Modem disc centrifuge technology has extended the range of application of sedimentation particle size analysis to include the submicron region. An overall size range of approximately 10 nm to 100 pm is now accessible. The principles of both the disc centrifuge photosedimentometer, which employs optical detection with full Mie light scattering corrections, and the X-ray disc centrifuge are described. Examples of their application to a variety of samples are given to illustrate the performance characteristics of the instruments including a direct comparison of resolving power with that of the laser diffraction technique.

The Puncoviscana Formation, largely cropping out in NW Argentina, is mainly composed of a pelite-greywacke turbidite sequence affected by incipient regional metamorphism and polyphase deformation. Metapelites, composed mainly of quartz, albite, dioctahedral mica and chlorite, were sampled in the Lules-Puncoviscana and Choromoro belts. Lattice-fringe images, selected area electron diffraction and analytical electron microscopy analyses, coupled with previous data from white mica crystallinity index, indicate a state of reaction progress for Puncoviscana slates consistent with medium anchizone- to epizone-grade metamorphism. The 2M polytype prevails in dioctahedral micas, coexisting in a few cases with the 1Md polytype as a consequence of lack of equilibrium. The 2Mpolytype coexists with 3T in two slates and long-range four-layer and ten-layer stacking sequences were identified in another sample. Samples with 3T and long-range stacking sequences present b values characteristic of intermediate–high pressure metamorphism and ordered chlorites (1L, 2L, 3L and 7L) prevail.

Based on the Si contents of dioctahedral micas and considering peak temperatures of ∼350 –400ºC, pressures from 5 kbar and 5 –7 kbar were derived for metapelites from the Lules- Puncoviscana and Choromoro belts, respectively. These values agree with facies series derived from the b values. Micas with a wide range of phengitic substitution, as evidenced by Fe + Mg and Si contents, coexist. These variations could not arise from the disturbing effect of detrital white K-mica because TEM evidence indicates that they are absent or represent <10% of the mica population. Thus, compositional variations suggest that dioctahedral micas of individual slates crystallized at different pressure conditions in response to the P-T path of the metamorphism. Moreover, in several biotite-free slates the illite crystallinity (IC) values lead to an underestimation of the metamorphic grade attained in these rocks.

The coexistence of IC corresponding to anchizone and the occurrence of biotite in some slates and felsic metavolcanic rocks intercalated in the Puncoviscana metasediments are interpreted to be the result of a metamorphic path including a relatively high-pressure/ low-temperature (HP/LT) event, followed by a lower-pressure overprint possibly at higher temperatures than the HP/LTevent. Small micas formed during the high-pressure stage would prevail in the <2 mm fraction, producing anchizone IC.

The use of pelitic geological materials for the treatment of muscle-bone-skin pathologies, by application of a cataplasm made of clay and mineral water mixture, is currently receiving attention and interest from the general public and scientific community. In Portugal there are several natural occurrences of clays/muds which are used for pelotherapy and/or geotherapy. These are carried out either indoors (thalassotherapy and thermal centres) or outdoors, in natural sites generally located near the seaside. The aim of this study is to assess the mineralogical and physicochemical properties of Portuguese raw materials for therapeutic purposes. These materials were collected from different Portuguese Mesozoic-Cenozoic geological formations located in the neighbourhood of thermal centres or at beaches known from their empirical applications. X-ray diffraction (XRD) and scanning electron microscopy (SEM-EDS) were used to assess the mineralogical composition of these clays. Physicochemical properties, such as specific surface area, cation exchange capacity, plasticity/abrasiveness indices and heat diffusiveness were also determined. Having distinct geological ages and genesis, the materials examined are mainly illitic. Less abundant kaolinite and smectite are also present. With respect to their physicochemical properties, all samples have good thermal properties which make them potentially suitable for therapeutic or aesthetic purposes.

Dark blue-green Fe(II)Fe(III) hydroxychlorides and -sulphates were described by Feitknecht & Keller (1950) and later by Bernal et al. (1959). To further understand the formation and transformation of these compounds, Taylor & McKenzie (1980) and Taylor (1980) prepared Fe(II)Al(III) and Fe(II)Fe(III) hydroxychlorides, -sulphates and -carbonates by a more controlled hydrolysis reaction. These compounds, referred to as ‘green rusts’ by Bernal et al. (1959), are isostructural with hydrotalcite. However, the X-ray diffraction patterns can vary with the M(II)/M(III) cation ratio as it departs from the ideal value of 3, and with the interlayer anion.

