test biotite of the clay fraction (<1 µm) and the medium silt fraction (5–10 µm) immersed into the AELоа horizon of podzolic soil for one or three years was performed. Partial transformation of biotite in the medium silt and clay fractions into irregular biotite–vermiculite under the modern pedogenesis conditions within one year of incubation in the AELоа horizon of podzolic soil was demonstrated. A considerable part of biotite was transformed into irregular biotite–vermiculite and biotite–vermiculite–pedogenic chlorite, and small amounts of vermiculite and pedogenic chlorite were formed after three years of incubation in the soil. Biotite transformation into expandable minerals was accompanied by the decrease in the layer charge, loss of interlayer K, and loss of Mg and Fe from the octahedral lattice. Mica transformation was most significant in the medium silt fraction: the overall decrease in the share of nonexpandable biotite layers and in the thickness of biotite crystallites after three years of incubation was more pronounced in this fraction than in the clay fraction.

Chemical and minero-petrographical changes on granulite rocks affected by weathering processes

The purpose of this work is to study the weathering processes of the granulite rocks of the Serre Massif (southern Calabria, Italy) using a multidisciplinary approach based on field studies, geochemical modeling, and minero-petrographical analyses. The granulite rocks are plagioclase-rich with minor amphibole, clinopyroxene, orthopyroxene, biotite, and garnet and their texture are coarse-grained. The reaction path modeling was performed to simulate the evolution of groundwaters upon interaction with local granulite by means of the software package EQ3/6, version 8.0a. Simulations were performed in kinetic (time) mode under a closed system at a constant temperature of 11.5°C, (which reproduces the average temperature of local area) and fixing the fugacity of CO2 at 10–2.34 bar (mean value). During the most advanced stage of weathering the main mineralogical changes are: partial destruction and transformation of biotite and plagioclase associated with neoformation of ferruginous products and secondary clay minerals producing a change in the origin rock fabric. The secondary solid phases observed during the geochemical modeling (kaolinite, vermiculite and ferrihydrite) are similar to those found in this natural system. Thus, the soil-like material mainly characterized by mostly sand to gravel grain-size fractions is the final result of the weathering processes.

Deformation-enhanced HP-UHP metamorphic transformation of two-pyroxene granite in ductile shear zones at Yangkou, Sulu UHP metamorphic belt, China

We report that high strain deformation in ductile shear zones greatly enhanced high to ultrahigh pressure (HP-UHP) metamorphic transformation of a two-pyroxene granite in deep continental subduction zone. Integrated structural and petrologic study of rocks from the two-pyroxene granite block and shear zones in the block in the UHP shear complex at Yangkou, Sulu UHP metamorphic belt, reveals that the undeformed granite has preserved granitic texture and primary mineral assemblage of hypersthene, augite, plagioclase, K-feldspar, quartz and biotite. Metamorphic transformation of the granite is limited to grain boundaries due to low fluid activity and low reaction kinetics. In contrast rocks from the shear zones have a mylonitic texture and most of the primary minerals are transformed to HP-UHP phase minerals. Dislocation creep accommodated by dynamic recrystallization results in significant grain size reduction of the primary minerals in the mylonite, which increases reaction surface area and enhances metamorphic transformation. Fluid released by biotite transformation to HP-UHP minerals leads to diffusion mass transfer that greatly accelerates the metamorphic process in the shear zone. Deformation conditions are estimated ca 546 °C and pressure 2.5 GPa.

Transformation of Trioctahedral Mica in the Upper Mineral Horizon of Podzolic Soil during the Two-Year-Long Field Experiment

An experiment on transformation of biotite (fraction <1 μm) particles placed into containers with different permeability in the AEL horizon of podzolic soil was performed in order to estimate the contribution of different factors to the transformation of biotite in the modern soil. After two-year-long incubation in the AEL horizon, biotite was transformed into vermiculite, mixed-layer biotite–vermiculite, and pedogenic chlorite. The most intense vermiculitization of the biotite took place under the impact of fungal hyphae and, to a lower degree, fine plant roots and components of the soil solution. The formation of labile structures from biotite was accompanied by thinning of the mica crystallites, the disturbance of the homogeneity of layers, the removal of interlayer K, the removal and oxidation of octahedral Fe, the increase in the sum of exchangeable cations, and the appearance of exchangeable Al. The process of chloritization was definitely diagnosed upon the action of plant roots and fungal hyphae on the biotite. Strong complexing anions released by fungal hyphae partly inhibited chloritization. Chloritization led to a decrease in the cation exchange capacity of vermiculitic structures.

