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  • 1.
    Nilsson, E.J. Charlotta
    et al.
    Lunds Universitet.
    Kristiansson, Per
    Lunds Universitet.
    Ros, Linus
    Lunds Universitet.
    De La Rosa, Nathaly
    Lunds Universitet.
    Elfman, Mikael
    Lunds Universitet.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Pallon, Jan
    Lunds Universitet.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    A nuclear geochemical analysis system for boron quantification using a focused ion beam2017In: Journal of Radioanalytical and Nuclear Chemistry, ISSN 0236-5731, E-ISSN 1588-2780, Vol. 311, 355-364 p.Article in journal (Refereed)
    Abstract [en]

    Ion beam analysis has for decades been used as a tool for geochemical analysis of trace elements using both X-rays (particle induced X-ray emission) and nuclear reaction analysis. With the geoanalytical setup at the Lund Ion Beam Analysis Facility, the boron content in geological samples with a spatial resolution of 1 µm is determined through nuclear reaction analysis. In the newly upgraded setup, a single detector has been replaced by a double sided silicon strip detector with 2048 segments. After optimization, boron content in geological samples as low as 1µg g-1 can be measured.

  • 2.
    Bosi, Ferdinando
    et al.
    Sapienza Università di Roma, Italy.
    Reznitskii, Leonid
    Russian Academy of Science, Irkutsk, Russia.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Crystal chemistry of Al-V-Cr oxy-tourmalines from Sludyanka complex, Lake Baikal, Russia2017In: European journal of mineralogy, ISSN 0935-1221, E-ISSN 1617-4011, Vol. 29, no 3, 457-472 p.Article in journal (Refereed)
  • 3.
    Bosi, Ferdinando
    et al.
    Sapienza Università di Roma, Italy.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Fregola, Rosa Anna
    Università di Bari Aldo Moro, Italy.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Crystal chemistry of spinels in the system MgAl2O4-MgV2O4-Mg2VO42016In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 101, 580-586 p.Article in journal (Refereed)
    Abstract [en]

    Eight spinel single-crystal samples belonging to the spinel sensu stricto-magnesiocoulsonite series (MgAl2O4-MgV2O4) were synthesized and crystal-chemically characterized by X‑ray diffraction, electron microprobe and optical absorption spectroscopy. Site populations show that the tetrahedrally coordinated site (T) is populated by Mg and minor Al for the spinel sensu stricto compositions, and only by Mg for the magnesiocoulsonite compositions, while the octahedrally coordinated site (M) is populated by Al, V3+, minor Mg, and very minor amounts of V4+. The latter occurs in appreciable amounts in the Al-free magnesium vanadate spinel, T(Mg)M(Mg0.26V3+1.48V4+0.26)O4, showing the presence of the inverse spinel VMg2O4. The studied samples are characterized by substitution of Al3+ for V3+ and (Mg2++V4+) for 2V3+ described in the system MgAl2O4-MgV2O4-VMg2O4.

    The present data in conjunction with data from the literature provide a basis for quantitative analyses of two solid-solution series MgAl2O4-MgV23+O4 and MgV23+O4-V4+Mg2O4. Unit-cell parameter increases with increasing V3+ along the series MgAl2O4-MgV2O4 (8.085–8.432 Å), but only slightly increases with increasing V3+ along the series VMg2O4-MgV2O4 (8.386–8.432 Å). Although a solid solution could be expected between the MgAl2O4 and VMg2O4 end-members, no evidence was found. Amounts of V4+ are nearly insignificant in all synthetic Al-bearing vanadate spinels, but are appreciable in Al-free vanadate spinel.

    An interesting observation of the present study is that despite the observed complete solid-solution along the MgAl2O4-MgV2O4 and MgV2O4-VMg2O4 series, the spinel structure seems to be unable to stabilize V4+ in any intermediate members on the MgAl2O4-Mg2VO4 join even at high oxygen fugacities. This behavior indicates that the accommodation of specific V-valences can be strongly influenced by crystal-structural constraints, and any evaluation of oxygen fugacities during mineral formation based exclusively on V cation valence distributions in spinel should be treated with caution. The present study underlines that the V valency distribution in spinels is not exclusively reflecting oxygen fugacities, but also depends on activities and solubilities of all chemical components in the crystallization environment.

  • 4.
    Weis, Franz
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Stalder, Roland
    University of Innsbruck.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Experimental hydration of natural volcanic clinopyroxene phenocrysts under hydrothermal pressures (0.5 – 3 kbar)2016In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 101, 2233-2247 p.Article in journal (Refereed)
  • 5.
    Weis, Franz A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Swedish Museum Nat Hist, Dept Geosci, Box 50007, SE-10405 Stockholm, Sweden.
    Stalder, Roland
    Univ Innsbruck, Inst Mineral & Petrog, A-6020 Innsbruck, Austria.
    Skogby, Henrik
    Swedish Museum Nat Hist, Dept Geosci, Box 50007, SE-10405 Stockholm, Sweden.
    Experimental hydration of natural volcanic clinopyroxene phenocrysts under hydrothermal pressures (0.5-3 kbar)2016In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 101, 2233-2247 p.Article in journal (Refereed)
    Abstract [en]

    Water is a key parameter in mantle rheology, magma genesis, magma evolution, and resulting eruption styles, because it controls the density and the viscosity, as well as the melting and crystallization behavior of a melt. The water content in nominally anhydrous minerals (NAMs) such as clinopyroxene recently has been used as a proxy for magmatic water contents. NAMs, however, may dehydrate during magma degassing and eruption. We performed rehydration experiments on potentially degassed clinopyroxene phenocrysts from various volcanic settings. The experiments were conducted in hydrogen gas at 1 atm or hydrothermal pressures ranging from 0.5 to 3 kbar to test the incorporation of water into natural clinopyroxene under water fugacities similar to those in a volcanic system. Our results show a dependence of the water content in the clinopyroxene crystals with pressure as the phenocrysts begin to dehydrate upon lower water fugacities in the experiments. Water loss or gain in a crystal occurs according to the relatively fast redox-reaction OH- + Fe2+ ↔ O2– + Fe3+ + ½ H2, which was confirmed by Mössbauer spectroscopy. The kinetics of this redox-process are independent of pressure and thus water fugacity. Water contents in rehydrated clinopyroxene crystals can be related to magmatic water contents at various levels in a volcanic system. Our results thus show that the water content in erupted clinopyroxene phenocrysts cannot be taken for granted to be representative of magmatic water contents prior to magma degassing. The conducted experiments indicate the simultaneous dehydration of clinopyroxene along with magma ascent and degassing. Rehydration experiments under hydrothermal pressures, however, may be able to reconstruct clinopyroxene water contents at crystallization prior to dehydration.

