Refinement of the crystal structure and chemical formula of selivanovaite

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Marco E. Ciriotti
Messaggi: 31675
Iscritto il: ven 25 giu, 2004 11:31
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Refinement of the crystal structure and chemical formula of selivanovaite

Messaggio da Marco E. Ciriotti » mer 25 mag, 2022 10:38

Prossima pubblicazione.

Referenza:
▪ Sokolova, E., Day, M.C., Hawthorne, F.C., Cámara, F. (2022): From structure topology to chemical Composition: XXXI. Refinement of the crystal structure and chemical formula of selivanovaite, NaFe3+Ti4(Si2O7)2O4(H2O)4, a murmanite-group (seidozerite-supergroup) TS-block mineral from the Lovozero Massif, Kola Peninsula, Russia. Canadian Mineralogist, 60, (in press).
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: Refinement of the crystal structure and chemical formula of selivanovaite

Messaggio da Marco E. Ciriotti » sab 28 mag, 2022 10:01

Pubblicazione effettuata.

Referenza:
▪ Sokolova, E., Day, M.C., Hawthorne, F.C., Cámara, F. (2022): From structure topology to chemical Composition: XXXI. Refinement of the crystal structure and chemical formula of selivanovaite, NaFe3+Ti4(Si2O7)2O4(H2O)4, a murmanite-group (seidozerite-supergroup) TS-block mineral from the Lovozero Massif, Kola Peninsula, Russia. Canadian Mineralogist, 60, 513-531.

Abstract:
Selivanovaite, ideally NaFe3+Ti4(Si2O7)2O4(H2O)4, is a murmanite-group (seidozerite supergroup) TS-block mineral from the Lovozero massif, Kola Peninsula, Russia. The crystal structure of selivanovaite was refined in space group C-1, a 10.524(6), b 13.815(6), c 12.213(14) Å, α 99.74(6), β 107.45(8), γ 90.15(10)°, V 1666.8(26) Å3, R1 = 21.40%. The previously given chemical analysis has been modified to better fit the crystal structure: Nb2O5 8.51, ZrO2 2.94, TiO2 31.96, SiO2 30.62, Al2O3 0.05, Fe2O3 5.08, FeO 3.23, MnO 3.36, CaO 2.14, MgO 0.75, Na2O 2.47, H2O 8.88, sum 99.99 wt.%; H2O was determined from structure-refinement results: H2O = 3.34 pfu, OH = 1.05 pfu. The empirical formula calculated on 22 O apfu is: (Na0.63Ca0.30Mn0.36)Σ1.29(Fe3+0.50Fe2+0.35)Σ0.85(Ti3.14Nb0.50Zr0.19Mg0.15Mn0.01Al0.01)Σ4.00Si3.99O22.00H7.73, Z = 4. The crystal structure of selivanovaite [basic structure type B1(MG)] is an array of TS blocks (Titanium Silicate) connected via hydrogen bonds. The TS block consists of HOH sheets (H = heteropolyhedral, O = octahedral) parallel to (001). In the O sheet, the Ti-dominant MO(1,2) sites, Na-dominant MO(3) site, and □-dominant MO(4) sites give ideally Na□Ti2pfu. In the H sheet, the Ti-dominant MH(1,2) sites, Fe3+-dominant AP(1) site, and vacant AP(2) sites give ideally Fe3+□Ti2pfu. The MH and AP(1) polyhedra and Si2O7 groups constitute the H sheet. The ideal structural formula of selivanovaite of the form AP2MH2MO4(Si2O7)2(XOM,A)4(XPM,A)4 is Fe3+□Ti2Na□Ti2(Si2O7)2O4(H2O)4. Selivanovaite is a Fe3+-bearing and OH-poor analogue of vigrishinite, ideally Zn□Ti2Na□Ti2(Si2O7)2O2O(OH)(H2O)4. Vigrishinite and selivanovaite are related by the following substitution: O(OH)–vig + H(Zn2+)vig ↔ O(O2–)sel + H(Fe3+)sel. Selivanovaite is a Fe3+-bearing and Na-poor analogue of murmanite, ideally Na2Ti2Na2Ti2(Si2O7)2O4(H2O)4. Murmanite and selivanovaite are related by the following substitution: O(Na+)mur + H(Na+2)mur ↔ O(□)sel + H(Fe3+)sel + H(□)sel. The doubling of the t1 and t2 translations of selivanovaite compared to those of murmanite is due to the ordering of Fe3+ and □ in the H sheet and Na and □ in the O sheet of selivanovaite.

NdR: Nonostante l'indice di raffinamento molto alto (21.40%), con una serie di aggiustamenti, il lavoro è di buona qualità e i risultati sono in linea con quelli delle specie del gruppo della murmanite.
Marco E. Ciriotti

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