A well-characterized suite of vesuvianite samples from the volcanic ejecta of Latium (Italy) was studied by SREF (single-crystal X-ray refinement), EMPA, SIMS (Secondary-Ion Mass Spectrometry) and single-crystal, polarized radiation, FTIR spectroscopy in the OH-stretching region. Light elements in particular were analyzed by SIMS using an ion microprobe (Cameca IMS 4f) at CNR.-Istituto di Geoscienze e Georisorse (Pavia). A 16O- primary ion beam accelerated at 12.5 kV, with a beam intensity of 3 nA and a beam diameter <= 5 ?m was employed. The SiO2 (wt%) content (from EMPA) was selected as an internal reference for H, Li, Be and B (Ottolini et al., 2002; Ottolini & Oberti, 2000). Most samples are B- (up to 3.67 wt%) and F-rich (up to 2.38 wt%). All IR spectra consist of a rather well-defined triplet of broad bands at higher-frequency (3700-3300 cm-1), and a very broad, composite absorption below 3300 cm-1. These spectra are characteristic of B-rich and F-rich vesuvianites (Groat et al., 1995). Measurements with E//c or E?c show that all bands are strongly polarized with maximum absorption for E//c, and agree with previous band assignment to the two O(11)-H(1) and O(10)-H(2) groups in the structure (Groat et al., 1995). Pleochroic measurements with changing direction of the E vector of the incident radiation shows that the orientation of the O(11)-H(1) dipole is OH^c ~ 35°, in excellent agreement with the neutron data of Lager et al. (1999). A calibration curve, based on SIMS data on the same crystals used for FTIR analysis is presented. The integrated molar absorption coefficient for vesuvianite is ?i = 97.000? 2000 l mol-1 cm-2. This value is in good agreement with the calibration curve for minerals established by Libowitzky and Rossman (1997). Preliminary data show that a quantitative determination of water in vesuvianites in also possible using powder IR spectroscopy, provided the sample is prepared in a well-standardized way. References GROAT, L.A., HAWTHORNE, F.C., ROSSMAN, G.R. & ERCIT, T.S. (1995): Eur. J. Mineral. 13: 1325-1331. LAGER, G.A., XIE, Q., ROSS, F.K., ROSSMAN, G.R., ARMBRUSTER, T., ROTELLA, F.J., SCHULTZ, A.J. (1999): Can. Mineral. 37: 763-768 LIBOWITZKY, E. & ROSSMAN, G.R. (1997): Am Mineral 82: 1111-1115. OTTOLINI L., CAMARA F., HAWTHORNE F.C., STIRLING J. (2002): Amer. Mineral. 87: 1477-1485. OTTOLINI, L., OBERTI, R. (2000): Analyt. Chem. 72: 3731-3738.
A SIMS calibration curve for the OH content of vesuvianite: a polarized single-crystal FTIR study
OTTOLINI L
2004
Abstract
A well-characterized suite of vesuvianite samples from the volcanic ejecta of Latium (Italy) was studied by SREF (single-crystal X-ray refinement), EMPA, SIMS (Secondary-Ion Mass Spectrometry) and single-crystal, polarized radiation, FTIR spectroscopy in the OH-stretching region. Light elements in particular were analyzed by SIMS using an ion microprobe (Cameca IMS 4f) at CNR.-Istituto di Geoscienze e Georisorse (Pavia). A 16O- primary ion beam accelerated at 12.5 kV, with a beam intensity of 3 nA and a beam diameter <= 5 ?m was employed. The SiO2 (wt%) content (from EMPA) was selected as an internal reference for H, Li, Be and B (Ottolini et al., 2002; Ottolini & Oberti, 2000). Most samples are B- (up to 3.67 wt%) and F-rich (up to 2.38 wt%). All IR spectra consist of a rather well-defined triplet of broad bands at higher-frequency (3700-3300 cm-1), and a very broad, composite absorption below 3300 cm-1. These spectra are characteristic of B-rich and F-rich vesuvianites (Groat et al., 1995). Measurements with E//c or E?c show that all bands are strongly polarized with maximum absorption for E//c, and agree with previous band assignment to the two O(11)-H(1) and O(10)-H(2) groups in the structure (Groat et al., 1995). Pleochroic measurements with changing direction of the E vector of the incident radiation shows that the orientation of the O(11)-H(1) dipole is OH^c ~ 35°, in excellent agreement with the neutron data of Lager et al. (1999). A calibration curve, based on SIMS data on the same crystals used for FTIR analysis is presented. The integrated molar absorption coefficient for vesuvianite is ?i = 97.000? 2000 l mol-1 cm-2. This value is in good agreement with the calibration curve for minerals established by Libowitzky and Rossman (1997). Preliminary data show that a quantitative determination of water in vesuvianites in also possible using powder IR spectroscopy, provided the sample is prepared in a well-standardized way. References GROAT, L.A., HAWTHORNE, F.C., ROSSMAN, G.R. & ERCIT, T.S. (1995): Eur. J. Mineral. 13: 1325-1331. LAGER, G.A., XIE, Q., ROSS, F.K., ROSSMAN, G.R., ARMBRUSTER, T., ROTELLA, F.J., SCHULTZ, A.J. (1999): Can. Mineral. 37: 763-768 LIBOWITZKY, E. & ROSSMAN, G.R. (1997): Am Mineral 82: 1111-1115. OTTOLINI L., CAMARA F., HAWTHORNE F.C., STIRLING J. (2002): Amer. Mineral. 87: 1477-1485. OTTOLINI, L., OBERTI, R. (2000): Analyt. Chem. 72: 3731-3738.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
