Dimensions of plagioclase (An65) crystals in a polished thin section of naturally weathered 3400 y old Hawaiian basalt were measured by scanning electron microscopy (in backscattered electron imaging mode). The three-dimensional shape, size, volume and surface area of the plagioclase crystals were then estimated using the method of Morgan and Jerram (2006). The weathering rate of plagioclase (mass loss divided by initial geometric surface area during 3400 y) is –12.116 log10 mol m–2 s–1. This weathering rate represents a time span (3.4 ka) intermediate between laboratory experimental timescales and the ages of regoliths in field studies of natural weathering rates. Weathering rates of the same plagioclase are recalculated using different assumptions concerning the method of estimating surface area, including simple geometric surface area and geometric surface area adjusted for surface roughness. Varying assumptions about surface area result in variations of up to two orders of magnitude in rates estimated from the same basic crystal geometry. The slowest rate estimated here approaches but does not fall within the range of previously determined field rates of plagioclase weathering.

A Devonian weathering profile was developed near the contact of Riphean dolostone containing disseminated carbonate-fluorapatite and intensively pyritized black shales. Samples from the profile were investigated by XRF, SEM, electron microprobe and ion microprobe. Rock-forming minerals are apatite, diaspore, chlorite and kaolinite, while accessory minerals are svanbergite, anatase, pyrite and zircon.

Primary marine carbonate-fluorapatite is represented by extremely weathered crystals concentrated near the footwall. Dissolution of apatite and pyrite provided an acidic environment that is expressed in the formation of S-rich apatite and svanbergite. The environment allowed Ti migration which formed anatase in weathered apatite grains. Coupled substitution Na+ + S6+ = Ca2+ + P5+ is suggested in S-rich apatite. A large volume of dissolved carbonate rocks was a source of Sr necessary for svanbergite formation. Apatite of the third generation formed at the final stage of weathering is represented by small (10—30 μm) very well shaped crystals.

In situ flow-cell ATR-FTIR using a hematite-coated germanium crystal was used to investigate the chemical interactions between Pseudomonas putida and hematite in real time, when compared with cells not attached to the mineral surface. ATR-FTIR spectra of bacteria growing on hematite showed a shift in the carboxylate signal when compared to the samples obtained from free cells, indicating a chemical interaction between the carboxylate groups and the Fe metal ions of the hematite surface. Small differences in the polysaccharide and phosphoryl regions of the IR spectra of bacteria attached to hematite were also observed. This work shows how the use of in-situ flow-cell experiments with a mineral-coated germanium crystal allows a better description of the bacterial interactions with minerals in real time, as an initial step to understand the fundamental mechanisms involved in the relationship between bacteria and mineral surfaces.

An investigation and evaluation of the redox conditions around an underground rock cavern are important from the viewpoint of the safety assessment of the subsurface geological disposal of radioactive wastes. The in situ redox conditions around a cavern excavated in Neogene pyroclastic rocks were investigated. Rock samples were collected from a tunnel wall crossing the oxidation front, and the properties of pore water seeping into small holes drilled in the tunnel wall were determined. Chemical analysis of the rock samples revealed that pyrite-bearing rocks belowthe oxidation front were oxidized by the dissolved oxygen in the groundwater infiltrating from the surface. The water properties changed with increasing oxidation of the rocks. From the amount of oxygen-consuming components in the rocks, the migration rate of the oxidation front was estimated to be ~0.2 mm/y due to the flowrate of groundwater (0.1 m/y) containing oxygen.

Experiments were performed to investigate the transformation of natural aragonite crystals to calcite by reaction with aqueous solutions of calcium carbonate at hydrothermal conditions for different periods of time. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and Laser ablation inductively coupled mass spectrometry (LA-ICP-MS) were used to characterize the reaction product. The results indicate that the replacement of aragonite by calcite follows an interface-coupled dissolution-precipitation mechanism.

