ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Structure, ordering and cation interactions in Ca-free P2 1 /c clinopyroxenes (1998)
    Springer
    Physics and chemistry of minerals 25 (1998), S. 249-258 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  A suite of 14 synthetic Ca-free P2 1 /c low-clinopyroxenes of compositions across the enstatite-ferrosilite (En-Fs) join have been studied by X-ray powder diffraction and Mössbauer spectroscopy. The crystal structure of one sample with composition X Fs=0.39 was determined by single-crystal X-ray diffraction. The powder diffraction data show that there is no significant (〈0.25% at X Fs=0.5) excess volume of mixing on the enstatite-ferrosilite join. The molar volumes are described by V=31.261(17)+1.677(23) X Fs cm3.mol(MSiO3)–1. The linear behaviour of volume with composition arises from the compensating effects of non-linear changes in the unit-cell parameters with composition. Unweighted fits to the data yielded the relationships: a=9.6100(15)+0.105(2)X Fs, b=8.8156(28)+0.218(12)X Fs+0.0481(117)X 2 Fs , c =5.1702(4)+0.0879(21)X Fs–0.0214(21)X 2 Fs , β=108.345(8)+0.947(30)X Fs–0.805(26)X 2 Fs . The strong positive deviation of β from linearity is directly correlated to the difference in site occupancies between M1 and M2 as determined by Mössbauer spectroscopy and arises directly from the expansion of M2-O1 and M2-O3 bonds upon initial substitution of Fe for Mg in enstatite. The hyperfine parameters from Mössbauer spectra are consistent with variations in the average local environment as recorded by the X-ray data. Asymmetric line broadening of the Mössbauer spectra provides evidence for next-nearest neighbour effects, and is consistent with no significant clustering of Fe or Mg within the samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050111
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Phase relations in the system fayalite–magnetite at high pressures and temperatures (2000)
    Springer
    Contributions to mineralogy and petrology 139 (2000), S. 734-747 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The phase relations in the Fe2SiO4–Fe3O4 binary system have been determined between 900 and 1200 °C and from 2.0 to 9.0 GPa. At low to moderate pressures magnetite can accommodate significant Si, reaching XFe2SiO4=0.1 and 0.2 at 3.0 and 5.0 GPa respectively, with temperature having only a secondary influence. At pressures below 3.5 GPa at 900 °C and 2.6 GPa at 1100 °C magnetite-rich spinel coexists with pure fayalite. This assemblage becomes unstable at higher pressures with respect to three intermediate phases that are spinelloid polytypes isostructural to spinelloids II, III and V in the Ni-aluminosilicate system. The phase relations between the spinelloid phases are complex. At pressures above ≈8.0 GPa at 1100 °C, the spinelloid phases give way to a complete spinel solid solution between Fe3O4 and Fe2SiO4. The presence of small amounts of Fe3+ stabilises the spinel structure to lower pressures compared to the Fe2SiO4 end member. This means that the fayalite–γ-spinel transition is generally unsuitable as a pressure calibration point for experimental apparatuses. The molar volumes of the spinel solid solutions vary nearly linearly with composition, having a small negative deviation from ideal behaviour described by Wv=−0.15(6) cm3. Extrapolation yields V°(298) = 41.981(14) cm3 for the Fe2SiO4-spinel end member. The cell parameters and molar volumes of the three spinelloid polytypes vary systematically with composition. Cation disorder is an important factor in stabilising the spinelloid polytypes. Each polytype exhibits a particular solid solution range that is directly influenced by the interplay between its structure and the cation distributions that are energetically favourable. In the FeO–FeO1.5–SiO2 ternary system Fe7SiO10 (“iscorite”) coexists with the spinelloid phases at intermediate pressures on the SiO2-poor, or Fe3+-poor side of the Fe2SiO4–Fe3O4 join. On the SiO2 and Fe3+-rich side of the join, orthopyroxene or high-P clinopyroxene coexists with the spinelloids and spinel solid solutions. The assemblage pyroxene+spinel+SiO2 is stable over a wide range of bulk composition. The stability of spinelloid III is of particular petrologic interest since this phase has the same structure as (Mg,Fe)2SiO4–wadsleyite, indicating that Fe3+ can be easily incorporated in this important phase in the Earth's transition zone, in addition to silicate spinel. This has important implications for the redox state of the Earth's transition zone and for the depth at which the olivine to spinel transition occurs in the mantle, potentially leading to a shift in the “410 km” seismic discontinuity to shallower depths depending on the prevailing redox state. In addition, a coupled tetrahedral substitution of Fe3++OH for Si+O could provide a further mechanism for the incorporation of H2O in wadsleyite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004100000168
