This paper examines, from a Thomistic perspective, the possible consequences of the twentieth-century reform of the ‘Kyrie eleison’ from ninefold set of invocations to a sixfold call-and-response structure. First, we present Aquinas’s distinctly Trinitarian exegesis of the ‘Kyrie’ in light of the history of troped liturgical texts. Next, we will account for the historical diversity of the troped ‘Kyrie’ genre while emphasizing importance of the Trinitarian elements. The third section recounts recent work on Aquinas’s theory of the passions and their effects of language formation; this leads to the fourth section, which casts a philosophical eye on the role of melisma in the liturgy. To conclude this study, we suggest the restoration of some troped ‘Kyrie’ texts in the Roman Rite.

The study of hard rock conversion into fine earths and clayey materials in the pedosphere is important in understanding the relative proportions of recent soil features to features that were inherited from ancient epochs. Cold environments are widely thought to be areas of physical weathering, but the coexistence of physical and chemical processes have also been shown. To further examine mafic rock (dolerite) weathering in soil environments and the conversion into clayey materials, Entic Podzols formed in the cold continental climate were studied. The key study was located in the central part of the flood basalt complex, or traps (traprocks), of the Central Siberian Plateau (Russia). The qualitative mineralogy was studied using X-ray diffraction and the quantitative mineral composition was determined using X-ray diffraction and subsequent Rietveld analysis. The micromorphological characteristics of the soils were studied in thin sections. Dolerite fragments and fine earths were sampled from soil profiles underlain by dolerite. XRD analyses indicated that pyroxene and especially plagioclase contents in the dolerite fragments and fine earths decreased from the bottom to the top soil horizons mostly in the mature soil profiles that were affected by chemical weathering of dolerite. The dioctahedral and trioctahedral smectites in the soils were inherited from a dolerite previously subjected to chemical weathering. The smectite was conserved in the inherited aggregates and protected against dissolution even in acidic soil horizons. Recent pedogenesis processes fractured individual fragments, converted it into soil micromass, and slightly decreased the total smectite content of the <1 µm soil fraction. However, in soil samples collected from the bottom to the top horizons of a mature soil profile, trioctahedral smectite contents decreased as dioctahedral smectite contents increased. This suggests that dioctahedral smectites formed by pedogenic alteration of inherited trioctahedral smectites.

A magnetic composite was prepared by wet-impregnating a powder of a natural zeolite with a magnetic Fe oxide-containing synthetic material. Both starting materials were first characterized with X-ray diffraction, scanning electron microscopy, Mössbauer spectroscopy, and by isoelectric-point using vibrating-sample magnetometry. The synthetic Fe oxide-containing material was characterized as a mixture of magnetite (Fe3O4) and goethite (α-FeOOH). From the Fe Mössbauer analysis, the relative subspectral area for magnetite corresponds to 93(2)%; the remaining spectrum is assignable to goethite. After the impregnation process, magnetite was still identified in the composite material as a magnetic layer surrounding the zeolite particles; no magnetically ordered goethite could be detected. The Mössbauer pattern for this sample indicates a much more complex structure than for the precursor material, based on Fe oxides, with some more altered magnetite and an intense central doublet of (super)paramagnetic Fe3+, probably due to small Fe (hydr)oxides and/or to a residual contribution of Fe-bearing species from the starting zeolite material. The composite preparation procedure also promoted the change of the characteristic A-type zeolite to mordenite. The resulting magnetic composite presented a magnetic coercivity of as much as 0.140 A m−1, at 77 K. The final composite is now being evaluated as an adsorbent: results to date confirm that this novel magnetic material may have applications in the remediation of contaminated water bodies.

