Kaolin deposits extending over an area of ~10 km2 in the western and southern parts of Limnos Island, northeast Aegean Sea, Greece, were studied. The kaolin deposits are alteration products of volcanic rocks, mainly trachytes, trachyandesites, andesites and dacites. Study of the collected samples was carried out using X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), energy-dispersive scanning electron microscopy (SEM-EDS), Fourier transform Raman spectroscopy (FT-Raman), Fourier transform infrared (FTIR) techniques and inductively-coupled plasma (ICP) bulk rock chemical analyses for major, trace and rare earth elements. The extensive alteration of the parent rocks resulted from the circulation of hydrothermal fluids through faults and fractures. The development of the various assemblages depends not only on the temperature and composition of the hydrothermal fluids but also on the distance of the rock from the fault or the channel of the ascending hydrothermal fluids.

Kaolinite, dickite, halloysite, illite, smectite and mixed-layer illite-smectite and jarosite were detected in the altered volcanic rocks forming locally various alteration zones. Smectite-rich zones and illite-rich zones are relatively infrequent. In the halloysite-rich zones, the kaolinization of feldspars is accomplished in four stages. The kaolinizaton of feldspars in the kaolinite-dickite-rich zones follows five discrete stages. In the less altered rocks, thin layers of kaolinite are formed on the surface of feldspars. With increasing kaolinization, kaolinite is developed on the surface of feldspars forming extended parallel booklets of newly formed kaolinite. In the third stage, feldspar crystals are partially altered to kaolinite booklets. As kaolinization advances, kaolinite becomes well formed and, in the most altered rocks, feldspars are partially or completely altered to dickite books, depending on the temperature of the hydrothermal fluids.

Centrifugal photosedimentation was used to determine the size distribution of dilute bentonite suspensions as a function of saturating cation. This method is shown to give a better estimate of the effect of saturating cation on tactoid size than the techniques that are currently used. The results indicate that tactoids may occur in preferred size ranges.

Transmission electron microscopy, X-ray radial distribution function analysis, chemical analysis, X-ray absorption edge spectroscopy, and Mössbauer spectroscopy combine to confirm an amorphous or gel structure for minerals of the hisingerite-neotocite series: (Fe,Mn)0.8SiO3.1.2H2O. A framework of (Fe,Mn)O6 octahedra and [SiO4] tetrahedra form hollow spheres, 50–100 Å in diameter, cross-bonded into a physically isotropic solid with as much as 10% interconnected pore space. The outer 10–20 Å of the spheres has a rudimentary structure, possibly marking the onset of segregation into Si-rich and (Fe,Mn)-rich layers. The Broken Hill mineral ‘sturtite’ is an intermediate member of the hisingerite-neotocite series.

In previous papers of this series it was shown that it is possible to determine both the amount of methanol adsorbed in the interlamellar space of charge-deficient Ca-montmorillonite or of homoionic clays and the amount of methanol occluded in a system of micropores between clay particles. This paper deals with the distinction between methanol molecules in the cation coordination shell within the interlamellar space from those not directly influenced by the cation. An OH stretching band at about 3520 cm−1 or an OD stretching band in the 2600–2650 cm−1 region permits this distinction. At 35°C and at relative methanol vapour pressures between 0·1 and 0·9, one molecule of CH3OD is influenced directly by Na+, 2 molecules are influenced by Ba2+, 1·3–1·8 molecules by Li and 4 molecules by Ca2+. Thus, only 20–50% of the adsorbed alcohol molecules may be within the coordination shell of the cation in the interlamellar space.

A comprehensive Mössbauer spectroscopic and X-ray diffraction study of six purified glauconites is presented. The Mössbauer spectra were computer-fitted with three Fe3+ and three Fe2+ doublets, both Fe species occupying the trans-OH and two cis-OH octahedral sites. In addition, a seventh smaller doublet is assigned to Fe3+ in tetrahedral coordination. It has been shown that an increasing IVFe3+ content directs VIFe3+ substitution to the cis-OH octahedrally coordinated sites. A correlation between the d(060) reflection and elemental composition is demonstrated.

A detailed survey of the most clay-rich rock units of the Meso-Cenozoic geological section exposed in the Algarve Basin (South Portugal) was performed and data were analysed for the grain-size distribution and mineralogy (whole rock and clay fraction), aimed at a compositional study of the clay-rich sediments and their depositional environment. Granulometry was obtained using wet sieving and laser diffraction by attenuation of X-rays, and the mineralogical study was carried out by X-ray diffraction.

