Crystal structure of orlovite, KLi2Ti(Si4O10)(OF)

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Marco E. Ciriotti
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Crystal structure of orlovite, KLi2Ti(Si4O10)(OF)

Messaggio da Marco E. Ciriotti » lun 26 feb, 2018 11:41

Prossima pubblicazione.

Referenza:
▪ Sokolova, E., Hawthorne, F.C., Agakhanov, A.A., Pautov, L.A., Karpenko, V.Yu. (2018): The crystal structure of orlovite, KLi2Ti(Si4O10)(OF): the first example of the short-range order of Ti in true trioctahedral micas. European Journal of Mineralogy, 30, (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: 24913
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
Contatta:

Re: Crystal structure of orlovite, KLi2Ti(Si4O10)(OF)

Messaggio da Marco E. Ciriotti » sab 09 giu, 2018 16:03

Referenza:
▪ Sokolova, E., Hawthorne, F.C., Agakhanov, A.A., Pautov, L.A., Karpenko, V.Yu. (2018): The crystal structure of orlovite, KLi2Ti(Si4O10)(OF): the first example of the short-range order of Ti in true trioctahedral micas. European Journal of Mineralogy, 30, (in press).

Abstract:
The crystal structure of orlovite, ideally KLi2Ti(Si4O10)(OF), from the Darai‑Pioz alkaline massif, Tien‑Shan, Garmskii district, northern Tajikistan, was solved and refined in the space C2/m to R1 = 3.56% based on 729 independent reflections with Fo > 4σF, a = 5.198(4), b = 9.046(7), c = 10.093(8) Å, β = 99.53(2)°, V = 468.1(1.1) Å3. In the O sheet of orlovite, there are two crystallographically independent M sites: M1 and M2. In many true trioctahedral micas with space group C2/m, the M1 site corresponds to the Wyckoff position c, with multiplicity of 2 and site symmetry of 2/m. In orlovite, M1 (= Ti) atoms are displaced from the inversion centre and hence the M1 site corresponds to the Wyckoff position i, with multiplicity of 4 and site symmetry of m. The M1 site is 50% occupied primarily by Ti, ideally Ti1.00 per formula unit (pfu), with 〈M1–ϕ〉 = 1.977 Å. The two points of the M1 site occur 0.432 Å apart. Each M1 atom is coordinated by four O2 atoms, with M1–O2 = 2.009 Å and two A anions of the composition (OF); M1–A = 1.699 Å, where A ═ O and M1–A = 2.130 Å, where A = F. This is the first occurrence of short-range order of Ti in a true trioctahedral mica. The M2 site is occupied solely by Li, giving Li2 pfu, with 〈M2–ϕ〉 = 2.106 Å. In the T sheet, there is one tetrahedrally coordinated T site occupied solely by Si, 〈T–O〉 = 1.624 Å. The interstitial [12]I site is occupied primarily by K, ideally K1.00 pfu, with 〈I–O〉 = 3.075 Å. The empirical formula of orlovite was calculated on the basis of 12 (O + F), with the constraint F + OH = 1 apfu: (K0.98Rb0.03Cs0.01)1.02Li2.01(Ti0.94Nb0.02Fe0.02Al0.02)1.00Si4O10[O1.00F0.95(OH)0.05]2.00, Z = 2; Dcalc. = 2.814 g/cm3.
Marco E. Ciriotti

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