  • 6.
    Watenphul, Anke
    et al.
    University of Hamburg.
    Schlüter, Jochen
    University of Hamburg.
    Bosi, Ferdinando
    University of Rome "La Sapienza".
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Malcherek, Thomas
    University of Hamburg.
    Influence of the octahedral cationic-site occupancies on the framework vibrations of Li-free tourmalines, with implications for estimating temperature and oxygen fugacity in host rocks2016In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 101, 2554-2563 p.Article in journal (Refereed)
  • 7. Weis, Franz A.
    et al.
    Lazor, Peter
    Skogby, Henrik
    Stalder, Roland
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Polarized IR and Raman spectra of zoisite: insights into OH-dipole orientation and the luminescence2016In: European journal of mineralogy, ISSN 0935-1221, E-ISSN 1617-4011, Vol. 38, no 3, 537-543 p.Article in journal (Refereed)
    Abstract [en]

    The OH-dipole in the mineral zoisite has been a topic of discussion regarding its general orientation and vibrational modes. We present new polarized single-crystal Raman and infrared spectra and verify the orientation of the OH-dipole along the crystallographic c axis with a slight deviation towards the crystallographic a axis. Polarized Raman and FTIR spectra confirm that the OH band at 3150 cm(-1) corresponds to the O(10)-H center dot center dot center dot O(4) hydrogen bridge and exclude a previously suggested second hydrogen bridge O(10)-H center dot center dot center dot O(2). Further, Raman spectra provide insights on the luminescence of zoisite and the interference of luminescence peaks in the OH-region.

  • 8.
    Weis, Franz
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Lazor, Peter
    Uppsala universitet.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Stalder, Roland
    University of Innsbruck.
    Eriksson, Leif
    Stockholms universitet.
    Polarized IR and Raman spectra of zoisite: insights into the OH-dipole orientation and luminescence.2016In: European journal of mineralogy, ISSN 0935-1221, E-ISSN 1617-4011, Vol. 28, 537-543 p.Article in journal (Refereed)
  • 9.
    Bosi, Ferdinando
    et al.
    Sapienza Università di Roma, Rome, Italy.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Thermally induced cation redistribution in Fe‑bearing oxy‑dravite and potential geothermometric implications2016In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 171, no 5, 1-14 p., 47Article in journal (Refereed)
    Abstract [en]

    Iron-bearing oxy-dravite was thermally treated in air and hydrogen atmosphere at 800 °C to study potential changes in Fe, Mg and Al ordering over the octahedrally coordinated Y and Z sites and to explore possible applications to intersite geothermometry based on tourmaline. Overall, the experimental data (structural refinement, Mössbauer, infrared and optical absorption spectroscopy) show that heating Fe-bearing tourmalines results in disordering of Fe over Y and Z balanced by ordering of Mg at Y, whereas Al does not change appreciably. The Fe disorder depends on temperature, but less on redox conditions. The degree of Fe3+–Fe2+ reduction is limited despite strongly reducing conditions, indicating that the fO2 conditions do not exclusively control the Fe oxidation state at the present experimental conditions. Untreated and treated samples have similar short- and long-range crystal structures, which are explained by stable Al-extended clusters around the O1 and O3 sites. In contrast to the stable Al clusters that preclude any temperature-dependent Mg–Al order– disorder, there occurs Mg diffusion linked to temperaturedependent exchange with Fe. Ferric iron mainly resides around O2− at O1 rather than (OH), but its intersite disorder induced by thermal treatment indicates that Fe redistribution is the driving force for Mg–Fe exchange and that its diffusion rates are significant at these temperatures. With increasing temperature, Fe progressively disorders over Y and Z, whereas Mg orders at Y according to the order–disorder reaction: YFe + ZMg → ZFe + YMg. The presented findings are important for interpretation of the post-crystallization history of both tourmaline and tourmaline host rocks and imply that successful tourmaline geothermometers may be developed by thermal calibration of the Mg– Fe order–disorder reaction, whereas any thermometers based on Mg–Al disorder will be insensitive and involve large uncertainties.

  • 10. Ivarsson, Magnus
    et al.
    Bengtson, Stefan
    Skogby, Henrik
    Lazor, Peter
    Broman, Curt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Belivanova, Veneta
    Marone, Federica
    A Fungal-Prokaryotic Consortium at the Basalt-Zeolite Interface in Subseafloor Igneous Crust2015In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, no 10, e0140106Article in journal (Refereed)
    Abstract [en]

    We have after half a century of coordinated scientific drilling gained insight into Earth's largest microbial habitat, the subseafloor igneous crust, but still lack substantial understanding regarding its abundance, diversity and ecology. Here we describe a fossilized microbial consortium of prokaryotes and fungi at the basalt-zeolite interface of fractured subseafloor basalts from a depth of 240 m below seafloor (mbsf). The microbial consortium and its relationship with the surrounding physical environment are revealed by synchrotron-based X-ray tomographic microscopy (SRXTM), environmental scanning electron microscopy (ESEM), and Raman spectroscopy. The base of the consortium is represented by micro-stromatolites- remains of bacterial communities that oxidized reduced iron directly from the basalt. The microstromatolites and the surrounding basalt were overlaid by fungal cells and hyphae. The consortium was overgrown by hydrothermally formed zeolites but remained alive and active during this event. After its formation, fungal hyphae bored in the zeolite, producing millimetre-long tunnels through the mineral substrate. The dissolution could either serve to extract metals like Ca, Na and K essential for fungal growth and metabolism, or be a response to environmental stress owing to the mineral overgrowth. Our results show how microbial life may be maintained in a nutrient-poor and extreme environment by close ecological interplay and reveal an effective strategy for nutrient extraction from minerals. The prokaryotic portion of the consortium served as a carbon source for the eukaryotic portion. Such an approach may be a prerequisite for prokaryotic-eukaryotic colonisation of, and persistence in, subseafloor igneous crust.

