The Experts below are selected from a list of 6666 Experts worldwide ranked by ideXlab platform
Anna Travé - One of the best experts on this subject based on the ideXlab platform.
-
Permian–Triassic red-stained albitized profiles in the granitic basement of NE Spain: evidence for deep alteration related to the Triassic palaeosurface
International Journal of Earth Sciences, 2019Co-Authors: Carles Fàbrega, David Parcerisa, Andrey Gurenko, David Gòmez-gras, Christine Franke, Médard Thiry, Jesus Sole, Anna TravéAbstract:Extensive areas of the Variscan granitic basement in NE Spain display profiles of red-stained albitized facies characterized by albitization of Ca-plagioclase, chloritization of biotite and microclinization of Orthoclase, along with the alteration of igneous quartz to secondary CL-dark quartz. These profiles have a geopetal structure beneath the Triassic unconformity, with a very intense and pervasive alteration in the upper part that progressively decreases with depth to 150–200 m where the alteration is restricted to the walls of fractures. The red albitized facies contains secondary maghemite and hematite that indicate oxidizing conditions. Dating of microclinized Orthoclase and secondary monazite that have formed in the red-stained albitized facies yielded K–Ar and U–Th–Pb_total ages of 240 and 250 Ma, respectively, suggesting that the alteration developed during the Permian–Triassic period. The geopetal disposition of the red albitized profile with respect to the Triassic unconformity, its large regional extent, and the fracture-controlled alteration in the lower part of the profile indicate groundwater interaction. The δ ^18O values of albitized plagioclase (+ 11‰), microclinized Orthoclase (+ 13‰), and secondary CL-dark quartz (+ 12‰) suggest that the alteration temperature was about 55 °C. This “low” temperature suggests that the alteration occurred during interaction of the granitic rocks with Na-rich fluids below a surficial weathering mantle on the Permian–Triassic palaeosurface. The latter is possibly related to Triassic evaporitic environments in long-lasting, stable landscapes in which Na-rich solutions infiltrated deep regional groundwaters.
Neil C. Sturchio - One of the best experts on this subject based on the ideXlab platform.
-
In situ imaging of Orthoclase-aqueous solution interfaces with x-ray reflection interface microscopy
Journal of Applied Physics, 2011Co-Authors: Paul Fenter, Sang Soo Lee, Z. Zhang, Neil C. SturchioAbstract:The use of x-ray reflection interface microscopy (XRIM) to image molecular-scale topography at the aqueous–solid interface, in situ, is described. Specifically, we image interfacial topography of the Orthoclase-(001)–aqueous solution interface at room temperature and describe the challenges associated with in situ XRIM imaging. The measurements show that the reflectivity signal for in situ XRIM measurements is substantially smaller than that for ex situ measurements, because of both intrinsic and extrinsic factors. There is also a systematic temporal reduction in the image intensity with increasing x-ray dose, revealing that interaction of the focused x-ray beam with the Orthoclase interfaces leads to interfacial perturbations, presumably in the form of surface roughening. This image fading is localized to the x-ray beam footprint, suggesting that the primary damage mechanism is initiated by photoelectrons produced by x-ray beam absorption near the substrate–electrolyte interface. Finally, the role of aqu...