We have used a direct imaging technique, in situ atomic force microscopy(AFM) to observe the earliest stages of the dissolution of a biotite surface byoxalic acid at temperatures close to ambient conditions, using a speciallydesigned AFM liquid cell and non-invasive intermittent contact mode of operation. From the nm-resolution data sets in x, yand z dimensions, we have measured dissolution rates and determined activation energies for the process as a function of temperature, via a mass-loss calculation. The value of Ea obtained, 49±2 kJ mol-1, appears to be too high to indicate a diffusion-controlled process and is more in line with expectations based on a process limited by the rate of ligand-induced metal cation detachment from the (001) surface. This is consistent with visual observations of the relative rates of etch-pit formation and growth, and accepted knowledge of the biotite crystal structure. Separate calculations based on planar area etch-pit growth, and measurements of etch-pit perimeters confirm this result, and also indicate substantiallyhigher activation energy, up to 80 kJ mol-1, when the edge pits are in an incipient stage.

Mineral sequestration is among several promising methods of CO2 reduction. It involves incorporation of CO2 into a solid phase via precipitation of carbonate minerals. A prerequisite to carbonate precipitation is the availability of aqueous metal cations and a network of porous media for fluid flow and water-rock interactions. The Hellisheidi-Threngsli lava field in SW Iceland comprises ideal conditions for studying the feasibility of permanent CO2 storage as minerals in basaltic rocks. In this paper we report on a tracer test conducted between two wells at the Hellisheidi-Threngsli site to characterize the physical properties of the main aquifers. The results suggest that most of the water flow between the wells is through an homogenous thick layer with high tortuosity along flow paths and a high reactive surface area for water-rock interactions.

Ectomycorrhizal fungi are mutualistic symbionts of many forest trees and play a major role in nutrient uptake. They form diverse communities in boreal forest soils but functional differences within this group of fungi remain largely unknown. We study ectomycorrhzal fungi in mineral soil to determine how abiotic preferences influence their spatial distribution in stratified soil profiles. This is achieved by correlative field studies of species distribution and soil characteristics at a spatial resolution relevant to soil heterogeneity and mycelial size. Field sampling strategies are being evaluated to establish a protocol for simultaneous small-sample analysis of ectomycorrhizal community and soil chemical variables. Species-specific substrate preferences are examined by studies of regulation of enzymatic and biogeochemical activity in response to relevant organic and inorganic sources of phosphorus. Studies of four species in the genus Piloderma have demonstrated that different strategies to obtain phosphorus are reflected by their spatial distribution in a podzol soil profile.

Boreal forest trees influence mineral weathering rates via exudation and uptake processes. Most trees in the boreal forest live in symbiosis with ectomycorrhizal (EcM) fungi that sheath most of the root tips and form the main interface between the tree and the soil. Current weathering models do not take into account the nature and scale of fungal-mineral interactions. Here we show for the first time grain-scale effects of EcM fungi in symbiosis with a host plant on mineral weathering under sterile conditions. EcM fungi actively direct their growth and energy flow towards mineral grains containing essential nutrient elements for the tree and fungus.

Far-from-equilibrium dissolution experiments with diopside and basaltic glass in mixed-flow reactors at 70°C and pH 8.2 show that solute concentrations do not reach steady state over the experimental duration of 45—60 days. Chemical modelling indicates that during the dissolution experiments, solutions have become supersaturated with respect to carbonates in the case of diopside, and carbonates, clay minerals and zeolites in the case of the basaltic glass. Decreasing dissolution is therefore interpreted as a result of secondary surface precipitates blocking the reactive surface area. Calcite formation was supported in both experiments by a significant increase in Ca (and Sr) concentrations as pH was abruptly lowered from 8.2 to 7 because this change increased carbonate solubility and caused all potential carbonate precipitates to re-dissolve. The reduction in pH also led to an increase in Si concentration for diopside and a decrease in Si concentration for basaltic glass. This observation is in accordance with previous experiments on the pH-dependent dissolution rates of pyroxenes and basaltic glass.