Química mineral e condições de cristalização do Plúton Granítico Barcelona, extremo nordeste da Província Borborema, Nordeste do Brasil

O Plúton Granítico Barcelona (PGB) localiza-se na porção extremo nordeste da Província Borborema, oeste do Domínio São José do Campestre, com idade Ediacarana presumida. O PGB é formado por três fácies petrográficas/texturais distintas, a fácies granito porfirítico dominante no PGB, a partir da análise de micropetrografia associada às análises de química mineral. A fácies granito porfirítico (biotita monzogranito) possui plagioclásio (oligoclásio com An25-20%), K-feldspato (microclina pertítica) e quartzo compondo sempre (&gt; 70 % modal). O anfibólio é a hastingsita com moderadas razões Mg/(Mg+Fe), pressões de cristalização entre 5,0-6,0 kbar e temperatura de 700°C, finalizando com 3,0-5,0 kbar e 500°C no eutético ternário granítico. O conteúdo de AlT do anfibólio, os valores de pistacita Ps = 28 no epídoto e o processo de martitização da magnetita é indicativa de ambiente com ƒO2 moderada a elevada. As biotitas possuem trend com leve tendência para o pólo da annita, denotando reequilíbrio em estágio subsolidus/tardi-magmático. Em diagramas discriminantes de séries magmáticas as biotitas se comportam como às de afinidade geoquímica subalcalina, coerentes com a cálcio-alcalina médio a alto K dos granitos porfiríticos. Zonação em cristais de plagioclásio, K-feldspato e allanita, é indicativo da importância do processo de cristalização fracionada na evolução/cristalização da fácies porfirítica deste plúton. A atuação de fluidos ricos em H2 O e CO2 propicia a transformação tardia de biotita e feldspatos, além de geração de mirmequitas. A presença de agregados de pequenos cristais de plagioclásio mirmequíticos exibindo contatos com ângulos de 120° indica cristalização em equilíbrio eutético.

Evaluating the paleoclimatic significance of clay mineral records from a late Pleistocene loess-paleosol section of the Ili Basin, Central Asia

AbstractIn this study, we present clay mineral records from a late Pleistocene loess-paleosol sequence in the Ili Basin, Central Asia, and assess their significance for paleoclimatic reconstruction. The results show that the clay minerals are mainly illite (average 60%) and chlorite (28%), with minor kaolinite (9%) and smectite (3%). Illite was of detrital origin with no obvious modification to its crystal structure. Increases in illite content in the loess are ascribed to wind intensity rather than pedogenesis. High proportions of illite in the clay fraction, and of muscovite in the bulk samples of the paleosol units, may lead to an overestimation of the weathering intensity. Kaolinite was likely inherited from the sedimentary rocks, while chlorite might have been inherited from both sedimentary and metamorphic rocks. The paleoclimatic signals of kaolinite and chlorite were unclear, due to reworking by both fluvial and eolian systems. Smectite was more likely formed by the transformation of biotite and illite, and its variation in the loess sequence was also controlled by wind intensity; this was largely due to aggregation and is unlikely to reflect moisture changes. Although the interpretation of paleoclimate evolution may contain some uncertainties, clay mineralogy does provide the possibility of tracing dust provenance.