  • 11.
    Ivarsson, Magnus
    et al.
    Swedish Museum Nat Hist, Dept Palaeobiol, SE-10405 Stockholm, Sweden.;Swedish Museum Nat Hist, Nord Ctr Earth Evolut, SE-10405 Stockholm, Sweden..
    Bengtson, Stefan
    Swedish Museum Nat Hist, Dept Palaeobiol, SE-10405 Stockholm, Sweden.;Swedish Museum Nat Hist, Nord Ctr Earth Evolut, SE-10405 Stockholm, Sweden..
    Skogby, Henrik
    Swedish Museum Nat Hist, Dept Geosci, SE-10405 Stockholm, Sweden..
    Lazor, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Broman, Curt
    Stockholm Univ, Dept Geol Sci, SE-10691 Stockholm, Sweden..
    Belivanova, Veneta
    Swedish Museum Nat Hist, Dept Palaeobiol, SE-10405 Stockholm, Sweden..
    Marone, Federica
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    A Fungal-Prokaryotic Consortium at the Basalt-Zeolite Interface in Subseafloor Igneous Crust2015In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, no 10, e0140106Article in journal (Refereed)
    Abstract [en]

    We have after half a century of coordinated scientific drilling gained insight into Earth's largest microbial habitat, the subseafloor igneous crust, but still lack substantial understanding regarding its abundance, diversity and ecology. Here we describe a fossilized microbial consortium of prokaryotes and fungi at the basalt-zeolite interface of fractured subseafloor basalts from a depth of 240 m below seafloor (mbsf). The microbial consortium and its relationship with the surrounding physical environment are revealed by synchrotron-based X-ray tomographic microscopy (SRXTM), environmental scanning electron microscopy (ESEM), and Raman spectroscopy. The base of the consortium is represented by micro-stromatolites- remains of bacterial communities that oxidized reduced iron directly from the basalt. The microstromatolites and the surrounding basalt were overlaid by fungal cells and hyphae. The consortium was overgrown by hydrothermally formed zeolites but remained alive and active during this event. After its formation, fungal hyphae bored in the zeolite, producing millimetre-long tunnels through the mineral substrate. The dissolution could either serve to extract metals like Ca, Na and K essential for fungal growth and metabolism, or be a response to environmental stress owing to the mineral overgrowth. Our results show how microbial life may be maintained in a nutrient-poor and extreme environment by close ecological interplay and reveal an effective strategy for nutrient extraction from minerals. The prokaryotic portion of the consortium served as a carbon source for the eukaryotic portion. Such an approach may be a prerequisite for prokaryotic-eukaryotic colonisation of, and persistence in, subseafloor igneous crust.

  • 12.
    Ivarsson, Magnus
    et al.
    Swedish Museum of Natural History, Department of Paleobiology.
    Bengtson, Stefan
    Skogby, Henrik
    Lazor, Peter
    Broman, Curt
    Belivanova, Veneta
    Marone, Federica
    A fungal-prokaryotic consortium at the basalt-zeolite interface in subseafloor igneous crust2015In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203Article in journal (Refereed)
  • 13. Bosi, Ferdinando
    et al.
    Skogby, Henrik
    Lazor, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Reznitskii, Leonid
    Atomic arrangements around the O3 site in Al- and Cr-rich oxytourmalines: a combined EMP, SREF, FTIR and Raman study2015In: Physics and chemistry of minerals, ISSN 0342-1791, E-ISSN 1432-2021, Vol. 42, no 6, 441-453 p.Article in journal (Refereed)
  • 14.
    Bosi, Ferdinando
    et al.
    Sapienza Universita di Roma.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Lazor, Peter
    Uppsala Universitet.
    Reznitskii, Leonid
    Russian Academy of Sciences.
    Atomic arrangements around the O3 site in Al- and Cr-rich oxytourmalines: a combined EMP, SREF, FTIR and Raman study2015In: Physics and chemistry of minerals, ISSN 0342-1791, E-ISSN 1432-2021, Vol. 42, 441-453 p.Article in journal (Refereed)
  • 15.
    D'Ippolito, Veronica
    et al.
    Sapienza University, Rome, Italy.
    Andreozzi, Giovanni
    Sapienza University, Rome, Italy.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Hametner, Kathrin
    ETH, Zürich, Switzerland.
    Günther, Detlef
    ETH, Zürich, Swizerland.
    Color mechanisms in spinel: cobalt and iron interplay for the blue color2015In: Physics and chemistry of minerals, ISSN 0342-1791, E-ISSN 1432-2021, Vol. 42, no 6, 431-439 p.Article in journal (Refereed)
    Abstract [en]

    Six natural, blue colored spinel crystals were studied chemically by electron microprobe and laser ablation inductively coupled plasma mass spectrometry (LAICP-MS) techniques and optically by UV–VIS–NIR–MIR spectroscopy in the range 30,000–2,000 cm1  to investigate the causes of their blue color hues. The positions of the absorption bands vary only marginally with the principal composition of the samples (gahnite vs. spinel s.s .). Although blue colors in spinels are frequently the result of various electronic processes in Fe cations, we demonstrate by comparison with synthetic Co-bearing samplesthat Co acts as an important chromophore also in natural spinels. Already at concentration levels of a few ppm (e.g.,>10 ppm), cobalt gives rise to absorption bands at ~18,000, 17,000 and 16,000 cm1  that result in distinct blue coloration. In spinels with insignificant Co contents, different shades of paler blue (from purplish to greenish blue) colors are caused by electronic transitions in TFe2+, MFe2+, MFe3and Fe2+–Fe3 cation pairs.

