Physical alteration of magnetite-bearing antigorite grains is investigated in this study using Mössbauer, visible/near-infrared (VNIR) and mid-IR spectroscopy coupled with scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) analyses. An expected decrease in grain size with grinding is observed using SEM. The HRTEM images illustrate that the nanophase-sized grains which adhere to larger grains have 7 Å antigorite patterns. Mössbauer spectroscopy shows the presence of antigorite, magnetite and an amorphous phase. Visible/near infrared spectra exhibit features common in serpentine. These spectra also show an increasing continuum slope with grinding, an effect which is characteristic of thin coatings or tiny grains on surfaces. Mid-IR spectra indicate the formation of fine-grained Si-OH and carbonate in these samples with grinding.

Imogolite has been identified in small amounts in clays from a soil profile developed on pyroclastics of tephrite-bassanite composition. The major part of the fine clay was an allophanic material termed proto-imogolite, characterized by an infrared spectrum with some of the features given by imogolite, including a well-developed band at 346 cm−1. Similar products have been obtained in the laboratory.

Kaolinite deposits, hosted by rhyolitic tuffs, are found in the SE of the ‘Los Menucos’ area (Province of Rio Negro, Argentina). The most representative examples are from the Blanquita and Equivocada mines. To discover the origin of these deposits, a mineralogical, geochemical (major and trace element) and stable isotope study (O and H) of kaolinite was carried out. Mineralogically, Blanquita mine is characterized by the presence of dickite, kaolinite, alunite and pyrophyllite, whereas in Equivocada mine, kaolinite is accompanied by dickite and traces of alunite (without pyrophyllite). The trace element contents and ratios of kaolin samples (P vs. S, Zr vs. Ti, (Cr + Nb) vs. (Ti + Fe), and (Ce + Y + La) vs. (Ba + Sr)) suggest that they formed from the hydrothermal alteration of the enclosing rhyolites although a possible contribution of kaolinite from residual processes cannot be discounted. δ18O values of kaolinite range from +4.8 to +10.3‰, and δD varies from −88 to −116‰. The presence of pyrophyllite in Blanquita mine suggests temperatures of formation >350°C. The calculated isotopic composition of the fluid in equilibrium with kaolinite at 350°C varies from +3.6 to +9.2‰ for O and from −74 to −103‰ for H. These values are compatible with fluids of magmatic origin or with fluids of surficial origin isotopically equilibrated with a rhyolitic magma at high temperatures. The isotope composition of kaolinite from the Blanquita and Equivocada mines is clearly different from kaolinite of residual origin from deposits in the Chubut and Santa Cruz provinces. The isotopic signature has proved to be a useful tool in discriminating between different genetic processes in the formation of kaolin deposits.

X-ray diffraction, optical and microprobe studies of a kaolinized oligoclase—orthoclase—two-mica—granite (Southern Armorican Massif) indicated that low-temperature metasomatism had produced three series of minerals. 1. Partial alteration of muscovite resulted in the formation of ferrous-magnesium-phengite. Biotite was destabilized to a kaolinite-titanium oxide assemblage. 2. Phengite, unreacted muscovite and feldspars recrystallized to an aluminous, magnesian 1M sericite mineral ranging in composition from mica to illite. 3. Feldspars were entirely destabilized to produce the assemblage potassic-beidellite-kaolinite—Al-illite. Kaolinite was the predominant mineral in the most altered rock. A fourth stage of mineral equilibrium was also observed; this occurred after material from stage 3 had been reworked. In this environment, the potassic-beidellite was replaced by a calcic-montmorillonite. Potassic-beidellite was not stable under weathering conditions.

The influence of hydrological conditions and the pH of the environment on chlorite and mica transformations in the acidic weathering zone of pyrite-bearing schists was studied. Phyllosilicate transformations were investigated in the area of the abandoned pyrite open-pit mine in Wieściszowice (Lower Silesia, SW Poland) using X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy and chemical methods. (Mg, Fe)-chlorite, micas (muscovite and paragonite), quartz, feldspars and pyrite were reported to be the most abundant minerals occurring in pyrite-bearing schists. Phyllosilicate transformations were significantly stronger in dry conditions than in wet ones. This conclusion was supported by the fact that the inherited phyllosilicates predominated in the clay mineral fraction of waterlogged saprolites, whereas the secondary swelling minerals were minor components. In dry and extremely acidic saprolites (pH < 3), trioctahedral chlorite was dissolved and transformed into clay minerals (e.g. smectite and kaolinite), whereas swelling clays (smectite mainly) were formed at the expense of dioctahedral micas. The pH of water is an important factor influencing phyllosilicate transformations in waterlogged conditions. The phyllosilicate alterations under the influence of extremely acidic waters (pH < 3) were more advanced than in moderately acidic ones (pH of 4.6), as the secondary clay minerals seemed to be represented exclusively by smectite in the former, whereas HIMs and mixed-layer minerals such as R0 I-S-Ch, R0 I-S, as well as R1 Ch-V and/or R1 Ch-S occurred in the latter.

