Transformation Of Mica Research Articles

The Clay Minerals in the Soils of the Gypseous Belt of Barbastro, NE Spain

This article examines the clay mineralogy of twelve representative soils developed from gypsum-rich parent materials on several geomorphic positions. These soils were classified as Haploxerept, plus one profile as Humixerept and another as Xerorthent. The clay mineralogy, determined by X-ray diffraction, showed quite a similar clay composition in all profiles, with mica, chlorite, and smectite, from most to less abundant. Mica and chlorite are deemed inherited, while smectite—appearing in minor proportions—could result from both transformation and/or neoformation, because the leaching of bases by free drainage does not favor the transformation of mica to smectite. Therefore, the differences in clay mineralogy appeared to be lithogenic rather than pedogenic. These compositional data are an advance in the basic knowledge of the studied soils.

Effect of Accelerated Physical Weathering of Coarse Soils and Wetting and drying Cycle on Some Soil Physical Properties

soil samples were collected in May the 5th, 2021 from wadi Al-Muhammadi) Al-Mohammadi valley(in Al-Anbar governorate in western Iraq. The trail consisted of four treatments. In the first treatment, the sample Is passed through a 2000 μm metal sieve, while in the fourth treatment the sample is crushed or milled to size 70μm sieve. In the second treatment, the mixture ratio of soil was 25:75 (natural: Crushed). In the third treatment, the mixture ration of soil was 50:50 (natural: crushed). This paper determined in the soil coefficients for penetration, the density sustainability, soil porosity, as well as scanning soil aggregates using an electronic microscope samples passed through cycle of wetting and drying the results showed that the decrease was evident in soil penetration resistance in recent cycles in conjunction with the decrease in soil bulk density significant because of mechanical pulverization and cycles of wetting and drying along with an increase in soil porosity. the proportion of soil cracks resulting from shrinkage and swelling has been calculated and It was found that it increases with the percentage of clay in the soil. The electron microscope images show the soil was influenced by the mechanical pulverization during the first three cycles, as for the wetting and drying cycles, their effect appeared in the last cycles, the partial transformation of mica to mineral 2:1 was observed with the progression of wetting and drying cycles.

Studying the Effect of Agriculturally Exploited Soils on the Transformation of Mica Minerals using Infrared Spectroscopy (IR)

Five soil sites were selected in the Middle Euphrates region, represented by the governorates (Diwaniyah, Najaf, Babel, and Muthanna), for soils of different agricultural exploitation (rice, vegetables, wheat, and palm trees), in addition to an unexploited agricultural soil. The soils were distinguished by having the same topography and climatic conditions and similar texture in order to study the weathering of mica minerals by using the infrared technique. The appearance of the absorption spectrum at the frequency of 3550 cm-1, with medium broadening in the unexploited agriculture soil (Muthanna), indicated a gradual transformation of mica towards di-octahedra minerals, and reflected the increasing substitution of Al+3 in tetrahedral sheet in these soils. The results of the examination of clay particles in soils exploited for cultivation of rice (Diwaniyah) showed that the absorption spectrum at the wavelength of 1642 cm-1 represents the absorption of zeolite water, while the presence of absorption spectra at the frequencies of 796, 1036, 3418, and 3616 cm-1 indicated the presence of mica minerals in all rice soils, also the presence of the broad absorption spectrum band at the frequency of 3418 cm-1, which was accompanied by the presence of the spectrum band at the frequency of 1036 cm-1.

Origin and technology of the Georgian brick at Fade Mansion, Dublin, built c. 1728

This paper studies the provenance and firing technology of the Fade Mansion brick. The microstructure was studied with scanning electron microscopy (SEM), mineral associations and transformation were determined with X-ray diffraction (XRD) and petrographic analyses. The results evidenced that the bricks were made with a decalcified, silica-based clay of glacio-fluvial origin, gathered locally. This agrees with the position of the Mansion on a terrace of the River Liffey, and with previous research on historic bricks made with boulder clay. They were fired in kilns in an oxidising atmosphere. The rubbers at window heads reached lower temperatures which resulted in low vitrification, leading to weathering. Initial vitrification structures generally concur with the occurrence of clay minerals, indicating temperatures of c. 800°C. Continuous vitrification is associated to the disappearance of clay minerals, the sintering of hematite and/or high-temperature phases and mica transformation, indicating a wide temperature range >950-1200°C, which agrees with the inconsistent brick properties.