  • 16.
    Bosi, Ferdinando
    et al.
    Università di Roma, Italien.
    Andreozzi, Giovanni
    Università di Roma, Italien.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Experimental evidence for partial Fe2+ disorder at the Y and Z sites of tourmaline: a combined EMP, SREF, MS, IR and OAS study of schorl2015In: Mineralogical magazine, ISSN 0026-461X, E-ISSN 1471-8022, Vol. 79, no 3, 515-528 p.Article in journal (Refereed)
  • 17. Weis, Franz A.
    et al.
    Skogby, Henrik
    Troll, Valentin R.
    Deegan, Frances M.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Uppsala University, Sweden.
    Dahren, Börje
    Magmatic water contents determined through clinopyroxene: Examples from the Western Canary Islands, Spain2015In: Geochemistry Geophysics Geosystems, ISSN 1525-2027, Vol. 16, no 7, 2127-2146 p.Article in journal (Refereed)
    Abstract [en]

    Water is a key parameter in magma genesis, magma evolution, and resulting eruption styles, because it controls the density, the viscosity, as well as the melting and crystallization behavior of a melt. The parental water content of a magma is usually measured through melt inclusions in minerals such as olivine, a method which may be hampered, however, by the lack of melt inclusions suitable for analysis, or postentrapment changes in their water content. An alternative way to reconstruct the water content of a magma is to use nominally anhydrous minerals (NAMs), such as pyroxene, which take up low concentrations of hydrogen as a function of the magma's water content. During magma degassing and eruption, however, NAMs may dehydrate. We therefore tested a method to reconstruct the water contents of dehydrated clinopyroxene phenocrysts from the Western Canary islands (n=28) through rehydration experiments followed by infrared and Mossbauer spectroscopy. Employing currently available crystal/melt partitioning data, the results of the experiments were used to calculate parental water contents of 0.710.07 to 1.490.15 wt % H2O for Western Canary magmas during clinopyroxene crystallization at upper mantle conditions. This H2O range is in agreement with calculated water contents using plagioclase-liquid-hygrometry, and with previously published data for mafic lavas from the Canary Islands and comparable ocean island systems elsewhere. Utilizing NAMs in combination with hydrogen treatment can therefore serve as a proxy for pre-eruptive H2O contents, which we anticipate becoming a useful method applicable to mafic rocks where pyroxene is the main phenocryst phase.

  • 18.
    Weis, Franz A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Department of Geosciences, Swedish Museum of Natural History, Stockholm, Sweden.
    Skogby, Henrik
    Swedish Museum Nat Hist, Dept Geosci, Stockholm, Sweden..
    Troll, Valentin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Department of Physics (GEOVOL), University of Las Palmas de Gran Canaria, Las Palmas de Gran Canaria, Spain.
    Deegan, Frances
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Department of Geological Science, Stockholm University, Stockholm, Sweden.
    Dahrén, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Magmatic water contents determined through clinopyroxene: Examples from the Western Canary Islands, Spain2015In: Geochemistry Geophysics Geosystems, ISSN 1525-2027, E-ISSN 1525-2027, Vol. 16, no 7, 2127-2146 p.Article in journal (Refereed)
    Abstract [en]

    Water is a key parameter in magma genesis, magma evolution, and resulting eruption styles, because it controls the density, the viscosity, as well as the melting and crystallization behavior of a melt. The parental water content of a magma is usually measured through melt inclusions in minerals such as olivine, a method which may be hampered, however, by the lack of melt inclusions suitable for analysis, or postentrapment changes in their water content. An alternative way to reconstruct the water content of a magma is to use nominally anhydrous minerals (NAMs), such as pyroxene, which take up low concentrations of hydrogen as a function of the magma's water content. During magma degassing and eruption, however, NAMs may dehydrate. We therefore tested a method to reconstruct the water contents of dehydrated clinopyroxene phenocrysts from the Western Canary islands (n=28) through rehydration experiments followed by infrared and Mossbauer spectroscopy. Employing currently available crystal/melt partitioning data, the results of the experiments were used to calculate parental water contents of 0.710.07 to 1.490.15 wt % H2O for Western Canary magmas during clinopyroxene crystallization at upper mantle conditions. This H2O range is in agreement with calculated water contents using plagioclase-liquid-hygrometry, and with previously published data for mafic lavas from the Canary Islands and comparable ocean island systems elsewhere. Utilizing NAMs in combination with hydrogen treatment can therefore serve as a proxy for pre-eruptive H2O contents, which we anticipate becoming a useful method applicable to mafic rocks where pyroxene is the main phenocryst phase.