-
Adsorption of Rb+ and Sr2+ at the Orthoclase (001)-solution interface
Geochimica et Cosmochimica Acta, 2008Co-Authors: Paul Fenter, Changyong Park, Neil C. SturchioAbstract:Abstract Adsorption of Rb + and Sr 2+ at the Orthoclase (0 0 1)–solution interface is probed with high-resolution X-ray reflectivity and resonant anomalous X-ray reflectivity. Specular X-ray reflectivity data for Orthoclase in contact with 0.01 m RbCl solution at pH 5.5 reveal a systematic increase in electron density adjacent to the mineral surface with respect to that observed in contact with de-ionized water (DIW). Quantitative analysis indicates that Rb + adsorbs at a height of 0.83 ± 0.03 A with respect to the bulk K + site with a nominal coverage of 0.72 ± 0.10 ions per surface unit mesh (55.7 A 2 ). These results are consistent with an ion-exchange reaction in which Rb + occupies an inner-sphere adsorption (IS) site. In contrast, X-ray reflectivity data for Orthoclase in contact with 0.01 m Sr(NO 3 ) 2 solution at pH 5.3 reveal few significant changes with respect to DIW. Resonant anomalous X-ray reflectivity was used to probe Sr 2+ adsorption and to image its vertical distribution. This element-specific measurement reveals that Sr 2+ adsorbs with a total coverage of 0.37 ± 0.02 ions per surface unit mesh, at a substantially larger height (3.28 ± 0.05 A) than found for Rb + , and with a relatively broad density distribution (having a root-mean-square width of 1.88 ± 0.08 A for a single-peak model), implying that Sr 2+ adsorbs primarily as a fully-hydrated outer-sphere (OS), species. Comparison to a two-height model suggests that 13 ± 5% of the adsorbed Sr 2+ may be present as an IS species. This partitioning implies a ∼5 kJ/mol difference in free energy between the IS and OS Sr 2+ on Orthoclase. Differences in the partitioning of Sr 2+ between IS and OS species for Orthoclase (0 0 1) and muscovite (0 0 1) suggest control by the geometry of the IS adsorption site. Results for the OS distribution are compared to predictions of the Poisson–Boltzmann equation in the strong coupling regime, which predicts an intrinsically narrow vertical diffuse ion distribution; the OS distribution might thus be thought of as the diffuse ion profile in the limit of high surface charge.
-
adsorption of rb and sr2 at the Orthoclase 001 solution interface
Geochimica et Cosmochimica Acta, 2008Co-Authors: Paul Fenter, Changyong Park, Neil C. SturchioAbstract:Abstract Adsorption of Rb + and Sr 2+ at the Orthoclase (0 0 1)–solution interface is probed with high-resolution X-ray reflectivity and resonant anomalous X-ray reflectivity. Specular X-ray reflectivity data for Orthoclase in contact with 0.01 m RbCl solution at pH 5.5 reveal a systematic increase in electron density adjacent to the mineral surface with respect to that observed in contact with de-ionized water (DIW). Quantitative analysis indicates that Rb + adsorbs at a height of 0.83 ± 0.03 A with respect to the bulk K + site with a nominal coverage of 0.72 ± 0.10 ions per surface unit mesh (55.7 A 2 ). These results are consistent with an ion-exchange reaction in which Rb + occupies an inner-sphere adsorption (IS) site. In contrast, X-ray reflectivity data for Orthoclase in contact with 0.01 m Sr(NO 3 ) 2 solution at pH 5.3 reveal few significant changes with respect to DIW. Resonant anomalous X-ray reflectivity was used to probe Sr 2+ adsorption and to image its vertical distribution. This element-specific measurement reveals that Sr 2+ adsorbs with a total coverage of 0.37 ± 0.02 ions per surface unit mesh, at a substantially larger height (3.28 ± 0.05 A) than found for Rb + , and with a relatively broad density distribution (having a root-mean-square width of 1.88 ± 0.08 A for a single-peak model), implying that Sr 2+ adsorbs primarily as a fully-hydrated outer-sphere (OS), species. Comparison to a two-height model suggests that 13 ± 5% of the adsorbed Sr 2+ may be present as an IS species. This partitioning implies a ∼5 kJ/mol difference in free energy between the IS and OS Sr 2+ on Orthoclase. Differences in the partitioning of Sr 2+ between IS and OS species for Orthoclase (0 0 1) and muscovite (0 0 1) suggest control by the geometry of the IS adsorption site. Results for the OS distribution are compared to predictions of the Poisson–Boltzmann equation in the strong coupling regime, which predicts an intrinsically narrow vertical diffuse ion distribution; the OS distribution might thus be thought of as the diffuse ion profile in the limit of high surface charge.
