P21/m -->C2/m phase-transition in synthetic amphiboles in the system Li2O-Na2O-MgO-SiO2-H2O: a high-T FTIR study. (Articolo in rivista)

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  • P21/m -->C2/m phase-transition in synthetic amphiboles in the system Li2O-Na2O-MgO-SiO2-H2O: a high-T FTIR study. (Articolo in rivista) (literal)
Anno
  • 2008-01-01T00:00:00+01:00 (literal)
Alternative label
  • Della Ventura G.; Bellatreccia F.; Iezzi G.; Oberti R.; Cámara F. (2008)
    P21/m -->C2/m phase-transition in synthetic amphiboles in the system Li2O-Na2O-MgO-SiO2-H2O: a high-T FTIR study.
    in European journal of mineralogy (Print)
    (literal)
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  • Della Ventura G.; Bellatreccia F.; Iezzi G.; Oberti R.; Cámara F. (literal)
Pagina inizio
  • 1019 (literal)
Pagina fine
  • 1026 (literal)
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  • 20 (literal)
Rivista
Note
  • ISI Web of Science (WOS) (literal)
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  • Giancarlo DELLA VENTURA1,4,*, Fabio BELLATRECCIA1, Gianluca IEZZI2,3,5, Roberta OBERTI4 and Fernando CÁMARA4 1 Dipartimento di Scienze Geologiche, Università Roma Tre, Largo S. Leonardo Murialdo 1, 00146, Roma, Italy *Corresponding author, e-mail: dellaven@uniroma3.it 2 Dipartimento di Scienze della Terra, Università \"G. D'Annunzio\", 66013 Chieti Scalo, Italy 3 Department of Seismology and Tectonophysics, Istituto Nazionale di Geofisica e Vulcanologia, Roma, 00100 Italy 4 CNR-Istituto di Geoscienze e Georisorse, unità di Pavia, via Ferrata 1, 27100 Pavia, Italy 5 Presently at: Dipartimento di Geotecnologie per l'Ambiente ed il Territorio, Università G. D'Annunzio, 66013 Chieti, Italy (literal)
Titolo
  • P21/m -->C2/m phase-transition in synthetic amphiboles in the system Li2O-Na2O-MgO-SiO2-H2O: a high-T FTIR study. (literal)
Abstract
  • The P21/m ¡ê C2/m phase-transition has been studied by high-T FTIR analysis on a series of synthetic amphiboles in the Li2O.Na2O.MgO.SiO2.H2O (LNMSH) system. Spectra were collected in the T range 25.450 .C on KBr disks. All examined amphiboles have P21/m symmetry at room T. Their OH-stretching FTIR spectrum consists of two main bands at ¡­ 3740 and 3715 cm.1. At the transition temperature (Tc), these bands merge into one single absorption centred at ¡­ 3720 cm.1, and no further change is observed beyond this T. Significant modifications consisting in peak shifting and band broadening are also observed in the MIR (medium infrared) 1300.640 cm.1 region. Tc values for the different compositions were estimated based on various methods; the most reliable procedure is considered to be the fit of Landau 2-4-6 potentials using band shifts observed in the MIR region. The Tc values obtained for all samples are consistent with previous results obtained on two members of the series examined here by single-crystal or synchrotron powder HT-XRD (high-T X-ray diffraction). They correlate linearly with the aggregate cation radius at M(4) [Tc (.C) = 803.533 ?rM(4)?; R2 = 0.97]. This work thus provides a measure of the role played by the size of the M(4) polyhedron in determining the Tc in simple chemical systems where the B-site occupancy (and geometry) is the only variable. The slope of the equation is far less steep in the LNMSH system than in cummingtonite; crystal-chemical reasons for this behaviour are discussed, and the local order between A and monovalent B cations is suggested to be the major constraint. In more complex systems, inspection of the available data shows that other factors such as the aggregate size of the strip of octahedra must be taken into account. (literal)
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