Weathering of chlorite and mica in a new Brunswick Podzol developed on till derived from chlorite-mica schist

A study was made of the weathering of trioctahedral, iron-rich chlorite and dioctahedral mica in a Spodosol (Haplorthod) developed on till derived from chlorite-mica schist.Chlorite in the clay of the B and C horizons has weathered to small amounts of regularly interstratified chlorite-vermiculite, vermiculite and goethite. Chlorite vermiculitization is associated with a loss of iron and aluminum and appears to result in a change toward dioctahedral structure. Chlorite and its trioctahedral vermiculitic products are absent from the clay, silt and sand of the Ae horizon which is probably due to decomposition by organic acids.Mica in this soil weathers and expands to dioctahedral, regularly interstratified mica-ermiculite and discrete vermiculite products that increase in abundance towards the profile surface and are dominant in the clay of the Ae horizon. Amounts of mica-derived vermiculite products decrease with increase in particle size and are practically absent in the sand of the Ae horizon.Comparing mineral weathering in this Spodosol with that in other soils, developed on similar greenschist material but in warmer climates or during longer times, shows that amounts of chlorite-derived vermiculite in the subsoils of the latter soils are much larger, decrease towards the profile surface, and increase with larger particle size. The evidence indicates that weathering of chlorite to vermiculite and accumulation of the vermiculite products are optimal in non-eluvial, moderate weathering conditions.     

SANDSTONE-DERIVED SOILS OF A CATENA AT IPERU, NIGERIA

Chemical and mineralogical properties of five soil profiles of a catena in Iperu, Western State of Nigeria, are reported. The pH values of the subsoils are extremely acid. Acidity decreases with improved drainage in the subsoils (pH 4.0–5.8). The cation exchange capacity (C.E.C.) of the soils range from 3.0 to 16.2 me/100g of soil. The silt: silt+clay ratio, calcium: magnesium ratio and Fe₂O₃:Al₂O₃ ratio are used as weathering indices. The low values of the silt: silt + clay index indicate that the soils must have undergone advanced weathering. The magnitude of the Ca: Mg ratio indicates that more calcium than magnesium is available in the soils. The values for sodium and potassium are extremely low. More iron than aluminium was extracted from the soils by the dithionite-citrate method. Kaolinite is the most abundant clay mineral. Halloysite, interstratified clay materials, vermiculite, quartz, and mica are present in considerable amounts. The silt fraction in which quartz is the most abundant mineral, also contain some kaolinite and mica.     

Influence of pH on the formation of the hydroxy Al-montmorillonite complex

The presence of so-valled chlorite-like minerals has been reported in many soils of not only acid but also of alkaline reaction (1). The minerals have been designated by, many terms, for example, dioctahedral vermiculite (2), dioctahedral analogue of vermiculite (3), 14A mineral (4), chlorite-like mineral (5), interstratified chlorite-vermiculite (6), intergradient chlorite-expansible 2:1 layer silicate, intergradient chlorite-vermiculite, intergradient chlorite-vermiculite-montmorillonite, intergrade, or interlayered vermiculite (7), and 2: 1-2: 2 intergrade (1). The minerals designated by these terms are evidently of the same category, and some of them are synonymous. Although they are of intermediate properties, between true chlorite and true vermiculite or montomorillonite, they could be regarded as an independent group of minerals in the course of pedochemical weathering. Jackson (1), for instance, has given the minerals the position of “weathering index 9”, placing them between vermiculite and kaolin as equivalent to montmorillonite, or secondary chlorite and kaolin in his weathering sequence. An explanation of the diagenesis of the minerals has been recently attempted by synthesis of the chlorite-like structures from montmorillonite (8), (9) and vermiculite (10) and mineralogical analyses of soil clay fractions (7).     

