The crystal structure of perraultite from the Oktyabr'skii massif, Donetsk region, Ukraine (bafertisite group, seidozerite supergroup), ideally NaBaMn4Ti2(Si2O7)(2)O-2(OH)(2)F, Z = 4, was refined in space group C (1) over bar to R-1 = 2.08% on the basis of 4839 unique reflections [F-o > 4 sigma F-o]; a = 10.741(6), b = 13.841(8), c = 11.079(6) angstrom, alpha = 108.174(6), beta = 99.186(6), gamma = 89.99(1)degrees, V = 1542.7(2.7) angstrom(3). 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 M-[6](O) sites is Mn-4 apfu. There is no order of Mn and Fe2+ in the O sheet. The M-H octahedra and Si2O7 groups constitute the H sheet. The ideal composition of the two M-[6](H) sites is Ti-2 apfu. The TS blocks link via common vertices of M-H octahedra. The I block contains A(P)(1,2) and B-P(1,2) cation sites. The A(P)(1) site is occupied by Ba and the A(P)(2) site by K > Ba; the ideal composition of the A(P)(1,2) sites is Ba apfu. The B-P(1) and B-P(2) sites are each occupied by Na > Ca; the ideal composition of the B-P(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 C (1) over bar, R-1 = 2.85 %, a = 10.728(6), b = 13.845(8), c = 11.072(6) angstrom, alpha = 108.185(6), beta = 99.219(5), gamma = 90.001(8)8, V = 1540.0(2.5) angstrom(3); new EPMA data. We show that (1) perraultite and surkhobite have identical chemical composition and ideal formula NaBaMn4Ti2(Si2O7)(2)O-2(OH)(2)F; (2) perraultite and surkhobite are isostructural, with no order of Na and Ca at the B-P(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).

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 Oktyabr'skii Massif, Ukraine, and Discreditation of Surkhobite / E. Sokolova, M.C. Day, F.C. Hawthorne, A.A. Agakhanov, F. Cámara, Y.A. Uvarova, G. Della Ventura. - In: CANADIAN MINERALOGIST. - ISSN 0008-4476. - 59:2(2021), pp. 365-379. [10.3749/canmin.2000066]

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 Oktyabr'skii Massif, Ukraine, and Discreditation of Surkhobite

F. Cámara;
2021

Abstract

The crystal structure of perraultite from the Oktyabr'skii massif, Donetsk region, Ukraine (bafertisite group, seidozerite supergroup), ideally NaBaMn4Ti2(Si2O7)(2)O-2(OH)(2)F, Z = 4, was refined in space group C (1) over bar to R-1 = 2.08% on the basis of 4839 unique reflections [F-o > 4 sigma F-o]; a = 10.741(6), b = 13.841(8), c = 11.079(6) angstrom, alpha = 108.174(6), beta = 99.186(6), gamma = 89.99(1)degrees, V = 1542.7(2.7) angstrom(3). 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 M-[6](O) sites is Mn-4 apfu. There is no order of Mn and Fe2+ in the O sheet. The M-H octahedra and Si2O7 groups constitute the H sheet. The ideal composition of the two M-[6](H) sites is Ti-2 apfu. The TS blocks link via common vertices of M-H octahedra. The I block contains A(P)(1,2) and B-P(1,2) cation sites. The A(P)(1) site is occupied by Ba and the A(P)(2) site by K > Ba; the ideal composition of the A(P)(1,2) sites is Ba apfu. The B-P(1) and B-P(2) sites are each occupied by Na > Ca; the ideal composition of the B-P(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 C (1) over bar, R-1 = 2.85 %, a = 10.728(6), b = 13.845(8), c = 11.072(6) angstrom, alpha = 108.185(6), beta = 99.219(5), gamma = 90.001(8)8, V = 1540.0(2.5) angstrom(3); new EPMA data. We show that (1) perraultite and surkhobite have identical chemical composition and ideal formula NaBaMn4Ti2(Si2O7)(2)O-2(OH)(2)F; (2) perraultite and surkhobite are isostructural, with no order of Na and Ca at the B-P(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).
Bafertisite group; Crystal-structure refinement; Discreditation of surkhobite; Electron probe microanalysis; Perraultite; Seidozerite supergroup; TS block
Settore GEO/06 - Mineralogia
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/2434/862199
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