Weathering processes affecting granitoid profiles of Capo Vaticano (Calabria, southern Italy) based on petrographic, mineralogic and reaction path modelling approaches

This work focuses on developing multidisciplinary research on weathering profiles of granitoid rocks related to the tectonic and landscape evolution of the Capo Vaticano area, Calabria, southern Italy. During the Pleistocene, the Mediterranean climate plays, on the already decomposed plutonic rocks, important processes of alteration, on both the highest and inland areas and the coastal areas of the Calabrian region, such as the studied area. Field observations coupled to chemical, minero‐petrographical features and geochemical modelling are used to characterize the weathering processes affecting the granitoid complex. The granitoid cut slopes show a generally simple weathering profile characterized by a progressive increase in weathering towards the top of the slopes. The completely weathered rocks (class V) and residual soil (class VI) contain a high percentage of altered minerals, microfractures, and voids. The main mineralogical changes are the partial transformation of biotite and the partial destruction of feldspars (mainly plagioclase) that are associated with the neoformation of secondary clay minerals and ferruginous products during the most advanced stage of weathering. These transformations produce a substitution of the original rock fabric. Geochemical modelling showing the precipitation of kaolinite, illite, vermiculite, ferrihydrite and calcite. These secondary solid phases are similar to those found in this natural system. Thus, the final results of the weathering process is a soil‐like material mainly characterized by mostly a sand to gravel grain‐size fractions related to microfabric changes and mineralogical and chemical variations. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Effects of citrate on the dissolution and transformation of biotite, analyzed by chemical and atomic force microscopy

The aim of this study was to investigate the dissolution and transformation characteristics of phyllosilicate under low molecular weight organic acids in the farmland environment (pH 4.0–8.0). Changes of dissolution and morphology of biotite were evaluated using chemical extraction experiments and in situ/ex situ atomic force microscopy (AFM) with fluids of citric acid (CA) solution at pH 4.0, 6.0, and 8.0. Results of extracting experiments show that CA solutions contributed to the release rate of potassium (K), silicon (Si), and aluminum (Al) from biotite relative to a control aqueous solution. In situ AFM observations indicate that the dissolution of biotite from the biotite (001) surface occurred on the terrace, segment, and fringe of pits, while new etch pits did not readily form on biotite (001) surfaces in aqueous solutions. However, dissolution rates of terraces can be greatly accelerated with the help of citrate. In pH 4.0 CA solution, 70min dissolution reactions of biotite (001) surfaces result in more etch pits than in pH 6.0 and 8.0 solutions. In addition, the transformation of biotite occurred simultaneously with the dissolution process. Secondary coating was observed on the biotite (001) surface after 140h of immersion in a weak acid environment. Thus, the protons have a dominant role in the dissolution process of biotite with organic (carboxyl) acting as a catalyst under acidic condition. Based on the theory of interactions on a water–mineral interface in a weak acid environment, dissolution of biotite starts from defect/kink sites on the surface, one layer by one layer, and develops along the [hk0] direction. A secondary coating that forms on the biotite (001) surface may restrain the formation and growth of etch pits, whereas this process may have a positive role on the stability of soil structure during long-term soil management.

Degradative crystal–chemical transformations of clay minerals under the influence of cyanobacterium-actinomycetal symbiotic associations

Cyanobacteria and actinomycetes are essential components of soil microbial community and play an active role in ash elements leaching from minerals of the parent rock. Content and composition of clay minerals in soil determine the sorption properties of the soil horizons, water-holding capacity of the soil, stickiness, plasticity, etc. The transformative effect of cyanobacterial–actinomycetes associations on the structure of clay minerals – kaolinite, vermiculite, montmorillonite, biotite and muscovite – was observed, with the greatest structural lattice transformation revealed under the influence of association in comparison with monocultures of cyanobacterium and actinomycete. The range of the transformative effect depended both on the type of biota (component composition of association) and on the crystal–chemical parameters of the mineral itself (trioctahedral mica – biotite, was more prone to microbial degradation than the dioctahedral – muscovite). The formation of the swelling phase – the product of biotite transformation into the mica–vermicullite mixed-layered formation was revealed as a result of association cultivation. Crystal chemical transformation of vermiculite was accompanied by the removal of potassium (К), magnesium (Mg) and aluminum (Al) from the crystal lattice. The study of such prokaryotic communities existed even in the early stages of the Earth's history helps to understand the causes and nature of the transformations undergone by the atmosphere, hydrosphere and lithosphere of the planet.contribution of treatments on structure induces and model parameters are discussed in the paper.

