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Moelo, Y. & Biagioni, C. (2020) Contribution to the crystal chemistry of lead-antimony sulfosalts: systematic Pb-versus-Sb crossed substitution in the plagionite homologous series, Ph2N-1(Pb1-xSbx)(2) (Sb1-xPbx)(2)Sb6S13+2N. Eur. J. Mineral. 32 623–635.
Added by: Richard Baschera (2020-12-17 08:13:00) Last edited by: Richard Baschera (2020-12-17 08:15:36) |
| Type de référence: Article DOI: 10.5194/ejm-32-623-2020 Numéro d'identification (ISBN etc.): 0935-1221 Clé BibTeX: Moelo2020a Voir tous les détails bibliographiques  |
Catégories: IMN, INTERNATIONAL Mots-clés: deposit, fuloppite, massif, metals, mineralizations, zn Créateurs: Biagioni, Moelo Collection: Eur. J. Mineral. |
Consultations : 1/469
Indice de consultation : 8% Indice de popularité : 2% |
| Résumé |
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The plagionite homologous series contains four well-defined members with the general formula Pb1+2NSb8S13+2N: fliloppite (N = 1), plagionite (N = 2), heteromorphite (N = 3), and semseyite (N = 4). The crystal structure of several natural and synthetic samples of fuloppite, plagionite, and semseyite have been refined through single-crystal X-ray diffraction, confirming the systematic Pb-versus-Sb crossed substitution observed previously in semseyite and ftiloppite. This crossed substitution takes place mainly in two adjacent cation sites in the middle of the constitutive SnS-type layer. The substitution coefficient x appears variable, even for a given species, with the highest values observed in synthetic fliloppite samples. The developed structural formula of the plagionite homologues can be given as Pb2N-1(Pb1-xSbx)(2)(Sb1-xPbx)(2)Sb6S13+2N . In the studied samples, x varies between - 0.10 and 0.40. In the ribbons within the SnS-type layer, (Pb/Sb) mixing can be considered the result of the combination, in a variable ratio, of two cation sequences, i.e. (Sb-Sb-Sb)-Pb-Sb-(...), major in plagionite and semseyite, and (Sb-Sb-Sb)-Sb-Pb-(...), major in fliloppite and, probably, in heteromorphite. The published crystal structure of synthetic "Pb-free ftiloppite" is revised according to this approach. It would correspond to a Na derivative, with a proposed structural formula of (Na0.5Sb0.5)(Na0.2Sb0.8)(2)(Na0.3Sb0.7)(2)Sb6S is, ideally NaL5Sb9.5S15. In fliloppite, increasing x induces a flattening of the unit cell along c, with a slight volume decrease. Such a general Pb-versus-Sb crossed substitution would attenuate steric distortions in the middle of the SnS-type layer of the plagionite homologous series. Crystallization kinetics seem the main physical factor that controls such an isochemical substitution.
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Place: Gottingen Publisher: Copernicus Gesellschaft Mbh WOS:000592748300001
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