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.

A Comparative Study of the Properties of Mica in Rhizosphere and Bulk Soil Under Different Plant Covering.

Results of x-ray diffractions for Bulk soil, represented by the horizontal distance 50H, show the presence of low-crystalline chlorite, smectite and regular interstratified chlorite- smectite in soil under Citrus aurantium trees. Re sults of clay sample in soil of palm tree show a presence of smectite and swelling chlorite, while the presence of the interstratified minerals is very low. Also the results show a presence of swelling chlorite, smectite and Biotite in soil of Morus trees. Generally, the results show that the process of mica transformation into 2:1 minerals in the Bulk soil, is very weak. The x-ray results show that the rhizosphere soil(0) of Citrus aurantium trees content is smectite and mica, with regular interstratified mica-smectite, while the results show the presence of smectite, chlorite, and regular interstratified chlorite- smectite and mica-smectite, in rhizosphere soil of palm trees. As well as the inspection of clay samples of Morus trees, show the presence of chlorite and smectite with two types of interstratified minerals, irregular smectite-mica and regular mica-smectite. In general, the results of x-ray show that the transformation process of mica to 2:1 expandable minerals in rhizosphere soil exceeds the Bulk soil of all type of trees. While the superiority of mica weathering, and increase of Smectite content in all rhizosphere soils are taken as in the following sequence: Morus trees soil > Palm trees soil > Citrus aurantium trees soil

A nano-scale study of the mechanisms of non-exchangeable potassium release from micas

Non-exchangeable potassium (NEK) is released from minerals by chemical extraction methods through dissolution and cation-exchange reactions. Assessing the contribution of these two processes to release budgets is important to predicting plant/mineral interactions and soil sustainability. Three NEK extraction methods, 1M boiling nitric acid (HNO3), 2M hot hydrochloric acid (HCl) and 0.2M sodium tetraphenylboron (NaTPB), were applied to investigate the mechanisms of NEK release from trioctahedral biotite and dioctahedral muscovite. Atomic force microscopy and X-ray diffraction were used to investigate the surface morphology and transformation of mica, respectively. NEK released from biotite and muscovite through cation-exchange reaction accounted for 87.88%, 85.93% and 83.23%, 78.31% of the total extracted K when extracted by boiling HNO3 and hot HCl, respectively, with channel and elliptical dissolution pits on mica surface. NEK extracted by NaTPB was an almost complete cation-exchange reaction, and the extracted micas showed an obvious vermiculitic character and no dissolution features. Results showed the release of NEK from micas is essentially a cation-exchange reactions in both acid and salt solutions, indicating that NEK released through cation-exchange reaction but not via dissolution may make up the main soil K pool available to plant.

Characterization of two low charge vermiculites after hydrochloric acid treatment

Two natural vermiculites (Ver) with very similar chemical composition but slightly different low charge on the layers were investigated to find an answer the question, how to change their structural and chemical properties after exposure to different concentrations of HCl solutions. Vermiculite from Bulgaria (Ver-B) with the layer charge 0.47 eq/O10(OH)2 and from Brazil (VerSL) with the layer charge 0.36 eq/O10(OH)2 were studied on their particle size fraction less than 40 μm after treatment at different HCl concentrations (0.5 M HCl and 1 M HCl). Both samples represent a mixed-layer structure after incomplete transformation of mica (biotite) to vermiculite. Based on the XRD patterns, Ver-B may be considered as the mixed-layer vermiculite interstratified with small proportion of mica layers and Ver-SL as the mixed-layer micavermiculite. The leaching with 0.5 M HCl increased SA of Ver-B from 29.5 m 2 .g -1 to 261 m 2 .g -1

Effect of granite crystal grain size on soil properties and pedogenic processes along a lithosequence

