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Sökning: L773:0935 1221

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1.
  • Chukanov, Nikita V., et al. (författare)
  • Långbanshyttanite, a new low-temperature arsenate mineral with a novel structure from Långban, Sweden
  • 2011
  • Ingår i: European journal of mineralogy. - 0935-1221 .- 1617-4011. ; 23:4, s. 675-681
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The new mineral långbanshyttanite was discovered in a specimen from the Långban mine (59.86 degrees N, 14.27 degrees E), Filipstad district, Varmland County, Bergslagen ore province, Sweden. Associated minerals are calcite, Mn-bearing phlogopite, spinels of the jacobsite-magnetite series, antigorite and trigonite. The mineral is named after the old name of the mine, smelter and mining village: Långbanshyttan. Långbanshyttanite is transparent, colourless. It occurs in late-stage fractures or corroded pockets, forming soft, radial and random aggregates (up to 1 mm) of acicular crystals up to 5 x 20 x 400 mu m. D(calc) is 3.951 g/cm(3). The new mineral is biaxial (+), alpha = 1.700(5), beta = 1.741(5), gamma = 1.792(5), 2V (meas.) approximate to 90 degrees, 2V (calc.) = 86 degrees. Dispersion is strong, r &lt; v. The IR spectrum is given. The chemical composition is (electron microprobe, mean of five analyses, wt%): PbO 44.71, MgO 3.79, MnO 13.34, FeO 1.89, P(2)O(5) 0.65, As(2)O(5) 22.90, H(2)O (determined by gas chromatographic analysis of the products of ignition at 1200 degrees C) 14.4; total 101.68. The empirical formula based on 18 O atoms is: Pb(1.97)Mn(1.85)Mg(0.93)Fe(0.26)(AsO(4))(1.96)(PO(4))(0.09)(OH)(3.87)cen ter dot 5.93H(2)O. The simplified formula is: Pb(2)Mn(2)Mg(AsO(4))(2)(OH)(4)center dot 6H(2)O. Single-crystal diffraction data obtained using synchrotron radiation indicate that långbanshyttanite is triclinic, P&lt;(1)over bar&gt;, a = 5.0528(10), b = 5.7671(6), c = 14.617(3) angstrom, alpha = 85.656(14), beta = 82.029(17), gamma = 88.728(13)degrees, V = 420.6(2) angstrom(3), Z = 1, and is a representative of a new structure type. In the structure, edge-sharing MnO(2)(OH)(4) octahedra form zig-zag columns that are linked by isolated AsO(4) tetrahedra. Pb cations having six-fold coordination are located between the AsO(4) tetrahedra. Isolated Mg(H(2)O)(6) octahedra are located in the inter-block space. The strongest lines of the powder diffraction pattern [d, angstrom (I,%) (hkl)] are: 14.48 (100) (001), 7.21 (43) (002), 4.969 (34) (100, 101), 4.798 (28) (003), 3.571 (54) (112, 1-1-1, 01-3, 11-1), 2.857 (45) (020, 021, 114), 2.800 (34) (11-3). Parts of the holotype specimen are deposited in the Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow, Russia, with the registration number 4032/1 and in the collections of the Swedish Museum of Natural History, Stockholm, Sweden, under catalogue number NRM 20100076.</p>
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  • Ladenberger, Anna, et al. (författare)
  • CO2 fluid inclusions in mantle xenoliths from Lower Silesia (SW Poland) : formation conditions and decompression history
  • 2009
  • Ingår i: European journal of mineralogy. - 0935-1221 .- 1617-4011. ; 21:4, s. 751-761
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Raman spectroscopy has been applied to determine the density and pressure of formation of CO2 fluid inclusions in mantle xenoliths, carried to the surface at Wilcza Gora in southwestern Poland by early Miocene alkaline magmas. The magmas were generated by partial melting in the transition zone between the spinel and garnet stability fields. Determination of the densities of CO2 inclusions allows calculation of the partial pressures and reconstruction of the depth of xenolith origin as well as their history en route to the surface. The density of CO2 inclusions ranges from 0.06 to 1.10 g/cm(3) in olivines and 0.17 to 1.11 g/cm(3) in orthopyroxenes. Only inclusions with a density above 0.8 g/cm(3) reflect lower crust (ca. 15-30 km) and upper mantle (ca. 30-38 km) conditions. Slight differences in density of the inclusions between olivines and orthopyroxenes can be attributed to their different theological properties during magma ascent. Modelling of pressure and depth within the temperature range in which the xenoliths equilibrated with the magmas yields information about the complex eruption history of basanitic volcanoes. Our estimates are consistent with seismic data that show a regional high-velocity layer at the Moho (ca. 30-35 km deep) with p-wave velocities up to 8 km/s which have been attributed to mafic and ultramafic lithologies.</p>