Fine silt and clay mineralogical changes of a soil chronosequence in the Langtang valley (Central Nepal)

Chemical and mineralogical properties of a soil chronosequence in the high mountain zone between 3857 m and 4120 m a.s.l. in Central Nepal (Langtang valley) are presented. The soils have been developed in moraine deposits which consist of acid gneisses. They were classified as Entisols, and Spodosols. XRD analyses of the clay and fine silt fraction show increasing changes with distance from the recent Lirung glacier, depending on the time of deposition, resp. soil age. Alteration of illite to interstratified minerals and to hydroxy-Al interlayered minerals or pedogenic chlorite with increasing soil development could be observed. The interstratified minerals could be identified as random and regular illite-interlayered vermiculite mixed-layer minerals. Intensification of the X-ray signals of the fine silt fraction is given compared to the clay. With increasing soil development differences between the clay and fine silt fraction seem to increase. Indications are given of interstratification of the mica-pedogenic chlorite and chloriteinterlayered vermiculite type in the more intensively weathered soils.     

Clay mineral evolution along a soil chronosequence in an Alpine proglacial area

As a consequence of global warming, additional areas will become ice-free and subject to weathering and soil formation. The most evident soil changes in the Alps will occur in proglacial areas where young soils will continuously develop due to glacier retreat. Little is known about the initial stages of weathering and soil formation, i.e. during the first decades of soil genesis. In this study, we investigated clay minerals formation during a time span 0-150 years in the proglacial area of Morteratsch (Swiss Alps). The soils developed on granitic till and were Lithic Leptosols.Mineralogical measurements of the clay (< 2 μm) and fine silt fraction (2-32 μm) were carried out using XRD (X-ray Diffraction) and DRIFT (Diffuse Reflectance Infrared Fourier Transform). Fast formation and transformation mechanisms were measured in the clay fraction. The decreasing proportion of trioctahedral phases with time confirmed active chemical weathering. Since the start of soil formation, smectite was actively formed. Some smectite (low charge) and vermiculite (high charge) was however already present in the parent material. Main source of smectite formation was biotite, hornblende and probably plagioclase. Furthermore, irregularly and regularly interstratified clay minerals (mica-HIV or mica-vermiculite) were formed immediately after the start of moraine exposure to weathering. In addition, hydroxy-interlayered smectite (HIS) as a transitory weathering product from mica to smectite was detected. Furthermore, since the start of soil evolution, kaolinite was progressively formed. In the silt fraction, only little changes could be detected; i.e. some formation of an interstratified mica-HIV or mica-vermiculite phase.The detected clay mineral formation and transformation mechanisms within this short time span confirmed the high reactivity of freshly exposed sediments, even in a cryic environment.     

Biotite weathering in peaty-podzolic gleyic soil under conditions of a model field experiment

Changes in biotite (fraction 1–5 μm) after exposure in the T2, H, Eih, and E horizons of peatypodzolic gleyic soil under conditions of a model field experiment were studied by X-ray diffraction. It was found that the main transformations of the biotite in all horizons included the degradation of its crystal lattice into regularly interstratified biotite-vermiculite and randomly interstratified biotite-smectite structures and vermiculite. The transformation intensity decreased down the profile simultaneously with a reduction in the content of organic matter, roots, and microbiota population and activity. Chloritized structures were also present among the biotite weathering products in the E horizon. The main identified products of biotite weathering formed in horizons Eih and E over a five-year period of the model experiment were detected in the clay and fine silt fractions of these horizons and in native peaty-podzolic gleyic soils. This suggests that vermiculite and soil chlorite in the soils studied are products of soil functioning. It follows from the results, with consideration for literature data, that the weathering of biotite results in the formation of a potassium-buffering system.     

Mineral Composition and Weathering of Soils Derived from Xiashu Loess

Mineralogical, physical and chemical analyses of the soils derived from Xiashu loess were carried out. The primary minerals of these soils were found to be mainly composed of light minerals, such as quartz, feldspar and mica, with traces of heavy minerals. Clay minerals, more complicate in composition, were dominated by hydromica, accompanied by smectite, vermiculite, chlorite, kaolinite, 2:1/1:1 randomly interstratified minerals and small amounts of quartz, goethite, lepidocrocite and hematite, Clay minerals were characterized by low crystallinity and fine particle size. In light of the quartz/feldspars ratio of the 0.01-0.05mm silt fraction, and the clay mineral composition, the freeness of iron oxide, and the silica/sesquioxide and silica/alumina ratios in < 0.002mm clay fraction, it is concluded that the weathering intensity of these soils was lower than those of red soil and yellow earth, but higher than that of brown earth, and that the soil allitization, depotassication and hydroxylation of cl     

