FROM STRUCTURE TOPOLOGY TO CHEMICAL COMPOSITION. XV. TITANIUM SILICATES: REVISION OF THE CRYSTAL STRUCTURE AND CHEMICAL FORMULA OF SCHÜLLERITE, Na2Ba2Mg2Ti2(Si2O7)2O2F2, FROM THE EIFEL VOLCANIC REGION, GERMANY

AbstractThe crystal structure of hejtmanite, Ba2Mn4Ti2(Si2O7)2O2(OH)2F2, from Mbolve Hill, Mkushi River area, Central Province, Zambia (holotype material) has been refined on a twinned crystal toR1= 1.88% on the basis of 4539 [|F| > 4|F|] reflections. Hejtmanite is triclinic,C1̅,a= 10.716(2),b= 13.795(3),c= 11.778 (2) , = 90.07(3), = 112.24(3), = 90.03(3),V= 1612(2)3. Chemical analysis (electron microprobe) gives: Ta2O50.09, Nb2O51.27, ZrO20.65, TiO214.35, SiO223.13, BaO 26.68, SrO 0.19, FeO 11.28, MnO 15.12, Cs2O 0.05, K2O 0.33, F 3.82, H2Ocalc. 1.63, O = F 1.61, total 97.10 wt.%, where the H2O content was calculated from the crystal-structure refinement, with (OH F) = 4 apfu. The empirical formula, calculated on the basis of 20 (O F) anions, is of the form(Si2O7)2(XO)4(XP)2, Z=4: (Ba1.82K0.07Sr0.02)Σ1.91(Mn2.33Zr0.04Mg0.03)Σ3.95(Ti1.88Nb0.10Zr0.02)Σ2(Si2.02O7)2O2[(OH)1.89F0.11]Σ2F2. The crystal structure is a combination of a TS (Titanium Silicate) block and an I (intermediate) block. The TS block consists of HOH sheets (H heteropolyhedral, O octahedral). The topology of the TS block is as in Group-II TS-block minerals: Ti ( Nb) = 2 apfu per (Si2O7)2[as defined by Sokolova (2006)]. In the O sheet, five[6]MOsites are occupied mainly by Mn, less Fe2and minor Zr and Mg, with <MOφ> = 2.198 (φ = O,OH), ideally giving Mn4apfu. In the H sheet, two[6]MHsites are occupied mainly by Ti, with <MHφ> = 1.962 (φ = O,F), ideally giving Ti2apfu; four[4]Sisites are occupied by Si, with < SiO> = 1.625 . The MHoctahedra and Si2O7groups constitute the H sheet. The two[12]Ba-dominant AP(1,2) sites, with <APφ> = 2.984 (φ = O, F), ideally give Ba2apfu. Two(1,2) and two(1,2) sites are occupied by O atoms and OH groups with minor F, respectively, ideally giving (XO)4= ()2()2=O2(OH)2pfu. Two(1,2) sites are occupied by F, giving F2apfu. TS blocks link via a layer of Ba atoms which constitute the I block. Simplified and end-member formulae of hejtmanite are Ba2(Mn,Fe2)4Ti2(Si2O7)2O2(OH,F)2F2and Ba2Mn4Ti2(Si2O7)2O2(OH)2F2,Z= 4. Hejtmanite is a Mn-analogue of bafertisite, Ba24 Ti2(Si2O7)2O2(OH)2F2.

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From structure topology to chemical composition. VI. Titanium silicates: the crystal structure and crystal chemistry of bornemanite, a group III Ti-disilicate mineral

Mineralogical Magazine ◽

10.1180/minmag.2007.071.6.593 ◽

2007 ◽

Vol 71 (06) ◽

pp. 593-610 ◽

Cited By ~ 11

Author(s):

F. Cámara ◽

E. Sokolova

Keyword(s):

Crystal Structure ◽

Chemical Composition ◽

Electron Microprobe ◽

Microprobe Analysis ◽

Electron Microprobe Analysis ◽

Titanium Silicate ◽

Group Iii ◽

Structure Topology ◽

Titanium Silicates ◽

Alkaline Massif

Abstract The crystal structure of bornemanite, ideally Na6☐BaTi2Nb(Si2O7)2(PO4)O2(OH)F, a = 5.4587(3), b = 7.1421(5), c = 24.528(2) Å, α = 96.790(1), β = 96.927(1), γ = 90.326(1)°, V = 942.4(2) Å3, space group (P1̄), Z = 2, Dcalc. = 3.342 g cm–3, from the Lovozero alkaline massif, Kola Peninsula, Russia, has been solved and refined to R1 = 6.36% on the basis of 4414 unique reflections (Fo >4sF). Electron microprobe analysis yielded the empirical formula (Na6.07Mn2+ 0.23Ca0.06☐0.64)Σ 7.00 (Ba0.73K0.13Sr0.06☐0.08)Σ 1.00(Ti2.05Nb0.80Zr0.02Ta5+ 0.01Fe3+ 0.03Al0.02Mn2+ 0.06Mg0.01)Σ 3.00(Si2O7)2(P0.97O4)O2 [F1.27(OH)0.74]Σ 2.01. The crystal structure of bornemanite is a combination of a TS (titanium silicate) block and an I (intermediate) block. The TS block consists of HOH sheets (H-heteropolyhedral, O-octahedral). The TS block exhibits linkage and stereochemistry typical for Group III (Ti = 3 a.p.f.u.) of Ti-disilicate minerals: two H sheets connect to the O sheet such that two (Si2O7) groups link to the trans edges of a Ti octahedron of the O sheet. The O sheet cations give Na3Ti (4 a.p.f.u.). The TS block has two different H sheets, H1 and H2, where (Si2O7) groups link to [5]Ti and [6]Nb polyhedra, and there are two peripheral sites which are occupied by Ba and Na, respectively. There are two I blocks: the I1 block is a layer of Ba atoms; the I2 block consists of Na polyhedra and (PO4) tetrahedra.