Calcite growth rates were measured in the presence of sulphate using mixed-flow reactors and in situ Atomic Force Microscopy. Preliminary observations reveal that the kinetics and mechanism of the calcite growth was altered by the presence of sulphate. Calcite growth rates in the presence of sulphate (≥ mM) were decreased and two-dimensional nuclei tend to grow on top of existing nuclei, rather than spreading. The height of new nuclei was ~4 Å, 1 Å greater than that of pure calcite growth. This difference reflects the incorporation of tetrahedral SO2-4 anions into the calcite lattice.

Naturally weathered olivine from metamorphosed, tectonized metadunite is corroded by funnel-shaped etch pits. Large etch pits form by weathering, and are not inherited from pre-weathering alteration of these rocks. Comparison of etch pits on olivine in naturally weathered metadunite with naturally weathered olivine phenocrysts from volcanic rocks suggests that olivine etch pits are similar in all sample suites, despite differences in crystallization and weathering/exposure ages, and regolith history.

The spatial and temporal changes in hydrology and pore water elemental and 87/86Sr compositions were used to determine contemporary weathering rates in a 65 to 226 ky old soil chronosequence formed from granitic sediments deposited on marine terraces along coastal California. Cl-corrected Na, K and Si increased with depth denoting inputs from the weathering of plagioclase and K-feldspar. Solute 87/86Sr exhibited progressive mixing of sea water-dominated precipitation with inputs from less radiogenic plagioclase. Linear approximations to these weathering gradients were used to determine plagioclase weathering rates of between 0.38 and 8.9x10-15 moles m-2 s-1. The lack of corresponding weathering gradients for Ca and Sr indicated short-term equilibrium with the clay ion exchange pool which requires periodic resetting by natural perturbations to maintain continuity, in spite of soil composition changes reflecting the effects of long-term weathering.

Far-from-equilibrium dissolution rates of crystalline basalt were measured in a mixed-flow reactor at pH 4 and 10, and at temperatures from 25 to 75ºC. The material used was obtained from a dyke on Stapafell Mountain on Reykjanes peninsula in Iceland because of its similarity with previous experiments on dissolution rates on basaltic glass by Oelkers and Gislason (2001) and Gislason and Oelkers (2003). Comparison of dissolution rates of basaltic glass and of crystalline basalt of similar chemical composition (from Gislason and Oelkers, 2003) indicates lower rates for crystalline material.

The formation and transformation of hydroxysulphate (GRSO4) and hydroxycarbonate (GRCO3) Green Rusts were studied in situ using synchrotron-based time-resolved small and wide angle X-ray scattering. The time-resolved data revealed, for the first time, the pH dependent transition from poorly-ordered schwertmannite (pH <6.5) into GRSO4 (pH ~6.8) followed by GRCO3 (at pH ~9.6). These data also showed that the addition of Zn to the starting sulphate Fe2+/Fe3+ solution resulted in a change in size of the GR unit-cell due to substitution of Zn into the GR structure.

Thin sections of shells from different species of mollusc have been analysed by X-ray synchrotron diffraction using the BM16 at the European Synchrotron Radiation Facility (ESRF), Grenoble, France. A sequence of 2-D X-ray diffraction patterns were acquired in transmission mode at regular intervals across the shell thickness. From the 2D patterns, 2θ- and χ-scans were calculatedan d analysed. We studied the evolution of the shell microstructures by analysing several parameters from calculated scans: (1) the intensity of the most intense aragonite reflections in the calculated 2θ scans; (2) the crystallinity calculated from the full width at half maximum values of the main reflections in those scans; and (3) the degree of orientation of crystals, measured from the angular width (in angle) of the arches displayed in the Debye-Scherrer rings which appeared in the 2D diffraction patterns. The determined parameters displayed sharp changes at the transitions between microstructurally distinct shell layers indicating that the microstructural switch occurred very rapidly and was precisely controlled.