Mineralogy of a podzol formed in sandy materials in northern denmark

This paper deals with possible mineralogical changes from one particle size fraction to another and from one horizon to another in a Typic Haplorthod. X-ray diffraction and chemical analysis were the main methods used. The investigation indicates that a large part of the fine material in the soil is developed during weathering in situ. Less resistant minerals seem to be protected by being parts of rock fragments in coarser fractions, but once freed from that protection they quickly undergo fragmentation into finer particles. Most of the sand and silt fractions are quartz. The K-feldspar content ranges between about 10 and 20%, the Na-feldspar content from about 15 to 30% and the Ca-feldspar content is very small. The clay minerals are mostly kaolinite and mica and in the A2 horizon, expandable 2:1 minerals containing both smectite and vermiculite layers. The B horizon contains 14 A minerals that resemble interstratified vermiculite—chlorite. In the C horizon both vermiculite—chlorite and clorite occur.     

Genesis of a Xeralf on feldspathic sandstone, South Australia

A Xeralf on feldspathic sandstone was sampled from a hillslope in the Mount Lofty Ranges in order to study its genesis and, in particular, the origin of the strong texture contrast. Micromorphological study demonstrated that the clay present in void argillans and papules in the B2 horizon accounted for only a small amount of the clay present. Elemental analysis of the whole soil (< 2 mm) and sand, silt and clay fractions showed that there had been considerable weathering of both quartz and microcline, which were the dominant minerals present. Kaolinite is the dominant clay mineral weathering product. Illite appears to be forming from vermiculite in the A horizon. Using zircon as an internal standard, it was shown that elemental losses of SiO₂ and reductions in weight and volume were similar in A and B horizons. Losses of aluminium and potassium were greatest in the A horizon, least in the B3. There has been an absolute increase in the amount of iron. A possible source is iron from heavy mineral bands upslope. It was concluded from the similarity of the quartz particle-size distributions of the A2, B2 and B3 horizons that the intensity of weathering of quartz was the same in A and B horizons. In the case of feldspar (mostly microcline), there is a greater proportion of feldspar in the fine sand and silt fractions of the A2 horizon than in the B horizon. Weathering of feldspar is greatest in the A horizon. The texture profile is principally a function of greater lateral loss of clay from the A horizons compared to the B horizons.     

Mineralogic evolution in hydromorphic sandy soils and podzols in “landes du médoc”, France

Soils of the nearly level “Landes du Médoc” in southwestern France have a pattern of alternating bodies of hydromorphic podzols (Haplaquods) and low humic hydromorphic soils (Psammaquents). The soils are formed in a sedimentary mantle of coarse, quartzose sands with a slight microrelief consisting of low, elongated ridges and shallow, intervening troughs. The water table is at shallow depths throughout the plain, even at the surface in places. The podzols on the crests of the low ridges have distinct A₂ and cemented B₂ h horizons. Podzols persist down the sides of ridges but going downslope first lose the A₂ horizon and then the cementation of the Bh horizon. Soils in the shallow troughs have A₁ and Cg horizons without B horizons.The fine silt (2–20 μm) and clay (0–2 μm) fractions of the parent sand contain primary trioctahedral chlorite, mica, feldspars, and quartz, with the last mineral predominant. During soil development, the first three minerals undergo weathering at different rates and to different extents. Chlorite is most strongly weathered, followed in order by plagioclases and K-minerals. In the fine silt fraction, weathering seems to occur mostly by fragmentation of particles. In the clay fraction, the phyllosilicates successively form irregularly interstratified minerals with contractible but not expandable vermiculitic layers, interstratified minerals with contractible and expandable smectitic layers, and finally smectites.The extent to which the silicate minerals are weathered becomes progressively greater from the low humic hydromorphic soils to the podzols with friable Bh horizons to the podzols with cemented Bh horizons. Smectite is present only in the A₂ horizons of these last podzols.The aluminum release by weathering of silicate minerals is translocated in part in the form of organo-metal complexes into the Bh horizons of the podzols. Greatest concentrations of Al are associated with coatings of monomorphic organic matter on mineral grains in the cemented Bh horizons, in which some Al has also crystallized into gibbsite. That mineral was not detected in friable B horizons of podzols nor in the low humic hydromorphic soil. Contrary to expectations, the mobile Al did not enter interlayer spaces of expanding 2:1 clay minerals.     