Regression analysis of high-precision structural and chemical data on trioctahedral and dioctahedral micas yielded interrelationships between unit-cell parameters, chemical composition and structural details. Regression equations relating b and csinβ parameters of micas to composition were used for estimating composition from cell data in order to analyse P-T conditions of rock formation. Algorithms for computing atomic coordinates for 2M1 37' and 1M dioctahedral micas having either centrosymmetric or non-centrosymmetric layers and 1M trioctahedral micas are presented. Deviations of computed atomic coordinates from experimental values are, on average, 0·002 Å for octahedral cations and 0·005-0·010 Å for other atoms. Discrepancies between calculated and experimental individual interatomic distances seldom exceed 0·01 Å. Computed atomic coordinates were used to calculate X-ray diffraction patterns for glauconite and illite. Results indicate a close fit between the calculated and experimental patterns. The local structure around an octahedral cation of interest can be determined.

The clay fractions from a 1191-cm long sediment core in the SW Basin of the Atlantis II Deep, Red Sea, were investigated by XRD, electron microscopy and chemical analysis. Talc dominates in the botton portion of the core, near the brine discharge vent. At 1183 cm depth, the clay consists of vermiculite/chlorite and chrysotile. These minerals are of hydrothermal origin and two possible formation pathways are proposed: (i) vermiculite/chlorite and chrysotile formed by the submarine alteration of previously deposited talc; (ii) vermiculite/chlorite and chrysotile authigenically precipitated as a result of changes in the chemical composition of the brine. At 1170 cm depth, a new depositional sequence results from the progressive alteration of swelling 2:1 minerals into vermiculite. At 1025 cm, Mg-rich clay minerals such as chlorite, chrysotile and talc again become prominent. The upper part of the core is characterized by a transition from non-expanding Mg-rich clay minerals to Fe-rich expanding clays, principally nontronite. Periodically, the content of well-crystallized oxides such as hematite in the layers increases. At 1025 cm, some of the Fe-oxides have a morphology similar to that of akaganéite. In the uppermost part of the core, iron oxides appear to consist of a poorly crystalline hydrothermal hematite. An attempt has been made to correlate the various mineralogical assemblages geochemically.

Les hydrates à une couche des vermiculites présentent cinq modes d'empilement. Aux cations de petit et de grand rayon ionique (Li et Ba) correspondent des modes d'empilement particuliers. Les cations (Na, Mg, Ca et Sr) conduisent chacun à deux modes d'empilement correspondant à deux stades différents d'hydratation.

The mineralogical nature of clays from the Catalan coastal range corresponding to Bunter, Muschelkalk and Keuper in stratigraphic sequence has been investigated. The predominant minerals present are illite, quartz, carbonate (calcium and/or magnesium) and chlorite in the Keuper and Muschelkalk and in the Bunter kaolinite is found in addition. Attention is drawn to the occurrence of interstratified chlorite and swelling chlorite, which association may be typical of clays deposited during Triassic time.

A long-standing unresolved puzzle related to the Danish temperate humid climate is the presence of extended areas with large Fe contents, where goethite and ferrihydrite are present in the topsoil along with hematite and maghemite. Hematite and, particularly, maghemite would normally be interpreted as the result of high temperature as found after forest fires. However, a body of evidence argues against these sites having been exposed to fire. In an attempt to get closer to an explanation of this Fe mineralogy, an experimental forest fire was produced. The results showed a clear mineralogical zonation down to 10 cm depth. This was not observed at the natural sites, which contained a mixture of goethite/ferrihydrite, hematite and maghemite down to 20 cm depth. The experimental forest fire left charcoal and ashes at the topsoil, produced high pH and decreased organic matter content, all of which is in contrast to the natural sites. The conclusion from this work is that the mineralogy of these sites is not consistent with exposure to forest fire, but may instead result from long-term transformation in a reducing environment, possibly involving microbiology.

Glaucony is present in the Palaeocene sediments of the London Basin, from the Thanet Sand Formation to the gravel beds at the base of the Lower Mottled Beds of the Reading Formation. The Upnor Formation glaucony is a rare example of formation in warm, shallow, brackish water and this, combined with the ready availability of fresh material from boreholes, make this study important in developing our understanding of this mineral. Glaucony comprises up to 50% of the Upnor Formation, a grey to green sandstone, of variable thickness and composition, which was deposited in awarm, shallow, marine to estuarine environment, ∼55.6–56.2 Ma. Using morphological criteria, X-ray diffraction data and K+ abundance, the Upnor glaucony may be defined as evolved. The underlying shallow marine Thanet Sand contains <5% of nascent to slightly evolved glaucony. The rare earth element (REE) data for the Upnor Formation suggest more than one source for the sediment from which the Upnor glaucony formed, while the Thanet REE data are consistent with a large detrital clay component.