  • 19.
    Weis, Franz A.
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Troll, Valentin R.
    Uppsala University.
    Deegan, Frances M.
    Uppsala University.
    Dahren, Börje
    Uppsala University.
    Magmatic water contents determined through clinopyroxene: Examples from the Western Canary Islands, Spain2015In: Geochemistry Geophysics Geosystems, ISSN 1525-2027, E-ISSN 1525-2027, Vol. 16, no 7, 2127-2146 p.Article in journal (Refereed)
    Abstract [en]

    Water is a key parameter in magma genesis, magma evolution, and resulting eruption styles,because it controls the density, the viscosity, as well as the melting and crystallization behavior of a melt. Theparental water content of a magma is usually measured through melt inclusions in minerals such as olivine, amethod which may be hampered, however, by the lack of melt inclusions suitable for analysis, or postentrapmentchanges in their water content. An alternative way to reconstruct the water content of a magma is touse nominally anhydrous minerals (NAMs), such as pyroxene, which take up low concentrations of hydrogenas a function of the magma’s water content. During magma degassing and eruption, however, NAMs maydehydrate. We therefore tested a method to reconstruct the water contents of dehydrated clinopyroxene phenocrystsfrom the Western Canary islands (n=28) through rehydration experiments followed by infrared andM€ossbauer spectroscopy. Employing currently available crystal/melt partitioning data, the results of the experimentswere used to calculate parental water contents of 0.71±0.07 to 1.49±0.15 wt % H2O for WesternCanary magmas during clinopyroxene crystallization at upper mantle conditions. This H2O range is in agreementwith calculated water contents using plagioclase-liquid-hygrometry, and with previously published datafor mafic lavas from the Canary Islands and comparable ocean island systems elsewhere. Utilizing NAMs incombination with hydrogen treatment can therefore serve as a proxy for pre-eruptive H2O contents, which weanticipate becoming a useful method applicable to mafic rocks where pyroxene is the main phenocryst phase.

  • 20.
    Reznitskii, Leonid
    et al.
    Russian Academy of Science, Irkutsk, Russia.
    Clark, Christine M.
    University of Manitoba, Winnipeg, Canada.
    Hawthorne, Frank C.
    University of Manitoba, Winnipeg, Canada.
    Grice, Joel D.
    Canadian Museum of Natural History, Ottawa, Canada.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Bosi, Ferdinando
    Sapienza Università di Roma, Rome, Italy.
    Chromo-­alumino-­povondraite,  NaCr3(Al4Mg2)(Si6O18)(BO3)3(OH)3O,  a  new  mineral  species   of  the  tourmaline  supergroup2014In: American Mineralogist, ISSN 0003-004X, Vol. 99, 1767-1773 p.Article in journal (Refereed)
  • 21.
    Bosi, Ferdinando
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Crystal chemistry of the ulvöspinel-qandilite series2014In: American Mineralogist, ISSN 0003-004X, Vol. 99, 847-851 p.Article in journal (Refereed)
  • 22.
    Fregola, Rosa Anna
    et al.
    University of Bari.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Bosi, Ferdinando
    Swedish Museum of Natural History, Department of Geology.
    D'Ippolito, Veronica
    Sapienza University of Rome.
    Andreozzi, Giovanni
    Sapienza University of Rome.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Optical absorption spectroscopy study of the causes for color variations in natural Fe-bearing gahnite: insights from iron valency and site distribution data.2014In: American Mineralogist, ISSN 0003-004X, Vol. 99, 2187-2195 p.Article in journal (Refereed)
  • 23.
    Kristiansson, Per
    et al.
    Lunds universitet.
    Borysiuk, Maciek
    Lunds universitet.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Mosenfelder, Jed
    Caltech, Pasadena, CA, USA.
    Ros, Linus
    Lunds universitet.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Abdel, Naseem
    Lunds universitet.
    Elfman, Mikael
    Lunds universitet.
    Nilsson, Charlotta
    Lunds universitet.
    Pallon, Jan
    Lunds universitet.
    The implementation of a DSSSD in the upgraded boron analysis at LIBAF for applications in geochemistry2014In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, Vol. 332, 207-211 p.Article in journal (Refereed)
  • 24.
    Bosi, Ferdinando
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Reznitskii, Leonid
    Russian Academy of Science.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Vanadio-oxy-chromium-dravite, NaV3(Cr4Mg2)(Si6O18)(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup 2014In: American Mineralogist, ISSN 0003-004X, Vol. 99, 1155-1162 p.Article in journal (Refereed)
  • 25.
    Bosi, Ferdinando
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Reznitskii, Leonid
    Russian Academy of Science, Irkutsk.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Vanadio-oxy-dravite, NaV3(Al4Mg2)(Si6O18)(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup2014In: American Mineralogist, ISSN 0003-004X, Vol. 99, 218-224 p.Article in journal (Refereed)
  • 26.
    Nazzareni, Sabrina
    et al.
    Perugia University.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Crystal chemistry of Sc-bearing synthetic diopsides2013In: Physics and chemistry of minerals, ISSN 0342-1791, E-ISSN 1432-2021, Vol. 40, 789-798 p.Article in journal (Refereed)
  • 27.
    Bosi, Ferdinando
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Reznitskii, Leonid
    Russian Academy of Science, Irkutsk.
    Crystallographic and spectroscopic characterization of Fe-bearing chromo-alumino-povondraite and its relationships with oxy-chromium-dravite and oxy-dravite2013In: American Mineralogist, ISSN 0003-004X, Vol. 98, 1557-1564 p.Article in journal (Refereed)
  • 28.
    Ivarsson, Magnus
    et al.
    Swedish Museum of Natural History, Department of Paleobiology.
    Bengtson, Stefan
    Swedish Museum of Natural History, Department of Paleobiology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Belivanova, Veneta
    Swedish Museum of Natural History, Department of Paleobiology.
    Marone, Federica
    Paul Scherrer Institute.
    Fungal colonies in open fractures of subseafloor basalt.2013In: Geo-Marine Letters, ISSN 0276-0460, E-ISSN 1432-1157, Vol. 33, no 4, 233-234 p.Article in journal (Refereed)
    Abstract [en]

    The deep subseafloor crust is one of the few great frontiers of unknown biology on Earth and, still today, the notion of the deep biosphere is commonly based on the fossil record. Interpretation of palaeobiological information is thus central in the exploration of this hidden biosphere and, for each new discovery, criteria used to establish biogenicity are challenged and need careful consideration. In this paper networks of fossilized filamentous structures are for the first time described in open fractures of subseafloor basalts collected at the Emperor Seamounts, Pacific Ocean. These structures have been investigated with optical microscopy, environmental scanning electron microscope, energy dispersive spectrometer, X-ray powder diffraction as well as synchrotron-radiation X-ray tomographic microscopy, and interpreted as fossilized fungal mycelia.Morphological features such as hyphae, yeastlike growth and sclerotia were observed. The fossilized fungi are mineralized by montmorillonite, a process that probably began while the fungi were alive. It seems plausible that the fungi produced mucilaginous polysaccharides and/or extracellular polymeric substances that attracted minerals or clay particles, resulting in complete fossilization by montmorillonite. The findings are in agreement with previous observations of fossilized fungi in subseafloor basalts and establish fungi as regular inhabitants of such settings. They further show that fossilized microorganisms are not restricted to pore spaces filled by secondary mineralizations but can be found in open pore spaces as well. This challenges standard protocols for establishing biogenicity and calls for extra care in data interpretation.

