A mixed-layer kaolinite/smectite (K/S) containing trace amounts of quartz, discrete kaolinite, goethite-hematite, and calcite was hydrothermally reacted with deionized water at 150°, 200°, and 250°C for 1 to 12 months. The starting K/S contained 50% smectite consisting of 15% low-charge and 35% high-charge layers. The X-ray powder diffraction and chemical analyses of the reacted products indicated a progressive reaction from high-charge to low-charge smectite as a function of time and temperature. The reaction reached completion after 4 months at 250°C, at which point high-charge smectite layers entirely reacted to low-charge smectite layers, the latter maintaining a constant proportion of about 90% for longer run durations. For long reaction times, discrete kaolinite totally reacted, whereas quartz showed only partial dissolution and iron oxides remained stable. Thus, the reaction of high-charge to low-charge smectite layers may be expressed as: high-charge smectite + kaolinite (both interstratified and discrete component) + quartz → low-charge smectite.

The porosity of a propylitized granite from Charroux (France), with no fractures or sealed fractures, increases by more than four times from the unaltered (0.3%) to the altered rock (1.4%). This evolution results from several local porosity modifications which occur at different scales in the rock: (1) at the core scale, from 10−1 to 10−5 m, where rock porosity changes as a function of rock-forming mineralogical composition; (2) at the mineral scale, from 10−3 to 10−7 m, where porosity depends both on the nature of the rock-forming mineral and its clay mineral alteration. Mineralogical and porosity data collected from the granite using a mineralogical map (after chemical staining and scanning electron microscopy images combined with autoradiographs) indicate that (1) the ferromagnesian rock-forming minerals — biotite and magnesiohornblende — act as the main porosity source in the unaltered granite, and (2) the nature of the clay minerals replacing rock-forming minerals in the altered granite appears to control the porosity value through two major alteration processes: chloritization and phengitization which affect the ferromagnesian minerals and produce non-porous chloritic and porous phengitic areas, respectively, at the studied scales. The observation that incipient porosity formation in granites is strongly linked to the pathway of ferromagnesian silicate alteration and subsequent clay mineral formation underlines the need to study parent-rock texture and mineralogy and their effects on subsequent near-surface weathering of granites.

Under closed geochemical conditions, the weathering of a serpentinite rock composed of serpentine (70–85%) and magnesian chlorite (10–15%) associated with magnetite and chromite leads to the complete replacement of serpentine and chlorite by 2:1 layer silicates and produces new Fe oxides. The serpentine minerals crystallize under different habits issued from the serpentinization processes: mesh and hourglass pseudomorphic textures were formed from olivine, and thin-bladed pseudomorphic textures from pyroxene and amphibole crystals. Serpentine veins crosscut the whole rock with locally non-pseudomorphic interpenetrating and interlocking serpentines.

Specific weathering microsystem habits with specific clay mineral crystallizations originate from these different habits: a poorly aluminous saponite in thin-bladed textures, two Fe-rich montmorillonites in mesh and hourglass (MH) textures, and in veins (V) which differentiate on Al, Mg and Fe contents. Magnesian chlorites, isolated from serpentine by hand-picking under a stereomicroscope, are found to weather to trioctahedral vermiculite. Magnetite and chromite extracted from the bulk samples are replaced by newly formed Fe oxides, maghemite, goethite and hematite, which give way to specific Fe accumulation habits in the regolith zone of the weathering profile.

The early stages of amphibole weathering result in the crystallization of several clay mineral species: tri- and dioctahedral smectites, interstratified dioctahedral kaolinite-smectite (K-S), and halloysite. Each clay mineral crystallizes into specific microsites which develop from etch pits along specific crystallographic directions in the host amphibole. Two types of microsites are recognized according to their location in the amphibole crystal and their clay mineral crystallizations. The first type is a plane surface related to the (110) amphibole cleavages where saponite particles crystallize in a characteristic honeycomb texture. The second type is a ‘sawtooth’ (001) fracture surface generated by etch-pit coalescence where (1) platy K-S particles crystallize directly in contact with the amphibole at the top of ‘teeth’, (2) halloysite particles with tubular habits crystallize directly in contact with the amphibole on the side of the ‘teeth’, and/or on the K-S particles, and (3) montmorillonite crystallizes in the central part of the (001) fracture as a layer with honeycomb texture in contact with the K-S platelets located at the top of ‘teeth’. The microtextural relationships between the clay minerals and their host mineral suggest the following crystallization sequence: (1) saponite and montmorillonite crystallize first on the (110) and (001) surfaces, respectively; (2) as amphibole dissolution proceeds perpendicular to the (001) fracture planes, montmorillonites continue to form in the middle part of the widening fracture whereas K-S crystallizes on the ‘sawtooth’ termination; (3) in the last stage of weathering, tubular halloysite crystallizes on the side of the ‘teeth’, and/or on the K-S.