In the Upnor Formation, the large proportion of glaucony that occurs as granule fragments rather than whole granules, and the high-energy estuarine to shallow-marine environment of deposition, are indicative of reworking. The Upnor glaucony is inferred to be intraformationally reworked, rather than derived from the Thanet Sand Formation. The glaucony may have formed in sediments deposited away from the main estuarine channel, and been subsequently reworked into higher-energy sediments.Warm seas with freshwater mixing are more typically characteristic of verdine formation than of glaucony. The shallow, brackish environment of deposition suggests that there is not a clear distinction between the environmental requirements of verdine (or odinite) and glaucony (or glauconite), as is often proposed. The highly fractured, delicate nature of some granules indicates that they have experienced somematuration in situ, after reworking.

The oxygen and hydrogen isotopic compositions of Upnor Formation shark teeth and glaucony point to formation in low-salinity water at ∼23 ± 3°C, also consistent with formation in the Upnor Formation, rather than in a fully marine sediment and subsequent reworking. A higher than normal temperature of formation may have increased the rate of evolution of glaucony.

Our multidisciplinary study considers many of the factors relating to depositional environment that must be considered when glaucony-rich facies are encountered in comparable palaeo-environmental settings elsewhere in the geological record.

Adsorption and desorption of cationic surfactants, cetyl pyridinium bromide, cetyl trimethyl ammonium bromide, dodecyl pyridinium bromide on bentonite, kaolinite and illite, and their diffusion through a bentonite membrane have been studied.

The binding of these compounds on the mineral surface takes place much beyond the exchange capacity. For excessive saturations with long chain compounds like these, the chains stand erect to the surface. A correlation of area per exchange site and area associated with surfactant molecule on clay surface also supports this view. The increase in the extent of adsorption with the size of the organic cation is due to an increase in the van der Waal's forces between clay and surfactant molecule. Isosteric heats of adsorption at different stages of surface covered with surfactant have also been determined and the same was found to pass through a minimum point. Larger ions desorb less, owing to the lesser solubility and larger contribution of dispersion forces.

Permeability of these surfactants and energy of activation of the diffusion process through the H- bentonite membrane has also been investigated. Diffusion of these cations takes place via exchange positions through the membrane and the order is exactly the reverse of their adsorption on the clay surface.

Well-crystallized kaolinite was found to exhibit marked proton conductivity at pre-dehydration temperatures. Direct current conductivity and thermopotential measurements were performed. By comparing the results obtained with Au electrodes (proton blocking) to those obtained with Pd electrodes (proton injecting), non-protonic contributions could be separated from proton conductivity. The majority charge carriers appeared to be defect proton (negative sign), corresponding chemically to an O2− replacing OH− in the lattice, but excess protons were also noted (positive sign). Below 275°C the activation energy was of the order of 7–8 kcal mole−1; between 275–450°C it was about 18–20 kcal mole−1. This indicated a two-step defect proton-excess proton conductivity mechanism involving, in succession, the two kinds of OH− in the kaolinite structure: (i) OH− located within the six-membered ring formed by the SiO4 tetrahedral sheet, (ii) the close OH− array formed by the octahedral sheet. The conductivity results were supported by IR spectroscopic measurements.

The Maastrichtian-Palaeogene series of the Western High Atlas and Meseta Basins in Morocco are particularly rich in palygorskite. The present work is aimed at clarifying the genesis of palygorskite from the interbedded facies and gaining an understanding of their relationships with the depositional environment. The mineralogical characteristics of palygorskite from these series were studied by X-ray diffraction (XRD) and electron microscopy (SEM/TEM). The palygorskite content and microstructure show large geographical and stratigraphical variations in the deposits studied. The palygorskite occurrence is directly related to palaeobathymetry, since it is the dominant clay mineral in shallow marine and restricted environments. According to the morphology of palygorskite crystallites, four types of textures were distinguished. These types of palygorskite are polygenetic, formed by chemical precipitation, by the recrystallization of smectite clays or reworked by wind or water from sub-aerial environments. The difference between the two studied sub-basins with respect to palygorskite occurrence is attributed to the palaeomorphology of the hinterlands, to the tectonic differentiation and to the physical-chemical conditions of seawater.

The genesis of the products of the alteration of acid pyroclastic material is discussed and interpreted on the basis of the distribution, sedimentation conditions, post-sedimentation activity, mineral and chemical compositions of pyroclastic deposits in Bulgaria and Slovakia.

It is found that the disordered nonequilibrium nature of the volcanic glass induces a diagenetic devitrification of the tuffs and formation of clinoptilolitic, adularia-cristobalite and bentonite rocks. With increasing temperature, the volcanic glass tends forward a stable state through a series of zeolite mineral associations: clinoptilolite-mordenite-analcime-feldspar. The change in mineral composition of this series of rocks occurs without a change in the chemical composition of the rocks, which could be explained by the closed nature of zeolite systems. The formation of bentonites is associated with the removal of alkaline ions under diagenetic conditions, while the formation of halloysite rocks is caused by hydrothermal activity.