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  • Sundvall, Rickard, 1976-, et al. (författare)
  • Dehydration-hydration mechanisms in synthetic Fe-poor diopside
  • 2009
  • Ingår i: European journal of mineralogy. - Stuttgart : E. Schweizerbart'sche Verlagsbuchhandlung. - 0935-1221 .- 1617-4011. ; 21:1, s. 17-26
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Small amounts (ppm) of OH in nominally anhydrous minerals (NAMs) can have a dramatic effect on the physical properties of the upper mantle. The pyroxenes of the upper mantle have been shown to incorporate substantial numbers of protons forming hydroxyl ions. Enstatite and diopside are the most important endmembers of the pyroxenes in terms of bulk volume in the upper mantle. To further constrain the behavior of hydroxyl ions in clinopyroxene, the dehydration-hydration mechanisms of synthetic <sup>57</sup>Fe-doped diopside were investigated. Dehydration was carried out by stepwise heating in air of crystals synthesized at high pressure under water-saturated conditions. FTIR spectra were obtained after each step. Mössbauer spectra were recorded for three of the crystals when there had been a significant decrease in FTIR absorbance intensity. From the Mössbauer spectra we see an increase in the Fe<sup>3+</sup> doublet with successive dehydration, although this increase is less than the decrease in OH in terms of atoms per formula unit. This means that the dehydration only partly follows the redox reaction OH<sup>−</sup> + Fe<sup>2+</sup> = O<sup>2−</sup> + Fe<sup>3+</sup> + ½H<sub>2</sub>, and that additional reactions occur. Hydration experiments were conducted on one crystal in the same manner as the dehydrations, with the exception that hydrogen gas was used during heating. Hydration experiments resulted in re-hydration of the sample to 73 % of the original amount of OH.</p> <p> </p> <p>The calculated Arrhenius equation derived from the diffusion rates during dehydration along [010] yields an activation energy (<em>E</em><sub>a</sub>) of −292 ± 50 kJ mol<sup>−1</sup>, and <em>D</em><sub>0</sub> = 10<sup>±1.9 + 2.3</sup> m<sup>2</sup> s<sup>−1</sup>. The result of the rehydration experiment agrees well with the established diffusion law. Diffusion rates determined for synthetic diopside are almost two orders of magnitude slower than for synthetic enstatite with comparable Fe contents. Compared to natural diopside, diffusion rates in these synthetic samples are slower, probably because of the low iron content. <em>E</em><sub>a</sub> is similar to that of dehydration of pure and low-Fe enstatite.</p>
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  • Sundvall, Rickard, 1976-, et al. (författare)
  • Hydrogen diffusion in synthetic Fe-free diopside
  • 2009
  • Ingår i: European journal of mineralogy. - Stuttgart : E. Schweizerbart'sche Verlagsbuchhandlung. - 0935-1221 .- 1617-4011. ; 21:5, s. 963-970
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Hydrogen is a widespread trace element in many nominally anhydrous minerals (NAMs) in the Earth's crust and mantle and has profound influence on the physical properties of the host mineral. Of all NAMs from the upper mantle, clinopyroxenes have been shown to contain the highest amount of hydrogen. This study focuses on the dehydration kinetics of pure diopside along [010] and [100]* by thermal annealing under normal atmospheric pressure. The diopside crystals used were synthesized at high pressure under water-saturated conditions. FTIR spectra were obtained after each step, including untreated samples. The Arrhenius equation gives an activation energy (<em>E</em><sub>a</sub>) of -331 ± 50 kJ mol<sup>-1</sup> and <em>D</em><sub>0</sub> = 10<sup>0.9 ± 2.3</sup> m<sup>2</sup> s<sup>-1 </sup>for diffusion along [010]. Diffusion along [100]* gives an <em>E</em><sub>a</sub>-value of -312 ± 55 kJ mol<sup>-1</sup> with <em>D</em><sub>0</sub> = 10<sup>0.5 ± 2.4</sup> m<sup>2</sup> s<sup>-1</sup>.<sup> </sup>Therefore, our experimental results show no difference between diffusion along [010] and [100]* (within error limits). The diffusion rate in pure synthetic diopside is about one order of magnitude faster than for synthetic diopside with very low Fe contents. A suitable explanation for this behavior is that in the case of low Fe diopside, the rate-limiting process for the protons associated with Fe is probably Fe-diffusion. In contrast, in pure diopside all protons are associated to Mg-defects, which are more mobile than Fe. Nevertheless, compared to natural diopside with appreciable Fe contents, diffusion rates in these synthetic samples are several orders of magnitude slower.</p>
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