-
Structure of the Orthoclase (001)- and (010)-water interfaces by high-resolution X-ray reflectivity
Geochimica et Cosmochimica Acta, 2003Co-Authors: Paul Fenter, L. Cheng, Changyong Park, Zhaofeng Zhang, Neil C. SturchioAbstract:High-resolution in situ X-ray specular reflectivity was used to measure the structures of Orthoclase (001) and (010) cleavage surfaces in contact with deionized water at 25°C. X-ray reflectivity data demonstrate a high degree of structural similarity between these two Orthoclase-water interfaces. Both interfacial structures include cleavage along the plane of minimal bond breakage resulting in surfaces terminated by non-bridging oxygens; structured water within 5 A of the Orthoclase surface (consisting of adsorbed species at the surface and layered water above the surface), with a featureless water profile beyond 5 A; substitution of outermost K+ ions by an oxygen containing species (presumably H3O+); and small structural displacements of the near surface atoms. The interfacial water structure, in comparison with recent results for other mineral-water interfaces, is intermediate between the minimal structure found at calcite-, barite-, and quartz-water interfaces and the more extensive structure found at the muscovite-water interface.
-
Resolving Orthoclase dissolution processes with atomic force microscopy and X-ray reflectivity
Geochimica et Cosmochimica Acta, 2001Co-Authors: H. Henry Teng, Paul Fenter, L. Cheng, Neil C. SturchioAbstract:Abstract Direct measuremens of Orthoclase (001) were performed using in situ atomic force microscopy (AFM) and synchrotron X-ray reflectivity to reveal the A-scale dissolution process as a function of pH and temperature. Distinct processes were observed, involving mainly terrace roughening at pH = 1.1 and step motion at pH = 12.9. A gel-like surface coating was observed to form at acidic pH under slow fluid flow-rate conditions. No coating was observed either at alkaline pH or at acidic pH under high fluid flow-rate conditions. The corresponding dissolution rates were measured directly at pH = 1.1 and 12.9 at ∼50°C using real-time X-ray reflectivity measurements, and reacted interface structures were derived from crystal truncation rod measurements after reaction at both acidic and alkaline pH. Our observations reveal, under these experimental conditions, that 1) Orthoclase dissolution is controlled by at least two separate surface reactions having distinct reactive sites; 2) dissolution is stoichiometric at alkaline pH and only minimally nonstoichiometric (limited to one unit-cell depth) at acidic pH; previously identified nonstoichiometric layer thicknesses derived from macroscopic measurements are associated with the formation of the gel-like coatings; 3) dissolution rates measured at freshly cleaved (001) surfaces are comparable to those derived from steady-state powder dissolution rates for both alkaline and acidic pH; and 4) elevated transient dissolution rates are not observed for freshly cleaved surfaces but are obtained under alkaline conditions after reacting the Orthoclase (001) surface at acidic pH. These observations clarify differences in Orthoclase dissolution mechanisms as a function of pH, demonstrate the utility of AFM and X-ray scattering methods for measuring A-scale structures and face-specific dissolution rates on single crystals and place new constraints on the understanding of alkali feldspar weathering processes.
Carles Fàbrega - One of the best experts on this subject based on the ideXlab platform.
