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T Von Dobeneck - One of the best experts on this subject based on the ideXlab platform.
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low temperature magnetic properties of Rhodochrosite mnco3
Physics of the Earth and Planetary Interiors, 2006Co-Authors: Andrei Kosterov, Thomas Frederichs, T Von DobeneckAbstract:Abstract We have measured magnetic hysteresis loops, zero-field-cooled (ZFC) and field-cooled (FC) remanence, and low-field AC susceptibility as a function of temperature between 2 and 40 K for a single crystal several mm in size and for two powders of manganese carbonate (mineral Rhodochrosite, MnCO 3 ), one ground from a natural precipitate (grainsize ∼100 μm) and another synthesized in the laboratory (grainsize ∼10 μm). For the single crystal, measurements carried out both in the basal (easy magnetization) plane and along the trigonal (hard magnetization) axis yielded, expectedly, grossly different magnetic properties. In the basal plane, hysteresis appears to be mostly controlled by domain wall movement at the two lowest temperatures studied, 5 and 15 K, as indicated by a fairly broad switching field distribution. At 25 K and above, however, magnetization reversal occurs at a single, well defined magnetic field, which we interpret as a characteristic field of the in-plane magnetic anisotropy. Hysteresis in the basal plane is observed up to 36 K which is above the nominal Neel temperature of Rhodochrosite (34.3 K). In addition, a sharp coercivity peak occurs at 34.5 K. Rather unexpectedly, hysteresis is also observed for the magnetic field applied along the trigonal axis. It is very small at 5 K but develops gradually with increasing temperature, coercivity reaching maximum of 100 mT at 28 K and remanence peaking at slightly higher temperature (30–31 K). Hysteresis along the trigonal axis is observed up to 37 K. Hysteresis temperature dependence conforms with the AC susceptibility versus temperature curve which shows a maximum at 36.5 K. ZFC/FC remanence curves also closely match the temperature dependence of remanence extracted from hysteresis loops. We suggest that this behavior could be due to the presence of a minor, about 1 at.% amount of Fe 2+ substituting for Mn in the crystalline lattice of Rhodochrosite. Hysteresis measurements on powders have revealed a significant enhance in coercivity, up to 50 mT for the 100-μm powder and up to 150 mT for the 10-μm one. FC/ZFC ratio amounts to about 2 for the natural powder, while for the synthetic one, which is essentially pure material, it barely exceeds unity. FC/ZFC ratio can thus be viewed as a sensitive indicator of iron incorporation into Rhodochrosite.
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towards the identification of siderite Rhodochrosite and vivianite in sediments by their low temperature magnetic properties
Physics and Chemistry of The Earth, 2003Co-Authors: Thomas Frederichs, T Von Dobeneck, Ulrich Bleil, Mark J DekkersAbstract:Siderite (FeCO3), Rhodochrosite (MnCO3), and vivianite ((Fe3(PO4)2) � 8H 2O) are well-known authigenic minerals in a number of sedimentary settings. Here, we explore the potential of low-temperature mineral magnetic techniques for their identification at low concentration in bulk samples thus expanding mineral magnetic proxies for environmental purposes. The basic rock magnetic properties of these minerals, which are paramagnetic at ambient temperature, were determined with aMagnetic Properties Mea- surement System'. Well-crystalline chemically analyzed material of natural origin was used to gather these data. The diagnostic value of the observed specific magnetic properties was tested on two mid-Eocene sediment samples from the Norwegian Sea (ODP Leg 104, Site 643) known to contain these minerals. The observed Ntemperatures of siderite (37 K) and Rhodochrosite (34 K) conform with literature data. Both carbonates show a fairly strong spin-canted remanence (� 0.4 Am 2 /kg) from cooling in a 5 T magnetic field. Different ratios of field-cooled and zero- field-cooled remanences, however, allow a discrimination between the two minerals. A characteristic of Rhodochrosite is its ex- tremely high magnetic susceptibility just below the Ne temperature. An almost vertical slope in very low fields of the hysteresis loop also testifies to this high susceptibility. It is assigned to a weak anisotropic ferromagnetism confined to the basal plane in which the spontaneous magnetization can almost freely rotate. A prominent magnetic property of siderite is its metamagnetism, resulting in a progressively upward bending of the hysteresis curve in magnetic fields above 5 T. Vivianite also shows an onset of meta- magnetic transition below 5 K in 5 T fields and atwo-stage' increase in susceptibility between 2 and 12 K attributed to successive short- and long-range magnetic ordering. The magnetic properties of the two authigenic marine sediments could be largely explained by combining characteristics of Rhodochrosite and manganosiderite. Shifting of the Npoints to lower temperatures and less well pronounced magnetic phenomena are attributed to element substitution and non-stoichiometry which occur commonly in sedi- mentary environments. � 2003 Elsevier Ltd. All rights reserved.