  • 29.
    Fregola, Rosa Anna
    et al.
    Università di Bari.
    Bosi, Ferdinando
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Cation ordering over short range and long range scales in the MgAl2O4-CuAl2O4 series2012In: American Mineralogist, ISSN 0003-004X, Vol. 97, 1821-1827 p.Article in journal (Refereed)
  • 30. Skogby, Henrik
    et al.
    Bosi, Ferdinando
    Lazor, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Short-range order in tourmaline: A vibrational spectroscopic approach to elbaite2012In: Physics and chemistry of minerals, ISSN 0342-1791, E-ISSN 1432-2021, Vol. 39, no 10, 811-816 p.Article in journal (Refereed)
    Abstract [en]

    Polarized Fourier-transform infrared and Raman spectra were acquired on an elbaite sample previously characterized by electron- and ion microprobe analysis, X-ray diffraction and structure refinement. Spectra from the two vibrational spectroscopy techniques reveal a close similarity in the OH-stretching region, with three main absorption bands strongly polarized in the c-axis direction. By means of bond-valence theory arguments, the observed OH bands are interpreted and assigned to specific local cation arrangements around the O1 (≡W) and O3 (≡V) anion sites. In combination with the relatively simple composition of the studied sample, bond-valence constraints are used to identify stable anion-cation arrangements, which permit the occurrence of short-range ordering to be assessed. Evidence for nearly complete short-range order at the O1 site, with the stable arrangements Y(LiAlAl) 0. 6- W(OH) 0. 6 and Y(LiLiAl) 0. 4- W(F) 0. 4, are presented. These two local arrangements can be further expanded to obtain the larger ordered clusters [ W(OH)- Y(LiAl 2)- V(OH) 3- Z(Al) 6] 0. 6 and [ W(F)- Y(Li 2Al)- V(OH) 3- Z(Al) 6] 0. 4.

  • 31.
    Hålenius, Ulf
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Bosi, Ferdinando
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    A first record of strong structural relaxation of TO4 tetrahedra in a spinel solid solution2011In: American Mineralogist, ISSN 0003-004X, Vol. 96, 617-622 p.Article in journal (Refereed)
  • 32.
    Sundvall, Rickard
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Skogby, Henrik
    Enheten för mineralogi, Naturhistoriska riksmuseet, Box 50007, 10405 Stockholm .
    Hydrogen defect saturation in natural pyroxene2011In: Physics and chemistry of minerals, ISSN 0342-1791, E-ISSN 1432-2021, Vol. 38, no 5, 335-344 p.Article in journal (Refereed)
    Abstract [en]

    Dehydration via the redox reaction: OH- + Fe2+ ↔ O2- + Fe3+ + ½H2, is believed to be a commonly occurring process in pyroxenes and other nominally anhydrous minerals (NAMs) from the upper mantle and appears to be fast enough to allow significant dehydration during magma ascent. Nevertheless, the mobility of hydrogen incorporating defects is controlled by cation diffusion with approximately two orders of magnitude slower reaction kinetics than the iron redox-reaction, and host defects have a much higher likelihood to be preserved than the hydrogen itself. Therefore, restoring hydrogen into the structure would be possible by driving the redox-reaction backwards, as long as temperature and time are limited so not to change the defect state of the crystal structure. Here we investigate the re-hydration capacity of megacryst and xenocryst ortho- and clinopyroxene by stepwise thermal annealing of crystallographically oriented samples in 1 atm. H2. H concentration was measured by FTIR spectroscopy after each annealing step. Most samples show only a small increase in water content up to a presumed saturation level, after which further heat treatments in H2 resulted in a slight decrease in water contents. However, two of the studied samples, both fairly Fe rich megacrysts, are significantly rehydrated. Some samples or crystal sections exhibit a practically inert behavior, with minor fluctuations around initial water concentrations. Present results indicate that most mantle pyroxene has not been substantially dehydrated during late stage magma processes, and that restoring water is possible in samples which have lost considerable amounts of water.

  • 33.
    Hålenius, Ulf
    et al.
    Naturhistoriska riksmuseet.
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Skogby, Henrik
    Naturhistoriska riksmuseet.
    Nazzareni, Sabrina
    Perugia University.
    Kristiansson, Per
    Lunds universitet.
    Resmark, Jeppa
    Lunds universitet.
    Coordination of Boron in Nominally Boron-Free Rock Forming Silicates: Evidence for Incorporation of BO3 groups in Clinopyroxene2010In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 0016-1258, Vol. 74, 5672-5679 p.Article in journal (Refereed)
    Abstract [en]

    To explore mechanisms of B-incorporation in common chain silicates we have investigated synthetic diopside samples produced under boron-saturated conditions by 11B and 29Si magic-angle spinning (MAS) NMR and single-crystal NRA, FTIR, EMP and XRD/SREF techniques. Our samples contain 0.14–0.65 wt.% B2O3. NMR reveals that B is predominantly present in trigonal coordination in the clinopyroxene structure. This observation is supported by vibrational bands characteristic for B–O stretching in BO3 groups in the range 1250–1400 cm−1 in polarised single crystal FTIR-spectra. Single crystal structure refinements suggest that boron replaces Si at the T site. Combined, these results suggest that boron replacement for Si at the T-site leads to disruption of one of the T–O bonds of the nominal clinopyroxene structure resulting in replacement of SiO4 tetrahedra by BO3 groups. Our results show that high concentrations of boron can be incorporated in the nominally boron-free diopside. Elevated B-concentrations in the present calcic clinopyroxenes are accompanied by modifications of the diopside crystal structure involving the breaking of one T–O bond and simultaneous formation of vacancies at the octahedral M2 site. These structural modifications destabilize the structure and constitute thereby limiting factors for incorporating higher boron concentrations in diopside.