Characterization of granitoid profiles in the Sila Massif (Calabria, southern Italy) and reconstruction of weathering processes by mineralogy, chemistry, and reaction path modeling

This paper concerns the development of a multidisciplinary research on weathering profiles of granitoid rocks in the Sila Massif (Calabria, southern Italy), based on field investigations, chemical and minero-petrographic data, and geochemical modeling. It aims at evaluating modes and degree of weathering and focuses on the main transformation processes of the parent rock, integrating information obtained by direct observations/analyses on samples with results of simulations of pertinent water–rock interaction processes, carried out through the reaction-path-modeling approach. Physical responses to geological hammer hitting and morphological weathering features were used to characterize increasing weathering grade (I–VI weathering classes) of a representative weathering profile. Also, the main microfabric and minero-petrographic features were observed in thin sections; XRPD and SEM-EDS were used to identify primary minerals and neoformed products. Progressive dissolution of the granitoid rock was simulated using the software package EQ3/6, 8.0 and a modified version of the thermodynamic database data0.ymp.R5. A kinetic mode under closed-system conditions was applied with respect to a defined set of secondary solid phases, which are allowed to precipitate. The partial transformation of biotite and the partial destruction of feldspars, associated with the neoformation of secondary minerals and a substitution of the original rock fabric are the main mineralogical changes observed. Neoformed clay minerals and ferric products replaced feldspars and biotite during the most advanced weathering stage. Microfractures and morphological variations occur on the original rock. The final result of weathering process is a soil-like rock characterized by sand-gravel grain-size fraction. Results of geochemical modeling suggest that the chemical weathering processes occurring in the study area are relatively close to an iso-chemical transformation of the original granitoid rock, based on the small predicted changes in the concentrations of solutes from the initial to the final state of the simulation. The CO2-controlled dissolution of albite-rich plagioclase is the most important reaction, followed by the dissolution of K-feldspar, biotite, chlorite, and muscovite, in order of decreasing importance. The precipitating secondary minerals are ferrihydrite, saponite, vermiculite, illite, and kaolinite in order of decreasing pH values. The order of appearance and the quantities of secondary (product) minerals depend on the setup of geochemical modeling. Based on the standard thermodynamic properties of different illite endmembers, calculated in this work, it was possible to predict the varying compositions of the illite solid solution, which resulted to be similar to those observed in natural systems.

Characterization of granitoid and gneissic weathering profiles of the Mucone River basin (Calabria, southern Italy)

The paper deals with the development of a multidisciplinary research on weathering profiles of granitoid and gneissic rocks related to tectonic and landscape evolution of the western Sila Grande Massif (Calabria, southern Italy). Field scale observations and petrographical and mineralogical features are used to characterize in detail the weathering processes. The weathering profiles of the granitoid cut slopes are generally simple showing a progressive weathering increase toward the top of the slopes, whereas the weathering profiles of the gneissic cut slopes are generally complex with irregularities in the spatial distribution of weathered horizons. The microfabric and petrographic analyses show that gneissic samples (classes V–VI of weathering grade) are characterized by higher percentage of altered minerals and microfracture and void rather than granitoid samples (classes V–VI of weathering grade). The main mineralogical changes concern the partial transformation of biotite and the partial destruction of feldspars (mainly plagioclases), associated with the neoformation of secondary minerals (clay minerals and Fe-oxides) and with a substitution of the original rock fabric. Neoformed clay minerals and ferruginous products replaced feldspars and biotite during the most advanced weathering stage. Referred as physical changes coupled with chemical variations, the final results of weathering process are a soil-like material characterized by sand–gravel grain-size fraction for the granitoid rocks and by both silt–clay and sand–silt grain-size fraction for the gneissic rocks. This generally produces a greater value of the SGI (Sand Generation Index) for granitoids and explains the great productivity in sandy deposits of this lithology.