Pin Christian - One of the best experts on this subject based on the ideXlab platform.
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Coticules of the Belgian type area (Stavelot-Venn Massif): Limy turbidites within the nascent Rheic oceanic basin
'Elsevier BV', 2016Co-Authors: Herbosch Alain, Liégeois Jean-paul, Pin ChristianAbstract:International audienceCoticule is the name originating in Belgium for a fine-grained metasedimentary yellowish rock mainly composed of quartz, spessartine and mica, which is repeatedly interstratified in the hematite-rich purple slates of the Lower Ordovician of the Ardenne region. It was described for the first time in the nineteenth century in the Stavelot-Venn Massif (Ardenne), which is accordingly the type-area for this peculiar lithology. Since then, numerous occurrences were described all over the world in metamorphic rocks of various grades and ages. The exact nature of the Belgian coticule protolith remained hypothetical, although intensively discussed for a long time in the literature. After an extensive review of all the stratigraphical, sedimentological and geochemical results and new field, geochemical (major and trace elements) and Nd isotopic investigations, we propose a significantly improved and sustained genetic model: the thin coticule layers were deposited offshore in a deep oceanic basin as limy mud turbidites. During the early Floian (c. 477 Ma, Early Ordovician), density currents came from the north, from the shelf which bordered the emergent Brabant Massif at that time and flowed down the slope to the deep basin-plain. The purple shales enclosing the coticule layers represent the normal pelagic sedimentation in the basin. These shales are exceptionally rich in Fe and Mn, because of the hydrothermal activity of the nearby and young Rheic Ocean ridge. Indeed, the Rheic Ocean opened in the Early Ordovician (c. 482 Ma). During diagenesis, the strongly oxidizing depositional environment favoured the mobility of Mn2 +, as opposed to Fe3 + that remained insoluble and immobile. This allowed for the migration of divalent manganese from the pelagic shales and for replacing calcium in the turbiditic carbonate fraction, to form Rhodochrosite. Later, epizonal metamorphism transformed the clay-quartz-Rhodochrosite paragenesis of the protolith into the muscovite-quartz-spessartine paragenesis of the coticule. Hence, in the type-area, coticule genesis needed a peculiar environment including a continental shelf with limy mud deposits, a continental slope generating periodical turbidites and a nearby oceanic ridge, here the nascent Rheic Ocean, delivering hydrothermal iron and manganese
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Coticules of the Belgian type area (Stavelot-Venn Massif): Limy turbidites within the nascent Rheic oceanic basin
'Elsevier BV', 2016Co-Authors: Herbosch Alain, Liégeois Jean-paul, Pin ChristianAbstract:Coticule is the name originating in Belgium for a fine-grained metasedimentary yellowish rock mainly composed of quartz, spessartine and mica, which is repeatedly interstratified in the hematite-rich purple slates of the Lower Ordovician of the Ardenne region. It was described for the first time in the nineteenth century in the Stavelot-Venn Massif (Ardenne), which is accordingly the type-area for this peculiar lithology. Since then, numerous occurrences were described all over the world in metamorphic rocks of various grades and ages. The exact nature of the Belgian coticule protolith remained hypothetical, although intensively discussed for a long time in the literature. After an extensive review of all the stratigraphical, sedimentological and geochemical results and new field, geochemical (major and trace elements) and Nd isotopic investigations, we propose a significantly improved and sustained genetic model: the thin coticule layers were deposited offshore in a deep oceanic basin as limy mud turbidites. During the early Floian (c. 477 Ma, Early Ordovician), density currents came from the north, from the shelf which bordered the emergent Brabant Massif at that time and flowed down the slope to the deep basin-plain. The purple shales enclosing the coticule layers represent the normal pelagic sedimentation in the basin. These shales are exceptionally rich in Fe and Mn, because of the hydrothermal activity of the nearby and young Rheic Ocean ridge. Indeed, the Rheic Ocean opened in the Early Ordovician (c. 482 Ma). During diagenesis, the strongly oxidizing depositional environment favoured the mobility of Mn2+, as opposed to Fe3+ that remained insoluble and immobile. This allowed for the migration of divalent manganese from the pelagic shales and for replacing calcium in the turbiditic carbonate fraction, to form Rhodochrosite. Later, epizonal metamorphism transformed the clay-quartz-Rhodochrosite paragenesis of the protolith into the muscovite-quartz-spessartine paragenesis of the coticule. Hence, in the type-area, coticule genesis needed a peculiar environment including a continental shelf with limy mud deposits, a continental slope generating periodical turbidites and a nearby oceanic ridge, here the nascent Rheic Ocean, delivering hydrothermal iron and manganese.SCOPUS: re.jinfo:eu-repo/semantics/publishe