Most clay-rich rock units of the Algarve are classified as silty clays and clayey silts, and only a minority is coarser. The mineralogical study enabled us to define two main types of clays: (1) noncalcareous clays, consisting largely of quartz and clay minerals, with goethite as the typical Fe-rich phase (sediments of Carboniferous, Neogene and Quaternary age and Cretaceous siliciclastic clays); and (2) calcareous clays, which can be calcite-rich clays (Middle and Upper Jurassic) or dolomiterich clays (Triassic and Lower Jurassic), the latter typically containing hematite as an accessory phase. Plagioclase, K-feldspar, and Ti-oxides are often accessory phases, whereas ankerite, anhydrite, gypsum and opal are rare.

In the clay fraction illite generally predominates, resulting probably from weathering of preexisting rocks, as well as the less frequent Fe-chlorite, pointing to incipient chemical alteration under semi-arid climatic conditions. Kaolinite occurs in diverse proportions, being especially abundant in Cretaceous and Cenozoic units; it is mainly related to chemical weathering in continental environments under humid conditions. As the Atlantic Ocean opened during Triassic and the continental environment evolved to a shallow-marine environment with evaporitic conditions, smectite became more expressive, being sometimes accompanied by other Mg-rich phases (chlorite, sepiolite, corrensite and palygorskite). Especially during the Cenozoic the proportion of different phases in the clay mineral association of the sediments reflects the control of tectonic movements and fluctuations in sea level during their deposition.

Corrensite and chlorite-rich chlorite-smectite (Chl-S) mixed-layers occurring in the Macigno Formation of northwestern Tuscany were investigated by XRPD/SEM techniques. The samples from the Macigno outcrops were affected by metamorphism corresponding to the high-diagenesis/low-anchizone transition boundary. The basal spacing of corrensite measured from 00l reflections on EG–Mg2+-saturated samples ranges from 30.97 to 31.18 Å with a coefficient of variation (CV) of 0.46–0.77%, consistent with the rational pattern of a 1:1 Chl-S periodic stacking sequence. X-ray patterns of heated K+-saturated specimens reveal the presence of two types of corrensite, probably with different interlayer charges on their respective smectite-like layers. The chlorite-rich Chl-S mixed layers coexisting with corrensite consist of R2 chlorite (0.70–0.75)/S and chlorite (0.90)/S with long-range ordering R ⩾ 1. SEM observations show that corrensite and chlorite-rich Chl-S mixed-layers are closely mixed on a sub-micron scale. Some grains of corrensite and chlorite-rich Chl-S mixed-layers include zones (2–10 μm) of chlorite composition, as shown by microprobe analyses.

The hydrothermal reactivity of a smectite saturated with K was studied experimentally at 300°C and 100 bar in (Na,K) chloride solutions (Na/K = 0, 50 and 100, liquid/solid ratio = 10/1). X-ray diffraction, TEM and microprobe results show: (1) a partial to total dissolution of the initial smectite layers; and (2) the crystallization of newly-formed euhedral I-S. Random I-S is formed after 7 days, but an ordered mixed-layer I-S containing <30% expandable layers formed in the longest runs (112 days). The I-S is characterized by non-expandable layers of two distinct types: dehydrated smectite and illite. The Si content is lower in the I-S than in the initial smectite, thus creating a charge deficit, mostly compensated by the introduction of Na to the interlayer space, and yielding a silica release to the solution and subsequent crystallization of quartz and cristobalite.

The Ga for A1 substitution in kaolinites and smectites was studied using clay synthesis from initial gels having an (Al + Ga)/Si ratio of kaolinites and MGa = Ga/(Ga + A1) ratio ranging from 0 to 1. Only kaolinite was obtained for MGa in the range 0-0.10. For higher MGa, synthesized clays were both kaolinite and beidellite, or pure beidellites. The evolution of b cell parameters, and the appearance of a vAI-OH-Ga absorption band at 3600 cm-1 in FFIR spectra, proves the progressive substitution of AI by Ga in kaolinite. The low substitution of AI by Ga in kaolinite can be correlated with the large difference in ionic radii between Al3+ and Ga3+ which causes a large increase in cell dimensions. By contrast, the incorporation of Ga in smectites is easy and can be complete.