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Microanalysis of Fe3+/ΣFe in oxide and silicate minerals by investigation of electron energy-loss near-edge structures (ELNES) at the Fe M 2,3 edge (1999)
    Springer
    Physics and chemistry of minerals 26 (1999), S. 584-590 
    Details
    ISSN: 1432-2021
    Keywords: Key words Ferrous/ferric ratio ; Electron energy-loss spectroscopy ; Electron energy-loss near-edge structure ; Transmission electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The Fe M 2,3-edge spectra of solid solutions of garnets (almandine-skiagite Fe3(Al1–xFex)2[SiO4]3 and andradite-skiagite (Fe1–xCax)3Fe2[SiO4]3), pyroxenes (acmite-hedenbergite (Ca1–xNax)(Fe2+ 1−xFe3+ x)Si2O6), and spinels (magnetite-hercynite Fe(Al1–xFex)2O4) have been measured using the technique of parallel electron energy-loss spectroscopy (EELS) conducted in a transmission electron microscope (TEM). The Fe M 2,3 electron energy-loss near-edge structures (ELNES) of the minerals exhibit a characteristic peak located at 4.2 eV and 2.2 eV for trivalent and divalent iron, respectively, prior to the main maximum at about 57 eV. The intensity and energy of the pre-edge feature varies depending on Fe3+/ΣFe. We demonstrate a new quantitative method to extract the ferrous/ferric ratio in minerals. A systematic relationship between Fe3+/ΣFe and the integral intensity ratio of the main maximum and the pre-edge peak of the Fe M 2,3 edge is observed. Since the partial cross sections of the Fe M 2,3 edges are some orders of magnitude higher than those of the Fe L 2,3 edges, the Fe M 2,3 edges are interesting for valence-specific imaging of Fe. The possibility of iron valence-specific imaging is illustrated by Fe M 2,3-ELNES investigations with high lateral resolution from a sample of ilmenite containing hematite exsolution lamellae that shows different edge shapes consistent with variations in the Fe3+/ΣFe ratio over distances on the order of 100 nm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050222
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    facet.materialart.
    Unknown
    A complex magmatic system beneath the Devès volcanic field, Massif Central, France: evidence from clinopyroxene megacrysts (2007)
    Springer
    Details
    Publication Date: 2007-01-23
    Print ISSN: 0010-7999
    Electronic ISSN: 1432-0967
    Topics: Geosciences
    Published by Springer
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 5
    facet.materialart.
    Unknown
    Equation of state of hercynite, FeAl2O4, and high-pressure systematics of Mg-Fe-Cr-Al spinels (2015)
    Mineralogical Society of Great Britain and Ireland
    Details
    Publication Date: 2015-07-03
    Description: In this work a single crystal of synthetic hercynite, FeAl 2 O 4 , was investigated by X-ray diffraction up to 7.5 GPa and at room temperature, in order to determine its pressure–volume equation of state. The unit-cell volume decreases non-linearly with a reduction of 3.4% (i.e. 18.43 Å 3 ). The pressure–volume data were fitted to a third-order Birch-Murnaghan equation of state providing the following coefficients: V 0 = 542.58(3) Å 3 , K T0 = 193.9(1.7) GPa, K ' = 6.0(5). These results are consistent with previous investigations of Cr and Al spinels measured with the same experimental approach but the K T0 differs significantly from the experimental determination carried out more than 40 years ago by Wang and Simmons ( 1972 ) by the pulse echo overlap method. Our new results were used to redetermine the FeAl 2 O 4(hercynite) = FeO (wüstite) + Al 2 O 3(corundum) equilibrium in P–T space and obtain geobarometric information for Cr-Al spinels found as inclusions in diamond.
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
    Published by Mineralogical Society of Great Britain and Ireland
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 6
    facet.materialart.