Alumina-pillared montmorillonite clays (Al-PILC), prepared under ultrasonic (US) agitation and normal stirring (S) methods, have been used as a host material to encapsulate Co phthalocyanine (CoPc) complex. The amount of Co varies from 0.27 to 1.48 wt.% in the samples, depending on the input concentration of Co. Powder X-ray diffraction and other characterization techniques reveal that the structure of Al-PILC remains intact after the incorporation of the complex into the pores through a pyridine solution of the complex by ultrasonic agitation. A substantial decrease in the BET surface area and total pore volume of Al-PILC points to the occupation of the CoPc moieties within the porous structure of the pillared clay. This is further supported by the observation of a band at 1489 cm−1 in the Fourier transform infrared (FTIR) spectra of the encapsulated samples. The FTIR and diffuse reflectance ultraviolet-visible (DRUV-Vis) spectral results indicate that the encapsulated CoPc complex in the clay matrix undergoes distortion in order to accommodate itself within the pores of the Al-PILC. The encapsulated samples prepared by ultrasonification show better dispersion of the complex than the samples prepared under normal stirring conditions. Compared to the ‘neat’ complex, the encapsulated samples (CoPc in Al-PILC) exhibit greater turnover in the test reaction of the oxidation of benzyl alcohol to benzaldehyde with tertbutyl hydroperoxide as the oxidant at 373 K. The method of preparation and consequent site isolation of CoPc in Al-PILC influence the catalytic activity.

Soil formation usually results in an increase in magnetic susceptibility. The magnetic properties of the products of transformation of ferrihydrite, a typical precursor of other soil Fe oxides, were examined in the present work. Synthetic 2-line ferrihydrite was aged at two temperatures (25 and 50°C) and two different relative humidities (80 and 100%) in the presence of silicate, phosphate, citrate, and tartrate as adsorbed ligands (molar anion/Fe ratio = 1–3%). The ligands delayed or prevented the transformation of ferrihydrite to hematite. The magnetic susceptibility of the ferrihydrite transformation products increased with aging, the rate of increase depending on the type of ligand added and its concentration. The largest increase in magnetic susceptibility, sixfold, was obtained with ferrihydrite in a citrate/Fe ratio of 1%, after 1500 days. The resulting magnetic products exihibited superparamagnetic behavior at room temperature and high coercivity at 5 K. The formation of an intermediate ferrimagnetic phase in the ferrihydrite-to-hematite transformation might explain the magnetic enhancement observed in many aerobic soils lacking other sources of magnetic minerals.

The structure and composition of short-range ordered aluminosilicates (SROAS) may control their affinity for organic acids with potential effects on soil organic matter stabilization. Adsorption mechanisms of model organic acids were studied to resolve the effect of Si incorporation. Adsorption of oxalic, salicylic, and octanoic acid on Al-rich (Al:Si = 3.7) and Si-rich (Al:Si = 1.4) SROAS was quantified by analyses of dissolved organic carbon using catalytic high-temperature combustion. The initial pH of 5 and 6.5 increased to 6.3–8.2 during adsorption of oxalic and salicylic acid, demonstrating hydroxyl release by ligand exchange. Minor changes in pH indicated weak interactions of octanoic acid with both SROAS. Adsorbates were characterized by Fourier-transform infrared spectroscopy. Asymmetric stretching of carboxylate groups at 1720 and 1700 cm–1, and symmetric stretching at 1430 cm–1 evinced the formation of chelate complexes for oxalic acid. An absorption band centered at 1545 cm–1 indicated partial inner-sphere binding of salicylic acid on both SROAS. Silicon-rich SROAS adsorbed 80–90% less than Al-rich SROAS, suggesting that adsorption of oxalic and salicylic acid was controlled by surface aluminol groups. Fast kinetics of oxalate adsorption on Al sites was studied by a conductivity-based stopped-flow technique. Ligand exchange proceeded at a rate constant of 3.5 s–1 (25°C), similar to solute Al complexation, with an activation energy of up to 34.1 kJ mol–1. A slow process with a rate constant of 0.13 s–1 (25°C) was attributed to diffusion of oxalate at the surface or into SROAS particles. As supported by structural characterization of Si-rich SROAS, the much lower susceptibility of Si-rich SROAS to ligand exchange relates to Al speciation. The formation of tetrahedral Al precludes its complexation by carboxyl groups.

