Crystal-chemistry of B-rich vesuvianites: a combined EPMA, SIMS, XRD, and FTIR study (Abstract/Poster in atti di convegno)

Type
Label
  • Crystal-chemistry of B-rich vesuvianites: a combined EPMA, SIMS, XRD, and FTIR study (Abstract/Poster in atti di convegno) (literal)
Anno
  • 2005-01-01T00:00:00+01:00 (literal)
Alternative label
  • Bellatreccia F.; Ottolini L.P.; Della Ventura G.; Cámara F. (2005)
    Crystal-chemistry of B-rich vesuvianites: a combined EPMA, SIMS, XRD, and FTIR study
    in EMAS-IUMAS Intern. Meeting, Firenze, 22-26 maggio (2005)
    (literal)
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  • Bellatreccia F.; Ottolini L.P.; Della Ventura G.; Cámara F. (literal)
Pagina inizio
  • 248 (literal)
Pagina fine
  • 248 (literal)
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  • Book of Abstracts (literal)
Note
  • Abstract (literal)
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  • Bellatreccia F. 1); Ottolini L.P. 2); Della Ventura G. 1); Cámara F. 2). 1) Dipartimento di Scienze Geologiche, Università Roma Tre, Largo S. Leonardo Murialdo 1, I-00146 Roma, Italy; 2) CNR-Istituto di Geoscienze e Georisorse, Sezione di Pavia, via Ferrata 1, I-27100 Pavia, Italy. (literal)
Titolo
  • Crystal-chemistry of B-rich vesuvianites: a combined EPMA, SIMS, XRD, and FTIR study (literal)
Abstract
  • Vesuvianite is a hydrous sorosilicate with a complex composition which includes both light (H, B, F) and heavy elements, such as Rare Earth Elements (REE), Th and U. In the last few years there has been much work devoted to this mineral (e.g. Groat et al. 1992, 1994, 1996). Several aspects of its crystal chemistry, however, are not yet completely defined. For instance, the boron incorporation in the structure is known to be related to coupled substitutions involving H (Groat et al., 1994), but the possible hydrogarnet mechanism - whereby (H4O4)4- environments are created in Si-deficient samples (Galuskin et al., 2003) - is still not verified. In addition, the H-B distribution among the available sites, possibly affecting the physical (optical) properties of the mineral (Groat et al., 1994) is also not well constrained. These challenging crystal-chemical problems promoted the present work aimed at characterising a large suite of B-rich vesuvianites from Latium (Italy) by a combination of micro-beam techniques such as EMPA and SIMS, single-crystal X-ray diffraction and single-crystal, polarized radiation, Fourier-transform infrared (FTIR) spectroscopy. In this study, light and volatile elements (H, Li, Be, B, F), Y, Sr, REE and actinides (U, Th) were analysed with a Cameca IMS 4f ion microprobe (CNR-IGG, Pavia) using a 16O- primary beam of few ?m ?, at a current intensity of few nA. 1H+, 7Li+, 9Be+, 11B+ and 19F+ were investigated after degassing the crystal mount at the vacuum of ? 10-7 Pa in the ion microprobe sample chamber (together with the H standards) close to the spots previously selected for trace elements. Snarum and Durango apatite were used as standards for REE, Y, Sr; BB and LL stdB glasses for U and Th (Ottolini & Oberti, 2000). The elbaite no. 19 from Ottolini et al. (2002) was used to calibrate the ion signals for H, Li, B and F, while danalite was employed for Be. The crystal-chemical formulae were based on 18 Si atoms. As a result, the vesuvianite suite shows rather variable Mg + Fe, very low MnO contents, and TiO2 up to 1.94 wt%. Most samples are B- (up to 3.67 wt% B2O3) and F-rich (up to 2.38 wt%). The REE content is also significant with ?(REE,Y)ox. up to 4.63 wt%. Minor constituents are represented by the actinides [?(Th,U)ox up to 0.271 wt%] and BeO (up to 0.255 wt%). H2O ranges from 0.243 to 0.665 wt%. Li is present at a few hundred ppm. A calibration curve at ? 10% rel. accuracy (corresponding to 2?% error) based on SIMS data for H was used as reference for the quantitative analysis of H2O in the vesuvianite suite by polarized-radiation FTIR spectra. The resulting integrated molar absorption coefficient turned out to be ?i = 100.000? 2.000 l mol-1 cm-2, in excellent agreement with previous studies on similar matrixes (e.g. Bellatreccia et al., 2004). The data obtained by combining microchemistry with spectroscopy are also in good accord with single-crystal X-diffraction data. (literal)
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