Reports of scientific investigations published in Clays and Clay Minerals address a wide range of topics covering virtually every physical and natural science and thousands of industrial products and processes worldwide. Even though these nano-sized materials occur naturally throughout the Earth's crust, a large proportion of the studies carried out in the past regarding their origins, nature, and uses, as reported in Clays and Clay Minerals, have arisen predominantly from North America and Europe. In recent years, however, manuscript submissions from China have increased appreciably (Figure 1). In the current issue, a number of those studies were selected for a compilation in order to highlight the contributions being made by Chinese colleagues, which gives a glimpse into the types of clay research under way in that country. The manuscripts selected do not, of course, represent a comprehensive treatise of clay research in China, but rather an opportune emphasis that is intended to call attention to the work being done there.

Contaminant-transport modeling requires information about the charge of subsurface particle surfaces. Because values are commonly reused many times in a single simulation, small errors can be magnified greatly. Goethite (α-FeOOH) and pyrolusite (β-MnO2) are ubiquitous mineral phases that are especially contaminant reactive. The objective of the present study was to measure and compare the point of zero charge (PZC) using different methods. The pyrolusite PZC was measured with three methods: mass titration (MT) (PZC = 5.9±0.1), powder addition (PA) (PZC = 5.98±0.08), and isoelectric point, IEP (PZC = 4.4±0.1). The IEP measurement was in agreement with literature values. However, MT and PA resulted in a statistically larger PZC than the IEP measurement. The surface area of pyrolusite, 2.2 m2g−1, was too small to permit PZC determination by the potentiometric titration (PT) method. Goethite PZC values were measured using MT (7.5±0.1), PT (7.46±0.09), and PA (7.20±0.08). The present work presents the first reported instance where MT and PA have been applied to measure the point of zero charge of either pyrolusite or goethite. The results illustrate the importance of using multiple, complementary techniques to measure PZC values accurately.

Pillared clays (PILCs) with magnetic properties have significant potential for application in industry and the environment, but relatively few studies of these types of materials have been carried out. The aim of the present work was to gain insight into the magnetic and structural properties of pillared clays by examining in detail the influence of the calcination temperature and the nature of different pillared clays on these properties.

Magnetic layered systems from different pillared clays were prepared and characterized. Firstly, Ti-, Al-, and Zr-pillared clays (Ti-PILCs, Al-PILCs, and Zr-PILCs, respectively) were produced at different calcination temperatures and then magnetic pillared clays (Ti-M-PILCs, Al-M-PILCs, and Zr-M-PILCs) were prepared at ambient temperature. The synthesis involves a reduction in aqueous solution of the original Fe-exchanged pillared clay using NaBH4. The structural properties of pillared clays and their magnetic forms were investigated using X-ray diffraction, N2 adsorption, cation exchange capacity determination, and X-ray fluorescence (XRF) measurements. The properties of the magnetic pillared clays were investigated by superconducting quantum interference devices and Mössbauer spectroscopy. An evaluation of the data obtained allowed an estimation of the pillared structure in one PILC-model before and after magnetization. The model was determined on the basis of a simple geometric model and experimental data leading to the calculation of a filling factor (FF) which contained information about the number of intercalated pillared layers and the unaffected layers. In the case of Ti precursors, the best calcination temperature was 400°C, which maintained the highest specific surface area and pore volume with magnetic parameters suitable for magnetic application. Similar experiments with Al- and Zr-pillars have been discussed. A correlation between the XRF data, porosity, FF calculation, and magnetic properties led to the conclusion that the sample Al-M-PILC previously calcined at 500°C was the most stable material after the magnetization process. The same examination in the case of Zr materials suggested that the most stable sample had been calcined at 300°C (sample Zr-M-PILC-300).

The naturally occurring layered double hydroxides (LDH, or anionic clays) are of particular interest in environmental geochemistry because of their ability to retain hazardous cations and especially anions. However, incorporation of these minerals into predictive models of water-rock interaction in contaminant environments, including radioactive-waste repositories, is hampered by a lack of thermodynamic and stability data. To fill part of this gap the present authors have derived properties of one of the complex multicomponent solid solutions within the LDH family: the hydrotalcite-pyroaurite series, Mg3(Al1−xFex)(OH)8(CO3)0.5·2.5H2O.