Bulk mineralogical and chemical properties of a weathering profile derived from serpentinite were studied using classical pedological methods (Munsell soil colors, particle-size distribution, density, cation exchange capacity, exchangeable bases, among others) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) results. Bulk clay fractions were characterized using X-ray diffraction, thermal analysis, electron microprobe, Mössbauer and infrared spectroscopies. Bulk geochemical mass-balance calculated from ICP-AES results shows leaching of both Mg and Si which reflects the early weathering of serpentine minerals. As a consequence, newly formed clay minerals are enriched with the least mobile elements, i.e. Fe and Al, producing dioctahedral smectites. These dioctahedral smectites are complex, heterogeneous and consist mainly of two populations. One population is an Fe-rich montmorillonite with little or no tetrahedral charge and Fe3+ as the dominant octahedral cation whereas the second population exhibits tetrahedral charge. Both populations occur as interstratified layers in the lower horizon of the weathering profile but show increasing segregation into well-defined end-members towards the surface horizons. Considering total Al and Fe contents, these clays differentiate into two chemical composition domains, Fe-rich clays in the lower profile and Al-rich clays towards the surface horizons.

Illite/smectite mixed-layered minerals (I/S) occurring in hydrothermally altered dacite from the island of Martinique were studied using X-ray powder diffraction, electron microprobe and CEC measurement techniques. Microprobe analyses and X-ray identification of high- and low-charge smectite layers indicate that the I/S hydrothermal alteration operates from wall-rock to hydrothermal veins, with conversion of high-charge to low-charge smectite and formation of illite layers. The overall alteration reaction can be expressed as: mixed-layered high-charge smectite + Si4+ + K+ → mixed-layered low-charge smectite + illite. This reaction requires Si and K from external sources and differs from the currently invoked mechanisms for diagenetic illitization where Si is released. The proposed reaction appears, therefore, to be the first step of I/S alteration under low-temperature hydrothermal conditions, prior to the crystallization of newly-formed I/S.

The mineralogical and chemical changes of sheridanite were followed in different alteration horizons as weathering of its host amphibolite increased. Microscopic and microprobe analyses of phases produced in or around the chlorite allowed a classification of the different alteration stages relative to their position in the profile. In the unweathered rock, prehnite and a sericite—kaolinite assemblage appear to have formed at grain boundaries between chlorites and plagioclases. These represent low-pressure (PH2O < 2.5 ± 1 Kb) and low-temperature (320–360°C) metamorphic phases. In the saprock, where initial rock structure is still preserved, chlorites weather to a more or less regular mixed-layer chlorite-vermiculite. In the saprolite, large-grain (20 µm) vermiculite forms in the clayey zones (plasma) when rock structure is destroyed. The chemical composition of these newly-formed minerals is influenced by the original chlorites and mixed-layer minerals.

The weathering of two co-existing sodic (glaucophane) and calcic (actinolite) amphiboles in a glaucophane-schist was studied by optical microscopy. XRD and the electron microprobe. In the early stages of weathering, two trioctahedral expandable phases occur as internal weathering products in the amphiboles: a sodic saponite in the glaucophane and a calcic ‘hectorite’ in the actinolite. Further weathering leads to the replacement of the ‘hectorite’ by a calcic saponite in the actinolite, while the saponites formed in the weathered glaucophane exhibit progressive calcium enrichment in their interlayer sites. These observations demonstrate the influence of the primary mineral compositions on initial weathering products.