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Coticule of the Belgian type area (Stavelot-Venn Massif): Limy turbidites within the nascent Rheic oceanic basin
2016Co-Authors: Herbosch Alain, Liégeois Jean-paul, Pin ChristianAbstract:Coticule is the name originating in Belgium for a fine-grained metasedimentary yellowish rock mainly composed of quartz, spessartine and mica, which is repeatedly interstratified in the hematite-rich purple slates of the Lower Ordovician of the Ardenne region. It was described for the first time in the nineteenth century in the Stavelot- Venn Massif (Ardenne), which is accordingly the type-area for this peculiar lithology. Since then, numerous oc- currences were described all over the world in metamorphic rocks of various grades and ages. The exact nature of the Belgian coticule protolith remained hypothetical, although intensively discussed for a long time in the liter- ature. After an extensive review of all the stratigraphical, sedimentological and geochemical results and new field, geochemical (major and trace elements) and Nd isotopic investigations, we propose a significantly improved and sustained genetic model: the thin coticule layers were deposited offshore in a deep oceanic basin as limy mud turbidites. During the early Floian (c. 477 Ma, Early Ordovician), density currents came from the north, from the shelf which bordered the emergent Brabant Massif at that time and flowed down the slope to the deep basin-plain. The purple shales enclosing the coticule layers represent the normal pelagic sedimentation in the basin. These shales are exceptionally rich in Fe and Mn, because of the hydrothermal activity of the nearby and young Rheic Ocean ridge. Indeed, the Rheic Ocean opened in the Early Ordovician (c. 482 Ma). During diagenesis, the strongly oxidizing depositional environment favoured the mobility of Mn2 +, as opposed to Fe3 + that remained insoluble and immobile. This allowed for the migration of divalent manganese from the pelagic shales and for replacing calcium in the turbiditic carbonate fraction, to form Rhodochrosite. Later, epizonal metamor- phism transformed the clay-quartz-Rhodochrosite paragenesis of the protolith into the muscovite-quartz-spes- sartine paragenesis of the coticule. Hence, in the type-area, coticule genesis needed a peculiar environment including a continental shelf with limy mud deposits, a continental slope generating periodical turbidites and a nearby oceanic ridge, here the nascent Rheic Ocean, delivering hydrothermal iron and manganese.info:eu-repo/semantics/publishe
Scot T. Martin - One of the best experts on this subject based on the ideXlab platform.
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opposing effects of humidity on Rhodochrosite surface oxidation
Langmuir, 2015Co-Authors: Yuanzhi Tang, Haitao Wang, Scot T. MartinAbstract:Rhodochrosite (MnCO3) is a model mineral representing carbonate aerosol particles containing redox-active elements that can influence particle surface reconstruction in humid air, thereby affecting the heterogeneous transformation of important atmospheric constituents such as nitric oxides, sulfur dioxides, and organic acids. Using in situ atomic force microscopy, we show that the surface reconstruction of Rhodochrosite in humid oxygen leads to the formation and growth of oxide nanostructures. The oxidative reconstruction consists of two consecutive processes with distinctive time scales, including a long waiting period corresponding to slow nucleation and a rapid expansion phase corresponding to fast growth. By varying the relative humidity from 55 to 78%, we further show that increasing humidity has opposing effects on the two processes, accelerating nucleation from 2.8(±0.2) × 10(-3) to 3.0(±0.2) × 10(-2) h(-1) but decelerating growth from 7.5(±0.3) × 10(-3) to 3.1(±0.1) × 10(-3) μm(2) h(-1). Through quantitative analysis, we propose that nanostructure nucleation is controlled by Rhodochrosite surface dissolution, similar to the dissolution-precipitation mechanism proposed for carbonate mineral surface reconstruction in aqueous solution. To explain nanostructure growth in humid oxygen, a new Cabrera-Mott mechanism involving electron tunneling and solid-state diffusion is proposed.