Members of the hydrotalcite-pyroaurite series with fixed MgII/(AlIII+FeIII) = 3 and various FeIII/(FeIII+AlIII) ratios were synthesized by co-precipitation and dissolved in long-term experiments at 23±2°C and pH = 11.40±0.03. The chemical compositions of co-existing solid and aqueous phases were determined by inductively coupled plasma-optical emission spectroscopy, thermogravimetric analysis, and liquid scintillation counting of 55Fe tracers; X-ray diffraction and Raman were used to characterize the solids. Based on good evidence for reversible equilibrium in the experiments, the thermodynamic properties of the solid solution were examined using total-scale Lippmann solubility products, ΣΠT. No significant difference was observed between values of SPT from co-precipitation and from dissolution experiments throughout the whole range of Fe/Al ratios. A simple ideal solid-solution model with similar end-member ΣΠT values (a regular model with 0 < WG < 2 kJ mol −1 sufficient to describe the full range of intermediate mineral compositions. In turn, this yielded the first estimate of the standard Gibbs free energy of the pyroaurite end member, G298,Pyro = −3882.60±2.00 kJ/mol, consistent with G298,Htlco = −4339.85 kJ/mol of the hydrotalcite end member, and with the whole range of solubilities of the mixed phases. The molar volumes of the solid-solution at standard conditions were derived from X-ray data. Finally, Helgeson’s method was used to extend the estimates of standard molar entropy and heat capacity of the end members over the pressure-temperature range 0−70°C and 1–100 bar.

Among the many techniques used to remove toxic dyes from the environment, layered double hydroxides (LDH) are considered to be especially environmentally friendly, but, this quality may be altered by variations in the octahedral Mg/Al molar ratios in the LDH structure. The aim of the present study was to synthesize environmentally sound LDH for use as an economically viable sorbent for the adsorption of reactive brilliant orange X-GN. Layered double hydroxides with Mg/Al molar ratios of 2:1 and 4:1 were prepared by co-precipitation. The materials obtained were characterized by powder X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, X-ray fluorescence spectroscopy (XRF), and surface-area analysis. Batch experiments were carried out to investigate the effects of contact time, pH, adsorbent dosage, and initial dye concentration on the adsorption behavior of the reactive brilliant orange X-GN by Mg-Al LDH. The results showed that the optimum pH value for dye adsorption was 3.0, at which the adsorption capacities of the reactive brilliant orange X-GN by the 2:1 LDH and the 4:1 LDH at 298 K were 79.370 mg/g and 83.343 mg/g, respectively. Further analysis of the dye-adsorption kinetics show that they fit the pseudo second-order model well. The adsorption equilibrium data showed that the Langmuir model provided better correlation of the equilibrium data than the Freundlich model. This result indicates that LDH provide specific homogeneous sites where monolayer dye adsorption occurs. The results of XRD and FTIR analyses of LDH before and after the dye adsorption demonstrated that the adsorption mechanisms were ion exchange and coulombic attraction.

Kaolinite is a common gangue mineral in iron ore and sodium silicate has been used widely as a dispersant of silicate gangue minerals including kaolinite in various iron-ore flotation methods over a wide range of pH. Its actual dispersive effect on kaolinite under iron-ore flotation conditions has received very limited attention, however. The presence of hydrolyzable metal cations in process water further complicates sodium silicate—kaolinite interactions. In the present study, the dispersive effect of sodium silicate on kaolinite particles in distilled water as well as in CaCl2 and MgCl2 solutions was investigated systematically through electrophoretic mobility and colloid-stability studies. The studies were based on controlled pH, which eliminated the dispersive effect of sodium silicate induced by increasingpulp pH, in order to simulate the conditions of iron-ore processing. With pH controlled at constant levels, sodium silicate dispersed kaolinite only when positively charged sites were present on kaolinite surfaces and the zeta potential of kaolinite was more negative than ~−30 mV. Over the pH range from 5 to 10.5, a significant dispersive effect of sodium silicate was only observed at pH 7. In process water, when Ca and Mgwere present, the strong coagulation of kaolinite particles caused by the hydrolyzable metal cations could not be dispersed effectively with sodium silicate.

