Ferri-ottoliniite and ferriwhittakerite, two end-members of the new Group 5 for monoclinic amphiboles. (Abstract/Poster in atti di convegno)

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  • Ferri-ottoliniite and ferriwhittakerite, two end-members of the new Group 5 for monoclinic amphiboles. (Abstract/Poster in atti di convegno) (literal)
Anno
  • 2003-01-01T00:00:00+01:00 (literal)
Alternative label
  • R. Oberti1, F. Cámara1, J.M. Caballero2 (2003)
    Ferri-ottoliniite and ferriwhittakerite, two end-members of the new Group 5 for monoclinic amphiboles.
    in GEOITALIA 2003. Forum Italiano di Scienze della Terra., Bellaria, 16-18 settembre 2003
    (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#autori
  • R. Oberti1, F. Cámara1, J.M. Caballero2 (literal)
Pagina inizio
  • 646 (literal)
Pagina fine
  • 647 (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#titoloVolume
  • GEOITALIA 2003, Abstracts (literal)
Note
  • Abstract (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#affiliazioni
  • 1CNR-Istituto di Geoscienze e Georisorse, Sezione di Pavia 2Departamento de Petrología y Geoquímica, Universidad Complutense de Madrid (literal)
Titolo
  • Ferri-ottoliniite and ferriwhittakerite, two end-members of the new Group 5 for monoclinic amphiboles. (literal)
Abstract
  • Recent work on metamorphosed epysienites from the Pedriza Massif (Sierra de Guadarrama, Spain) brought to the discovery of very unusual Li-rich amphibole compositions, and to the recognition that no miscibility gap is present in the solid solution between Na and Li at the B-group sites (Oberti et al., 2003). During this work, a number of new monoclinic amphibole end-members has been characterized (Caballero et al. 1998, 2002; Oberti et al. 2000, 2003), the names of which were subsequently proposed and approved by the IMA-CNMMN based on the nomenclature scheme in force (Leake et al., 1997). That scheme is implicitly based on the assumption of limited solid solution between the large (Na, Ca) and the small (Mg,Fe,Mn,Li) cations occurring at the B sites. Therefore, the latest findings brought into light some inadequacies to deal with intermediate compositions, and provoked a debate within the IMA-CNMMN and the subcommittee on amphiboles about the criteria to be followed in these cases. The conclusions are provided in a new report on amphibole nomenclature (Leake et al., in press), and mainly consist in the definition of a new group (Group 5) which includes compositions with 0.50 < B(Mg,Fe,Mn,Li)< 1.50 atoms per formula unit (apfu) and 0.50 <= B(Ca,Na) <= 1.50 apfu. Focussing on the solid-solution between Na and Li at the B sites, two amphibole compositions found in the Pedriza Massif fall close to the stoichiometric intermediate B(Na1Li1) compositions predictable for this solid solution, and thus deserved new root-names. The composition with empty A site, ideally A? B(NaLi) C(Mg3Fe3+2) Si8 O22 (OH)2, was called ferri-ottoliniite (after Luisa Ottolini, CNR-IGG, Pavia), and that with complete A-site occupancy, ideally ANa B(NaLi) C(Mg2Fe3+2Li) Si8 O22 (OH)2 was called ferriwhittakerite (after Eric J.W. Whittaker, Oxford). The mineral description of these two new amphibole end-members will be provided, together with a discussion of their main crystal-chemical features and cation ordering patterns. Merits and blemishes of the new nomenclature scheme, as well as its impact on crystal-chemical studies of amphiboles, will also be highlighted. Caballero J.M., Monge A., La Iglesia A., Tornos, F. Am. Mineral., 83, 167-171. (1998) Caballero J.M., Oberti R., Ottolini L. Am. Mineral., 87, 976-982. (2002) Oberti R., Caballero J.M., Ottolini L., López-Andrés S., Herreros V. Am. Mineral., 85, 578-585 (2000). Oberti R., Cámara F., Ottolini L., Caballero J.M. Eur. J. Mineral., 15, 309-319(2003). (literal)
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