-
Permian–Triassic red-stained albitized profiles in the granitic basement of NE Spain: evidence for deep alteration related to the Triassic palaeosurface
International Journal of Earth Sciences, 2019Co-Authors: Carles Fàbrega, David Parcerisa, Andrey Gurenko, David Gòmez-gras, Christine Franke, Médard Thiry, Jesus Sole, Anna TravéAbstract:Extensive areas of the Variscan granitic basement in NE Spain display profiles of red-stained albitized facies characterized by albitization of Ca-plagioclase, chloritization of biotite and microclinization of Orthoclase, along with the alteration of igneous quartz to secondary CL-dark quartz. These profiles have a geopetal structure beneath the Triassic unconformity, with a very intense and pervasive alteration in the upper part that progressively decreases with depth to 150–200 m where the alteration is restricted to the walls of fractures. The red albitized facies contains secondary maghemite and hematite that indicate oxidizing conditions. Dating of microclinized Orthoclase and secondary monazite that have formed in the red-stained albitized facies yielded K–Ar and U–Th–Pb_total ages of 240 and 250 Ma, respectively, suggesting that the alteration developed during the Permian–Triassic period. The geopetal disposition of the red albitized profile with respect to the Triassic unconformity, its large regional extent, and the fracture-controlled alteration in the lower part of the profile indicate groundwater interaction. The δ ^18O values of albitized plagioclase (+ 11‰), microclinized Orthoclase (+ 13‰), and secondary CL-dark quartz (+ 12‰) suggest that the alteration temperature was about 55 °C. This “low” temperature suggests that the alteration occurred during interaction of the granitic rocks with Na-rich fluids below a surficial weathering mantle on the Permian–Triassic palaeosurface. The latter is possibly related to Triassic evaporitic environments in long-lasting, stable landscapes in which Na-rich solutions infiltrated deep regional groundwaters.
Paul Fenter - One of the best experts on this subject based on the ideXlab platform.
-
In situ imaging of Orthoclase-aqueous solution interfaces with x-ray reflection interface microscopy
Journal of Applied Physics, 2011Co-Authors: Paul Fenter, Sang Soo Lee, Z. Zhang, Neil C. SturchioAbstract:The use of x-ray reflection interface microscopy (XRIM) to image molecular-scale topography at the aqueous–solid interface, in situ, is described. Specifically, we image interfacial topography of the Orthoclase-(001)–aqueous solution interface at room temperature and describe the challenges associated with in situ XRIM imaging. The measurements show that the reflectivity signal for in situ XRIM measurements is substantially smaller than that for ex situ measurements, because of both intrinsic and extrinsic factors. There is also a systematic temporal reduction in the image intensity with increasing x-ray dose, revealing that interaction of the focused x-ray beam with the Orthoclase interfaces leads to interfacial perturbations, presumably in the form of surface roughening. This image fading is localized to the x-ray beam footprint, suggesting that the primary damage mechanism is initiated by photoelectrons produced by x-ray beam absorption near the substrate–electrolyte interface. Finally, the role of aqu...
-
Adsorption of Rb+ and Sr2+ at the Orthoclase (001)-solution interface
Geochimica et Cosmochimica Acta, 2008Co-Authors: Paul Fenter, Changyong Park, Neil C. SturchioAbstract:Abstract Adsorption of Rb + and Sr 2+ at the Orthoclase (0 0 1)–solution interface is probed with high-resolution X-ray reflectivity and resonant anomalous X-ray reflectivity. Specular X-ray reflectivity data for Orthoclase in contact with 0.01 m RbCl solution at pH 5.5 reveal a systematic increase in electron density adjacent to the mineral surface with respect to that observed in contact with de-ionized water (DIW). Quantitative analysis indicates that Rb + adsorbs at a height of 0.83 ± 0.03 A with respect to the bulk K + site with a nominal coverage of 0.72 ± 0.10 ions per surface unit mesh (55.7 A 2 ). These results are consistent with an ion-exchange reaction in which Rb + occupies an inner-sphere adsorption (IS) site. In contrast, X-ray reflectivity data for Orthoclase in contact with 0.01 m Sr(NO 3 ) 2 solution at pH 5.3 reveal few significant changes with respect to DIW. Resonant anomalous X-ray reflectivity was used to probe Sr 2+ adsorption and to image its vertical distribution. This element-specific measurement reveals that Sr 2+ adsorbs with a total coverage of 0.37 ± 0.02 ions per surface unit mesh, at a substantially larger height (3.28 ± 0.05 A) than found for Rb + , and with a relatively broad density distribution (having a root-mean-square width of 1.88 ± 0.08 A for a single-peak model), implying that Sr 2+ adsorbs primarily as a fully-hydrated outer-sphere (OS), species. Comparison to a two-height model suggests that 13 ± 5% of the adsorbed Sr 2+ may be present as an IS species. This partitioning implies a ∼5 kJ/mol difference in free energy between the IS and OS Sr 2+ on Orthoclase. Differences in the partitioning of Sr 2+ between IS and OS species for Orthoclase (0 0 1) and muscovite (0 0 1) suggest control by the geometry of the IS adsorption site. Results for the OS distribution are compared to predictions of the Poisson–Boltzmann equation in the strong coupling regime, which predicts an intrinsically narrow vertical diffuse ion distribution; the OS distribution might thus be thought of as the diffuse ion profile in the limit of high surface charge.