The availability of analytical methods that utilize the very intense and bright X-rays from synchrotron radiation sources has fundamentally changed the way in which geoscientists, environmental scientists and soil scientists study complex environmental samples and decipher the chemical and biological processes that impact the speciation, transport and potential bioavailability of environmental toxins (Brown et al., 2006). Such samples are often mixtures of crystalline and amorphous phases in particle-sizes ranging from cm to nm, adsorbed metal ions and organic molecules, natural organic matter, microbial organisms, algae, plant materials and aqueous solutions. The processes that affect the chemical forms and environmental fate of contaminants in such mixtures range from surface adsorption, desorption, precipitation and dissolution reactions, often involving a combination of hydrolysis, ligand exchange and electron transfer, to biological interactions in which microbial organisms, algae or plants interact with mineral surfaces and environmental contaminants.

The colours of natural and synthetic beryl (ideally Be3Al2Si6O18) have been attributed either tothe presence of chromophore ions partially replacing Al and/or Be (Cr3+, Fe2+/3+, Mn2+) or to the occurrence of colour centres related to the presence of multi-atomic groups. However, no full explanation has been proposed for the blue colour in natural beryl gemstones (aquamarine) despite it being well established that bluish-green synthetic aquamarines containing Fe turn blue when heated for 1 h at 400°C.

A X-ray absorption near-edge spectroscopy (XANES) study at the Fe K-edge was performed on blue beryl crystals from Licungo pegmatite (Mozambique) to ascertain the speciation state of this colouring element, reported in blue sapphire (ideally Al2O3) as a mixture of Fe2+ and Fe3+ in octahedral coordination. The general trend of the spectra is the same when synchrotron radiation (SR) impinges along the c axis of the hexagonal crystal, as well as along the a axis with c vertical. Conversely, a shoulder in the absorption edge is noticed when the incident beam is perpendicular to c, with this axis horizontal in the polarization plane of the SR beam, a reverse in the relative intensities of the two post-edge features is simultaneously observed. Pre-edge features accounting for Fe speciation (valence plus coordination) are identical in all three situations. Considering previous approaches which account for polarization, an explanation is suggested for the special effects observed on the Fe K-edge XANES spectra of analysed blue beryl crystals. Ideas on the origin of the blue colour of this mineral are also presented.

Advances in the design of environmental reaction cells and in the collection of X-ray diffraction data are transforming our ability to study mineral-fluid interactions. The resulting increase in time resolution now allows for the determination of rate laws for mineral reactions that are coupled to atomic-scale changes in crystal structure. Here we address the extension of time-resolved synchrotron diffraction techniques to four areas of critical importance to the cycling of metals in soils: (1) cation exchange; (2) biomineralization; (3) stable isotope fractionation during redox reactions; and (4) nucleation and growth of nanoscale oxyhydroxides.

The speciation of antimony is strongly influenced by its oxidation state (V, III, 0, —III). Redox processes under anaerobic groundwater conditions may therefore greatly alter the environmental behaviour of Sb. Employing X-ray absorption and photoelectron spectroscopy, we show here that Sb(V) is reduced to Sb(III) by magnetite and mackinawite, two ubiquitous Fe(II)-containing minerals, while Sb(III) is not reduced further. At the surface of magnetite, Sb(III) forms a highly symmetrical sorption complex at the position otherwise occupied by tetrahedral Fe(III). The Sb(V) reduction increases with pH, and at pH values >6.5 Sb(V) is completely reduced to Sb(III) within 30 days. In contrast, at the mackinawite surface, Sb(V) is completely reduced across a wide pH range and within 1 h. The Sb(V) reduction proceeds solely by oxidation of surface Fe(II), while the oxidation state of sulphide is conserved. Independent of whether Sb(V) or Sb(III) was added, an amorphous or nano-particulate SbS3-like solid formed.