The interaction of ammonia with Na—, NH4—, Ca—, Cu—, and Mg— forms of two vermiculites has been investigated by infrared spectroscopy and chemical analysis. Both NH4 ions and co-ordinated NH3 are produced in the interlayer space in amounts which depend on the exchangeable cation and the particle size of the vermiculite. With the exception of that in Cu-vermiculite, the co-ordinated NH3 is rapidly displaced by atmospheric water vapour. NH4 ions are slowly decomposed at normal humidity and more rapidly and completely at high humidity. The co-ordinated NH3 in Cu-vermiculite is converted to NH4. Relative amounts of NH4 and co-ordinated NH3 are influenced by particle size, smaller particles favouring NH4. The stabilities of both species to water vapour increase with particle size.

Alternative Fenton and Fenton-like systems based on natural Fe oxides are described. The collected materials were modified through controlled reduction with H2 and were characterized by chemical analysis, X-ray diffraction, saturation magnetization measurements, and Mössbauer spectroscopy at 298 and 110 K. The catalytic activities of these original and modified materials were tested by studying the decomposition of H2O2 and the discolouration of methylene blue. Iron oxides present in the samples were mainly hematite and subordinate goethite which, after controlled reduction, were converted to metallic iron and magnetite. The mixture of Fe0 and magnetite in one of these materials was significantly more efficient at H2O2 decomposition and the discolouration of methylene blue than the original Fe3+ oxides. These results suggest that Fe2+ is essential to produce an active Fenton system.

Hybrid material based on halloysite nanotubes (HNTs) and sodium perfluorooctanoate (NaPF8) was used as a consolidant for paper treatment. The consolidation efficiency was determined by thermogravimetry as well as by paper grammage determination. Morphological analysis of the treated paper was performed by means of scanning electron microscopy while the effect of modified HNTs on the thermal behaviour of the cellulose fibres was investigated by differential scanning calorimetry which determined the combustion enthalpy of the paper.Water contact angle measurements were performed to study the paper wettability. The physico-chemical properties investigated (mesoscopic structure, thermal stability and wettability) of the treated paper were correlated successfully with the consolidation loading and, consequently, to the affinity between the fluorinated modified HNTs and the fibrous cellulose structure. This study proposes a new green protocol for paper consolidation based on natural tubular nanoparticles with a flame retardant effect.

The Barzaman Formation exposed in the United Arab Emirates was deposited as a series of fluvial sediment sequences lying along the western margin of the Hajar Mountains, part of the Oman–UAE ophiolite. This formation consists of a sequence of rocks dominated by variably cemented and altered conglomerates comprising calcareous siltstones and calcareous clays deposited during the Miocene to Pliocene under a humid climate. The conglomerates are composed largely of ultramafic and lesser-mafic clasts. The present study was undertaken in order to understand the occurrence and genesis of palygorskite and sepiolite in relation to the environmental changes including evaporitic and sabkha environments.

Sediments were collected from two trenches and a drill hole of ∼22 m depth. Samples were analysed by optical petrograpy, X-ray diffraction and scanning electron microscopy. Pedogenesis occurred at the deeper level in well cemented conglomerate which constitutes the hard crust. Post-depositional erosion started in marine phreatic or vadose zones as shown by the neoformation of serpentine from the weathering of olivine as well as of calcite and dolomite. Neoformation of palygorskite, sepiolite, dolomite and halite occurred under evaporitic conditions on calcareous silty clay facies. Relatively hot, vadose and oxidizing environmental conditions affected the calcareous siltstone facies leading to the genesis of dolomite and palygorskite by direct precipitation from solution rich in Ca, Mg, Al, Fe and Si ions.

Mineralogical and chemical heterogeneity within three standard clay mineral samples have been identified by X-ray diffraction and chemical analysis of various size-fractions. This heterogeneity is partly attributed to accessory minerals, but mostly to structural and compositional variations in the 2:1 layer minerals of different particle size in the same specimen.