Mineralogical examination of a strongly chloritized amphibole-schist indicated that it had been subjected to two alteration episodes of different origin. Structural and petrographic evidence showed that the alteration processes operated per descensum from the bedrock surface down to shallow depth, thus eliminating any hydrothermal episode due to fluid ascension through deep fractures. The rock was first altered into interstratified chlorite-vermiculite minerals with potassic interlayers. These potassic clay minerals occur in an originally K-deficient rock and seem to have been generated by a marine alteration episode; this episode appears to be contemporaneous with the Cenomanian transgression which covered the amphibole-schist with sandy-clayey deposits. The potassic clay minerals were replaced during a later meteoric alteration episode by kaolinites, iron oxides, and smectites with Mg, Ca interlayer cations.

A comprehensive study of weathering in plagioclase-hornblende rock (amphibolite) from La Roche-l'Abeille, Massif Central, using optical and classical methods of clay mineralogy and electron microprobe determinations demonstrates the mineral reactions which can occur as amphibole and plagioclase weather. Both minerals decompose ultimately into beidellitic smectites but of different lattice compositions. It appears, depending on the host mineral, that an aluminous ‘intergrade’ mineral, similar to a hydroxy-complexed vermiculite, forms first, recrystallizing into the beidellites. Exchangeable ion composition of the beidellites suggests that all smectites were in equilibrium with waters of similar chemical activity for Ca and Mg ions at equivalent depths in the profile. The activities of the exchangeable interlayer ions of the newly-formed smectites are similar, regardless of the host mineral. Very local chemical potentials evidently dictate the lattice composition of the phases, ferribeidellite formed from amphiboles, aluminous beidellite formed from plagioclases, but longer range equilibria (centimetric) dictate the type of phase which will crystallize, i.e. smectite.

We present new radial velocities for 306 bright (R < 16) galaxies in a 77 deg2 region of the Shapley supercluster, measured with the FLAIR-II spectrograph on the UK Schmidt Telescope. The galaxies we measured were uniformly distributed over the survey area, in contrast to previous samples which were concentrated in several rich Abell clusters. Most of the galaxies (230) were members of the Shapley supercluster: they trace out two previously unknown sheets of galaxies linking the Abell clusters of the supercluster. In a 44 deg2 area of the supercluster excluding the Abell clusters, these sheets alone represent an overdensity of a factor of 2·0 ± 0·2 compared to a uniform galaxy distribution. The supercluster is not flattened in the Declination direction as has been suggested in previous papers. Within our survey area the new galaxies contribute an additional 50% to the known contents of the Shapley supercluster, with a corresponding increase in its contribution to the motion of the Local Group.

The photofission process has been recently considered for the production of neutron rich isotopes and the development of radioactive beams. The radioprotection hazard should be studied accordingly. A survey of the radiative electron energy loss theory is reported in order to estimate numerically the bremsstrahlung production of thick targets. The resulted bremsstrahlung angular and energy theoretical distributions delivered from W and UCx thick converters are presented and compared with previous results. This study is focused on initial kinetic energies of the electron beam included in the range 30-60 MeV, suitable for the production of large photon yields able to induce the 238U fission. The source term for 50 MeV incident electrons is reported for radioprotection purposes.

The ESO Slice Project (ESP) is a galaxy redshift survey we have recently completed as an ESO Key-Project over about 30 square degrees, in a region near the South Galactic Pole (Vettolani et al., submitted to A&A). The survey is nearly complete to the limiting magnitude bJ = 19.4 and consists of more than three thousands galaxies with reliable redshift determination.

We present preliminary results of a galaxy redshift survey we are accomplishing as an ESO Key Project over about 40 square degrees in a region near the South Galactic Pole, to a limiting magnitude bJ = 19.4. Up to now ∼ 50% of the survey has been completed, providing about 2000 galaxy redshifts.

In a comparative study, optical and radio spectra are presented in order to further investigate violent turbulent motions in starburst galaxies. Emission-line, HI and OH profiles of IRAS 10039-3338 exhibit signs of a highly perturbed far-infrared galaxy. Remarkably narrow and distinct OH components are shown in the megamaser spectra. A molecular mass of 1010 MO is deduced from CO observations. The presence of comparable numbers of blue and red-shifted components is apparently not in favor of an outflow interpretation.