中国福建省土壤的主要粘土矿物

The clay minerals of more than 200 soil samples collected from various sites of Fujian Province were studied by the X-ray diffraction method and transmission electron microscopy to study their distribution and evolution.Montmorillonite was found in coastal solonchak,paddy soils derived from marine deposit,lacustrine deposit and river deposit,and some lateritic red soil,red soil and yellow soil with a low weathering degree.Chlorite existed mainly in coastal solonchak and paddy soil developed from marine deposit.1.4nm intergradient mineral appeared frequently in yellow soil,red soil and lateritic red soil.The content of 1.4nm intergradient mineral increased with the decrease of weathering degree from lateritic red soil to red soil to yellow soil.Hydrous micas were more in coastal solonchak,paddy soils derived from marine deposit,lacustrine deposit and river deposit.and puple soil from purple shale than in other soils.Kaolinte was the most important clay mineral in the soils iun this province.The higher the soil weathering degree,the more the kaolinite existed.From yellow soil to red soil to lateritic red soil,kaolinite increased gradually,Kaolinite was the predominant clay mineral accompanied by few other minerals in typical lateritic red soil. Tubular halloysite was a widespread clay mineral in soils of Fujian Province with varying quantities.The soil derived from the paent rocks rich in feldspar contained more tubular halloysite.Spheroidal halloysite was found in a red soil and a paddy soil developed from olivine basalt gibbsite in the soils in this district was largely“primary gibbsite” which formed in the early weathering stage.Gibbsite decreased with the increase of weathering degree from yellow soil to red soil to lateritic red soil.Goethite also decreased in the same sequence while hematite increased.     

Spatial distribution of mineral components in microcombinations of agrogrey soils with the second humus horizon in the Vladimir opolie area

Mineralogical composition of silt and clay fractions (<1.1–5 and 5–10 µm) in heavy loamy agrogrey soils (Luvic Retic Phaeozems) considerably changes both in the vertical (along the soil profile) and horizontal (along soil microcatenas) directions. The eluvial–illuvial distribution pattern of the clay fraction in the podzolized agrogrey soils with the second humus horizon is replaced by the homogeneous distribution in the agrogrey soils with residual carbonates. The distribution of silt fractions in the soil profiles is relatively homogeneous. The clay (<1 µm) fraction of the parent material is represented by the poorly ordered micasmectite interstratifications minerals, the proportion between which changes in the soil profiles in dependence on the particular pedogenetic processes. Hydromicas represent the second important component of the clay fraction. They consist of di- and trioctahedral varieties, the proportion between which changes in the soil profiles. Kaolinite and iron–magnesium chlorite are present in smaller amounts. The second humus horizon is characterized by the lowest content of mica-smectite interstratifications minerals with the high content of smectitic layers and by the lowest content of the clay fraction. Silt fractions are composed of quartz, micas, potassium feldspars, and plagioclases.     

The weathering of ferruginous chlorite in a podzol from argyllshire,Scotland

The dominant mineral in the clay fractions from the basal horizons of a podzol developed on till derived mainly from chlorite-schists in Argyllshire is oxidized, iron-rich chlorite. Towards the profile surface, the chlorite decreases in amount, becoming absent in the A₂ horizon in which the dominant mineral is a complex dioctahedral interstratified phase formed from dioctahedral mica and composed of mica and vermiculite. The absence of any trioctahedral mineral in the A₂ horizon together with the marked loss of iron and magnesium from the clay fraction from this horizon indicates that the chlorite, a thuringite, has been destroyed, the only detectable product being goethite. In other apparently similar soils chlorite persists throughout the profiles. As the Eredine podzol contains translocated humus in the B₂ horizon, it is suggested that during podzolization, organic solutions percolated downwards from the surface, formed complexes with iron and aluminium from the chlorite structure, removing them to the B₂ horizon, and thus eventually dissolved out the chlorite from the A₂ horizon.     