A series of phlogopite and biotite samples were examined by wide-line NMR spectroscopy. Monitoring of the fluorine signal revealed the presence of homogeneous fluorine domains. The importance of these domains increased with increase in F and Fe contents. A model for the distribution of anions and cations in the octahedral sheet of micas is presented and discussed.

Statistical (Q-mode) analysis of the chemical compositions of 122 dioctahedral smectites obtained from the literature have enabled the main solid solution ranges (montmorillonite, beidellite and nontronite) to be distinguished on a triangular diagram. In the montmorillonite area, the Wyoming, Tatatilla, Otay, Chambers and Non-Ideal montmorillonite compositional ranges are identified. Certain crystallochemical features of the smectites may be correlated with different genetic environments.

Clay mineral analyses of Caribbean soils illustrate the differences in composition that can arise from differences in topography and parent material, and emphasize the differences between the groups of proposed new engineering classifications of the soils based on these factors. Within one set of environmental conditions the clay mineral assemblage was reasonably constant. Examples are given of local differences in clay type which were correlated with variations in climate and mode of formation.

Ethyl cinnamate/montmorillonite intercalation complexes were obtained by gaseous adsorption of the drug on the clay surface. They were characterized by powder X-ray diffraction, differential thermal and thermogravimetric analyses and by visible-UV and IR spectroscopies. It was found that after 1 day of adsorption, most of the drug enters the interlayer space of the clay by substitution of water molecules, and is removed only after heating at high temperature. In addition, a portion is physisorbed on the external surface of the crystallites, being removed easily below 100°C. The interlayer complex improves the protecting ability of the pure clay or the pure drug against ultraviolet radiation, specially in the so-called ‘C’ range (290–190 nm).

Amorphous silicate sediments comprise most of the upper part of the sedimentary column of the Atlantis II Deep, whereas more crystalline phases are found in the lower part. The objective of this study was to focus on the newly-formed, metastable, hydrothermal phases, that eventually transform into clays or Fe oxides.

Short-range ordered Si-Fe phases (Si/Fe = 0.2 0.6) rounded to elliptical in shape, and amorphous Si-Fe platy phases (Si/Fe = 0.09 pure Si) comprise some of the amorphous sediments in Atlantis II Deep. The rounded particles have distinct electron-dense (thicker, relatively ordered) margins and a less crystalline inner core. They have rhombohedral symmetry with unit-cell parameters of a= 0.504 nm and c= 1.08 nm. They presumably transform into crystalline clay minerals in statunascendi(at the formative stage) in the sediments. Synthesis in NaCl brines designed to simulate crystallization of the rounded particles, was performed successfully. Similar rounded phases (Si/Fe = 0.26) were synthesized under saline, neutral, hydrothermal conditions (40°C, pH 7, 2 M NaCl) with initial Si/Fe = 1.5. We suggest that the metastable rounded particles precipitate from the hot brine created by the encounter between Red Sea Deep Water and the hydrothermal brine underneath. Within a few thousands years they disintegrate and transform into clay minerals, probably nontronite.

The Hallaçlar kaolinite deposit of the Uşak Province (western Turkey) is hosted by dacite, andesite and siliceous materials of the Miocene Karaboldere volcanites. Mineralogical zonation, such as the prevalence of kaolinite at the centre of the deposit, coexisting with silica polymorphs such as quartz and cristobalite along with feldspar and hornblende, and a relative increase of smectite, illite, chlorite, and Fe-oxide/-hydroxide phases outward and upward, demonstrate that hydrothermal-alteration processes resulted in kaolinization. Micromorphologically, kaolinite occurs as pseudohexagonal blocky kaolinite with coarse-grained quartz in microfractures, and the presence of relatively fine-grained vermiform kaolinite that edges volcanic materials indicates that kaolinite developed in several phases coexisting with goethite, lepidocrocite, hematite, pyrite, jarosite, alunite, and gypsum/anhydrite with smectite in fractures. The highly crystallized Hallaçlar kaolinite is identified by: (1) sharp reflections at 7.23 and 3.57 Å, with triplet and doublet non-basal reflections; (2) sharp infrared spectral bands at 3687, 3651 and 3620 cm-1; (3) well defined, pseudohexagonal and hexagonal kaolinite crystal growth; (4) a chemical index of weathering of 98.6-100; and (5) SiO2/Al2O3 ratios between 1.04 and 1.45. Enrichment of Sr and depletion of Rb+Ba, Ti, and HREE relative to LREE, with a distinct negative Eu anomaly, are responses to the fractionation of feldspar and hornblende by the hydrothermal fluid; these results are also supported by the O- and H-isotopic character and formation temperatures of the Hallaçlar kaolinite and smectite; namely, 134.1-183.4°C and 65.6°C, respectively. The negative δ34S (-20.7‰) value of gypsum/anhydrite reflects its formation from geothermal-water-derived sulphur. Under the influence of a tectonically controlled hydrothermal process, feldspar, hornblende and volcanic glass were altered, resulting in the conservation of Al and depletion of Si, Na, Ca, K, Mg and Fe in an open hydrological system such that formation of kaolinite in the central part of the deposit under acidic conditions and development of smectite and illite upward and outward under basic conditions were favoured.

