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The P-C phase transition of synthetic amphiboles in the NCMSH system: an FTIR study
No full textDuring the last years, a series of experimental studies have been done to characterize the structural features of synthetic amphiboles in the Li2O-Na2O-MgO-SiO2-H2O (LNMSH system) under different T, P and X conditions. Camára et al. (2003) and Iezzi et al. (2004) showed that the Li-free Na0.8(Na0.8Mg1.2)Mg5Si8O22(OH)2 compound is P21/m at room-T, and Camára et al. (2003) characterized the displacive P21/m C2/m phase-transition by single-crystal XRD. The phase transition of this amphibole has a macroscopic second order character, with a transition temperature (TC) of 257 °C.
Iezzi et al. (2005) did a similar investigation on the Na(LiMg)Mg5Si8O22(OH)2 composition by means of synchrotron radiation HT-XRPD, and showed that this compound also undergoes a displacive phase transition as a function of T, but the transition has a tricritical character and TC = 326 °C. Furthermore Iezzi et al. (2006) showed that all amphiboles in the LNMSH system, independently of their Na-Li contents at the B site, have the P21/m symmetry at room conditions.
Natural Group 5 amphiboles which belong to the B(Na,Li)2, B(Na,Mn)2 and B(Ca,Mn)2 solid-solutions, whether their A site is filled or empty, have monoclinic C2/m symmetry. In contrast, the A-site filled synthetic samples belonging to the B(Na,Mg)2 and B(Li,Mg)2 solid-solutions, have P21/m symmetry at room T, and undergo phase-transitions at variable TC, depending on their chemical composition (Welch et al. 2007). The P21/m symmetry is restricted to amphiboles with a double-chain composition close to Si8 and is probably stabilized by small cations only at the B-group sites or by a B compositions where large monovalent cation (Na) and a small divalent cation (Mg) have a ratio close to 1:1. However, the dimension of the C-group cations also play a significant role in determining the transition behavior (cf. Welch et al. 2007 for more discussion).
In this work, we explore the effects on the phase transitions of a large divalent cation as Ca which progressively replaces BMg. The amphibole symmetry was monitored using in situ low- and high-T FTIR spectroscopy. Samples were prepared as conventional KBr disks (Iezzi et al., 2006); low-T spectra were collected using a nitrogen-cooled cryostat, while high-T spectra were collected using a Specac microfurnace. Previous work (Iezzi et al., 2004, 2006) show that OH-stretching FTIR spectroscopy is particularly useful in characterizing the symmetry changes associated with the P C transition in these amphiboles. For varying T conditions there are well-defined modifications of the room-T pattern, consisting of progressive band broadening and band splitting. Inspection of the data shows that for increasing BCa in the amphibole structure there is a linear decrease of the transition temperature TC for the Mg-richer samples, as also evidenced by the companion X-Ray diffraction study (Iezzi et al., this meeting).
References
Cámara F., Oberti R., Iezzi G., Della Ventura G. (2003) Phys. Chem. Miner., 30, 570-581.
Della Ventura G., Iezzi G., Bellatreccia F., Càmara F., Oberti R. (2004). Mitt. Oster. Min. Ges., 149: 23.
Iezzi G., Della Ventura G., Oberti R., Cámara F., Holtz F. (2004) Am. Miner., 89, 640–646.
Iezzi G., Tribaudino M., Della Ventura G., Nestola G., Bellatreccia F. (2005) Phys. Chem. Miner., 32, 515–523.
Iezzi G., Della Ventura G., Tribaudino M. (2006) Am. Miner., 91, 425-429.
Welch M.D., Cámara F., Della Ventura G., Iezzi G. (2007) Rev. Mineral. Geochem., 67, in press
Crystal-chemical characterization of fibrous amphiboles by FTIR and Mössbauer spectroscopies
No full textThe mechanism through which asbestos amphiboles may give rise to mesothelioma is still not completely understood. Several factors have been taken into account, and these include the morphological aspect of the fiber, the chemical composition, and a variety of surface properties which are ultimately responsible for the mineral-cellule interactions[1]. Studies in vitro demonstrate that the morphology of the fiber has a strong role in determining its biological danger, because very thin and long crystallites are hardly eliminated by the alveolar macrophages. However, recent studied show that lung injury after asbestos exposure is associated with an oxidative stress that is catalyzed by iron in the fiber[2]. It follows that the rapid determination of the chemical composition of asbestiform amphiboles, and of its Mg/Fe ratio in particular, is extremely important in environmental studies. The direct analysis can be achieved only by micro-chemical tools such as by EDS- or WDS-equipped electron microscopes. However, these techniques are extremely expensive and often unsuitable when dealing with extremely fibrous (diameter < 3 μm) materials. Therefore a rapid and easily accessible method is highly desirable in large scale environmental monitoring. The best alternative to EMPA is provided by FTIR spectroscopy, a technique which can be used on both single crystals (down to few μm in dimension) and powders. Here we present the results of a new calibration based on the analysis of a large set of well-characterized fibrous and prismatic natural amphiboles spanning a very large variety of chemical compositions and geological occurrences. All samples were previously studied using X-ray diffraction and EMPA. FTIR spectra in the principal OH-stretching region were collected on KBr disks prepared with a mineral:matrix = 5:150 mg ratio. Most spectra show four prominent bands which can be assigned to the combination of Mg and F2+ at the OH-coordinated M(1,3) sites[3,4,5,6]. The digitized spectra were fitted by interactive optimization followed by least-squares refinement; all bands were modelled as symmetric Gaussians. [3,4] showed that the binary site-occupancies at M(1) and M(3) in the amphibole structure are related to the observed intensities of the four (A to D) components in the principal IR OH-stretching spectrum. Using the original equations of [7]:
M(1,3)Mg = 3IA + 2IB + IC and M(1,3)M2+ = IB + 2IC + 3ID (with M2+ = Fe2+)
where IA-ID are the intensities measured for the corresponding A to D bands, one can derive the (Mg, M2+) site populations at M(1,3) with a high degree of confidence. This method is particularly suitable for asbestiform materials which cannot be properly characterized by EMP. The present work shows that the above spectroscopic tool can be applied to a large variety of amphibole types. For species were significant (Mg, Fe) are present at M(4) (i.e. anthophyllite–cummingtonite–grunerite) an additional information (e.g. Mössbauer) is however required for a complete characterization of the sample.