The discovery of phyllosilicates in terrains of Noachian age (>3.5 Ga) on Mars implies a period in the planet’s history that was characterized by wetter, warmer conditions that may have been more hospitable for life than the cold and dry conditions prevalent today. More specific information about the original locations and mechanisms of clay mineral formation on Mars is not as well constrained, however, in part because the origin of particular clay minerals is often non-unique. For example, Fe and Mg smectite-bearing deposits on Mars may have formed in various environments, including the weathering profiles of basic volcanic rocks, impact-induced hydrothermal sites, or in bodies of standing water. The identification of lacustrine deposits on Mars is of great interest due to their potential for the preservation of organic material, but identifying any given suite of sedimentary rocks as such is difficult when limited to mineralogy and morphology derived from orbital data. Here, the processes and conditions leading to clay mineral formation in lakes and evaporative marine basins on Earth are reviewed, with a focus on the spatial and stratigraphic distribution of clays in these settings. The goal is to provide criteria to determine if certain Martian clay deposits are consistent with such an origin, which in turn will aid in the identification of possible ancient habitable environments on Mars.

Fougerite (IMA 2003-057) was accepted by the Commission on New Minerals and Mineral Names of the International Mineralogical Association (IMA) in 2004 as a new mineral to represent the green rust (GR) family. The data on which it was approved, however, are inconsistent. X-ray diffraction patterns from the Fougères soils contain no peaks that could meaningfully be attributed to a GR phase. The sequential dissolution procedure used to identify GR in the soils was not rigorously tested for selectivity. If indeed it is selective, the results indicate the presence of 40–78% Fe in minerals other than GR. Other Fe-bearing phases were not included in the interpretation of the spectroscopy data that were presented. The data are consistent with the presence of Fe-bearing clays and other silicate minerals. In light of the ambiguous and conflicting data, we recommend that the case for fougerite as a mineral be re-evaluated by the IMA.

Nontronite is a significant component of commercially important nickel laterite ores. Its behavior during high-pressure acid leaching of such ores may have an impact upon the efficiency of the process. The present study was conducted in order to further investigate the response of this material during high-pressure acid leaching. In situ synchrotron powder X-ray diffraction data were collected from a number of nontronite samples during hydration and leaching reactions at ambient and elevated temperatures. The present study followed previous high-pressure acid-leaching studies of nontronite where unexpected contraction and expansion behavior of the clay was observed by means of in situ X-ray diffraction. In the earlier studies the data sets only extended to ~20 Å so that when the nontronite expanded to greater than 19.5 Å (hydrated) the main 001 peak was only partially visible in the observed d-spacing range. The aim of the current work was to collect similar in situ diffraction data over a greater d-spacing range to observe more fully the movement of the main 001 reflection in order to better understand the changes taking place. This work was undertaken at the powder diffraction beamline of the Australian Synchrotron which was configured such that an upper d-spacing limit of ~34.5 Å could be achieved. Suggestions arising out of the previous work were confirmed along with additional information from testing of samples from the Source Clays Repository of The ClayMinerals Society. These results also show contradictory behavior of clays with the layer charge distributed over tetrahedral and octahedral sheets.

Mesoporous materials with pore diameters in the range 2–50 nm forming tubular or fibrous structures are of great interest due to their unique properties. Because they are commonly used as sorbents and catalyst carriers, knowledge of their surface area and porosity is critical. A modified intercalation/deintercalation method was used to increase the efficiency of nanotube formation from kaolin-group minerals which differ in terms of their degree of structural order. Unlike previous experiments, in the procedure adopted in the present study, methanol was used instead of 1,3-butanediol for grafting reactions and octadecylamine intercalation was also performed. The samples were examined using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). The specific surface area and porosity of previously described and newly formed materials were investigated by N2 adsorption/desorption. Compared to results described earlier, the percent yield of nanotubes obtained in the present study was significantly greater only in the case of ‘Maria III’ kaolinite, which has high structural order. This increase was obtained mainly by the grafting reaction with methanol. Highly ordered stacking of kaolinite-methanol intercalates was noticed and, thus, the amine intercalation was more efficient. In particular, the use of long-chain octadecylamine significantly increased the nanotube yield. The grafting reaction with methanol procedure yielded fewer nanotubes, however, when applied to poorly ordered samples (‘Jaroszów’ kaolinite and ‘Dunino’ halloysite). In the case of the ‘Maria III’ kaolinite, the diameter of the rolled layers observed by TEM was ~30 nm and corresponded to average diameters of newly formed pores (DmN) determined using N2 adsorption/desorption, confirming that nanotubes contributed to an increase in surface area and total pore volume. In the case of ‘Jaroszów’ kaolinite and ‘Dunino’ halloysite mainly macropores (DmN > 100 nm) and mesopores (20 nm > DmN > 40 nm) were formed. The pores were attributed to interparticle and interaggregate spaces in the stacks of platy particles and to the small relative number of nanotubes.