This study generated new insight into the effect of bedrock grain sizes on pedogenesis under identical topographic and climatic environment. The physico-chemical and mineralogical properties of two adjacent Typic Dystrochrepts (USDA, 1999) respectively developed from fine and coarse textured granites were compared. This research study was performed in the Morvan Mountains (France). Analysis of the two underlying bedrocks revealed similar chemical and mineralogical properties, with the crystal grain size being the only parameter which differed. In these soils, bedrock played the key role in the particle size fraction distribution, the main factor controlling water retention in the soils. Weathering reactions of clay minerals were more marked in the fine textured granite soil. In this soil, both clay mineral swelling and mica transformation into expansible phyllosilicates were greater compared to the coarse textured granite soil. In the clay fraction of the fine textured granite soil, there were smaller amounts of low crystallised Fe and Al minerals, with higher carbon content in the topsoil, as compared to the coarse granite soil. The exchangeable cation analysis of the fine textured granite soil revealed a higher proportion of base saturation and a smaller proportion of Altit than in coarse textured granite soil which could be explained by preferential leaching of Al cations. The decrease in exchangeable Al, the higher swelling of the smectitic layer and the smaller proportion of Fe and Al-oxy-hydroxides could be explained by the complexing acid conditions, which increased mineral weathering and Al leaching. The higher water retention increased the time of contact between minerals and the soil solution, and the higher carbon content in the topsoil could have enhanced the complexing acid conditions.

Changes in the structures of mixed-layer illite-smectite during flooding of terrigenous oil reservoirs

A difference-spectrum method is proposed for the qualitative assessment of changes of illite-smectite structures accompanying the flooding of oil reservoirs. The method permits one to get an open system and reduce the application of procedures based on Markov’s chain formalism. A computer simulation is made to obtain spectra by subtracting the spectrum of an ethylene glycol-saturated sample from the spectrum of an air-dried preparation throughout the entire range of concentrations of illite and smectite components with a short-range order factor R = 0 or R = 3.It has been established that only in the presence of filtration are the maximum and minimum of the spectra in the range of 12.5-9.4 A complicated by a number of local extrema, whose position is specified by the structure of intermediate phases. The flooding process first involves mixed-layer phases with R = 0, leading to a partial segregation of the structures into phase with one and two networks of interlayer H2O. When the secondary mica particles break, phases with R = 3 appear along the boundaries of nanoblocks, first only with 1 H2O and then only with 2 H2O in labile interspaces. Their coexistence with the phases R = 0 in the sample proves the existence of percolation effects due to two-phase filtration in the porous medium. The fully flooded reservoir is always dominated by a mechanical mixture of illite-smectite phases of different nature with R = 0 and with different ratios of components. Transformation of mica that can drastically reduce oil production begins long before the appearance of flooding zones, which are revealed by standard logging methods.

Mineral composition vs. soil forming processes in loess soils — A case study from Kraków (Southern Poland)

The mineral composition of soil parent material has a clear impact on: soil formation, soil properties (especially chemical properties), and mineral transformation in soil environment. Despite many studies concerning loess soils, detailed, quantitative studies on the mineral composition and transformation of clay minerals in loess soils formed during Holocene and the influence of the mineral composition of parent material on the properties of loess soils are rare. The main aims of the present study were (1) to determine the influence of loess mineral composition on soil genesis and (2) to determine layer silicate transformations and clay mineral formation in loess soils in relation to soil-forming processes using qualitative and quantitative X-ray diffraction analyses (XRD and QXRD). The obtained results show that the occurrence of carbonate minerals (i.e. calcite) and their influence on chemical properties of soil play a crucial role in the evolution of loess soils. In loess that does not contain carbonates, dispersion and translocation of clay particles (including clay minerals) down the profile occur. This leads to the formation of Luvisols and Albeluvisols. In carbonate loess, clay minerals and soil organic matter form stable humus–mineral complexes leading to the accumulation of humus and the formation of Chernozems. The transformation of mica and/or smectite and/or vermiculite to hydroxy-interlayered minerals (HIMs) is the dominant process in the studied loess soils developed in a temperate climate because intense weathering of layer silicates is possible after removal of carbonates from soil profile. This indicates that the occurrence of carbonates which maintain soil pH on a level of about 7 or higher is most likely the main factor controlling the rate of weathering of layer silicates in a loess soil environment. In carbonate loess, the dissolution and leaching of carbonates prevail over the weathering of silicates. It is highly likely that the continuous leaching of carbonates – assuming that the climate will not change – will lead to more intense weathering of layer silicates.