The effect of heating on the water sorption capacity of a La-saturated montmorillonite, La-Mt, has been investigated. Sodium and Li as exchangeable ions have also been included for comparative purposes. XPS of La-Mt shows no migration of La(III) from interlamellar positions to octahedral sites on heating at 300°C. The water adsorbed as a multilayer on the external surface of the montmorillonite has been subtracted from the total sorbed water. Although the c-spacing of La-Mt corresponds to a two-layer hydrate, in the relative humidity range from 30 to 70%, the interlamellar water amounts to only 70% of the value for a complete monolayer. Heating at 300°C for 24 h has no influence on the uptake of molecular water between the structural layers of the La-Mt. The average numbers of water molecules per exchangeable ion sorbed into the interlamellar spacing up to 50% r.h. are: 5(Na-Mt), 3(Li-Mt) and 13(La-Mt).

Interaction between positively charged Fe-oxyhydroxide (β-FeOOH) particles and negatively charged particles of montmorillonite was studied as a function of particle concentration, pH and time. The results showed that the clay particles appear to bridge between FeOOH particles leading to associations in which the ratio of positive to negative particles varied between 1.4 and 2.56 depending on pH and particle concentrations. The data could be represented by isotherms of interaction of the high affinity type and, together with the interaction kinetics, could be described by Langmuir type formulations.

The high frequency OH-stretching band in micro-Raman spectra of kaolinites consistently exhibits two partly overlapping components with varying relative intensities. These bands, labelled A and Z, are located at ~3700–3690 and 3690–3680 cm-1, respectively. Band Z displays greater intensity in Raman spectra of highly crystallized kaolinites which have large coherent domains. Both components are also observed in the curve fitted infrared (IR) spectra of kaolinites; band Z is stronger in IR spectra of highly crystallized samples. Data for kaolinites with different particle size support the idea that bands A and Z are the longitudinal optic and transverse optic modes of the high frequency OH-stretching band.

The evolution of the nitrogen and boron content of shales during diagenesis and anchimetamorphism was studied in the Carboniferous rocks of Donbas by means of the bulk rock chemical analysis and the XRD quantification of mineral composition, aided by CEC and EGME sorption measurements. The contributions of the organic-bound N and B were taken into account, based on the literature data (B) and on the relationship established in the course of this study (N). 28–98% of the total N and 80–100% of the total B are contained in the mineral fraction of the investigated shales.

The mineral nitrogen is located mostly in illite and accounts for 3 to 64% of the sites available for its fixation in 1Md illite. The fixation of N by illite seems to diminish in the course of diagenesis, but additional fixation occurs in newly formed 2M1 illite during the anchimetamorphic stage. The volume of N contained in illite in most samples greatly surpasses the N available locally from the organic matter contained in shale. Modelling indicates that the measured level of N for K substitution in illite corresponds to the capture in 30 vol.% of shale of all N released in a basin containing 5 vol.% of coal.

Boron is held predominantly by the 1Md fraction (illite+smectite). During diagenesis boron is redistributed into the 1Md illite, and during anchimetamorphism it is released from the 1Md illite and incorporated into new 2M1 illite. No indication of the net enrichment of pore water in B due to the clay alteration process was found.

When phlogopites containing only a little iron are artificially altered with sodium tetraphenylboron solutions, the vermiculite-like products contain fewer interlayer cations than the original micas. Structural formulae of the products are calculated from the chemical analyses, together with infrared examination of the angular vibration band of water at 1650 cm−1 to distinguish between water of hydration and hydroxyl groups. The formulae obtained are consistent with the weight-loss curves and show that the products contain, more than 4(OH,F) per formula unit. The interpretation of these formulae is that the silicate layers lose net negative charge by protonation of structural oxygen anions to form new hydroxyl groups.

Celadonite and glauconite samples heated at different temperatures were studied by X-ray and electron diffraction. For dioctahedral micas the in-plane component of the translation between layers (ccosβ/a), which is strongly dependent on the position of the vacant octahedral site, significantly decreases at temperatures greater than the temperature of maximum dehydroxylation. The simulation of XRD patterns from different structural models reveals the actual crystal structure of dehydroxylated samples as well as the dynamics of the structural transformations. In the nonheated state the samples consist of tv (trans-vacant) 2:1 layers. During dehydroxylation, cations migrate from cis- into trans-octahedra and have 5-fold coordination. In the averaged unit-cell the ‘residual’ anions formed after the dehydroxylation reaction occupy the former OH sites with probability equal to 0.5. The migration of octahedral cations is accompanied by the transformation of the C-centred layer unit-cells into primitive ones. In contrast to Fe, Al and Mg cations have a greater ability to migrate.