Segelerite from the Mount Deverell variscite deposits, Western Australia: crystal structure refinement

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Marco E. Ciriotti
Messaggi: 31675
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Segelerite from the Mount Deverell variscite deposits, Western Australia: crystal structure refinement

Messaggio da Marco E. Ciriotti » sab 12 gen, 2019 11:58

Prossima pubblicazione.

Referenza:
▪ Grey, I.E., Mumme, W.G., Downes, P.J., Grguric, B.A., Gable, R.W. (2019): Segelerite from the Mount Deverell variscite deposits, Western Australia. Hydrogen bonding and relationship to jahnsite. European Journal of Mineralogy, 31, (in press).

Abstract:
The crystal structure of segelerite, Ca2Mg2Fe3+1:4Al0.6(PO4)4(OH)2(H2O)8, from the Mount Deverell variscite deposits, Western Australia, has been refined using single-crystal X-ray data to wRobs = 0.048 for 2082 unique reflections and all H atoms were located during the refinement. Cell parameters are a = 14.7772(2) Å, b = 18.7079(2) Å, c = 7.2424(1) Å, space group Pbca. The H-bonding scheme is described and compared to that for the combinatorial polymorph, jahnsite. The crystal structures of both minerals comprise heteropolyhedral slabs of composition [XM1Fe3+2(OH)2(PO4)4], that are linked together via corner-sharing of PO4 tetrahedra with isolated [M2(Op)2(H2O)4] octahedra. The structures differ in the mode of linkage of the M2 octahedra, which is via trans Op ligands in segelerite and via both trans and cis Op ligands in jahnsite. In segelerite, X = M1 = Ca, whereas in jahnsite-group minerals, X = Ca, Na, Mn2+ and M1 = Mn2+, Mg2+, Fe2+, Fe3+. X and M1 alternate along the 7 Å axis and it is proposed that different magnitudes of rotation of the Fe3+ octahedra about the 7 Å axis to accommodate the different coordination requirements of the X and M1 cations drives the symmetry changes in the two minerals so that a strong H-bonding network is maintained.
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: 31675
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
Contatta:

Re: Segelerite from the Mount Deverell variscite deposits, Western Australia: crystal structure refinement

Messaggio da Marco E. Ciriotti » gio 07 mag, 2020 11:45

Pubblicazione avvenuta.

Referenza:
▪ Grey, I.E., Mumme, W.G., Downes, P.J., Grguric, B.A., Gable, R.W. (2019): Segelerite from the Mount Deverell variscite deposits, Western Australia. Hydrogen bonding and relationship to jahnsite. European Journal of Mineralogy, 31, 465-471.
Marco E. Ciriotti

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

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