Experimental dissolution vs. transformation of micas under acidic soil conditions: Clues from boron isotopes

Minerals in soils evolve through contact with water and other weathering agents (protons, organic acids and ligands) from the atmosphere or released by the surrounding vegetation and associated fauna. Determining the respective contribution of these agents to weathering budgets and the mechanisms by which they interact with soil minerals is a key step toward obtaining refined models of soil development, plant/mineral interactions and, ultimately, soil sustainability.To test the influence of different chemical agents on the processes of mica weathering (dissolution and transformation), we conducted a series of laboratory flow-through experiments on biotite using three chemical groups of reactants found in forest soils: protons (HCl), organic acids (citric acid) and ligands (siderophores). These experiments were performed at two different pH values (pH 3 and pH 4.5) for 37days at 20°C. Biotite was chosen as a test-mineral because it is reactive with acids and water and because it is commonly found in granite soils. To investigate the weathering reactions, the chemical and isotopic compositions of B (δ11B) and the concentrations of predominant cation (Si, Al, Mg, K and Fe) were monitored in the outflowing solutions. The choice of B as a proxy for weathering processes is based on the fact that B is located in different crystallographic sites in biotite (interlayers and structural sites, named I- and S-sites, respectively). We observed a large δ11B contrast between these sites (Δ11BS–I sites∼80‰), which allows for a precise quantification of the respective contribution of I- and S-sites to B released during biotite weathering.The individual reaction rates for these crystallographic sites were inferred from the B chemical and isotopic compositions of the outflowing solutions. A comparison with the major elements reveals that B is preferentially released to solution under all tested experimental conditions (up to 4 times more), particularly in the presence of siderophores. A major finding of the present work is that the dissolution of δ11B is shown to be highly dependent on the nature of the weathering agent: the presence of citric acid leads to a near-stoichiometric contribution of I- and S-sites to dissolved B, whereas the presence of siderophores results in an almost exclusive release of B from the I-sites, which indicates a mineral transformation without significant dissolution. The presence of HCl leads to an intermediate situation that shows a higher B reactivity from the I-sites than from the S-sites, indicating that biotite minerals transform faster than they dissolve. Because the dissolution reactions imply the destruction of the mineral structure, whereas transformation reactions are non-destructive, assessing the proportions in which minerals evolve by dissolution and transformation reactions has important implications for predicting plant/mineral interactions and soil sustainability.

Transformation of micas of various crystal chemistry under influence of cyanobacteria and actinomycetes association

The ability of experimental cyanobacteria and actinomycetes associations to change the structure of micas has been revealed. It was noticed that the rates of mineral transformation depend on their crystalchemical composition—the structure of biotite—trioctahedral mica that transformed sustainably under the influence of cyanobacteria and actinomycetes association’s growth, which was detected by the emergence of mixed-layered biotite-vermiculite formation in the fraction sample. In the case of dioctahedral mica—muscovite—the significant transformational changes under the influence of association has not been revealed. The symmetry and high clearness of mineral reflexes after the association’s growth indicates a high tolerance of muscovite to biological weathering.

Transformation of mica to high-charge smectite, depending on the particle size, in a yellow-brown soil of China.

Clay mineralogical composition of a Yellow-brown soil of China was examined. Common to the A and C horizons, micas and their transformation products dominated the clay fraction. The transformation products of micas were, however, different between the fine (<0.2 μm) and coarse (0.2-2 μm) clay fractions. Irregularly interstratified mica/smectite or mica/vermiculite/smectite of the smectite-rich phase was found in the fine clay fraction, while smectite and regularly interstratified mica/smectite were detected in the coarse clay fraction. The endo-type and exo-type K-replacement models were proposed to explain the different transformation products between the two clay fractions

Submicroscopic accessory minerals overprinting clay mineral REE patterns (celadonite–glauconite group examples)