Most natural and synthetic rubbers have inherently high flammability, a property which limits their uses. The aim of the present work was to study the effect of organo-montmorillonite (OMMT) and modified OMMT on the flame-retardance and mechanical properties of natural rubber (NR) composites. The OMMT was modified with hyper-branched polymer via condensation polymerization between the intercalation agent, N,N-di(2-hydroxyethyl)-N-dodecyl-N-methylammonium chloride, and the monomer, N,N-dihydroxyl-3-aminomethyl propionate. This modified OMMT was then reacted with phosphate, and a novel flame-retardant hyper-branched organic montmorillonite (FR-HOMMT) was thus obtained. The surface morphology, interlayer space, interlamellar structure, and thermal properties of these modified clays were investigated by Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis. The FR-HOMMT showed increased basal spacing and better thermal stabilities due to the different arrangement and thermal stability of the novel organic macromolecular surfactant. Natural rubber NR/OMMT and NR/FR-HOMMT composites were prepared by conventional compounding with OMMT and the phosphorus-based organo-montmorillonite. The cure characteristics, tensile strength, wear resistance, thermal stabilities, and flame-retardant properties were researched and compared. The best dispersion of this modified clay was observed for 20 phr (parts per hundred of rubber) of FR-HOMMT-filled composite, which resulted in the best mechanical performance with an increase of 47% in tensile strength, of 40% in elongation at break, and decrease of 140% in abrasion loss compared with 20 phr of the OMMT-filled matrix. A mechanism for reinforcing and flame retardance is proposed here. The 'anchor' effect caused by the hyper-branched polymer may decrease the number and size of the voids in the NR matrix, and thus increase the crack path during tensile drawing. Meanwhile, the flame retardance of the OMMT and the phosphate may increase the number of carbonaceous layers, thus inhibiting the degree of pyrolysis of the NR matrix during burning.

Mercury ion removal from waste-waters has been the subject of extensive research. The aim of the present investigation was to report the incorporation of the n-alkylamine molecules onto a bentonite surface and the capacities of these new chelating moieties on this modified bentonite surface for mercury removal from water. Bentonite collected from the Amazon region, Brazil, was used in an intercalation process with polar n-alkylamine molecules of general formula H3C(CH2)n-NH2 (n = 1 to 4) in 1,2-dichloroethane. The natural and modified bentonite samples were characterized by elemental analysis, Xray diffraction, helium picnometry, mercury porosimetry, and 29Si, 27Al, and 13C nuclear magnetic resonance spectroscopy. Because of the increasing size of the molecules attached to the pendant chains, the metal-adsorption capability of the final chelating materials was measured in each case. The adsorption of Hg(II) on natural and modified bentonites was determined under different conditions. The effects of concentration of Hg(II), contact time, and pH were investigated; batch and dynamic adsorption experiments of Hg(II) were conducted on bentonite samples under various conditions. The ability of these materials to remove Hg(II) from aqueous solution was assessed by means of a series of adsorption isotherms at room temperature and pH 4.0. In order to evaluate the bentonite samples as adsorbents in a dynamic system, a glass column was filled with clay samples (1.0 g each) and fed with 1.8 × 10−4 mol dm−3 Hg(II) at pH 4.0. The energetic effects caused by adsorption of metal cations were determined by means of calorimetric titrations. Thermodynamics indicated the existence of favorable conditions for such Hg(II)-nitrogen interactions.