An XRD method for measurement of quartz content using ZnO as the internal standard was tested on different particle sizes between 0 and 20 µm. Calibration curves showed a good correlation coefficient for particle-size fractions up to 20 µm; the slope increased for the fractions from 0·7 to 5 µm and was relatively constant for coarser particle sizes. Fine quartz fractions were etched with hydrofluoric acid to remove the surface layer damaged during dry grinding. The use of such etched quartz increased the slopes of the calibration curves for small particle-size fractions and approximated the natural fine quartz fraction much better than the original dry-ground material. The mean of six measurements gave good accuracy provided that the slope of the calibration curve was adjusted for the particular particle-size fraction. This method was used on 0–2 µm, 0–0·2µm and 0·2–2 µm fractions of French silty soils and the results are in agreement with the data from chemical analysis and with the mineralogical interpretation.

The petrography, mineralogy and diagenesis of an overpressured Tertiary and Late Cretaceous mudrock sequence from a single well in the East Shetland Basin (North Sea) are described. The clay fraction is believed to be dominated by volcanic glass above 1400 m depth and by smectite below 1400 m. The smectite content increases with depth due to an increase in detrital smectite and to in situ alteration of volcanic glass and grains; this commenced almost immediately after deposition and is still not complete at burial depths >2300 m. There is little evidence of alteration of the smectite to illite despite a local available supply of K+ in the form of K-feldspar and the presence of K in the more deeply buried smectite. Very little leaching or precipitation of quartz has occurred. Microfossil tests filled with authigenic clays such as have been reported in other Tertiary mudrocks in the North Sea were not observed, though a few fossil cavities are filled with carbonate cements, and very rarely with microquartz. The suprisingly limited reactivity of this mudrock sequence may be due to the early development of overpressure, resulting in a “closed” system, and to the absence of interbedded higher permeability layers or open faults through which fluids could be exchanged.

Kaolinite hydroxyls in dimethylsulphoxide-intercalated (DMSO-intercalated) kaolinites have been determined using Raman spectroscopy at 298 and 77 K. The inner surface hydroxyl frequencies at 3650, 3670, 3684 and 3693 cm-1 move to higher wavenumbers upon cooling to 77 K and are observed at 3659, 3676, 3692 and 3702 cm-1. The inner hydroxyl frequency is at 3620 cm-1 at 298 K and is at 3615 cm-1 at 77 K. Upon intercalation with DMSO, additional bands are found at 3660, 3536 and 3501 cm-1 for the low-defect kaolinite and at 3664, 3543 and 3509 cm-1 for the high-defect kaolinite at 298 K. The 3660 cm-1 band at 298 K is resolved into two bands at 3658 and 3663 cm-1 at 77 K for the low-defect kaolinite and these bands are assigned to the inner surface hydroxyl groups, hydrogen-bonded to the DMSO molecule. It is proposed that the DMSO molecule exists with two different orientations in the intercalate and these two molecular forms are differentiated by the OH-stretching bands of the inner surface hydroxyl groups. This band for the high-defect kaolinite is found at 3664 cm-1 at 298 K and resolves into two bands at 3664 and 3673 cm-1 at 77 K.