Samples of glauconite, representing different stages of glauconitisation, as well as different formation environments, were analysed for rare earth elements (REE) and other trace elements using a combination of bulk sample and spatially-resolved in situ techniques. The results indicate that the high-sensitivity, spatially-resolved technique of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) produces values up to two orders of magnitude lower than the bulk sample analyses. This suggests that submicroscopic rare earth element-bearing phases are distributed within the glauconite aggregates comprising the bulk samples. Analytical scanning electron microscopy (ASEM) revealed the presence of micrometre-sized grains of apatite and pore filling precipitates of an unidentified (REE, Ca)-phosphate (approximate composition Ca 0.3–0.4(Ce 0.4La 0.1–0.2Nd 0.1)PO 4) in some glauconite grains. The inherent REE concentrations of the glauconite aggregates (i.e., glauconite crystallites without accidental mechanical inclusions or authigenic, not layer silicate mineral precipitates) was found to be relatively low (e.g., typically less than 100 ppm), and this value decreased with increasing glauconitisation (smectite–mica transformation through a series of recrystallisation processes). These results suggest that the REEs substitute for Ca in the interlayer space of the layer silicate structure and, therefore, the REE content decreases as Ca is progressively removed from the interlayer (smectite–mica transition). LA-ICP-MS, when combined with electron probe microanalysis (EPMA) or ASEM, offers an opportunity to exclude submicroscopic accessory minerals from glauconite trace element analyses, and so produces reliable trace element data for the respective minerals which host those elements. These results illustrate that accessory minerals are difficult to eliminate from clay samples, and that care needs to be taken in the interpretation of clay mineral REE distributions, irrespective of the aggregation state of the studied clay (i.e., whether finely dispersed within the sedimentary rock, or forming millimetre-sized aggregates). Model calculations showed that authigenic apatite associated with the studied green marine clays tends to have higher REE content than “bioapatites”, the total REE content being above 10 000 ppm.

Biodegradation of clay minerals under the influence of cyanobacterial-actinomycetal associations

The capacity of associations of cyanobacteria and actinomycetes to transform the structure of clay minerals (kaolin, vermiculite, mica, and montmorillonite) was experimentally revealed. First, easily weatherable vermiculite and biotite were transformed. The rate of transformation of micas to mixed-layered minerals depended on their structure: trioctahedral mica (biotite, the component of vermiculite) was changed much faster than dioctahedral mica (the component of kaolin). The lattices of all the phyllosilicates were altered (disordered and disaggregated) under the influence of the cyanobacterial-actinomycetal associations.

Root organic acid exudates and properties of rhizosphere soils of white spruce (Picea glauca) and subalpine fir (Abies lasiocarpa)

Rhizosphere processes, such as the production and release of organic acids, contribute to differences in properties between rhizosphere (R) and nonrhizosphere (NR) soils. We compared the organic acid composition/concentrations in the R and NR soil extracts of Picea glauca and Abies lasiocarpa, and in the root exudates of the same tree species. We also evaluated the chemical properties and mineral composition of the soil samples. Higher concentrations of organic acids were observed in R than in NR soils with aliphatic acids predominating in both soil extracts and root exudates. Acetic, formic, and protocatechuic acids were the predominant aliphatic and aromatic organic acids in R and NR soil extracts. Several organic acids in R soil extracts were not detected in NR soil extracts, with the reverse being true as well. Malonic and oxalic acids were predominant in the root exudates of both plant species. The total organic acid concentration was higher in P. glauca than in A. lasiocarpa. Glutaric and isocitric acids were found only in A. lasiocarpa, while gluconic, succinic, and protocatechuic acids were exclusive to P. glauca. Acetic and formic acids were detected in all R soil extracts, but not in root exudates. Glutaric acid (in P. glauca) and gluconic/succinic acids (A. lasiocarpa) were undetectable in root exudates, but were present in the corresponding R soil extracts. Soil pH was lower in the R than NR soil of P. glauca. Cation exchange capacity, and exchangeable Ca2+ and K+ were higher in R than in NR soils except for the A. lasiocarpa LFH horizon. Chlorite, mica, kaolinite, and vermiculite were detected in all soil samples. Smectite was detected more frequently in R than NR soils. Our results suggest that high amounts of organic acids might have played a significant role in the transformation of mica and chlorite into smectite in R soils.Key words: Rhizosphere, root exudates, organic acids

The illitization of dickite: chemical and structural evolution of illite from diagenetic to metamorphic conditions

