Transmission electron microscopic study of antiphase domains in CaAl2Ge2O8-Feldspar

Transmission electron microscopic study of synthetic CaAl₂Ge₂O₈-feldspar revealed two types of antiphase domains: type “b”-antiphase domains with the displacement vector 1/2 [110] and type “c”-antiphase domains with the displacement vector 1/2 [111]. The “b”-domains were on the order of 0.1 μm in size, while the “c”-domains displayed wall to wall distances mostly between 0.1 and 1 μm. The formation of the two types of antiphase domains is due to reductions in translational symmetry associated with the phase transitions \(C\bar 1 \to I\bar 1 \to P\bar 1\) . The antiphase domain textures of CaAl₂Ge₂O₈-feldspar are very similar to the textures found in natural and synthetic anorthite, CaAl₂Si₂O₈.     

Transfer functions simulating the coprecipitation of trace elements in unsaturated soils

Transfer functions describing the coprecipitation of various trace elements (TE; As, Cd, Co, Cu, Cr, Mo, Ni, Pb, Zn), precipitating with iron(oxihydr)oxides from an aqueous solution, were developed and implemented in the computer model ‘Seeper’. ‘Seeper’ was developed to predict the progression of the concentrations of inorganic pollutants in unsaturated soils underneath contaminated areas and to evaluate the prospective contamination of the groundwater. Transfer functions provide a straight and simple relation between the coprecipitation of TE and easy to obtain standard soil parameters, without excessive repercussions on the usability and computation time of the model. Laboratory experiments were conducted to quantify coprecipitation in solutions with pH values ranging from 5 to 12 and containing various iron and TE concentrations. For the examined TE, the transfer functions describe the coprecipitated fraction as a function of the pH value and the concentration ratio between precipitated iron and a TE. The transfer functions yielded a good prediction of cadmium, cobalt, copper, molybdenum, nickel, and zinc (R ² from 0.73 to 0.83). As for arsenic, chromium, and lead the correlation was not as good albeit a significant influence of precipitating iron on the mobility of these elements was observed and represented in the corresponding transfer functions.     

Lithium, boron and chlorine as tracers for metasomatism in high-pressure metamorphic rocks: a case study from Syros (Greece)

High-pressure metamorphic (HPM) rocks (derived from igneous protoliths) and their metasomatised rinds from the island of Syros (Greece) were analysed for their B and Cl whole-rock abundances and their H₂O content by prompt-gamma neutron-activation analysis (PGNAA) and for their Li and Be whole-rock abundances by ICP-OES. In the HPM rocks, B?/Be and Cl?/Be ratios correlate with H₂O contents and appear to be controlled by extraction of B and Cl during dehydration and prograde metamorphism. In contrast, samples of the metasomatised rinds show no such correlation. B?/Be ratios in the rinds are solely governed by the presence or absence of tourmaline, and Cl?/Be ratios vary significantly, possibly related to fluid inclusions. Li/Be ratios do not correlate with H₂O contents in the HPM rocks, which may in part be explained by a conservative behaviour of Li during dehydration. However, Li abundances exceed the vast majority of published values for Li abundances in fresh, altered, or differentiated oceanic igneous rocks and presumably result from metasomatic enrichment of Li. High Li concentrations and highly elevated Li/Be ratios in most metasomatised samples demonstrate an enrichment of Li in the Syros HP mélange during fluid infiltration. This study suggests that B and Cl abundances of HPM meta-igneous rocks can be used to trace prograde dehydration, while Li concentrations seem to be more sensitive for retrograde metasomatic processes in such lithologies.     

Genesis and distribution of mineral waters as a consequence of recent lithospheric dynamics: the Rhenish Massif,Central Europe

Three major, interdependent processes control the genesis and distribution of mineral and thermal waters in the Rhenish Massif, Central Europe: (a) Magmatic processes in the upper mantle provide most of the CO₂ to produce bicarbonate waters in shallow aquifers. (b) Extension of the brittle upper crust enables the ascent of sodium chloride waters. (c) Uplift and erosion shape the massif's relief, which determines the extent of flow systems and the distribution of thermal springs. The chemistry of mineral waters further depends on the aquifers' mineral composition. A comprehensive set of hydrological, chemical, tectonic and geophysical data on the Rhenish Massif has been compiled. It was used to classify the mineral waters and to map the spatial distribution of water properties. The composition of cuttings from several representative wells producing different water types shows that the hydrothermal alteration of the aquifer rocks consists mainly of kaolinization of chlorite and dissolution of feldspar. Numerical transport simulations favour two modes of groundwater flow: topography-driven flow and the pressure-driven ascent of basement brines along active faults. Thermal convection is less important.     