Two smectites with different layer charge localization were used to characterize the chemical and structural aspects of minerals treated with 1.9 × 10−2m and 1 m heavy metal solutions (Zn2+ and Pb2+). Natural and treated smectites were analysed by: (1) X-ray powder diffraction first at 25°C and relative humidity of 60% and then at increasing temperature up to 400°C; (2) thermo-gravimetric and differential thermal analysis; (3) X-ray fluorescence; (4) atomic absorption and UV visible spectrophotometries. The sorption of both metals depends on 2:1 layer features and is enhanced when the total layer charge is mostly due to substitution in the octahedral sheet. The variability between Zn2+- and Pb2+-treated smectites in the interlayer water content depends both upon cation electrostatic features and upon smectite layer charge localization. The greatest water content was observed in [Zn2+]1 m-treated smectite showing charge imbalance in the octahedral sheet. In smectites treated with [Zn2+]1 m solutions, an additional thermal reaction occurs at a temperature of ∼380°C, and the d(001) spacing, which is 10 Å at a temperature of ∼200°C, gradually decreases in the temperature range 200–400°C. In smectites treated with 1 m [Pb2+] solutions this value is reached at a temperature of ∼150°C and remains quite constant up to 400°C.

X-ray powder diffraction patterns of kaolinites have been studied with especial reference to the region of the 02, 11, band. Satisfactory correlations with calculated patterns based on the layer structure of dickite can be achieved for a range of kaolinites if account is taken of disorder between and within layers. Some indication of the amount of disorder within a kaolinite can be obtained.

A technique for preparing vermiculites for examination by high-resolution transmission electron microscopy (HRTEM) has been developed. A TEM-stable expanded phase can be obtained by intercalating n-alkylammonium ions between the silicate layers of a parent biotite. The vermiculite particles were embedded in Spurr resin and centrifuged to improve orientation. Ultra-thin specimens were prepared using an ultramicrotome, the quality and thickness of the sections being monitored by TEM. Lattice images of biotite, Ba-vermiculite and octylammonium-vermiculite, the latter showing a perpendicular arrangement of the alkyl chains relative to the silicate layers, were obtained with a resolution ∼2 Å. The reliability of these images was confirmed by computer simulation.

Present-day marine sediments around the emerged basaltic areas of Iceland and the Faeroe Islands are characterized by the abundance and predominance of smectites. Smectites increase regularly and systematically near volcanic areas. Their origin from (i) meteoric/deuteric weathering, (ii) hydrothermal products, (iii) neoformation in the marine environment or (iv) transformation during their transport to or stay in oceanic regions is considered in a comparative study of three types of environments on or near the Faeroe Islands. These are (1) a basaltic environment where phyllite minerals of deuteric and hydrothermal origin are abundant; (2) a soil environment formed on basaltic flows; (3) a marine sedimentary environment within adjacent sedimentary basins. This investigation clearly shows the link between hydrothermal and deuteric saponite-celadonite in basalt, Fe,Mg-smectite in Faeroe soils and Fe-smectite in marine sediments.

The effect of a Mg- and Al-containing layered double hydroxide (LDH), used as an additive or as a matrix, on the dissolution and solubility of two non-steroidal anti-inflammatory drugs (NSAIDs), namely, mefenamic and meclofenamic acids, is reported. The use of MgAl-LDH enhances the solubility of mefenamic acid at the three pH values tested, and the value is larger when the acid is intercalated as opposed to simply being mixed with the layered material. For pure mefenamic acid, the most unfavourable pH is 1.2, while for the physical mixture and the sample with the intercalated drug, the most unfavourable pH is 4.5, for which the minimum increase in the amount of dissolved acid is recorded. The (dissolution) release-rate for both drugs when they are intercalated between the layers is much slower than for the physical mixture or for the dissolution of the pure drug.

The ‘Fischschiefer formation’ has been identified as the likely source rock for petroleum in the western Molasse Basin of Austria. The investigated cores originate from different depths (1242 m to 4294 m) of the Fischschiefer horizon. The illitization observed in the <0.2 μm fraction proceeds slowly, probably because of the low geothermal gradient (3°C/100 m) in the Molasse Basin. The illite content in illite-smectite ranges from 30% (randomly ordered) for the shallowest sample to 65% (R0+R1 ordering) for the deepest sample. The oxygen index (OI) vs. hydrogen index (HI) plot implies type I to II kerogen for the organic matter. Vitrinite reflectance and Rock Eval parameters indicate an immature stage in the diagenesis of kerogen. Only the deepest sample (4294 m, 0.6% Rr) reaches the early oil window. There is a good correlation of the illitization trend of the mixed-layer mineral I-S and the organic maturity parameters.