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Surface-potential heterogeneity of reacted calcite and Rhodochrosite
Environmental Science & Technology, 2007Co-Authors: Chongzheng Na, Treavor A. Kendall, Scot T. MartinAbstract:Nanostructures can form on mineral surfaces through reactions with H2O or O2 in the natural environment. In this study, nanostructures on the (1014) surfaces of calcite and Rhodochrosite are characterized by their surface potentials using Kelvin probe force microscopy. Water-induced nanostructures on calcite have a topographic height of 1.1 (±0.6) nm and an excess surface potential of 126 (±31) mV at 45% relative humidity. The corresponding values for oxygen-induced nanostructures on Rhodochrosite at the same RH are 1.3 (±0.7) nm and 271 (±14) mV, respectively. For increasing relative humidity on calcite, the topographic height of the nanostructures increases while their excess surface potential remains unchanged. In comparison, on Rhodochrosite the topographic height remains unchanged for increasing relative humidity but excess surface potential decreases. The nonzero excess surface potentials indicate that the nanostructures have compositions different from their parent substrates. The surface-potentia...
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structure of the hydrated 1014 surface of Rhodochrosite mnco3
Environmental Science & Technology, 2007Co-Authors: Youngshin Jun, Sanjit Ghose, Thomas P Trainor, Peter J Eng, Scot T. MartinAbstract:The three-dimensional structure of the hydrated (1014) surface of MnCO3 at 90% relative humidity and 295 K is determined from measurements of X-ray scattering along ten crystal-truncation rods (CTRs). The scattering data provide both vertical and lateral information about the interfacial structure. The model that best fits the scattering data is a surface having a first layer of manganese carbonate and an overlayer of oxygen (as water). Within the measurement uncertainty, the overlayer of oxygen (Ow) and the first-layer of manganese (Mn1) have equal occupancies of 0.84. The Mn1−Ow distance between these layers is 2.59 ± 0.04 A. The overlayer O atoms are displaced laterally by 0.157 A in the x- and 0.626 A in the y-direction relative to the first-layer Mn atoms. The first-layer carbonate groups tilt by −4.2 ± 2.1° in phi (toward the surface plane) and −2.6 ± 1.2° in chi (an axis perpendicular to phi). The second-layer carbonate groups do not tilt, at least within measurement uncertainty. The spacing betwe...
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role of molecular oxygen in the dissolution of siderite and Rhodochrosite
Geochimica et Cosmochimica Acta, 2004Co-Authors: Owen W Duckworth, Scot T. MartinAbstract:Abstract The dissolution of siderite (FeCO3) and Rhodochrosite (MnCO3) under oxic and anoxic conditions is investigated at 298 K. The anoxic dissolution rate of siderite is 10−8.65 mol m−2 s−1 for 5.5 4 to pits elongated at one vertex for pH 10.3, the oxic dissolution rate is as high as 10−7.5 mol m−2 s−1, which is greater than under the corresponding anoxic conditions. A fast electron transfer reaction between solution O2 or [Fe3+(OH)4]− species and surficial >FeII hydroxyl groups is hypothesized to explain the dissolution kinetics. AFM micrographs do not show precipitation under these conditions. Anoxic dissolution of Rhodochrosite is physically observed as rhombohedral pit expansion for 3.7 7.7 under oxic conditions, the dissolution rate decreases from 10−8.45 to 10−9.0 mol m−2 s−1. Flattened hillock precipitates grow across the entire surface without apparent morphological influence by the underlying Rhodochrosite surface. XPS spectra and thermodynamic calculations implicate the precipitate as bixbyite for 5.8 7.7.