-
adsorption of rb and sr2 at the Orthoclase 001 solution interface
Geochimica et Cosmochimica Acta, 2008Co-Authors: Paul Fenter, Changyong Park, Neil C. SturchioAbstract:Abstract Adsorption of Rb + and Sr 2+ at the Orthoclase (0 0 1)–solution interface is probed with high-resolution X-ray reflectivity and resonant anomalous X-ray reflectivity. Specular X-ray reflectivity data for Orthoclase in contact with 0.01 m RbCl solution at pH 5.5 reveal a systematic increase in electron density adjacent to the mineral surface with respect to that observed in contact with de-ionized water (DIW). Quantitative analysis indicates that Rb + adsorbs at a height of 0.83 ± 0.03 A with respect to the bulk K + site with a nominal coverage of 0.72 ± 0.10 ions per surface unit mesh (55.7 A 2 ). These results are consistent with an ion-exchange reaction in which Rb + occupies an inner-sphere adsorption (IS) site. In contrast, X-ray reflectivity data for Orthoclase in contact with 0.01 m Sr(NO 3 ) 2 solution at pH 5.3 reveal few significant changes with respect to DIW. Resonant anomalous X-ray reflectivity was used to probe Sr 2+ adsorption and to image its vertical distribution. This element-specific measurement reveals that Sr 2+ adsorbs with a total coverage of 0.37 ± 0.02 ions per surface unit mesh, at a substantially larger height (3.28 ± 0.05 A) than found for Rb + , and with a relatively broad density distribution (having a root-mean-square width of 1.88 ± 0.08 A for a single-peak model), implying that Sr 2+ adsorbs primarily as a fully-hydrated outer-sphere (OS), species. Comparison to a two-height model suggests that 13 ± 5% of the adsorbed Sr 2+ may be present as an IS species. This partitioning implies a ∼5 kJ/mol difference in free energy between the IS and OS Sr 2+ on Orthoclase. Differences in the partitioning of Sr 2+ between IS and OS species for Orthoclase (0 0 1) and muscovite (0 0 1) suggest control by the geometry of the IS adsorption site. Results for the OS distribution are compared to predictions of the Poisson–Boltzmann equation in the strong coupling regime, which predicts an intrinsically narrow vertical diffuse ion distribution; the OS distribution might thus be thought of as the diffuse ion profile in the limit of high surface charge.
-
Structure of the Orthoclase (001)- and (010)-water interfaces by high-resolution X-ray reflectivity
Geochimica et Cosmochimica Acta, 2003Co-Authors: Paul Fenter, L. Cheng, Changyong Park, Zhaofeng Zhang, Neil C. SturchioAbstract:High-resolution in situ X-ray specular reflectivity was used to measure the structures of Orthoclase (001) and (010) cleavage surfaces in contact with deionized water at 25°C. X-ray reflectivity data demonstrate a high degree of structural similarity between these two Orthoclase-water interfaces. Both interfacial structures include cleavage along the plane of minimal bond breakage resulting in surfaces terminated by non-bridging oxygens; structured water within 5 A of the Orthoclase surface (consisting of adsorbed species at the surface and layered water above the surface), with a featureless water profile beyond 5 A; substitution of outermost K+ ions by an oxygen containing species (presumably H3O+); and small structural displacements of the near surface atoms. The interfacial water structure, in comparison with recent results for other mineral-water interfaces, is intermediate between the minimal structure found at calcite-, barite-, and quartz-water interfaces and the more extensive structure found at the muscovite-water interface.