CLAY MINERALS IN SOILS DERIVED FROM LOWER OLD RED SANDSTONE TILL: EFFECTS OF INHERITANCE AND PEDOGENESIS

The clay mineralogy of thirty-two profiles located mainly in the Vale of Strathmore and developed on glacial till derived from Lower Red Sandstone sediments and lavas has been investigated by X-ray diffraction. The soils were selected so that the parent material was related predominantly to one of the rock types common in the Lower Old Red Sandstone succession—namely, marl, sandstone, lava, or conglomerate. Comparison of the < 1.4μm fractions separated from fresh rock samples with those separated from the C horizons of the soils clearly established the dominant influence of parent rock on the soil-clay mineralogy. The clay minerals inherited by the soil often include unusual trioctahedral expansible minerals such as saponite, interstratified vermiculite-chlorite, and smectite-vermiculite, as well as more common types like mica, montmorillonite, and chlorite. Kaolinite is also found but it is not certain that it is only of inherited origin. Weathering of the clays during soil formation brings about complete degradation of the expansible trioctahedral minerals, a process usually well advanced in the B or even at the top of the C horizon, and vermiculitization of mica. The latter process occurs mainly in the A horizon, with concomitant precipitation of interlayer aquohydroxy-aluminium ions thereby forming a vermiculite-chlorite intergrade. Chlorite and kaolinite appear to be little affected by weathering. The weathering transformations are most pronounced in freely drained acid soils (pH < s) and are at a minimum in poorly drained soils and where the pH remains above 6. The susceptibility to weathering of the trioctahedral expansible minerals results in relatively high values for exchangeable magnesium at the base of the profile.     

Source minerals and formation of partially interlayered vermiculites in Dystrochrepts derived from Tertiary sediments

The formation of partially interlayered vermiculite (PIV) was studied in six Dystrochrepts derived from Tertiary sediments. Mineralogy of silt and clay fractions of gravel and fine earth separated from surface and subsurface samples were determined by X-ray diffraction. PIV, mica, vermiculite and regularly interstratified 1:1 PIV/chlorite (PIV/Ch(l:l)) were the dominant clay minerals. The contents of these minerals were compared between the specific particle-size fractions of gravel and fine earth for each sample and the difference was interpreted in terms of mineral transformation associated with soil formation. PIV was formed from mica and PIV/Ch(l:l) in soils with a pH(KCl) of 3.5 to 4.0 and little organic matter. Vermiculite was formed from mica in surface soils with a low pH (pH(KCl) 3.5) and abundant organic matter. PIV would form directly from mica without an intermediary phase of vermiculite and form from PIV/Ch(l:l) by partial dissolution of interlayers in chlorite layers.     

Changes caused by Norway spruce in an ochreous brown earth, assessed by the isoquartz method

Previous investigations had shown that about 80 years of Norway spruce monoculture on an ochreous brown earth of the Belgian Ardennes were sufficient to accentuate the weak podzolization process already present in the climax beechwood soil and to increase the weathering of several minerals, e.g. 2:2 clay minerals. In order to evaluate more accurately mineral weathering and spruce-induced losses of nutrient elements, an isoquartz assessment method has been applied to a pair of soil profiles, one developed under beech, the other under spruce.
Results show a clear decrease of several weatherable minerals in the soil of the spruce stand which was more marked than in the beechwood, especially for chloritic minerals: losses reach about 30% of the initial chlorite content in the cambic horizon and regularly increase up to 70% in the humic layer. There were severe spruce-induced losses of Mg and Na: 27% of the initial Mg reserve was removed from the whole soil and the losses reached 60% in the upper 20 cm.
It is concluded that 86 years of Norway spruce monoculture have appreciably increased weathering processes and removal of elements.     