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connections between surface complexation and geometric models of mineral dissolution investigated for Rhodochrosite
Geochimica et Cosmochimica Acta, 2003Co-Authors: Owen W Duckworth, Scot T. MartinAbstract:Mineral dissolution rates have been rationalized in the literature by surface complexation models (SCM) and morphological and geometric models (GM), and reconciliation of these conceptually different yet separately highly successful models is an important goal. In the current work, morphological alterations of the surface are observed in real time at the microscopic level by atomic force microscopy (AFM) while dissolution rates are simultaneously measured at the macroscopic level by utilizing the AFM fluid cell as a classic flow-through reactor. Rhodochrosite dissolution is studied from pH 2 to 11 at 298 K, and quantitative agreement is found between the dissolution rates determined from microscopic and macroscopic observations. Application of a SCM model for the interpretation of the kinetic data indicates that the surface concentration of CO3H regulates dissolution for pH 7 while the surface concentration of MnOH2 regulates dissolution for pH 7. A GM model explains well the microscopic observations, from which it is apparent that dissolution occurs at steps associated with anisotropic pit expansion. On the basis of the observations, we combine the SCM and GM models to propose a step-site surface complexation model (SSCM), in which the dissolution rates are quantitatively related to the surface chemical speciation of steps. The governing SSCM equation is as follows: R 1/2(kco kca)(CO3H) 1/2(kmo kma)(MnOH2 ), where R is the dissolution rate (mol m 2 s 1 ), 21/2 is the fraction of surface sites located at steps, (CO3H) and (MnOH2 ) are surface concentrations (mol m 2 ), and kco, kca, kmo, and kma are the respective dissolution rate coefficients (s 1 ) for the CO3H and the MnOH2 surface species on obtuse and acute steps. We find kco 2.7 s 1 , kca 2.1 10 1 s 1 , kmo 4.1 10 2 s 1 , kma 3.7 10 2 s 1 , and 1/2 0.015 0.005. The rate coefficients quantify the net result of complex surface step processes, including double-kink initiation and single-kink propagation. We propose that the SSCM model may have general applicability for dissolution far from equilibrium of flat mineral surfaces of ionic crystals, at least those that dissolve by step retreat. Copyright © 2003 Elsevier Science Ltd
Wenqing Qin - One of the best experts on this subject based on the ideXlab platform.
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flotation of Rhodochrosite fines induced by octyl hydroxamic acid as hydrophobic agglomerates
Powder Technology, 2021Co-Authors: Song Zou, Shuai Wang, Hong Zhong, Wenqing QinAbstract:Abstract In this study, the flotation of Rhodochrosite fines induced by octyl hydroxamic acid (OHA) as hydrophobic agglomerates was investigated through the measurements of micro-flotation, laser diffraction, microscopy observations and zeta potential. The experimental results showed that the apparent particle size and morphology of Rhodochrosite agglomerates were greatly affected by OHA concentration and stirring speed. Bigger agglomeration particle size and more regular agglomerates could be obtained at the OHA concentration of 60 mg/L, and appropriate stirring speed was required to form an optimum particle size of agglomerates for micro-flotation. The increased apparent particle size of Rhodochrosite was favorable for micro-flotation recovery even though the particles were negatively charged in the presence of OHA. It's considered that OHA adsorbed on the surface of Rhodochrosite through zeta potential results as well as the species distribution analysis of OHA and Rhodochrosite.
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hydrophobic agglomeration of Rhodochrosite fines in aqueous suspensions with sodium oleate
Powder Technology, 2021Co-Authors: Song Zou, Shuai Wang, Hong Zhong, Wenqing QinAbstract:Abstract Hydrophobic agglomeration of Rhodochrosite fines in aqueous suspensions with sodium oleate has been investigated through wettability measurement, optical microscopy observation, laser-based particle size detection, micro-flotation test, zeta potential measurement in this work. The experimental results indicated that the hydrophobicity of Rhodochrosite was a dominant factor for the hydrophobic agglomeration. And a higher sodium oleate concentration could contribute to bigger agglomeration particle size and more regular agglomerates. The increased apparent particle size of minerals through hydrophobic agglomeration interaction was conducive to the micro-flotation recovery improvement of Rhodochrosite fines in spite of a simultaneous increase in the negative zeta potential of Rhodochrosite, meaning that the chemical adsorption was the primary reason between sodium oleate and Rhodochrosite. Furtherly, the data calculated from extended DLVO theory was also convinced that hydrophobic interaction between the particles increased much more strongly than electrostatic repulsion from the adsorption of sodium oleate.
Olaf Medenbach - One of the best experts on this subject based on the ideXlab platform.
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Petrologic evidence for a Rhodochrosite precursor of spessartine in coticules of the Venn-Stavelot Massif, Belgium
Mineralogical Magazine, 1992Co-Authors: Werner Schreyer, Heinz-jürgen Bernhardt, Olaf MedenbachAbstract:Minute CaMg-bearing Rhodochrosite inclusions were discovered in spessartine crystals of small coticule globules enclosed within redschists that form the country rock of the famous coticule bands of Belgium. This points to a former metamorphic reaction relationship between the two minerals, such as Rhodochrosite + pyrophyllite = spessartine + quartz + CO2 + H20. The coexistence of spessartine with Mg-chlorite in the coticule globule could also indicate more complex reactions such as Rhodochrosite + sudoite + quartz = spessartine + Mg-chlorite + CO2 + H20. Our finding casts some doubt on the suggestion by Kramm (1976) that spessartine formed from Mn-montmorillonite in previously glassy volcanic tufts. KEVWORDS: Rhodochrosite, spessartine, coticule, Venn-Stavelot Massif, Belgium.
