| 1. |
- Andersson, Stefan S., et al.
(författare)
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Mineralogy, paragenesis, and mineral chemistry of REEs in the Olserum-Djupedal REE-phosphate mineralization, SE Sweden
- 2018
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Ingår i: American Mineralogist. - : MINERALOGICAL SOC AMER. - 0003-004X .- 1945-3027. ; 103:1, s. 125-142
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Tidskriftsartikel (refereegranskat)abstract
- The rapidly growing use of rare earth elements and yttrium (REE) in modern-day technologies, not least within the fields of green and carbon-free energy applications, requires exploitation of new REE deposits and deposit types. In this perspective, it is vital to develop a fundamental understanding of the behavior of REE in natural hydrothermal systems and the formation of hydrothermal REE deposits. In this study, we establish a mineralogical, textural, and mineral-chemical framework for a new type of deposit, the hydrothermal Olserum-Djupedal REE-phosphate mineralization in SE Sweden. An early, high-temperature REE stage is characterized by abundant monazite-(Ce) and xenotime-(Y) coexisting with fluorapatite and subordinate amounts of (Y,REE,U,Fe)-(Nb,Ta) oxides. During a subsequent stage, allanite-(Ce) and ferriallanite-(Ce) formed locally, partly resulting from the breakdown of primary monazite-(Ce). Alteration of allanite-(Ce) or ferriallanite-(Ce) to bastnasite-(Ce) and minor synchysite-(Ce) at lower temperatures represents the latest stage of REE mineral formation. The paragenetic sequence and mineral chemistry of the allanites record an increase in Ca content in the fluid. We suggest that this local increase in Ca, in conjunction with changes in oxidation state, were the key factors controlling the stability of monazite-(Ce) in the assemblages of the Olserum-Djupedal deposit. We interpret the alteration and replacement of primary monazite-(Ce), xenotime-(Y), fluorapatite, and minor (Y,REE,U,Fe)-(Nb, Ta) oxide phase(s), to be the consequence of coupled dissolution-reprecipitation processes. These processes mobilized REE,Th,U, and Nb-Ta, which caused the formation of secondary monazite-(Ce), xenotime-(Y), fluorapatite, and minor amounts of allanite-(Ce) and ferriallanite-(Ce). In addition, these alteration processes produced uraninite, thorite, columbite-(Fe), and uncharacterized (Th,U,Y,Ca)-silicates. Textural relations show that the dissolution-reprecipitation processes affecting fluorapatite preceded those affecting monazite-(Ce), xenotime-(Y), and the (Y, REE, U, Fe)-(Nb, Ta) oxide phase(s). The mineralogy of the primary ore mineralization and the subsequently formed alteration assemblages demonstrate the combined mobility of REE and HFSE in a natural F-bearing high-temperature hydrothermal system. The observed coprecipitation of monazite-(Ce), xenotime-(Y), and fluorapatite during the primary REE mineralization stage highlights the need for further research on the potentially important role of the phosphate ligand in hydrothermal REE transporting systems.
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| 2. |
- Ardit, Matteo, et al.
(författare)
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Vanadium-induced coloration in grossite (CaAl4O7) and hibonite (CaAl12O19)
- 2021
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Ingår i: American Mineralogist. - : Mineralogical Society of America. - 0003-004X .- 1945-3027. ; 106:4, s. 599-608
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Tidskriftsartikel (refereegranskat)abstract
- High concentrations of vanadium cause very unusual coloration in hibonite (purple) and grossite (light violet) crystals in an exotic mineral assemblage from Sierra de Comechingones (Argentina). In the hibonite (CaAl12O19) structure vanadium ions, in various valence states (divalent, trivalent, and tetravalent), may be distributed over five crystallographic sites with coordinations corresponding to different polyhedra, namely, three unequal octahedra [M1 (D3d), M4 (C3ν), and M5 (Cs)], one M3 tetrahedron (C3ν), and one unusual fivefold-coordinated trigonal bipyramid M2 (D3h). Possible locations of vanadium ions in grossite (CaAl4O7) are limited to two crystallographically distinct sites (T1 and T2, both C1) in tetrahedral coordination.The combination of single-crystal X-ray diffraction and absorption spectroscopy techniques aided by chemical analyses has yielded details on the nature of the vanadium-induced color in both hibonite and grossite crystals. In hibonite, both M4 face-sharing octahedral and M2 trigonal bipyramid sites of the R-block are partially occupied by V3+. Strongly polarized bands recorded at relatively low energies in optical absorption spectra indicate that V2+ is located at the M4 octahedral site of the hibonite R-block. Chemical analyses coupled with an accurate determination of the electron densities at structural sites in hibonite suggest that the vanadium ions occupy about 10 and 5% of the M4 and M2 sites, respectively. For grossite, polarized optical absorption spectra reveal no indications of V2+; all observed absorption bands can be assigned to V3+ in tetrahedral coordination. Although not evident by the observed electron densities at the T sites of grossite (due to the low-V content), longer bond distances, and a higher degree of polyhedral distortion suggest that V3+ is located at the T2 site.