Monitoring of biophysicochemical changes in a silty clay soil contaminated with LNAPLs

The interdependence between time domain induced polarization measurements at uncontaminated and artificially contaminated soil samples with diesel and biophysicochemical alterations caused by diesel degradation was investigated during 12months. The research was performed on a slightly alkaline soil, with high content of organic matter (148g/kg) and silty clay texture. Soil clay mineralogy was mainly composed of plagioclase, amphibole, biotite, interstratified mica-smectite, goethite and some vestigial kaolinite. A decrease on resistivity and induced polarization (IP) in contaminated soil was observed during the 12months. This reduction on geoelectrical parameters was related to: 1) the increase on the electrolyte conductivity; 2) the increase on interfacial surface area, as result of biotite transformation and weathering of other ferromagnesian minerals and 3) a slight increase in soil aggregation, caused by diesel-degrading microorganisms (a significant increase of the numbers of specific carbon degraders was observed). After 4months, the IP response was lowest in the contaminated soil which was explained by inhibition of the cation exchange capacity due to two possible processes: 1) clay particles coating by organic molecules and 2) attachment of microbial cells (biofilms) to clay particles and/or soil aggregates. The results suggest that the content and mineralogy of the clay fraction as well as the aggregation state of the soils contaminated with LNAPL's affect the IP response. This response is a diagnostic of the biophysicochemical alterations occurring during diesel degradation as a result of biological activity.

Clay Minerals as Climate Change Indicators—A Case Study

The clay mineralogy of the Late Pliocene-Early Pleistocene Pinjor Formation of the type area, northwestern Himalaya, India has been investigated to understand the paleoclimatic conditions and paleotectonic regime prevailing in the frontal Himalayan terrain during 2.5 Ma to 1.7 Ma. The clay minerals were investigated by X-ray diffraction analysis and scanning electron microscope studies. Study of the oriented aggregates of 47 representative clay samples of the Pinjor Formation of the type area reveals that illite is the most dominant mineral followed by chlorite, kaolinite, vermiculite and mixed layer clay minerals. The distribution of the clay minerals in the three lithostratigraphic units of the Formation, namely the Kona Clay Member, the Tanda Bhagwanpur Wacke Member and the Chauki Nadah Pebbly Bed Member which are well exposed along the Berwala-Mandhna section, the Kona-Karaundanwala section and the Ghaggar River-Chauki Nadah section, is nearly uniform suggesting thereby the prevalence of similar sedimentation environments in the Himalayan foreland basin. The presence of illite and kaolinite suggests their derivation from crystalline rocks containing felspar and mica as also from pre-existing soils and sedimentary rocks. Further, the paleoclimatic conditions were moderate. Presence of chlorite suggests the weathering of intermediate and basic crystalline rocks and low grade metamorphic rocks in the positive areas. The presence of kaolinite in the Pinjor Formation is mainly attributed to the weathering and subsequent leaching of the mineral from granitic and basic rocks in the hinterland. Vermiculite has been mainly formed by weathering and transformation of biotite. Warm and humid climatic conditions prevailed for a major part during the deposition of the detritus which favored weathering and transformation of minerals. During the terminal phase of sedimentation there was renewed tectonic activity which had a significant impact on climate as precipitation and mechanical weathering rates increased substantially. Post 1.7 Ma there was a marked shift in temperature patterns and subsequent cooling of the landmass, which resulted in a decreased vegetation cover and a subsequent decrease in animal population thriving on it.

Weathering of biotite in the presence of arbuscular mycorrhizae in selected agricultural crops

The mutual association of roots and fungus, mycorrhizae, benefits the general ecosystem by producing soil clays from primary phyllosilicates. In laboratory experiments, X-ray diffraction analyses of clay materials showed that the fungus Glomus when inoculated onto barley and canola produced various types of less K-containing phyllosilicates (e.g., illites, smectites and hydroxy-interlayered vermiculites) from biotite and left some biotite (the K-rich mineral) intact. Non-inoculated plants left no intact biotite. Both non-inoculated and inoculated alfalfa produced only some illites from biotite. We propose that mycorrhizae inoculated samples exhibit selective K-extraction from some biotite particles to benefit plant growth and at the same time leaving unaltered biotite for future extractions. However, results from molecular DNA analysis (i.e., PCR) of fungal population, X-ray absorption near edge spectroscopic analysis of the oxidation of Fe2+ to Fe3+ and K-uptake by plants seems to indicate that the K-extraction process from biotite is by no means simple. The transformation of biotite and K (and Mg)-uptake depend on the plant–fungus symbiotic system, and the formation of clay minerals will then be a function of plant type and symbiotic relations in the soils.