Interaction of bentonite colloids with Cs, Eu, Th and U in presence of humic acid: A flow field-flow fractionation study

The interaction of Cs(I), Eu(III), Th(IV) and U(VI) with montmorillonite colloids was investigated in natural Grimsel Test Site groundwater over a 3 years period. The asymmetric flow field-flow fractionation combined with various detectors was applied to study size variations of colloids and to monitor colloid association of trace metals. The colloids suspended directly in the low ionic strength (I), slightly alkaline granitic groundwater (I = 10⁻³ mol/L, pH 9.6) showed a gradual agglomeration with a size distribution shift from initially 10-200 nm to 50-400 nm within over 3 years. The Ca²⁺ concentration of 2.1 × 10⁻⁴ mol/L in the ground water is believed to be responsible for the slow agglomeration due to Ca²⁺ ion exchange against Li⁺ and Na⁺ at the permanently charged basal clay planes. Furthermore, the Ca²⁺ concentration lies close to the critical coagulation concentration (CCC) of 10⁻³ mol L⁻¹ for clay colloids. Slow destabilization may delimit clay colloid migration in this specific groundwater over long time scales. Eu(III) and Th(IV) are found predominantly bound to clay colloids, while U(VI) prevails as the UO₂(OH)₃⁻ complex and Cs(I) remains mainly as aquo ion under our experimental conditions. Speciation calculations qualitatively represent the experimental data. A focus was set on the reversibility of metal ion-colloid binding. Addition of humic acid as a competing ligand induces rapid metal ion dissociation from clay colloids in the case of Eu(III) even after previous aging for about 3 years. Interestingly only partial dissociation occurs in the case of Th(IV). Experiments and calculations prove that the humate complexes dominate the speciation of all metal ions under given conditions. The partial irreversibility of clay bound Th(IV) is presently not understood but might play an important role for the colloid-mediated transport of polyvalent actinides over wide distances in natural groundwater.     

Nocturnal drainage flow on simple slopes

Observations of nocturnal slope flow have been made at two sites with quite different topography and vegetation. In both cases, continuous measurements of wind and temperature profiles were made from towers that extended through the depth of the katabatic flow. At the simpler site, which approximates a tilted plane, three towers were located at different distances down the slope to measure the development of slope flow with downslope distance.Slope flow depth, downslope wind speed, and temperature deficit are found to change with downslope distance at rates that are consistent with the predictions of Manins and Sawford's (1979) layer-averaged model of slope flow, while measured entrainment rates are found to be comparable to those predicted by Ellison and Turner's (1959) laboratory experiments. The depth of slope flow is found to be roughly 0.05 times the vertical drop from the top of the slope, a relationship that also follows from combining Manins and Sawford's model and Ellison and Turner's laboratory data. Analysis of the wind spectra and a simple numerical model suggest that the turbulent kinetic energy profiles in slope flow are dependent on the speed and direction of the ambient wind and can differ substantially from those found over flat terrain. At the more complex of the two measurement sites, the occurrence of slope flow was found to correlate well with a dimensionless number 5 that is a function of the ridge-top wind speed and of the strength and depth of the inversion and that is an estimate of the ratio of the buoyancy deficit to the external horizontal pressure gradient.Prepared for the U.S. Department of Energy under Contract DE-AC06-76RLO 1830     

Colour measurements in ore-microscopy

By means of recently developed, photoelectric measuring equipment the reflectivity of ore-minerals can be determined under the microscope over a sufficiently large spectral range with such a degree of accuracy and reliability that the dispersion curves can be plotted. Quantitative coefficients for the corresponding reflection colours, as well as for the visual reflectivity, can be computed from these curves. After a short introduction the tristimulus values for some ore minerals are given, as can be calculated from known reflectivity values. The quantitative values are compared with the known qualitative values for colour and reflectivity impression and for the reflection pleochroism. It is shown that reflectivity and colour differences can be determined colorimetrically with at least the same accuracy as by an experienced observer. The following characteristics are emphasized as advantages of quantitative colorimetry: 1. the objective method of determination, 2. the unambiguity and reproducibility of colour and reflectivity characteristics, 3. the simple and internationally comprehensible terminology, 4. the possibility of cataloguing ore minerals according to a quantitative colour system, and 5. the fact that even a colour-blind microscopist can determine any colour with the same certainty as an experienced observer.

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Zusammenfassung Mit neueren photoelektrischen Meßanordnungen ist das Reflexionsvermögen von Erzmineralen unter dem Mikroskop über einen ausreichend großen Spektralbereich so genau und sicher bestimmbar, daß man die maßgebenden Dispersionskurven konstruieren kann. Aus diesen lassen sich quantitative Maßzahlen für die entspr. Reflexionsfarben und für das visuelle Reflexionsvermögen errechnen. Nach kurzer Einführung werden die Farbwerte einiger Erzminerale angegeben, wie sie sich aus bekannten Reflexionswerten errechnen ließen. Die quantitativen Werte werden mit herkömmlichen qualitativen Angaben über Farb- und Reflexionseindruck und über den Reflexionspleochroismus verglichen, und es wird gezeigt, daß die Reflexions- und Farbdifferenzen mit mindestens derselben Genauigkeit farbmetrisch erfaßbar sind wie durch das Auge eines erfahrenen Beobachters. Als Vorteile werden herausgestellt: 1. das objektive Bestimmungsverfahren, 2. die Eindeutigkeit und Reproduzierbarkeit der Farb- und Reflexionscharakteristik, 3. die einfache und international verständliche Terminologie, 4. die Katalogisierbarkeit der Erzminerale nach einem quantitativen Farbsystem, 5. die Tatsache, daß sogar ein farbuntüchtiger Mikroskopiker jede Farbe mit der gleichen Sicherheit erfassen kann wie der erfahrene Beobachter.

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Standard Specification, published by the Deutscher Normenausschuß DIN 5033. Farbmessung (Measurement of Colour) 1962/64.

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Paper on Instructions for Use, Messrs. CARL ZEISS, Oberkochen. The Principles of Colour Measurement, 50-669/I-e (1962).