Crystal-chemical aspects of the roméite group, A2Sb2O6Y, of the pyrochlore supergroup

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Marco E. Ciriotti
Messaggi: 23479
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Crystal-chemical aspects of the roméite group, A2Sb2O6Y, of the pyrochlore supergroup

Messaggio da Marco E. Ciriotti » gio 24 nov, 2016 8:53

Prossima pubblicazione.

Referenza:
▪ Bosi, F., Christy, A.G., Halenius, U. (2017): Crystal-chemical aspects of the roméite group, A2Sb2O6Y, of the pyrochlore supergroup. Mineralogical Magazine, 81, (in press).

Abstract:
Four specimens of the roméite group minerals oxyplumboroméite and fluorcalcioroméite from the Långban Mn-Fe deposit in Central Sweden were structurally and chemically characterized by single-crystal X-ray diffraction, electron microprobe analysis and infrared spectroscopy. The data obtained and those on additional roméite samples from literature show that the main structural variations within the roméite group are related to variations in the content of Pb2+, which is incorporated into the roméite structure via the substitution Pb2+ → A2+ where A2+ = Ca, Mn and Sr. Additionally, the cation occupancy at the six-fold coordinated B site, which is associated with the heterovalent substitution BFe3+ + Y → BSb5+ + YO2–, can strongly affect structural parameters. Chemical formulae of the roméite minerals group are discussed. According to crystal-chemical information, the species associated with the name “kenoplumboroméite”, hydroxycalcioroméite and fluorcalcioroméite most closely approximate endmember compositions Pb2(SbFe3+)O6vacancy, Ca2(Sb5+Ti)O6(OH) and (CaNa)Sb2O6F, respectively. However, in 33 accord with yrochlore nomenclature rules, their names correspond to multiple endmembers and are best described by the general formulae: (Pb,#)2(Sb,#)2O6vacancy, (Ca,#)2(Sb,#)2O6(OH) and (Ca,#)Sb2(O,#)6F, where “#” indicates an unspecified charge-balancing chemical substituent, including vacancies.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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Marco E. Ciriotti
Messaggi: 23479
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Re: Crystal-chemical aspects of the roméite group, A2Sb2O6Y, of the pyrochlore supergroup

Messaggio da Marco E. Ciriotti » mar 31 ott, 2017 11:46

Pubblicazione effettuata.

Referenza:
▪ Bosi, F., Christy, A.G., Halenius, U. (2017): Crystal-chemical aspects of the roméite group, A2Sb2O6Y, of the pyrochlore supergroup. Mineralogical Magazine, 81, 1287-1302.

Abstract:
Four specimens of the roméite group minerals oxyplumboroméite and fluorcalcioroméite from the Långban Mn-Fe deposit in Central Sweden were structurally and chemically characterized by single-crystal X-ray diffraction, electron microprobe analysis and infrared spectroscopy. The data obtained and those on additional roméite samples from literature show that the main structural variations within the roméite group are related to variations in the content of Pb2+, which is incorporated into the roméite structure via the substitution Pb2+ → A2+ where A2+ = Ca, Mn and Sr. Additionally, the cation occupancy at the six-fold coordinated B site, which is associated with the heterovalent substitution BFe3+ + Y → BSb5+ + YO2–, can strongly affect structural parameters. Chemical formulae of the roméite minerals group are discussed. According to crystal-chemical information, the species associated with the name “kenoplumboroméite”, hydroxycalcioroméite and fluorcalcioroméite most closely approximate endmember compositions Pb2(SbFe3+)O6vacancy, Ca2(Sb5+Ti)O6(OH) and (CaNa)Sb2O6F, respectively. However, in 33 accord with yrochlore nomenclature rules, their names correspond to multiple endmembers and are best described by the general formulae: (Pb,#)2(Sb,#)2O6vacancy, (Ca,#)2(Sb,#)2O6(OH) and (Ca,#)Sb2(O,#)6F, where “#” indicates an unspecified charge-balancing chemical substituent, including vacancies.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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