Rb–Sr and K–Ar systems of biotite in surface environments regulated by weathering processes with implications for isotopic dating and hydrological cycles of Sr isotopes

Biotite is widely used for Rb–Sr and K–Ar isotopic dating and influences Sr isotope geochemistry of hydrological regimes. The isotopic system of biotite behaves diversely in response to surface weathering; i.e. the complete preservation of original Rb–Sr and K–Ar isotopic ages or dramatic reduction. In this study, we have explored the relation between the behavior of isotopic systems and complex weathering processes of biotites in the weathering profiles distributed on the Mesozoic granitoids in South Korea. In the lower parts of the profiles, biotite in the early stages of weathering was transformed into either oxidized biotite or hydrobiotite, with a mass release of 87Sr and 40Ar forced by the rapid oxidation of ferrous iron. During the transformation to oxidized biotite, 87Sr and 40Ar were preferentially released relative to Rb and K, respectively, via solid-state diffusion through the biotite lattice, resulting in a drastic reduction of original isotopic age. The reduction of Rb–Sr age was greater than that of K–Ar age because K was preferentially released over Rb whereas 87Sr and 40Ar were released proportionally to each other. However, during the transformation of biotite to hydrobiotite (i.e., to regularly interstratified biotite-vermiculite), 87Sr, Rb, 40Ar, and K were completely retained in the alternating biotite interlayer, and thus the original isotopic age can be preserved. In the upper parts of the profiles, where iron oxidation was almost completed, 87Sr, Rb, 40Ar, and K were gradually and proportionally released, with no further significant change in isotopic age during the gradual transformation of the early-formed oxidized biotite into hydrobiotite and vermiculite or during their final decomposition to kaolinite. The ratios and amounts of isotopes released from weathered biotites are dependent upon the degree of iron oxidation and the pathways of mineralogical transformation. Regional and local variations in isotopic systems affected by particular weathering processes should be considered when dating biotite or biotite-bearing rocks in weathering environments, modeling the transfer of Sr isotopes to hydrologic regimes, and tracking the provenance of sediments.

Vertisol genesis in a humid climate of the coastal plain of Texas, U.S.A.

Numerous genetic studies of Vertisols have been conducted using qualitative and semi-quantitative methods across a broad range of climates. However, no detailed investigations exist on Vertisols formed in humid climates using multiple pedogenic techniques on both a microlow (ML) and microhigh (MH). Hence, we sampled and characterized a ML and MH from a Lake Charles pedon (mean annual rainfall=1090 mm, mean annual temperature=20 °C) in the late Pleistocene coastal plain Beaumont Formation of east Texas. According to the official series description the Lake Charles classifies as a fine, smectitic, hyperthermic Typic Hapludert with mollic and calcic diagnostic horizons. Coupled with field morphology and characterization data, micromorphology and constituent mass balance interpretations were used to reconstruct the major pathway of pedogenesis. In response to greater water recharge, the ML contains darker colors, more organic carbon, greater depth of carbonate leaching, and lower pH. The proportion of oxalate-extractable iron increases toward the surface and is in greater abundance in the ML than MH. In contrast, dithionite-extractable iron increases with depth and has similar quantities in both the ML and MH. The parent material and lower profiles contain asepic microfabric dominated by micaceous-rich coarse clay and silt. The asepic zone deep contains an abundance of soft carbonate masses and iron manganese segregations that appear to be forming contemporaneously, with the presence of argillans substantiating clay translocation during the early history of soil formation. Sepic microfabric dominates the upper profiles of both the ML and MH in part from the transformation of biotite to smectite, which is more pronounced in the microlow because of more intense weathering. Hard carbonate nodules and iron manganese concretions are abundant in the upper sepic zone and contain skelsepic microfabric, suggesting that they are no longer growing. Dilation was the dominant strain force during pedogenesis from volume expansion in response to crack infills and shrink–swell processes. Mass flux calculations indicate that total clay gains occurred in both the ML and MH during pedogenesis. Late Pleistocene Vertisols appear to approach steady state when forming in humid climates. The soil mechanics model best explains the observed depth distribution of properties, including slickensides, with pedoturbation playing a secondary role in the genesis of these humid-climate Vertisols.