    Unknown
    Complete substitution of Fe2+ by Mg in Fe4O5: The crystal structure of the Mg2Fe2O5 end-member (2015)
    Mineralogical Society of America
    Details
    Publication Date: 2015-02-13
    Description: The crystal structure of a novel Mg 2 Fe 2 O 5 oxide synthetized at 15 GPa and 1550 °C has been determined by means of single-crystal X-ray diffraction. This compound is isostructural with Fe 4 O 5 and can be considered as the other end-member of a solid solution between these two oxides involving the substitution of Fe 2+ for Mg. The resulting unit-cell lattice parameters a = 2.8889(4), b = 9.7282(4), and c = 12.5523(7) Å are smaller than those of Fe 4 O 5 . Mg and Fe 3+ cations are found to be disordered among the three crystallographic sites of the Mg 2 Fe 2 O 5 structure, although preference of Mg for the trigonal prism coordination (M3) is observed. Substitution of Mg into the Fe 4 O 5 structure reduces the octahedral distortion of both the M1 and M2 sites. Like Mg, Cr has recently been found to substitute into Fe 4 O 5 , so that Fe 3+ /Fe can vary from 0 to 1.0 in the Mg-Cr-Fe oxides system. Substitution of both Mg and Cr in Fe 4 O 5 also makes this phase more relevant for bulk compositions expected in the Earth’s transition zone and deep upper mantle. M 4 O 5 phases having the CaFe 3 O 5 -type structure, therefore, need to be considered as a new addition to the phase relations of several simple oxide systems at pressure and temperature conditions at which the spinel-structured phases become unstable.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Published by Mineralogical Society of America
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 7
    facet.materialart.
    Unknown
    Accurate determination of ferric iron in garnets by bulk Mossbauer spectroscopy and synchrotron micro-XANES (2012)
    Mineralogical Society of America
    Details
    Publication Date: 2012-10-01
    Description: Measurements of Fe 3+ /Fe in geological materials have been intractable because of lack of access to appropriate facilities, the time-consuming nature of most analyses, and the lack of precision and reproducibility in most techniques. Accurate use of bulk Mössbauer spectroscopy is limited by largely unconstrained recoilless fraction ( f ), which is used to convert spectral peak area ratios into valid estimates of species concentrations and is unique to different mineral groups and compositions. Use of petrographic-scale synchrotron micro-XANES has been handicapped by the lack of a consistent model to relate spectral features to Fe 3+ /Fe. This paper addresses these two deficiencies, focusing specifically on a set of garnet group minerals. Variable-temperature Mössbauer spectra of the Fe 2+ -bearing almandine and Fe 3+ -bearing andradite end-members are used to characterize f in garnets, allowing Fe 3+ /Fe to be measured accurately. Mössbauer spectra of 19 garnets with varying composition were acquired and fit, producing a set of garnet-specific standards for Fe 3+ analyses. High-resolution XANES data were then acquired from these and 15 additional previously studied samples to create a calibration suite representing a broad range of Fe 3+ and garnet composition. Several previously proposed techniques for using simple linear regression methods to predict Fe 3+ /Fe were evaluated, along with the multivariate analysis technique of partial least-squares regression (PLS). Results show that PLS analysis of the entire XANES spectral region yields the most accurate predictions of Fe 3+ in garnets with both robustness and generalizability. Together, these two techniques present reliable choices for bulk and microanalysis of garnet group minerals.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Published by Mineralogical Society of America
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 8
    facet.materialart.
    Unknown
    Experimental constraints in the CMAS system on the Ca-Eskola content of eclogitic clinopyroxene (2013)
    Schweizerbart
    Details
    Publication Date: 2013-12-10
    Description: The seismic X-Discontinuity, occasionally observed at ~300 km depth, has been attributed partly to the exsolution of the calcium-Eskola (Ca 0.5 0.5 AlSi 2 O 6 , CaEs) component from eclogitic clinopyroxene upon reaching the coesite–stishovite transition. To test if this is a viable mechanism, we have undertaken high-pressure experiments between 4 and 11.5 GPa at 1000–1350 °C in order to further investigate the factors controlling CaEs incorporation in clinopyroxene at upper mantle conditions up to coesite–stishovite transition. Bulk compositions had pyroxene stoichiometry in the simple system CaO–MgO–Al 2 O 3 –SiO 2 ± Na 2 O (CMAS ± Na), which restricts possible end-member components to diopside (di), calcium-Tschermaks (CaTs), calcium-Eskola (CaEs), and clinoenstatite (en), ±jadeite. All run products had a typical eclogitic mineral assemblage with clinopyroxene always in equilibrium with garnet and coesite or stishovite, and in some runs kyanite. Clinopyroxene is non-stoichiometric due to the defect-bearing CaEs component. CaEs and CaTs contents vary systematically with P , T and bulk composition. CaEs reaches up to 0.22 mol % at 4 GPa and 1200 °C, and for a given bulk composition CaEs decreases continuously with pressure from 4 to 11.5 GPa. Our experiments, along with experiments performed with more complex compositions reveal different systematics when Na is present, since it is only accommodated in clinopyroxene. Incorporation of a jadeite component drives down the CaTs content and also influences the CaEs content. Generally, maximizing the CaEs content requires a coexisting free SiO 2 phase and an elevated Al 2 O 3 content, but it is not clear if kyanite must be part of the assemblage, or whether buffering of Al by garnet is adequate. At P 〉 9 GPa, the systematics of clinopyroxene composition change as garnet becomes majoritic and also begins to accommodate significant Na. In both simple and complex bulk compositions CaEs content in clinopyroxene decreases steadily from ~4 GPa so that no sharp change occurs at pressures corresponding to the coesite–stishovite phase transition. Calculations reveal that only small (1–2 wt %) amounts of free stishovite can be exsolved from CaEs-bearing clinopyroxene, which are insufficient to produce a large enough impedance contrast to explain a significant contribution to the X-Discontinuity. If the X-Discontinuity is related to the coesite–stishovite phase transition in eclogite, as proposed in the literature, then free SiO 2 must be already present in the mineral assemblage rather than being exsolved from CaEs-bearing clinopyroxene upon entering the stability field of stishovite.