     

     

  • 34.
    Hålenius, Ulf
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Edén, Mattias
    Stockholm universitet.
    Nazzareni, Sabrina
    Università di Perugia.
    Kristiansson, Per
    Lunds universitet.
    Resmark, Jeppa
    Lunds universitet.
    Coordination of boron in nominally boron-free rock forming silicates: evidence for incorporation of BO3 groups in clinopyroxene2010In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 0016-1258, Vol. 74, 5672-5679 p.Article in journal (Refereed)
  • 35.
    Bosi, Ferdinando
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Crystal chemistry of the MgAl2O4-MgMn2O4-MnMn2O4 system: Analysis of structural distortion in spinel and hausmannite-type structures2010In: American Mineralogist, ISSN 0003-004X, Vol. 95, 602-607 p.Article in journal (Refereed)
  • 36.
    Hålenius, Ulf
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Andreozzi, Giovanni B.
    Sapienza Università di Roma.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Structural relaxation around Cr3+ and the red-green color change in the spinel s.s.-magnesiochromite (MgAl2O4–MgCr2O4) and gahnite-zincochromite (ZnAl2O4–ZnCr2O4) solid solution series2010In: American Mineralogist, ISSN 0003-004X, Vol. 95, 456-462 p.Article in journal (Refereed)
  • 37.
    Bosi, Ferdinando
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Crystal chemistry of the magnetite-ulvöspinel series2009In: American Mineralogist, ISSN 0003-004X, Vol. 94, 181-189 p.Article in journal (Refereed)
  • 38.
    Sundvall, Rickard
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Skogby, Henrik
    Sektionen för Mineralogi, Naturhistoriska Riksmuseet.
    Stalder, Roland
    Institut für Mineralogie und Petrographie, Universität Innsbruck, Österrike.
    Dehydration-hydration mechanisms in synthetic Fe-poor diopside2009In: European journal of mineralogy, ISSN 0935-1221, E-ISSN 1617-4011, Vol. 21, no 1, 17-26 p.Article in journal (Refereed)
    Abstract [en]

    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 57Fe-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 Fe3+ 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 + Fe2+ = O2− + Fe3+ + ½H2, 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.

     

    The calculated Arrhenius equation derived from the diffusion rates during dehydration along [010] yields an activation energy (Ea) of −292 ± 50 kJ mol−1, and D0 = 10±1.9 + 2.3 m2 s−1. 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. Ea is similar to that of dehydration of pure and low-Fe enstatite.

  • 39.
    Sundvall, Rickard
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Skogby, Henrik
    Sektionen för Mineralogi, Naturhistoriska Riksmuseet.
    Stalder, Roland
    Institut für Mineralogie und Petrographie, Universität Innsbruck, Österrike.
    Hydrogen diffusion in synthetic Fe-free diopside2009In: European journal of mineralogy, ISSN 0935-1221, E-ISSN 1617-4011, Vol. 21, no 5, 963-970 p.Article in journal (Refereed)
    Abstract [en]

    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 (Ea) of -331 ± 50 kJ mol-1 and D0 = 100.9 ± 2.3 m2 s-1 for diffusion along [010]. Diffusion along [100]* gives an Ea-value of -312 ± 55 kJ mol-1 with D0 = 100.5 ± 2.4 m2 s-1. 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.

  • 40.
    Skogby, Henrik
    et al.
    Sektionen för Mineralogi, Naturhistoriska Riksmuseet, Box 50007, 10405 Stockholm.
    Stalder, Roland
    Department of Earth Sciences, University of Göttingen, Goldschmidtstrasse 1, D-37077 Göttingen, Germany.
    Sundvall, Rickard
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Sektionen för Mineralogi, Naturhistoriska Riksmuseet, Box 50007, 10405 Stockholm.
    Dehydration mechanisms in synthetic ortho- and clinopyroxene2008In: Abstract volume of the 2nd EuroMinScI Conference, Giens, France, 31 March – 02 April 2008, 2008Conference paper (Other academic)
    Abstract [en]

    Pyroxenes are among the many nominally anhydrous minerals that have been shown to contain low but significant amounts of water, structurally bound as OH defects. The pyroxenes appear to be important hosts for water in the upper mantle, and it is therefore relevant to study the thermal stability of hydrogen and related exchange mechanisms.

    In two parallel studies we have investigated the dehydration and rehydration behaviour in Fe-doped ortho- and clinopyroxene, synthesised by piston-cylinder techniques at 20 - 25 kbar, by step-wise heat treatments in air and H2 atmosphere at 800 - 1000ºC. The change in OH content and Fe valence state was traced by FTIR and Mössbauer spectroscopy.

    Results show that hydrogen exchange to a substantial extent occurs via the redox reaction OH- + Fe2+ = O2- + Fe3+ + 1/2H2, but that additional reactions are also active. Some of the OH absorption bands in ortho- and clinopyroxene spectra have previously been shown to be related to Fe3+. These bands show a different behaviour during heat treatment in air and H2 atmosphere compared to bands that are not related to Fe3+. The different behaviour of the bands can be explained by a model with two reactions with different kinetics by which Fe3+-related defects are being produced and consumed. Application of the results to natural samples is not straightforward, as natural samples generally do not exhibit Fe3+-related absorption bands. Therefore only a maximum value can be estimated for the amount of water which has left the crystal by redox dehydration.