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| 3. |
- Balic-Zunic, Tonci, et al.
(författare)
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Full analysis of feldspar texture and crystal structure by combining X-ray and electron techniques
- 2013
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Ingår i: American Mineralogist. - : Mineralogical Society of America. - 0003-004X .- 1945-3027. ; 98:1, s. 41-52
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Tidskriftsartikel (refereegranskat)abstract
- Feldspar crystals typically show a range of exsolution and polysynthetic twinning textures that can present problems for their full characterization, but at the same time give important information about their genesis. We present an integrated procedure for the micro-texture analysis, twin law identification plus crystal structure refinement of all components in a feldspar intergrowth. This procedure was applied to perthitic intergrowths in feldspars from two different pegmatites in the Larvik plutonic complex in the southern part of the Oslo region, Norway. It revealed that the two starting high-temperature (HT) feldspars had similar global chemical compositions but underwent significantly different cooling histories, with cooling times probably differing by over an order of magnitude. Powder X-ray diffraction with Rietveld refinement was used for a preliminary identification of the mineral components and concluding quantitative phase analysis. Electron microprobe analysis was used to bracket the chemical compositions of the constituents. Electron backscatter diffraction was used to reveal the texture of the samples, twin laws and spatial distribution and crystallographic orientation of the crystal domains. Single-grain X-ray diffraction recorded by an area detector was applied for a simultaneous integration of reflection intensities for all crystallographic domains with different orientations and severe diffraction overlaps. The crystal structures were refined using the program JANA2006 that allows a simultaneous calculation for structurally different components. Combined results of various methods helped improve accuracy and resolve ambiguities that arise from the application of a single technique. The approach is widely applicable to the study of mineral intergrowths and bridges an existing gap in the routinely accessible data on the structural characteristics of rock constituents.
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| 4. |
- Baron, V, et al.
(författare)
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The influence of iron substitution on the magnetic properties of hausmannite, Mn2+(Fe,Mn)(2)(3+)O-4
- 1998
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Ingår i: AMERICAN MINERALOGIST. - : MINERALOGICAL SOC AMER. - 0003-004X. ; 83:7-8, s. 786-793
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The occurrence of hausmannite with an apparent Curie temperature close to 750 K, instead of 41.8 K was recently described from hydrothermally altered manganese ore from the Kalahari manganese field, South Africa. The unusual magnetic properties were relat
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| 5. |
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| 6. |
- Belonoshko, AB, et al.
(författare)
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Molecular dynamics of NaCl (B1 and B2) and MgO (B1) melting: Two-phase simulation
- 1996
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Ingår i: AMERICAN MINERALOGIST. - : MINERALOGICAL SOC AMER. - 0003-004X. ; 81:3-4, s. 303-316
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Melting of NaCl and MgO has been simulated with a two-phase molecular dynamics method at constant pressure using newly developed interaction potentials. Equations of state for NaCl and MgO simulated by molecular dynamics are in good agreement with availab
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| 7. |
- Benazzouz, Brahim K., et al.
(författare)
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Determination of the melting temperature of kaolinite by means of the Z-method
- 2013
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Ingår i: American Mineralogist. - : Mineralogical Society of America. - 0003-004X .- 1945-3027. ; 98:10, s. 1881-1885
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Tidskriftsartikel (refereegranskat)abstract
- The melting temperature of materials is an important thermodynamic property. Despite the importance of kaolinite, one of the most common clay minerals on the Earth's surface, its thermal and melting behavior is poorly understood. We apply here the Z-method to determine the melting temperature (T-m) and the limit of superheating (T-LS) of kaolinite. The T-m is found at 1818 K (8.85 GPa), and T-LS at 1971 K (6.8 GPa). The diffusion coefficient for all atoms has been calculated in a broad temperature range. The calculated characteristics and, in particular, their dependence on temperature have confirmed the solid-liquid transition and strongly support the calculated melting point. In addition, some computed quantities, such as the radial distribution function, coordination numbers and mean-square displacement, were used to confirm the liquid state of kaolinite from the melting temperature as well as at other temperatures in the liquid branch. The diffusion coefficient for different atoms has been calculated throughout the isochore. These quantities and in particular their evolution under temperature have confirmed the solid-liquid states of kaolinite and the presence of the melting point. The latter quantity constitutes the first ever melting simulation of a clay mineral with close agreement to the experimental one.
