Benvenuti nell'Anagrafe della Ricerca d'Ateneo
La valutazione delle attività di ricerca che si svolgono nelle università ha assunto un'importanza rilevante sia per l'intero sistema universitario sia all'interno di ogni singolo ateneo. Roma Tre si è quindi dotata di idonei strumenti informativi in grado di supportare al meglio le azioni di monitoraggio e di valutazione delle attività di ricerca svolte nei propri dipartimentied ha realizzato una Anagrafe della Ricerca di Ateneo.
EnglishThe crystal structure of gem-quality pargasite from Soper River, near Kimmirut, Baffin Island, Nunavut, Canada, (K0.24Na0.73)(Sigma0.97) (Ca1.86Na0.14)(Sigma2.00) (Mg4.15Fe0.07Mn0.01Al0.71Ti0.06)(Sigma5.00) (Si6.45Al1.55) O-22 [(OH)(1.25)F0.63O0.122-](Sigma2.00), a 9.8814(6), b 17.967(1), c 5.2927(4) Angstrom, beta 105.263(5)degrees, V 906,5 Angstrom(3), C2/m, Z = 2, has been refined to an R index of 2.9% using 1506 observed intensities measured with MoKalpha X-radiation. The crystal used for collection of the X-ray intensity data was then analyzed with an electron microprobe. The amphibole composition is very close to that of end-member pargasite. There is significant disorder of Al over the M(2) [1.40 Mg + 0.54 Al + 0.06 Fe3+] and M(3) [0.81 Mg + 0.17 Al + 0.02 Fe2+] sites. Such disorder has been observed in Mg-rich pargasite from a high-pressure paragenesis in the western Alps. The infrared spectrum of this amphibole in the principal OH-stretching region shows a complex envelope that can be resolved into six bands by analogy with the spectra of synthetic (OH,F)-bearing pargasite in the literature. The relative intensities of the component bands are in accord with the observed OH:F ratio in this pargasite, and indicate complete short-range disorder of OH and F. The occurrence of Al-Mg disorder over M(2) and M(3) in the Soper River pargasite, from a lower-pressure environment, indicates that this disorder is a compositional feature of pargasite, rather than a result of crystallization or equilibration at high pressure and temperature. The pattern of electron density in the A cavity of the structure may be interpreted in terms of K and Na at the A(m) site and Na at the A(2) site. Moreover, the specific site-populations are conformable with the composition of this amphibole and the most favorable patterns of short-range order.
KIMBERLY T.T., HAWTHORNE F.C., & DELLA VENTURA G (2001). Al-Mg disorder in a gem-quality pargasite from Baffin Island, Nanavut, Canada. CANADIAN MINERALOGIST, 39, 1725-1732 [10.2113/gscanmin.39.6.1725].
| Titolo: | Al-Mg disorder in a gem-quality pargasite from Baffin Island, Nanavut, Canada | |
| Autori: | ||
| Data di pubblicazione: | 2001 | |
| Rivista: | ||
| Citazione: | KIMBERLY T.T., HAWTHORNE F.C., & DELLA VENTURA G (2001). Al-Mg disorder in a gem-quality pargasite from Baffin Island, Nanavut, Canada. CANADIAN MINERALOGIST, 39, 1725-1732 [10.2113/gscanmin.39.6.1725]. | |
| Abstract: | The crystal structure of gem-quality pargasite from Soper River, near Kimmirut, Baffin Island, Nunavut, Canada, (K0.24Na0.73)(Sigma0.97) (Ca1.86Na0.14)(Sigma2.00) (Mg4.15Fe0.07Mn0.01Al0.71Ti0.06)(Sigma5.00) (Si6.45Al1.55) O-22 [(OH)(1.25)F0.63O0.122-](Sigma2.00), a 9.8814(6), b 17.967(1), c 5.2927(4) Angstrom, beta 105.263(5)degrees, V 906,5 Angstrom(3), C2/m, Z = 2, has been refined to an R index of 2.9% using 1506 observed intensities measured with MoKalpha X-radiation. The crystal used for collection of the X-ray intensity data was then analyzed with an electron microprobe. The amphibole composition is very close to that of end-member pargasite. There is significant disorder of Al over the M(2) [1.40 Mg + 0.54 Al + 0.06 Fe3+] and M(3) [0.81 Mg + 0.17 Al + 0.02 Fe2+] sites. Such disorder has been observed in Mg-rich pargasite from a high-pressure paragenesis in the western Alps. The infrared spectrum of this amphibole in the principal OH-stretching region shows a complex envelope that can be resolved into six bands by analogy with the spectra of synthetic (OH,F)-bearing pargasite in the literature. The relative intensities of the component bands are in accord with the observed OH:F ratio in this pargasite, and indicate complete short-range disorder of OH and F. The occurrence of Al-Mg disorder over M(2) and M(3) in the Soper River pargasite, from a lower-pressure environment, indicates that this disorder is a compositional feature of pargasite, rather than a result of crystallization or equilibration at high pressure and temperature. The pattern of electron density in the A cavity of the structure may be interpreted in terms of K and Na at the A(m) site and Na at the A(2) site. Moreover, the specific site-populations are conformable with the composition of this amphibole and the most favorable patterns of short-range order. | |
| Handle: | http://hdl.handle.net/11590/156745 | |
| Appare nelle tipologie: | 1.1 Articolo in rivista |
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