Increasing use of irrigation in India has exacerbated the problems of soil salinity and sodicity. The present study was undertaken on shrink-swell soils from Maharastra State to determine if changes in soil chemistry due to irrigation have affected the clay mineralogy. Twenty six samples (15 locations) of irrigation-induced, saline-sodic, shrink-swell soils and 27 samples (22 locations) of normal un-irrigated (rain-fed) shrink-swell soils were studied using X-ray powder diffraction (XRPD), infrared spectroscopy (FTIR), and scanning and transmission electron microscopy (SEM, TEM). The XRPD analysis of the <0.2 µm fraction of rain-fed, shrink-swell soils indicates a predominance of dioctahedral smectite with minor to trace amounts of kaolinite and chlorite. Traces of palygorskite (1–4%) were detected in three samples. In contrast, palygorskite is a common component (1–20%) of the fine-clay fraction of saline-sodic soils. Quantitative analysis of palygorskite by XRPD in whole-soil (<2 mm) samples showed that saline-sodic soils contain up to 20 wt.% of palygorskite, whereas palygorskite was only detectable (1.5 wt.%) in one sample of the rain-fed set. The SEM, TEM, and FTIR confirm the presence of Fe-rich palygorskite in saline-sodic soils and demonstrate that the fibrous palygorskite crystals are exceedingly small (∼0.5 µm long). Delicate palygorskite fibers radiate from the margins of smectite plates suggestive of a pedogenic origin and a close genetic relationship between smectite and palygorskite. The compositions of saturation-paste extracts display a shift from the stability field of smectite in rain-fed soils to that of palygorskite in saline-sodic soils. Thus the occurrence and formation of palygorskite appears to be related to the change in land management from rain-fed to irrigated agriculture. This change has occurred over a period of no more than 40–50 y, implying that palygorskite formation in the irrigated, saline-sodic soils has been an extremely rapid process.

The aim of the present study was to examine effects of black liquor-montmorillonite (BL-Mnt) complexes on the mechanical and thermal properties of epichlorohydrin rubber. Considering the stability effect of lignin and the barrier property of clay minerals, a significant enhancement of thermo-oxidative aging properties of ECO/BL-Mnt composites was expected. Poly (epichlorohydrin-co-ethylene oxide) (ECO) composites filled with BL-Mnt complex were prepared by mechanical mixing on a two-roll mill. The ECO/BL-Mnt composites were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Both XRD and TEM data showed that the filler particles were well dispersed throughout the ECO/BL-Mnt composites. The tensile strength, elongation at break, and 100% modulus of the rubber composite were 14.0 MPa, 457%, and 3.9 MPa, respectively, at a 50% loading of BL-Mnt. The retention of tensile strength was 99% after thermal oxidative aging in an air-circulating oven for 72 h at 100°C. Evidence indicated that ECO/BL-Mnt composites with good mechanical properties and thermo-oxidative aging properties were obtained.

Siderophores are low molecular weight organic ligands synthesized by aerobic microorganisms to acquire Fe. In addition to Fe(III), siderophores may complex other metals such as Pb and Cd. This study compared the effects of the trihydroxamate siderophores desferrioxamine-B (DFO-B), desferrioxamine-D1 (DFO-D1), desferrioxamine-E (DFO-E), and the monohydroxamate siderophore-like ligand acetohydroxamic acid (aHA) on Pb and Cd (except for DFO-E) adsorption to kaolinite (KGa-1b) at pH 4.5 to 9, in 0.1 M NaClO4, at 22°C, in the dark. At pH >6, all of the studied ligands decreased Pb adsorption to kaolinite: aHA by 5–40% and DFO-B, DFO-D1 and DFO-E by 30–75%; the greater effects were at higher pH. The studied ligands decreased Cd adsorption to kaolinite at pH >8: aHA by 5–20% and the trihydroxamates by as much as 80%. We also observed enhancement of Pb adsorption in the presence of DFO-B at pH ≈5–6.0, probably due to adsorption of the doubly positively charged H3Pb (DFO-B)2+ complex, although spectroscopic evidence is needed.