[1] van Oss, C.J., Naim, J.O., Costanza, P.M., Giese, R.F. Jr., Wu, W., Sorling, A.F. (1999) Clays and Clay Minerals, 47, 697-707.
[2] Xinchao, W., Wu, Y., Stonehuerner, J.G., Dailey, L.A., Richards, J.D., Jaspers, I., Piantadosi, C.A., Ghio, A.J. (2006) Am. J. Respir. Cell. Mol. Biol., 34, 286–292.
[3] Della Ventura, G., Robert, J.-L., Hawthorne, F.C. (1996) Geochimica and Cosmochimica Acta, vol. spec. 5, 55-63.
[4] Della Ventura, G., Robert, J.-L., Raudsepp, M., Hawthorne, F.C., Welch, M. (1997) American Mineralogist, 82, 291-301.
[5] Iezzi, G., Della Ventura, G., Hawthorne, F.C., Pedrazzi, G., Robert, J.-L., Novembre, D. (2005) European Journal of Mineralogy, 17, 733-740.
[6] Iezzi, G., Della Ventura, G., Bellatreccia, F., Lo Mastro, S., Gunther, M., Bandly, (2007) Mineralogical Magazine, in press.
[7] Burns, R.G. and Strens, R.G.J. (1966) Science, 153, 890-892
The analysis of fibrous amphiboles by FTIR spectroscopy in the OH-stretching region
No full textThe mechanism through which fibrous amphiboles may give rise to mesothelioma is still not completely understood. Several factors have been taken into account, and these include the morphological aspect (length:width ratio), the chemical composition, and a variety of surface properties which are ultimately responsible for the mineral-cellule interactions (e.g. van Oss et al., 1999). Studies in vitro demonstrate that the morphology of the fiber has a strong role in determining its biological danger, because very thin and long crystallites are hardly eliminated by the alveolar macrophages. However, a second factor which seems to influence the biological attack of a fiber is its Fe content; iron can in fact be involved in complex biochemical reactions with oxygen and cause DNA damages. It follows that the rapid determination of the chemical composition of a fiber, and of its Mg/Fe ratio in particular, is extremely important in environmental studies. The direct analysis can be achieved only by micro-chemical tools such as by EDS- or WDS-equipped electron microscopes. However, these techniques are extremely expensive and often unsuitable when dealing with extremely fibrous (diameter 2+ at the OH-coordinated M(1,3) sites (Della Ventura et al. 1996, 1997, Iezzi et al. 2005, 2007). The digitized spectra were fitted by interactive optimization followed by least-squares refinement; all bands were modelled as symmetric Gaussians. Della Ventura et al. (1996, 1997) showed that the binary site-occupancies at M(1) and M(3) in the amphibole structure are related to the observed intensities of the four (A to D) components in the principal IR OH-stretching spectrum. Using the original equations of Burns and Strens (1966):
M(1,3)Mg = 3IA + 2IB + IC and M(1,3)M2+ = IB + 2IC + 3ID (with M2+ = Fe2+)
where IA-ID are the intensities measured for the corresponding A to D bands, one can derive the (Mg, M2+) site populations at M(1,3) with a high degree of confidence. This method is particularly suitable for asbestiform materials which cannot be properly characterized by EMP. The present work shows that the above spectroscopic tool can be applied to a large variety of amphibole types. For species were significant (Mg, Fe) are present at M(4) (i.e. anthophyllite –cummingtonite - grunerite) an additional information (e.g. Mössbauer) is however required for a complete characterization of the sample.
References
Burns, R.G. and Strens, R.G.J. (1966) Science, 153, 890-892.
Della Ventura, G., Robert, J.-L., Hawthorne, F.C. (1996) Geochimica and Cosmochimica Acta, vol. spec. 5, 55-63.
Della Ventura, G., Robert, J.-L., Raudsepp, M., Hawthorne, F.C., Welch, M. (1997) American Mineralogist, 82, 291-301.
Iezzi, G., Della Ventura, G., Hawthorne, F.C., Pedrazzi, G., Robert, J.-L., Novembre, D. (2005) European Journal of Mineralogy, 17, 733-740.
Iezzi, G., Della Ventura, G., Bellatreccia, F., Lo Mastro, S., Gunther, M., Bandly, (2007) Mineralogical Magazine, in press.
van Oss, C.J., Naim, J.O., Costanza, P.M., Giese, R.F. Jr., Wu, W., Sorling, A.F. (1999) Clays and Clay Minerals, 47, 697-707
Histological aspects of maxillary sinus lifting with beta-tricalcium-phosphate (CERASORB)
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A Mössbauer and FTIR study of synthetic amphiboles along the magnesio-riebeckite – ferri-clinoholmquistite join
No full textHydrochemistry and stable Isotope (2H, 18O) for groundwater hydrodynamics analysis in southern latium (Central Italy).
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Fissazione e trasferimento dell'azoto fissato dal favino al frumento duro in successione
No full textRiduzione delle lavorazioni e della concimazione azotata nell’avvicendamento biennale frumento duro-girasole nella collina marchigiana.
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