  • 41.
    Bosi, Ferdinando
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Stoichiometry of synthetic ulvöspinel single crystals2008In: American Mineralogist, ISSN 0003-004X, Vol. 93, 1312-1316 p.Article in journal (Refereed)
  • 42.
    Sundvall, Rickard
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Skogby, Henrik
    Sektionen för Mineralogi, Naturhistoriska Riksmuséet, Box 50007, 10405 Stockholm.
    Stalder, Roland
    Geowissenschaftliches Zentrum der Universität Göttingen, Abteilung Mineralogie, Goldschmidtstraβe 1, 37077 Göttingen, Germany.
    Dehydration-hydration mechanisms in synthetic diopside2007In: Abstract volume of the 6th European Conference on Mineralogy and Spectroscopy, Stockholm 2007, p. 77, 2007Conference paper (Other academic)
    Abstract [en]

    DEHYDRATION-HYDRATION MECHANISMS IN SYNTHETIC DIOPSIDE

    Rickard Sundvall(1,2), Henrik Skogby(1), Roland Stalder(3).

    1, Dept. of Mineralogy, Swedish Museum of Natural History, Box 50007, 10405 Stockholm, Sweden. Rickard.sundvall@nrm.se.

    2, Dept. of Geology and Geochemistry, Svante Arrhenius väg 8C, 106 91 Stockholm, Sweden.

    3, Geowissenschaftliches Zentrum der Universität Göttingen, Abteilung Angewandte und Experimentelle Mineralogie, Goldschmidtstraβe 1, 37077 Göttingen, Germany.

    Small amounts (ppm) of OH in nominally anhydrous minerals (NAM:s) can have a dramatic effect on the chemical and physical properties of the upper mantle. The pyroxenes of the upper mantle have been shown to carry substantial amounts of water in the form of hydroxyl ions. Enstatite and diopside are the most important 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 57Fe-doped diopside were investigated. Dehydration was carried out by stepwise heating in air of three crystals from the same synthesis run. The crystals were synthesized in a piston-cylinder apparatus at 20 kbar by slow cooling from 1330oC to 1100oC under water-saturated conditions with excess silica.

    A series of FTIR-spectra and corresponding Mössbauer-spectra were obtained after each step.

    From the Mössbauer-spectra we see an increase in the Fe3+ doublet with successive dehydration, although the increase in Fe3+ 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- + Fe2+ = O2- + Fe3+ + ½H2, and that additional reactions are also active. Hydration experiments were conducted in the same manner as the dehydrations, with the exception that hydrogen gas was used during heating. Hydration experiments were only conducted on one crystal.

    The calculated diffusion for the dehydration reactions yields a -logD (D in m2/s) of 13.0 (1000oC), 15.1 (900oC), and 15.3 (800oC). Re-hydration of #218 (1000oC) gives a –logD of 13.3. All crystals were oriented parallel to (010). Diffusion rates are in the same order of magnitude as 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. The Arrhenius equation yields an activation energy (Ea) of -300 kJ mol-1, from the mean of the three reactions at three different temperatures. This Ea is very similar to that of dehydration of pure and low-Fe enstatite.

  • 43.
    Hålenius, Ulf
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Bosi, Ferdinando
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Galaxite, MnAl2O4, a spectroscopic standard for tetrahedrally coordinated Mn2+ in oxygen-based mineral structures2007In: American Mineralogist, ISSN 0003-004X, Vol. 92, 1225-1231 p.Article in journal (Refereed)
  • 44.
    Bosi, Ferdinando
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Andreozzi, Giovanni B.
    Sapienza Università di Roma.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Lucchesi, Sergio
    Sapienza Università di Roma.
    Structural refinement of Mn-doped spinel: a case for tetrahedrally coordinated Mn3+ in an oxygen-based structure2007In: American Mineralogist, ISSN 0003-004X, Vol. 92, 27-33 p.Article in journal (Refereed)
  • 45.
    Lenaz, Davide
    et al.
    Università degli Studi di Trieste.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Princivalle, Francesco
    Università degli Studi di Trieste.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    The MgCr2O4-MgFe2O4 solid solution series: Effects of octahedrally coordinated Fe3+ on T-O bond lengths2006In: Physics and chemistry of minerals, ISSN 0342-1791, E-ISSN 1432-2021, Vol. 33, 465-474 p.Article in journal (Refereed)
  • 46.
    Skogby, Henrik
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Kristiansson, Per
    Lunds universitet.
    Ohashi, Harou
    Hashi Institute for Silicate Science, Tokyo.
    Ti-incorporation and VITi3+-IVTi4+ intervalence charge transfer in Na and Ti substituted diopside2006In: American Mineralogist, ISSN 0003-004X, Vol. 91, 1794-1801 p.Article in journal (Refereed)
  • 47.
    Nysten, Per
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences.
    Skogby, Henrik
    Manganese ferro-ferri-winchite from Harstigen, Filipstad, central Sweden1994In: Mineralogical Magazine, ISSN 0026-461X, Vol. 58, 166-170 p.Article in journal (Refereed)
  • 48.
    Skogby, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology.
    Intracrystalline cation distribution and kinetics of order-disorder reactions in calcic amphiboles1987Doctoral thesis, comprehensive summary (Other academic)
  • 49. Weis, Franz A.
    et al.
    Lazor, Peter
    Skogby, Henrik
    Reichart, Patrick
    Hydrogen analysis in nominally anhydrous minerals by transmission Raman spectroscopyManuscript (preprint) (Other academic)
  • 50. Weis, Franz A.
    et al.
    Ros, Linus
    Reichart, Patrick
    Skogby, Henrik
    De La Rosa, Nathaly
    Kristiansson, Per
    Dollinger, Günther
    Hydrogen concentration analysis in clinopyroxene using proton-proton scatteringManuscript (preprint) (Other academic)
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