    Print ISSN: 0935-1221
    Electronic ISSN: 1617-4011
    Topics: Geosciences
    Published by Schweizerbart
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 9
    facet.materialart.
    Unknown
    Oxidation State of the Lithospheric Mantle below the Massif Central, France (2014)
    Oxford University Press
    Details
    Publication Date: 2014-12-14
    Description: Oxidation state is a sensitive indicator of geochemical processes within the upper mantle. Here we report results of a regional study of the oxidation state of spinel peridotite xenoliths from 45 volcanic centers distributed over ~20 000 km 2 in the Massif Central, France. The log f O 2 values relative to the fayalite–magnetite–quartz oxygen buffer (FMQ) were determined from the equilibrium between the Fe-bearing components in olivine, orthopyroxene and spinel, with the Fe 3+ content of spinel measured either by Mössbauer spectroscopy or by electron microprobe using secondary spinel standards. For the entire suite of samples, log f O 2 values range between FMQ – 0·47 and FMQ + 1·66. Our data confirm the presence of two distinct lithospheric mantle domains, previously reported in the literature, lying north and south of 45°30'N, respectively. The northern domain, with its refractory bulk composition, tends to record more oxidized conditions, having log f O 2 values mostly at or above FMQ + 1. The log f O 2 in the southern domain is more variable, including values below FMQ. Assuming that increasing equilibration temperatures among xenoliths reflect increasing depths of origin, samples from the northern domain suggest that the shallower part of the subcontinental lithospheric mantle (SCLM) is somewhat more oxidized than at deeper levels. On the other hand, such a general observation cannot be made for the southern domain. The high log f O 2 values of harzburgites suggest that they are more sensitive to resetting of their oxidation state by metasomatism than lherzolites. In terms of modally metasomatized xenoliths, the ‘melt’ leading to the addition of clinopyroxene apparently had a higher oxidation state (log f O 2 〉 FMQ + 1) than the agent responsible for crystallization of amphibole (log f O 2 ~ FMQ + 0·6). Furthermore, amphibole-bearing and amphibole-free peridotites exhibit the same range in f O 2 . Cryptic metasomatism can also reset oxidation state, sometimes very effectively. Metasomatic processes are probably the reason why the xenolith suite from the Massif Central records relatively high log f O 2 values compared with ‘normal’ non-cratonic SCLM. This study demonstrates the utility of using oxidation state to help characterize and delineate domains in the lithospheric mantle.
    Print ISSN: 0022-3530
    Electronic ISSN: 1460-2415
    Topics: Geosciences
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 10
    facet.materialart.
    Unknown
    Quantitative mapping of the oxidative effects of mantle metasomatism (2013)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2013-05-21
    Description: The oxidation state of Fe in garnets in a garnet peridotite xenolith from the Wesselton kimberlite (South Africa) was quantitatively mapped using X-ray absorption near edge structure (XANES) spectroscopy. Maps of Fe 3+ /Fe were produced by recording the fluorescence intensity at discrete energies rather than recording the full spectrum at each point. The intensity at each point in the map was quantitatively converted to Fe 3+ /Fe with reference to a linear calibration derived from garnet standards for which Fe 3+ /Fe had been determined previously by Mössbauer spectroscopy. The resolution of these maps approaches that of elemental maps obtained using an electron microprobe. The maps reveal zoning in Fe 3+ /Fe between the core (0.075) and rim (0.125) that correlates with zoning of other elements. The rims record an oxidizing metasomatic event in the lithospheric mantle. The oxygen fugacity ( f O 2 ) of this metasomatism is considerably higher than expected from studies of homogeneous garnets that exhibit metasomatic signatures; such garnets may represent a re-equilibrated average of the original (core) and metasomatic (rim) f O 2 values. Metasomatism of the lithospheric mantle may thus have a greater impact on diamond stability than previously thought.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...