-
Resolving Orthoclase dissolution processes with atomic force microscopy and X-ray reflectivity
Geochimica et Cosmochimica Acta, 2001Co-Authors: H. Henry Teng, Paul Fenter, L. Cheng, Neil C. SturchioAbstract:Abstract Direct measuremens of Orthoclase (001) were performed using in situ atomic force microscopy (AFM) and synchrotron X-ray reflectivity to reveal the A-scale dissolution process as a function of pH and temperature. Distinct processes were observed, involving mainly terrace roughening at pH = 1.1 and step motion at pH = 12.9. A gel-like surface coating was observed to form at acidic pH under slow fluid flow-rate conditions. No coating was observed either at alkaline pH or at acidic pH under high fluid flow-rate conditions. The corresponding dissolution rates were measured directly at pH = 1.1 and 12.9 at ∼50°C using real-time X-ray reflectivity measurements, and reacted interface structures were derived from crystal truncation rod measurements after reaction at both acidic and alkaline pH. Our observations reveal, under these experimental conditions, that 1) Orthoclase dissolution is controlled by at least two separate surface reactions having distinct reactive sites; 2) dissolution is stoichiometric at alkaline pH and only minimally nonstoichiometric (limited to one unit-cell depth) at acidic pH; previously identified nonstoichiometric layer thicknesses derived from macroscopic measurements are associated with the formation of the gel-like coatings; 3) dissolution rates measured at freshly cleaved (001) surfaces are comparable to those derived from steady-state powder dissolution rates for both alkaline and acidic pH; and 4) elevated transient dissolution rates are not observed for freshly cleaved surfaces but are obtained under alkaline conditions after reacting the Orthoclase (001) surface at acidic pH. These observations clarify differences in Orthoclase dissolution mechanisms as a function of pH, demonstrate the utility of AFM and X-ray scattering methods for measuring A-scale structures and face-specific dissolution rates on single crystals and place new constraints on the understanding of alkali feldspar weathering processes.
Médard Thiry - One of the best experts on this subject based on the ideXlab platform.
-
Permian–Triassic red-stained albitized profiles in the granitic basement of NE Spain: evidence for deep alteration related to the Triassic palaeosurface
International Journal of Earth Sciences, 2019Co-Authors: Carles Fàbrega, David Parcerisa, Andrey Gurenko, David Gòmez-gras, Christine Franke, Médard Thiry, Jesus Sole, Anna TravéAbstract:Extensive areas of the Variscan granitic basement in NE Spain display profiles of red-stained albitized facies characterized by albitization of Ca-plagioclase, chloritization of biotite and microclinization of Orthoclase, along with the alteration of igneous quartz to secondary CL-dark quartz. These profiles have a geopetal structure beneath the Triassic unconformity, with a very intense and pervasive alteration in the upper part that progressively decreases with depth to 150–200 m where the alteration is restricted to the walls of fractures. The red albitized facies contains secondary maghemite and hematite that indicate oxidizing conditions. Dating of microclinized Orthoclase and secondary monazite that have formed in the red-stained albitized facies yielded K–Ar and U–Th–Pb_total ages of 240 and 250 Ma, respectively, suggesting that the alteration developed during the Permian–Triassic period. The geopetal disposition of the red albitized profile with respect to the Triassic unconformity, its large regional extent, and the fracture-controlled alteration in the lower part of the profile indicate groundwater interaction. The δ ^18O values of albitized plagioclase (+ 11‰), microclinized Orthoclase (+ 13‰), and secondary CL-dark quartz (+ 12‰) suggest that the alteration temperature was about 55 °C. This “low” temperature suggests that the alteration occurred during interaction of the granitic rocks with Na-rich fluids below a surficial weathering mantle on the Permian–Triassic palaeosurface. The latter is possibly related to Triassic evaporitic environments in long-lasting, stable landscapes in which Na-rich solutions infiltrated deep regional groundwaters.