Similarity between alkali–aggregate reaction and the natural alteration of rocks

This article aims to demonstrate that the mechanisms governing the natural alteration of rock also lead to the development of alkali–aggregate reaction. We have used the alteration of granite to pinpoint two processes that are often involved. In the first, existing minerals are transformed into minerals with expansive properties (such as the transformation of biotite into chlorite and expansive smectite). In this case, the expansion occurs in the structural layers of the mineral and may cause relatively localized deterioration in the original material. In the second process, the mineral constituents are initially hydrolyzed in the surrounding water, which gradually becomes saturated with silica, alumina, and various cations. New phases evolve from this water, yielding gels or well-crystallized products. In the case of the granite investigated, the product is laumontite (Al 2O 3·4SiO 2·CaO·4H 2O), which is formed from the water in the cracks. The crystallization of this zeolite generated significant cracking in the samples examined. We have demonstrated experimentally that similar type of zeolite (Al 2O 3·2SiO 2·CaO·5H 2O) forms readily when a mixture of lime and metakaolin is reacted with water in the presence of sodium hydroxide. This mixture contributes the silica, alumina, and cations required to initiate the reactions.

Pedogenic Smectites in Podzols from Central Finland: An Analytical Electron Microscopy Study

AbstractTransmission electron microscopy (TEM) including high-resolution transmission electron microscopy (HRTEM) and analytical electron microscopy (AEM) were used to study the fine clay fraction (&lt;0.1 μm) from the eluvial E horizon of podzols located in central Finland that had developed from till materials. Soils of increasing age (6500-9850 y BP) were selected to represent a chronosequence of soil development. Expandable phyllosilicates (vermiculite, smectites) are formed in the eluvial E horizon of podzols in a short time (6500 y). TEM observations show that dissolution and physical-breakdown processes affect the clay particles. As the age of the soils increases, fragmentation and exfoliation of large precursor minerals lead to thinner clay particles of two to three layers thick. The chemical compositions of individual particles obtained by AEM indicate that expandable phyllosilicates from the E horizon of podzols are heterogeneous, involving a mixture of vermiculite, Mg-bearing smectites, and aluminous beidellite. Results suggest that heterogeneity is related to the nature of their precursors. Vermiculite and Mg-bearing smectites are derived from biotite and chlorite weathering whereas phengitic micas alter to aluminous beidellite. Because the transformation of biotite and chlorite is more rapid than phengitic micas, biotite and chlorite contributes predominantly to smectites in the younger soils, as long as ferromagnesian phyllosilicates are present in the E horizons. If not, a larger proportion of smectites is derived from phengitic micas in the older soils. Direct measurement of d(001 ) values on lattice fringe images from alkylammonium-saturated samples shows that interlayer charge varies from high-charge expandable minerals (0.6–0.75 per half unit cell) in the younger soils to 0.5–0.6 per half unit cell in the oldest soils. Thus, the proportion of the components in the clay assemblage, as well as their chemistry and interlayer charge, change over time with soil evolution.

Les syénites du castillet (massif de l'agly, pyrénées orientales, France): une roche exceptionnelle dans les pyrénées

Le Castillet syenites (Agly massif) are unusual rocks in the eastern Pyrenees made up of more than 95 % of potash feldspar and albite. These rocks are hosted in the Variscan Saint-Arnac granite and form small domes, the shape of which suggests an emplacement by magmatic stopping. Syenites and their closest host rocks suffered various hydrothermal alterations, the most obvious being transformation of biotite into muscovite + rutile. Discussion of the origin of these syenites is difficult because of those alterations: many magmatic features are well preserved but metasomatic transformation may have very much modified the primary rocks.