The formation of mixed-metal-Al layered double hydroxide (LDH) phases similar to hydrotalcite has been identified as a significant mechanism for immobilization of trace metals in some environmental systems. These precipitate phases become increasingly stable as they age, and their formation may therefore be an important pathway for sequestration of toxic metals in contaminated soils. However, the lack of thermodynamic data for LDH phases makes it difficult to model their behavior in natural systems. In this work, enthalpies of formation for Ni LDH phases with nitrate and sulfate interlayers were determined and compared to recently published data on carbonate interlayer LDHs. Differences in the identity of the anion interlayer resulted in substantial changes in the enthalpies of formation of the LDH phases, in the order of increasing enthalpy carbonate<sulfate<nitrate. Substitution of silica for carbonate resulted in an even more exothermic enthalpy of formation, confirming that silica substitution increases the stability of LDH precipitates. Both mechanical mixture and solid-solution models could be used to predict the thermodynamic properties of the LDH phases. Modeling results based on these thermodynamic data indicated that the formation of LDH phases on soil mineral substrates decreased Ni solubility compared to Ni(OH)2 over pH 5–9 when soluble Al is present in the soil substrate. Over time, both of these precipitate phases will transform to more stable Ni phyllosilicates.

Clay minerals in Gamalama volcanic soil have not yet been identified thoroughly. The soil is estimated to contain nanoscale natural clays, such as halloysite or imogolite. The occurrence of nanoclays in the soil will support the development of many applications in nanotechnologies from nature. The objective of the present study was to characterize soil samples from five different locations around the volcano at three different depths from the soil surface. A total of 50 g of dry soil sample was stirred slowly in 300 mL of distilled water. Stirring was stopped after the addition of 10 mL of 30% H2O2 and then allowed to stand for 24 h. The small floating particles with dimensions of <2 μm were separated from the mixture and collected using a centrifuge at 4000 rpm (1790×g) for 30 min. About 5 g of solid sample was obtained for further characterization. X-ray diffraction results showed the presence of halloysite, allophane, and kaolinite. Morphology analysis by scanning and transmission electron microscopy of some representative samples showed short tubes 10–20 nm in diameter and 50–100 nm long with the halloysite structure. Halloysite was found at 70 cm depth from the soil surface at almost all locations. The surface area determined by the surface area analyzer using the BET equation was as much as 112.51 m2/g. This surface area is thought to be the largest ever determined for a natural nanoclay, paving the way for future application as catalytic or photocatalytic-supporting materials.

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.

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

The formation of hydroxylated phases was investigated using K-depleted biotite (Na-biotite) and K-depleted muscovite (Na-muscovite) under hydrothermal treatment with alkali (Li+, K+, NH4+, Rb+ and Cs+), alkaline earth (Mg2+, Ca2+, Sr2+ and Ba2+), and aluminum (Al3+) cations at 200°C for 1 and/or 3 days. The K-depleted biotite treated with alkali cations produced anhydrous hydroxylated phases, while the K-depleted muscovite did not significantly exchange alkali cations but dehydrated to form Na-muscovite in all cases. The alkaline earth cations, however, produced hydrous hydroxylated phases with both K-depleted micas. The degree of hydration energy of cations and the charge density of micas were found to influence the formation of anhydrous and hydrous phases from the K-depleted micas. This type of topotactic cation exchange potentially could be used for fixation and immobilization of radioactive species such as Cs, Sr, Ra, etc. in the transformed micas. The K-depleted biotite and muscovite treated with Al3+ were transformed to hydroxy-Al interlayered vermiculites (HIV) because of hydrolysis and polymerization of Al3+. These HIV phases could also serve as useful adsorbents for soil and groundwater contaminants.

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).

Organic pollutants are widespread and a known problem for the environment. p-nitrophenol (PNP) is one such pollutant found in effluents from various industries involved with pesticides, pharmaceuticals, petrochemicals, plastic, paper, and other materials. The objective of this research was to prepare and test organically modified clays using four different surfactants and to evaluate the removal efficiency of PNP from aqueous solutions. Organically modified clays have attracted great interest due to their wide applications in industry and environmental protection as sorbents for organic pollutants. Two natural smectite-dominated clay types from outcrops in Latvia and Lithuania as well as industrially manufactured montmorillonite (Mt) clay were modified using different nonionic (4-methylmorpholine N-oxide (NMO) and dimethyldodecylamine N-oxide (DDAO)) and cationic (benzyltrimethyl ammonium chloride (BTMAC) and dodecyltrimethyl ammonium chloride (DTAC)) surfactants. Modified clay materials were characterized by Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and the Brunauer-Emmett-Teller method (BET) for surface area analysis. Sorption of PNP was investigated under various conditions, e.g. surfactant loading, initial PNP concentration, contact time, and pH. The novelty of the present study was to prepare innovative organo-sorbents based on manufactured as well as natural clay samples using cationic surfactants and nonconventional nonionic surfactants as modifiers. The sorption data combined with FTIR and XRD supplementary results suggests that nonionic organo-clay (Mt-DDAO_2) is the most effective sorbent and may serve as a low-toxicity immobilizer of pollutants such as phenols.

