IMA 2020-A = discreditaion of surkhobite and revised crystal structure of perraultite

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Marco E. Ciriotti
Messaggi: 31675
Iscritto il: ven 25 giu, 2004 11:31
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IMA 2020-A = discreditaion of surkhobite and revised crystal structure of perraultite

Messaggio da Marco E. Ciriotti » ven 09 ott, 2020 15:33

Prossima pubblicazione.

Referenza:
▪ Sokolova, E., Day, M., Hawthorne, F.C., Agakhanov, A.A., Cámara, F., Uvarova, Y.A., Della Ventura, G. (2021): From structure topology to chemical composition. XXIX. Revision of the crystal structure of perraultite, NaBaMn4Ti2(Si2O7)2O2(OH)2F, a seidozerite-supergroup TS-block mineral from the Oktobyabr'skii, Massif, Ukraine, and Discreditation of surkhobite. Canadian Mineralogist, 59, (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
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Re: IMA 2020-A = discreditaion of surkhobite and revised crystal structure of perraultite

Messaggio da Marco E. Ciriotti » mar 15 giu, 2021 11:30

Prossima pubblicazione.

Referenza:
▪ Sokolova, E., Day, M., Hawthorne, F.C., Agakhanov, A.A., Cámara, F., Uvarova, Y.A., Della Ventura, G. (2021): From structure topology to chemical composition. XXIX. Revision of the crystal structure of perraultite, NaBaMn4Ti2(Si2O7)2O2(OH)2F, a seidozerite-supergroup TS-block mineral from the Oktobyabr'skii, Massif, Ukraine, and Discreditation of surkhobite. Canadian Mineralogist, 59, (in press).

Abstract:
The crystal structure of perraultite from the Oktyabr’skii massif, Donetsk region, Ukraine (bafertisite group, seidozerite supergroup), ideally NaBaMn4Ti2(Si2O7)2O2(OH)2F, Z 4, was refined in space group C-1 to R-1 2.08% on the basis of 4839 unique reflections [Fo . 4rFo]; a 10.741(6), b 13.841(8), c 11.079(6)° A, alpha 108.174(6), beta 99.186(6), gamma 89.99(1)8, V 1542.7(2.7)°A3. Refinement was done using data from a crystal with three twin domains which was part of a grain used for electron probe microanalysis. In the perraultite structure [structure type B1(BG), B – basic, BG – bafertisite group], there is one type of TS (Titanium-Silicate) block and one type of I (Intermediate) block; they alternate along c. The TS block consists of HOH sheets (H – heteropolyhedral, O – octahedral). In the O sheet, the ideal composition of the five [6]MO sites is Mn4 apfu. There is no order of Mn and Fe2+ in the O sheet. The MH octahedra and Si2O7 groups constitute the H sheet. The ideal composition of the two [6]MH sites is Ti2 apfu. The TS blocks link via common vertices of MH octahedra. The I block contains AP(1,2) and BP(1,2) cation sites. The AP(1) site is occupied by Ba and the AP(2) site by K . Ba; the ideal composition of the AP(1,2) sites is Ba apfu. The BP(1) and BP(2) sites are each occupied by Na . Ca; the ideal composition of the BP(1,2) sites is Na apfu. We compare perraultite and surkhobite based on the work of Sokolova et al. (2020) on the holotype sample of surkhobite: space group C1, R1 2.85 %, a 10.728(6), b 13.845(8), c 11.072(6)° A, alpha 108.185(6), beta 99.219(5), gamma 90.001(8)8, V 1540.0(2.5)°A3; new EPMA data. We show that (1) perraultite and surkhobite have identical chemical composition and ideal formula NaBaMn4Ti2(Si2O7)2O2(OH)2F; (2) perraultite and surkhobite are isostructural, with no order of Na and Ca at the BP(1,2) sites. Perraultite was described in 1991 and has precedence over surkhobite, which was redefined as ‘‘a Ca-ordered analogue of perraultite’’ in 2008. Surkhobite is not a valid mineral species and its discreditation was approved by CNMNC IMA (IMA 20-A).
Marco E. Ciriotti

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