Bruce Velde

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...

Field and laboratory observations based on X-ray diffraction techniques suggest that 2:1 clay minerals behave as a K reservoir. However, 2:1 soil clay assemblages are most often composed of a mixture of different 2:1 clay mineral populations and the role of these different clay mineral populations in K absorption or K release are not fully understood. This present work addressed

The thermal stability of bentonites is of particular interest for containment barriers in nuclear waste storage facilities. The kinetics of smectite reactions have been investigated under laboratory conditions for some time. The variables of time, chemical composition and temperature have been varied in these experiments. The results of such an assessment are that there are about as many kinetic values deduced from experiments as there are experiments.Experiments using natural bentonite to study the smectite-to-illite conversion have been interpreted as a progressive transformation of montmorillonite to illite. It is highly probable that the initial reaction product is not illite but a high-charge beidellite + saponite + quartz mineral assemblage which gives, then, beidellite-mica interstratified mixed-layer minerals. These experimental reactions are noticeably different from those of diagenesis, being closer to reactions in hydrothermal systems.

... études archéologiques, on peut en conclure que, dans les cas particuliers de céramiques contenant un ou plusieurs minéraux remarquables, une détermination précise de ces minéraux est la voie la plus rapide pour la reconnaissance des productions céramiques ayant une ...

... 330 8.3 The Impact of Plant Regime on Clay Minerals in Soils . . ... of water-clay mixtures which was exploited during the Neolithic period for the production of pottery. Soils, and consequentlyclay minerals, are the support of the most fundamental activities of mankind: agriculture ...

Fractal measurements using the Cantor's dust method in a linear one-dimensional analysis mode were made on the fracture patterns revealed on two-dimensional, planar surfaces in four granites. This method allows one to conclude that: (1) The fracture systems seen on two-dimensional surfaces in granites are consistent with the part of fractal theory that predicts a repetition of patterns on different scales of observation, self similarity. Fractal analysis gives essentially the same values of D on the scale of kilometres, metres and centimetres (five orders of magnitude) using mapped, surface fracture patterns in a Sierra Nevada granite batholith (Mt. Abbot quadrangle, Calif.). (2) Fractures show the same fractal values at different depths in a given batholith. Mapped fractures (main stage ore veins) at three mining levels (over a 700 m depth interval) of the Boulder batholith, Butte, Mont. show the same fractal values although the fracture disposition appears to be different at different levels. (3) Different sets of fracture planes in a granite batholith, Central France, and in experimental deformation can have different fractal values. In these examples shear and tension modes have the same fractal values while compressional fractures follow a different fractal mode of failure. The composite fracture patterns are also fractal but with a different, median, fractal value compared to the individual values for the fracture plane sets. These observations indicate that the fractal method can possibly be used to distinguish fractures of different origins in a complex system. It is concluded that granites fracture in a fractal manner which can be followed at many scales. It appears that fracture planes of different origins can be characterized using linear fractal analysis.

Clay fractions and fluid inclusions were studied in the Aulnay sous Bois and Cerneaux (CER-1 and CER-P6) wells located 10 km, 1.3 and 0.6 km, respectively, from the Pays de Bray'' fault (Paris Basin, France). It was shown that a connection was probably established between the Dogger and Triassic reservoirs during the active period of the fault. Chemical and heat transfers have locally modified the diagenesis conditions in the Dogger formation, inducing an overmaturation of clay minerals. These effects, although attenuated, are still identifiable in the Aulnay and CER-1 wells. A maximum temperature of about 90 C was maintained in CER-P6 site even during the uplift stage of the basin.

ABSTRACT Recent data based upon observations of field experiments and laboratory experiments suggest that changes in phyllosilicate mineralogy, as seen by X-ray diffraction analysis, which is induced by plant action can be reversed in relatively short periods of time. Changes from diagenetic or metamorphic mineral structures (illite and chlorite) to those found in soils (mixed layered minerals in the smectite, hydroxy-interlayer mineral and illites) observed in Delaware Bay salt marsh sediments in periods of tens of years and observed under different biologic (mycorhize) actions in coniferous forests in the soil environment can be found to be reversed under other natural conditions. Reversal of this process (chloritisation of smectitic minerals in soils) has been observed in natural situations over a period of just 14 years under sequoia gigantia. Formation of smectite minerals from illite (potassic mica-like minerals) has been observed to occur under intensive agriculture conditions over periods of 80 years or so under intensive zea mais production. Laboratory experiments using rye grass show that this same process can be accomplished to a somewhat lesser extent after one growing season. However experiments using alfalfa for 30 year growing periods show that much of the illite content of a soil can be reconstituted or even increased. Observations on experiments using zea mais under various fertilizer and mycorhize treatments indicate that within a single growing season potassium can be extracted from the clay (illite layers) but at the end of the season the potassium can be restored to the clay structures and more replaced that extracted. Hence it is clear that the change in clay mineralogy normally considered to be irreversible, illite to smectite or chlorite to smectite observed in soils, is a reversible process where plant systems control the soil chemistry and the soil mineralogy. The changes in clay mineralogy concern mostly the chemical composition of the interlayer ion population of a 2:1 clay structure. However the differences in interlayer ion chemistry give us such mineral names as chloritic hydroxyinterlayered mineral (Mg, OH interlayer), illite (K interlayer), and smectite (essentially hydrated Ca interlayer ions). Extraction of these interlayer ions can be reversed by chemistry engendered by plant regimes.

ABSTRACT Soil mineral phases strongly influence soil organic carbon (SOC) dynamics. Clay-size particles have been recognized as protecting SOC from microbial decomposition. Among clay-size minerals, phyllosilicates (clay minerals) have been shown to efficiently protect SOC. There is an important variety of phyllosilicate types present in soils which have contrasting surface properties (specific surface area, charge density). Although these differing surface properties should influence their ability in protecting SOC, this has not been clearly established yet. Publications comparing the ability of the different phyllosilicates to protect SOC are reviewed in this study. Relatively few studies dealing with the link between phyllosilicate mineralogy and SOC protection exist. The few existing studies have followed different methodologies and are based on various analytical techniques, such that direct comparisons among them are difficult. More problematic, they provide different conclusions. Indeed, if experiments conducted in suspension using pure clay phases and recent meta-analyses suggest that phyllosilicate mineralogy has a significant importance for SOC stabilization and SOC stock response to land-use change, these results are not clearly corroborated by studies conducted on a reduced number of soils. The recent technical developments which allow improving both quantitative and qualitative descriptions of the soil clay mineral assemblages, together with nanoscale investigations of phyllosilicate/OM interactions, offer exciting perspectives for determining more accurately the efficiency of the different phyllosilicate types in SOC protection. Such information may provide a much clearer understanding of the impact of phyllosilicate mineralogy on SOC dynamics in the coming years.