Differentiation of layered silicates and biogenic silica in meadow podbel soils of the Central Amur Lowland

Mineralogy of the fine component of meadow podbel soil in the Central Amur Lowland significantly varies depending on texture differentiation within the profile and clay categories with different binding strengths (water-peptized and aggregated clay). In the eluvial part of the profile, hydromicas are predominant, which are accompanied by kaolinite and mica-smectites with a low content of smectite layers; there are many finely dispersed quartz and feldspars; plagioclases are less abundant. The illuvial part of the profile is characterized by a high content of smectite minerals (mica-smectite and kaolinite-smectite interstratifications). Kaolinite, chlorite, and chlorite-vermiculite are also found. Fragmentary components pass into a peptized state: micas-hydromicas, kaolinite, finely dispersed quartz, feldspars, plagioclases, amphiboles, and diatom skeletons (mainly in the illuvial part of the profile). Aggregated clays are characterized by a high content of interstratifications with smectite layers. The mineral composition of two clay categories is strongly differentiated according to eluvial-illuvial type. The bulk chemical composition confirms the textural differentiation of the finely dispersed component within the profile. The chemistry of silty sand cutans on the faces of structural units in the illuvial part of the profile significantly differs from the chemistry of the enclosing horizon and is analogous to that of the eluvial part of the profile. The involvement of silica in the meadow podbel fractions with different binding strengths has been revealed.     

THE WEATHERING OF CHLORITIC MINERALS IN SOME SCOTTISH SOILS

The mineralogy of 14 chloritic soils of various drainage classes developed on different parent materials from the Loch Awe area of Argyllshire, Caithness, and the Southern Uplands reveals only minor variations'in clay mineralogy with profile depth, the frequent presence of primary minerals indicating that all the soils are immature, and that weathering is at an early stage. Iron-rich chlorite generally persists throughout the profiles, varying little in amount or chemical composition between horizons; where identifiable, the polytype is II b. Oxidation of iron modifies the thermal characteristics of the chlorite in all the freely-drained soils but usually only in the surface horizons of gleys. Irrespective of soil type or drainage class, in most profiles chlorite weathers only slightly, probably by vermiculitization around the edges of flakes.     

Mineralogical and geo-chemical characterization of a diapiric formation in the North of Spain

We have selected seven profiles located in a diapiric formation in the North of Spain. The profiles have been analyzed for the mineralogy and the chemical composition of original materials, soils developed above them and clay fractions. Three soils formed on basic rock of volcanic origin (ophite) and rich in alterable minerals, three others formed on clay marl and one soil formed on gypsiferous marl. Plagioclases, pyroxenes, vermiculites, and biotites are the main minerals found in the soil samples and ophitic rocks. Biotite, smectite, chlorite and interstratified chlorite–vermiculite make up the predominant mineralogical association in the clay fraction of the soils. Calcite, biotite and on top of all chlorite are the main minerals in the marls and the soils developed on them, with gypsum predominant in the gypsiferous marl. The mineralogy of its clay fraction is comprised mainly of chlorite and biotite. The variations in content of Al₂O₃, TiO₂ and Na₂O in the ophites are considered to be associated with the differences in the evolution of the pyroxenes. The variability of the chemical composition of the Keuper sediments and the soils is attributed more to the chaotic disposition of the Triassic materials in the formation of the diapir than to intense chemical weathering. The low concentrations of silica, iron, and aluminum extractable with ammonium oxalate indicate the low proportion of non-crystalline products. Fundamentally, it is the semiarid conditions in the study zone, together with the processes of extrusion and hydrothermal activity affecting the formation of the diapir, that are responsible for the genesis of the minerals.     

Biotite weathering in podzolic soil under conditions of a model field experiment

The biotite changes in the 1–5 μm fraction after its occurrence in the F, H, AE, and E horizons of a pale-podzolic soil for five years under conditions of a model field experiment were assessed by X-ray diffraction analysis. It was found that the main changes of the biotite in all the horizons included the degradational transformation of its crystal lattice to interstratified mica-vermiculite structures and vermiculite. The intensity of this process gradually decreased from the F horizon down the profile in parallel with the decrease in the amount of roots and the abundance and activity of microbiota. Chloritized structures were present among the products of the biotite weathering in the H, AE, and E horizons; the degree of chloritization gradually increased from the H horizon to the E horizon. The main identified products of the biotite weathering in the AE and E horizons formed during the 5 years of the model experiment were identified in the clay and fine-silt fractions from these horizons of the native pale-podzolic soils. Therefore, the vermiculite, soil chlorite, and mixed-layer illite-vermiculite minerals in the soils studied could be considered as products of the recent soil functioning. The obtained results and literature data showed that the weathering of biotite resulted in the formation of K- and Al-buffer systems.