We have examined the nature and origin of smectites in glaciomarine sediments of the AND-2A drill core (McMurdo Sound, Antarctica) by means of X-ray diffraction (XRD) analyses on the clay fraction, field emission scanning electron microscopy (FESEM), scanning electron microscopy (SEM) observations and SEM-EDS microanalyses on smectite particles. Relying on the smectite variation throughout the drill core it was possible to split the sequence into three units. Smectites throughout the core are either detrital or authigenic. Detrital smectites are close to montmorillonite-beidellite in composition while newly-formed smectites frequently have higher Fe-Mg contents and intermediate compositions between the saponite and nontronite field, with lower amounts in the montmorillonite-beidellite field. In the upper sedimentary sections (Unit I, and Unit II, 36-440 mbsf, 0.7-16.5 Ma) smectites are interpreted to be predominantly detrital, whereas in the lower portion of the core (Unit III, 440-1123.20 mbsf, 16.5-20.2 Ma) authigenic smectites are the most common feature. The predominance of mica, the abundance of chlorite, and the nature of smectites in the upper units indicate physical weathering under cold and dry climate, and a dominant provenance for the clay minerals from the Transantarctic Mountains. Smectites in the lower unit are considered mostly authigenic and they are most likely to be the result of early diagenetic processes, being formed from the alteration of volcanic material (glass, pyroxenes and feldspars) and/or through precipitation from fluids of a possible hydrothermal origin. Our survey attests to the importance of discriminating between a detrital and authigenic nature of smectites as the occurrence of authigenic clay minerals in ancient sedimentary successions might lead to incorrect palaeoclimatic interpretations, since they can be affected by diagenetic processes, thus obliterating the climatic signal.

Samples from deep wells of the Palaeozoic Illinois Basin show the evolution of the illite-smectite (I-S) mineral transformation under low temperatures for very long periods of time. Curve decomposition of the XRD traces was used to identify and follow the evolution of the different clay minerals. All samples showed the presence of a large amount of illite (fine and coarse grained micaceous material) and a much smaller quantity of I-S. In a vertical section the R=1, I-S diffraction peak initially changes with depth indicating change from 80 to 95% illite content but it changes little with further depth. The I-S intensity decreases with depth compared with the illite peaks. These relations indicate that the clays in the Palaeozoic sequence of the Illinois Basin evolve continuously in the deep well, It appears that the final stages of I-S mineral transformation can reach a compositional stagnation (smectite content) as the I-S phase is dissolved to produce illite.

Using a kinetic model to describe the smectite to illite clay transformation, it is deduced that the Illinois basin had a longer period of deposition than indicated by present stratigraphy and that almost 1.5 km of sediments deposited in the Mesozoic were eroded in later Tertiary times. These conclusions are confirmed by published data on the maturation of organic matter.

Imogolite, protoimogolite and two synthetic allophanes (A and B) with very different Si/Al ratios have been pyrolysed over a range of temperatures, and the reactions followed by high-resolution solid-state 27AI and 29Si nuclear magnetic resonance (NMR) spectroscopy. The Si(OAloct)3OH groups of protoimogolite are destroyed at relatively low (∼ 200°C temperatures, whereas the same structures in imogolite are stable to ∼ 300°C. During pyrolysis of both materials there is little change in the observed coordination of AI at temperatures of < 500°C but at 500°C or higher, ∼25% of the NMR-visible Al is converted to tetrahedral coordination. The mechanism of decomposition of both protoimogolite and imogolite is shown to involve the formation of highly branched Si-O-Si chains. As far as can be discerned by 27Al and 29Si NMR, allophanes A and B both appear to produce products similar to protoimogolite on pyrolysis.

The kinetics of dissolution of Amazonian metakaolin in hydrochloric acid (HCl) was studied using the ‘Shrinking Core Model’ for spherical and ‘flat plate’ particles of constant size. The Amazonian kaolin was calcined at 700°C for 2 h. The calcined samples (metakaolins) were leached in an HCl solution with 5% excess at 70, 80 and 95 ± 3°C for 3 h. Samples were collected every 15 min and subjected to Al analysis by the EDTA titrimetric method. Experimental data showed that the spherical morphology produced a better fit with respect to the regression coefficients. The activation energy of the reaction was 90.6 kJ/mol. The chemical process is a first-order leaching reaction. The results of the present study are consistent with those from previous research on this topic, which used HCl with an excess of >90%.

Clay-mineral type and content, bulk mineralogical composition and alteration of bentonite are very important factors for the ultra-long-term stabilization of barriers and backfills in radioactive waste disposal. This study investigates the effects of clay-mineral type and content on the swelling characteristics and permeability of bentonite–sand mixtures with clay minerals using one-dimensional swelling-pressure and constant-pressure permeability tests. The hydraulic conductivity of bentonite–sand–clay mineral mixtures increased with increasing content of non-swelling alteration products of montmorillonite. Furthermore, hydraulic conductivity was comparable to that determined with the Kozeny–Carman equation for a specific surface area, suggesting that hydraulic conductivity may be estimated based on the abundance of expected alteration products of montmorillonite. This study provides a basis for evaluation of the hydraulic conductivity of bentonite–sand mixtures with known quantities of expected alteration products of montmorillonite.