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| 8. |
- Biagion, Cristian, et al.
(författare)
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The crystal structure of turneaureite, Ca5(AsO4)3Cl, the arsenate analog of chlorapatite and its relationships with the arsenate apatites johnbaumite and svabite
- 2017
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Ingår i: American Mineralogist. - : Mineralogical Society of America. - 0003-004X .- 1945-3027. ; 102, s. 1981-1986
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Tidskriftsartikel (refereegranskat)abstract
- The crystal structure of turneaureite, ideally Ca5(AsO4)3Cl, was studied using a specimen from the Brattfors mine, Nordmark, Värmland, Sweden, by means of single-crystal X-ray diffraction data. The structure was refinedto R1 = 0.017 on the basis of 716 unique reflectios with Fo > 4σ(Fo) in the P63/m space group, with unit-cell parameters a = 9.9218(3), c = 6.8638(2) Å, V = 585.16(4) Å3. The chemical composition of the sample, determined by electron-microprobe analysis, is (in wt%; average of 10 spot analyses): SO3 0.22, P2O5 0.20, V2O5 0.01, As2O5 51.76, SiO2 0.06, CaO 41.39, MnO 1.89, SrO 0.12, BaO 0.52, PbO 0.10, Na2O 0.02, F 0.32, Cl 2.56, H2Ocalc 0.58, O(≡F+Cl) –0.71, total 99.04. On the basis of 13 anions per formula unit, the empirical formula corresponds to (Ca4.82Mn0.17Ba0.02Sr0.01)∑5.02 (As2.94P0.02S0.02Si0.01)∑2.99O12[Cl0.47(OH)0.42F0.11]∑1.00.Turneaureite is topologically similar to the other members of the apatite supergroup: columns of face-sharing M1 polyhedra running along c are connected through TO4 tetrahedra with channels hosting M2 cations and X anions. Owing to its particular chemical composition, the studied turneaureite can be considered as a ternary calcium arsenate apatite; consequently it has several partially filledanion sites within the anion columns. Polarized single-crystal FTIR spectra of the studied sample indicate stronger hydrogen bonding and less diverse short-range atom arrangements around (OH) groups in turneaureite as compared to the related minerals johnbaumite and svabite. An accurate knowledge of the atomic arrangement of this apatite-remediation mineral represents an improvement in our understanding of minerals able to sequester and stabilize heavy metals such as arsenic in polluted areas.
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| 9. |
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| 10. |
- Biagioni, Cristian, et al.
(författare)
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The crystal structure of svabite, Ca5(AsO4)3F, an arsenate member of the apatite supergroup
- 2016
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Ingår i: American Mineralogist. - : Mineralogical Society of America. - 0003-004X .- 1945-3027. ; 101, s. 1750-1755
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Tidskriftsartikel (refereegranskat)abstract
- The crystal structure of svabite, ideally Ca5(AsO4)3F, was studied using a specimen from the Jakobsberg mine, Värmland, Sweden, by means of single-crystal X‑ray diffraction data. The structure was refined to R1 = 0.032 on the basis of 928 unique reflections with Fo > 4s(Fo) in the P63/m space group, with unit-cell parameters a = 9.7268(5), c = 6.9820(4) Å, V = 572.07(5) Å3. The chemical composition of the sample, determined by electron-microprobe analysis, is (in wt%, average of 10 spot analyses): SO3 0.49, P2O5 0.21, V2O5 0.04, As2O5 51.21, SiO2 0.19, CaO 39.31, MnO 0.48, SrO 0.03, PbO 5.19, Na2O 0.13, F 2.12, Cl 0.08, H2Ocalc 0.33, O (≡ F+Cl) –0.91, total 98.90. On the basis of 13 anions per formula unit, the empirical formula corresponds to (Ca4.66Pb0.16Mn0.04Na0.03)Σ4.89(As2.96S0.04Si0.02P0.02)Σ3.04O12[F0.74(OH)0.24Cl0.01]. Svabite is topologically similar to the other members of the apatite supergroup: columns of face-sharing M1 polyhedra running along c are connected through TO4 tetrahedra with channels hosting M2 cations and X anions. The crystal structure of synthetic Ca5(AsO4)3F was previously reported as triclinic. On the contrary, the present refinement of the crystal structure of svabite shows no deviations from the hexagonal symmetry. An accurate knowledge of the atomic arrangement of this apatite-remediation mineral represents an improvement in our understanding of minerals able to sequester and stabilize heavy metals such as arsenic in polluted areas.
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