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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

The Canadian Mineralogist ◽

10.3749/canmin.2000066 ◽

2021 ◽

Author(s):

Elena Sokolova ◽

Maxwell C. Day ◽

Frank C. Hawthorne ◽

Atali A. Agakhanov ◽

Fernando Cámara ◽

...

Keyword(s):

Crystal Structure ◽

Chemical Composition ◽

Structure Type ◽

Titanium Silicate ◽

Space Group ◽

Structure Topology ◽

Ideal Composition ◽

Using Data ◽

Cation Sites ◽

The Ideal

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 to R1 = 2.08% on the basis of 4839 unique reflections [Fo > 4σFo]; a = 10.741(6), b = 13.841(8), c = 11.079(6) Å, α = 108.174(6), β = 99.186(6), γ = 89.99(1)°, V = 1542.7(2.7) Å3. 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 C , R1 = 2.85 %, a = 10.728(6), b = 13.845(8), c = 11.072(6) Å, α = 108.185(6), β = 99.219(5), γ = 90.001(8)°, V = 1540.0(2.5) Å3; 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).

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From structure topology to chemical composition. XXIII. Revision of the crystal structure and chemical formula of zvyaginite, Na2ZnTiNb2(Si2O7)2O2(OH)2(H2O)4, a seidozerite-supergroup mineral from the Lovozero alkaline massif, Kola peninsula, Russia

Mineralogical Magazine ◽

10.1180/minmag.2017.081.015 ◽

2017 ◽

Vol 81 (6) ◽

pp. 1533-1550 ◽

Cited By ~ 4

Author(s):

E. Sokolova ◽

A. Genovese ◽

A. Falqui ◽

F.C. Hawthorne ◽

F. Cámara

Keyword(s):

Crystal Structure ◽

Kola Peninsula ◽

Microprobe Analysis ◽

Structural Formula ◽

Chemical Formula ◽

Titanium Silicate ◽

Structure Topology ◽

Diffraction Patterns ◽

Alkaline Massif ◽

The Ideal

AbstractThe crystal structure and chemical formula of zvyaginite, ideally Na2ZnTiNb2(Si2O7)2O2(OH)2(H2O)4, a lamprophyllite-group mineral of the seidozerite supergroup from the type locality, Mt. Malyi Punkaruaiv, Lovozero alkaline massif, Kola Peninsula, Russia have been revised. The crystal structurewas refined with a new origin in space group C1, a = 10.769(2), b = 14.276(3), c = 12.101(2) Å, α = 105.45(3), β = 95.17(3), γ = 90.04(3)°, V = 1785.3(3.2) Å3, R1 = 9.23%. The electron-microprobe analysis gave the following empirical formula [calculated on 22 (O + F)]: (Na0.75Ca0.09K0.04□1.12)Σ2 (Na1.12Zn0.88Mn0.17Fe2+0.04□0.79)Σ3 (Nb1.68Ti1.25Al0.07)Σ3 (Si4.03O14)O2 [(OH)1.11F0.89]Σ2(H2O)4, Z = 4. Electron-diffraction patterns have prominent streaking along c* and HRTEM images show an intergrowth of crystalline zvyaginite with two distinct phases, both of which are partially amorphous. The crystal structure of zvyaginite is an array of TS (Titanium-Silicate) blocks connected via hydrogen bonds between H2O groups. The TS block consists of HOH sheets (H = heteropolyhedral, O = octahedral) parallel to (001). In the O sheet, the [6]MO(1,4,5) sites are occupied mainly by Ti, Zn and Na and the [6]MO(2,3) sites are occupied by Na at less than 50%. In the H sheet, the [6]MH(1,2) sites are occupied mainly by Nb and the [8]AP(1) and [8]AP(2) sites are occupied mainly by Na and □. The MH and AP polyhedra and Si2O7 groups constitute the H sheet. The ideal structural formula is Na□Nb2NaZn□Ti(Si2O7)2O2(OH)2(H2O)4. Zvyaginite is a Zn-bearing and Na-poor analogue of epistolite, ideally (Na□)Nb2Na3Ti(Si2O7)2O2(OH)2(H2O)4. Epistolite and zvyaginite are related by the following substitution in the O sheet of the TS-block: (Naþ 2 )epi↔Zn2+ zvy +□zvy. The doubling of the t1 and t2 translations of zvyaginite relative to those of epistolite is due to the order of Zn and Na along a (t1) and b (t2) in the O sheet of zvyaginite.

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