The aim of the present study was to discriminate between distinct types of clay units by applying multivariate statistical techniques, which have seldom been applied to the exploitation of ceramic clays. At the outcrop scale, texturally similar argillaceous or clayey layers of different ceramic types cannot be effectively distinguished, which can result in the misuse and loss of raw materials. Representative samples of clayey raw materials from central Portugal Cenozoic deposits with potential use in the manufacture of structural clay products were first assessed for granulometric, mineralogical, chemical, and technological properties. Based on those properties and the use of multivariate statistical techniques, i.e., factor analysis (FA) and cluster analysis (CA), a novel statistical approach that combined all these variable properties was produced. This approach made it possible to distinguish the ceramic suitability and perceive which parameters most influence that suitability. The use of R-mode FA made it feasible to differentiate and group samples based on the most influential variables: the contents of Al2O3, Fe, illite, quartz, feldspars, and K2O. The use of R-mode CA substantiated the FA results in the identification of influential variables, such as Al2O3, Fe, and illite. The use of Q-mode CA established two main clusters: clayey-silt samples and sandy and/or feldspathic samples, the clayey-silt samples encompassed three sub-clusters. These three sub-clusters match ceramic types with different suitabilities and relate sample stratigraphic setting to the encompassing stratigraphic units. Diagrams that relate the grain size, the content of different oxides, the content of different minerals, and the plasticity to the ceramic suitability illustrate the CA groupings. An adequate blend of sand and clay for red stoneware (bricks and tiles) manufacture was indicated as a major requirement for most raw materials of the clayey-silt cluster. Raw materials represented by the sandy and/or feldspathic cluster can either be used to blend with materials that lack sand or to blend with excessively plastic samples.

Halloysite and kaolinite occur in gneissic weathering profiles developed under a temperate climate in the Leucogia area of NE Greece. X-ray diffraction analyses of samples from three profiles of partially weathered gneisses have revealed that kaolinite becomes more abundant than halloysite with increasing intensity of the decomposition processes. To resolve the genetic relationship between halloysite and kaolinite, microtextures were examined by scanning electron microscopy using polished thin-sections and freshly exposed fracture surfaces, and their chemical compositions were determined using an analytical scanning electron microscope fitted with energy dispersive and wavelength dispersive spectrometers. Different morphological forms of halloysite and kaolinite were detected within the same rock mass. In the earliest stage of weathering, spheroidal aggregates consisting of microcrystalline halloysite are formed on the plagioclase surface. With progressive weathering, spheroidal halloysite converts to tubular halloysite. As weathering advances, tubular halloysite converts to platy halloysite, which in turn converts to kaolinite. Halloysite and kaolinite may coexist in the upper parts of the profiles. Electron microprobe analyses of spheroidal, tubular and platy halloysite and kaolinite show that the chemical composition of the various forms indicate a progressive Fe enrichment and Al depletion with advancing kaolinization, from VIFe0.08VIAl3.70 a.p.f.u. in spheroidal halloysite through VIFe0.29VIAl3.50 in platy halloysite to VIFe0.53VIAl3.32 in newly formed kaolinite. Final-stage, book-type kaolinite approaches its ideal chemical composition (VIFe0.04VIAl3.95). The mineralogy and composition of the kaolin minerals and the development of the various morphological forms of halloysite and kaolinite in different parts of the profiles are attributed to the chemistry of the ambient solutions. However, other physical and microenvironmental conditions (e.g. time and space available) also seem to have strong influence on the precipitation processes producing the morphological variations.