Magnetite (Fe3O4) is a key economically valuable component in iron ore and is extracted by dissolution processes, but among the Fe (oxyhydr)oxides its solubility behavior is one of the least understood. The objective of this study was to improve understanding of magnetite dissolution mechanisms leading to thermodynamic equilibrium by comparing the dissolution of two solid samples, one synthetic and one industrial, using oxalic, sulfuric, and nitric acids at varying concentrations and temperatures. Of the three solid-liquid systems investigated, only the system consisting of magnetite and oxalic acid reached an equilibrium state within the duration of an individual experiment (6 h). In this system, increasing the acid concentration resulted in a significant increase in the equilibrium concentration of dissolved Fe. When dissolving synthetic and industrial magnetite, increasing the temperature not only increased the rate of reaction but also affected the concentration of dissolved Fe. Significant effects were observed when increasing the temperature from 15 to 35°C, but only slight differences were seen on further increases in temperature. Observations regarding the equilibrium state of the sulfuric and nitric acid systems could not be made because equilibrium was not reached. The most important individual observation regarding the equilibrium state of the nitric- and sulfuric-acid systems seems to be that in future studies a much longer reaction time is necessary, due to slow kinetics of the dissolution mechanism. A proton-based mechanism has been hypothesized as the one governing the dissolution of magnetite by these two acids, but only the dissolution of the industrial sample yielded results that were similar for these two acids and consistent with that hypothesis.

The enhanced spatial and spectral resolution provided by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on the Mars Reconnaissance Orbiter (MRO) has led to the discovery of numerous hydrated silicate minerals on Mars, particularly in the ancient, cratered crust comprising the southern highlands. Phases recently identified using visible/near-infrared spectra include: smectite, chlorite, prehnite, high-charge phyllosilicates (illite or muscovite), the zeolite analcime, opaline silica, and serpentine. Some mineral assemblages represent the products of aqueous alteration at elevated temperatures. Geologic occurrences of these mineral assemblages are described using examples from west of the Isidis basin near the Nili Fossae and with reference to differences in implied temperature, fluid composition, and starting materials during alteration. The alteration minerals are not distributed homogeneously. Rather, certain craters host distinctive alteration assemblages: (1) prehnite-chloritesilica, (2) analcime-silica-Fe,Mg-smectite-chlorite, (3) chlorite-illite (muscovite), and (4) serpentine, which furthermore has been found in bedrock units. These assemblages contrast with the prevalence of solely Fe,Mg-smectites in most phyllosilicate-bearing terrains on Mars, and they represent materials altered at depth then exposed by cratering. Of the minerals found to date, prehnite provides the clearest evidence for subsurface, hydrothermal/metamorphic alteration, as it forms only under highly restricted conditions (T = 200–400°C). Multiple mechanisms exist for forming the other individual minerals; however, the most likely formation mechanisms for the characteristic mineralogic assemblages observed are, for (1) and (2), low-grade metamorphism or hydrothermal (<400°C) circulation of fluids in basalt; for (3), transformation of trioctahedral smectites to chlorite and dioctahedral smectites to illite during diagenesis; and for (4), low-grade metamorphism or hydrothermal (<400°C) circulation of fluids in ultramafic rocks. Evidence for high-grade metamorphism at elevated pressures or temperatures >400°C has not been found.

Toxic dyes must be removed from waste water coming from the textile and paint industries. Adsorption is one possible method of removing dyes under ‘soft’ conditions, without the generation of secondary hazardous materials. The present study used the carbonate-containing layered double hydroxides (LDH), Mg-Al and Mg-Zn-Al (with a M2+/M3+ ratio of 3), as adsorbents to remove two industrial colorants, Astrazon Remazol Brilliant Blue and Direct Red, present in low concentrations in aqueous solutions. The physicochemical properties of adsorbents at the surfaces of LDH, as well as the properties of the solutions containing the dyes control how the colorants are removed. Both fresh and calcined LDH were effective in the removal experiments, with effectiveness ranging from 50 to 100%. Analysis of kinetic data demonstrated that the adsorption process fitted the pseudo-second-order model better than the pseudo-first order model, information which is useful for system design in the treatment of wastes from the textile industry. Parameters such as pH of solutions and concentration of dye in solution influenced mainly the initial adsorption rate.