The illitization of dickite is commonly observed at diagenetic to low-grade metamorphic conditions in Triassic rocks from the Betic-Rif Cordillera. It has been studied by X-ray diffraction and by scanning and transmission/analytical electron microscopy. Dickite is a well-ordered diagenetic phase that occurs filling the secondary porosity in sandstones and conglomerates. In diagenetic samples, the alteration of dickite to illite produces thin 1 M mica crystals with incomplete interlayer occupancy (illite), wide chemical variability, and low Na contents. Under low anchizonal conditions, the illitization process is more advanced and 2 M 1 K-illite coexists with minor dickite, sudoite, and 1 M intermediate Na–K-illite. At higher anchizonal conditions only relics of dickite persist, whereas pyrophyllite coexists with 2 M 1 illite/muscovite with K-rich composition, indicating an approach to equilibrium. Alteration of dickite to illite and sudoite mainly progresses along the dickite layers and produces progressively larger packets of 1 M and 2 M 1 white mica. Alteration of dickite to pyrophyllite advances parallel and transverse to the dickite layers. The entry of appreciable amounts of Na into the illite structure seems to depend not on the rock composition but on the metamorphic conditions, i.e . temperature. The dickite to Na–K white mica transformation is an alternative, and probably common way, not previously described, for forming Na-bearing mica in coarse-grained smectite-poor rocks.

Mineralogy and Genesis of Smectites in an Alkaline-Saline Environment of Pantanal Wetland, Brazil

AbstractSmectite formation in alkaline-saline environments has been attributed to direct precipitation from solution and/or transformation from precursor minerals, but these mechanisms are not universally agreed upon in the literature. The objective of this work was to investigate the mineralogy of smectites in the soils surrounding a representative alkaline-saline lake of Nhecolândia, a sub-region of the Pantanal wetland, Brazil, and then to identify the mechanisms of their formation.Soils were sampled along a toposequence and analyzed by X-ray diffraction, transmission electron microscopy-energy dispersive X-ray analysis, and inductively coupled plasma-mass spectrometry. Water was collected along a transect involving the studied toposequence and equilibrium diagrams were calculated using the databases PHREEQC and AQUA.The fine-clay fraction is dominated by smectite, mica, and kaolinite. Smectites are concentrated at two places in the toposequence: an upper zone, which includes the soil horizons rarely reached by the lake-level variation; and a lower zone, which includes the surface horizon within the area of seasonal lake-level variation. Within the upper zone, the smectite is dioctahedral, rich in Al and Fe, and is classified as ferribeidellite. This phase is interstratified with mica and vermiculite and has an Fe content similar to that of the mica identified. These characteristics suggest that the ferribeidellite originates from transformation of micas and that vermiculite is an intermediate phase in this transformation. Within the lower zone, smectites are dominantly trioctahedral, Mg-rich, and are saponitic and stevensitic minerals. In addition, samples enriched in these minerals have much smaller rare-earth element (REE) contents than other soil samples. The water chemistry shows a geochemical control of Mg and saturation with respect to Mg-smectites in the more saline waters. The REE contents, water chemistry, and the presence of Mg-smectite where maximum evaporation is expected, suggest that saponitic and stevensitic minerals originate by chemical precipitation from the water column of the alkaline-saline lake.

EFFECTS OF SECONDARY SOIL FORMING PROCESSES AFTER DEPOSITTION ON THE CLAY MINERALOGICAL COMPOSITION OF SALINE SOILS AND ACID SULFATE SOILS IN VIETNAM

The clay mineralogical composition was examined for 4 profiles of each of saline soils and acid sulfate soils collected from some important river systems of Vietnam. Predominant clay minerals of saline and acid sulfate soils were found to be mica and kaolinite, accompanied with mica/vermiculite/smectite∼mica/smectite mixed-layer mineral, vermiculite, chlorite and smectite. The clay mineralogical composition of these soils was compared with that of alluvial soils from the corresponding river systems/agro-ecological regions in order to clarify the effects of the secondary soil forming processes of salinization and acidification (as a result of pyrite oxidization) on the clay mineralogical composition of the soils. It was hardly observed the mineralogical differences based on the distribution pattern of major clay minerals in the clay fraction. Then, examination of correlation between mineral contents was taken for the selected pairs of clay minerals, and the clay mineralogical alteration was somewhat indicated. In saline soils, it was the transformation of mica into expansible 2:1 layer silicate minerals. In alkaline saline soils, the transformation of mica into vermiculite occurred principally due to presence of a large amount of Ca and Mg salts in soil. In case of acid sulfate soils, the transformation into kaolinite (1:1 layer mineral) was suggested. However, such clay mineral transformations have occurred limitedly in soils. This is probably due to prevention of the development of salinization and oxidation by the secondary soil forming processes under paddy-rice cultivation and mangrove forestation. Based on these results, it could be asserted that saline soils and acid sulfate soils, in general, still kept the essence of the original alluvial soils.