Beidellites may exist on Mars and represent intermediate alteration products; their presence would indicate different alteration environments than previously identified because montmorillonite is a low-grade alteration mineral whereas beidellite is a higher-temperature alteration mineral, and often represents a step toward illite formation. The reflectance spectra of beidellites are under study to support their orbital detection on Mars, where spectral signatures of other Al-rich phyllosilicates have been observed. Reflectance spectra of ten Al-rich smectites are presented here which include pure beidellites and Al smectites having compositions between those of beidellite and montmorillonite, and emphasis is placed here on the OH combination bands near 4545 cm−1 (2.2 μm) as these vibrational features are commonly used in the identification of phyllosilicates on Mars. Shifts were observed in the Al2OH band centers, which occur near 4590 cm−1 (2.18 μm) in reflectance spectra of beidellite and near 4525 cm−1 (2.21 μm) in reflectance spectra of montmorillonite. These are compared with the Al2OH bending vibrations observed near 941–948 cm−1 (10.5–10.6 μm) for beidellite and near 918–926 cm−1 (10.8–10.9 μm) for montmorillonite. Although the octahedral site cation composition provides the greatest influence on the vibrational energies of the M2OH groups, the tetrahedral site cation composition also influences these vibrations. Shifts were observed in the Si-O-Al bending vibrations from 552 and 480 cm−1 (18.1 and 20.8 μm) in beidellite spectra to 544 and 475 cm−1 (18.4 and 21.0 μm) in montmorillonite spectra. Gaussian modeling of the 4545 cm−1 (2.2 μm) bands led to the discrimination of four overlapping bands in each of the ten Al smectite spectra examined in this study. Shifts in the band center and area of the primary spectral band are coordinated with substitution of Al for Si in the tetrahedral sheet. This is consistent with beidellites having a greater tetrahedral layer charge than montmorillonites. The observed spectral differences were sufficiently large that these Al-rich smectites can be differentiated in orbital data of Mars. A pure beidellite-type spectrum is observed in an isolated Al phyllosilicate-bearing outcrop in Libya Montes, a region where Fe-rich smectite is common but Al-rich smectite is rare. Beidellite-type reflectance spectra were also observed in one area of the Nili Fossae region. In contrast, a variety of Al phyllosilicates were found in the ancient rocks at Mawrth Vallis, including some smaller clay-bearing regions exhibiting spectral signatures more consistent with beidellite-like than montmorillonite-like chemistry.

Intense mineral transformations that produce acid soils from weathering zones of pyritebearing rocks, including alterations of layer silicates, are of critical importance to agricultural and environmental interests in various regions of the world. To date, the transformations of layer silicates in these soils have not been studied in detail. The aim of the present investigation was to examine the weathering pathways controlling processes of clay-mineral formation in acidic soils developed near the abandoned pyrite mine in Wieściszowice (Lower Silesia, SW Poland). A sequence of soils, from weakly developed technogenic soils (located on the mine dumps) to well developed natural soils, was selected. Bulk soil material and separated clay fractions were analyzed using X-ray diffractometry, Fouriertransform infrared spectroscopy, and scanning electron microscopy-energy dispersive spectrometry. The profiles analyzed were developed on pyrite-bearing schists containing trioctahedral Mg,Fe-chlorite and dioctahedral micas (muscovite and paragonite). Because of pyrite weathering, all the soils studied were strongly acidic (pH 2.8–4.4). Inherited chlorite and micas (K- and Na-mica) predominated in the clay fractions of soils developed on the mine dumps, whereas clays from natural soils were rich in pedogenic minerals (i.e. smectite, vermiculite, and mixed-layer minerals containing hydrated interlayers). The formation of both vermiculite and smectite at the expense of chlorite was observed in the soils studied. The transformation probably led to smectite formation via intermediate stages of mixed-layer minerals (i.e. chlorite-vermiculite, chlorite-smectite, and/or vermiculite-smectite). The process of chlorite dissolution took place simultaneously with the transformation. Micas were mainly transformed to smectite and mixedlayer mica-smectite. Neoformation of kaolinite occurring in A horizons of the soils investigated was also documented. Metal-hydroxy interlayers in Bw horizons of well developed soils were found. The process of interlayer development appeared to be pH dependent and took place at pH ⩾4.2. The processes of claymineral formation in soils developed in the weathering zone of a pyrite-bearing schist are similar to those occurring in podzols (Spodosols).