From structure topology to chemical composition. XXVI. Crystal structure and chemical composition of a possible new mineral of the murmanite group (seidozerite supergroup), ideally Na2CaTi4(Si2O7)2O4(H2O)4, from the Lovozero alkaline massif, Kola Peninsula, Russia

2018 ◽  
Vol 83 (02) ◽  
pp. 199-207
Author(s):  
Elena Sokolova ◽  
Frank C. Hawthorne
Keyword(s):  
Crystal Structure ◽  
Chemical Composition ◽  
Kola Peninsula ◽  
Structure Refinement ◽  
Structural Formula ◽  
New Mineral ◽  
Titanium Silicate ◽  
Structure Topology ◽  
Alkaline Massif ◽  
The Ideal

AbstractThe crystal structure of a murmanite-related mineral (MRM) of the murmanite group (seidozerite supergroup), ideally Na2CaTi4(Si2O7)2O4(H2O)4, from Mt. Pyalkimpor, the Lovozero alkaline massif, Kola Peninsula, Russia, was refined in space group P$ {\bar 1} $ with a = 5.363(2), b = 7.071(2), c = 12.176(5) Å, α = 92.724(3), β = 107.542(7), γ = 90.13(2)°, V = 439.7(4) Å3 and R1 = 5.72%. On the basis of electron-microprobe analysis, the empirical formula calculated on 22 (O + F), with two constraints derived from structure refinement, OH = 0.11 per formula unit (pfu) and H2O = 3.89 pfu, is (Na2.12K0.07Sr0.01)Σ2.20Ca0.85(Ti3.01Nb0.39Mn0.20Fe2+0.19Mg0.17Zr0.01Al0.01)Σ3.98(Si4.20O14)[O3.90F0.10]Σ4[(H2O)3.89(OH)0.11]Σ4{P0.03}, with Z = 1. It seems unlikely that {P0.03} belongs to MRM itself. The crystal structure of MRM 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 MO1 site and Ca-dominant MO2 site give ideally (Ca□)Ti2 pfu. In the H sheet, the Ti-dominant MH site and Na-dominant AP site give ideally Na2Ti2 pfu. The MH and AP polyhedra and Si2O7 groups constitute the H sheet. The ideal structural formula of MRM of the form AP2MH2MO4(Si2O7)2(XOM,A)4(XOA)2(XPM,A)4 is Na2Ti2(Ca□)Ti2(Si2O7)2O4(H2O)4. MRM is a Ca-rich and Na-poor analogue of murmanite, ideally Na2Ti2Na2Ti2(Si2O7)2O4(H2O)4 and a Na-rich and (OH)-poor analogue of calciomurmanite, ideally (Ca□)Ti2(Na□)Ti2(Si2O7)2O2[O(OH)](H2O)4. MRM and (murmanite and calciomurmanite) are related by the following substitutions: O(Ca2+□)MRM ↔ O(Na+2)mur and O(Ca2+□)MRM + H(Na+2)MRM + O(O2–)MRM ↔ O(Na+□)cal + H(Ca2+□)cal + O[(OH)–]cal. MRM is a possible new mineral of the murmanite group (seidozerite supergroup) where Ti + Mn + Mg = 4 apfu.

From structure topology to chemical composition. XXIV. Revision of the crystal structure and chemical formula of vigrishinite, NaZnTi4(Si2O7)2O3(OH)(H2O)4, a seidozerite-supergroup mineral from the Lovozero alkaline massif, Kola peninsula, Russia

2018 ◽  
Vol 82 (4) ◽  
pp. 787-807 ◽  
Author(s):  
Elena Sokolova ◽  
Frank C. Hawthorne
Keyword(s):  
Crystal Structure ◽  
Kola Peninsula ◽  
Microprobe Analysis ◽  
Electron Microprobe Analysis ◽  
Structure Refinement ◽  
Structural Formula ◽  
Titanium Silicate ◽  
Structure Topology ◽  
Alkaline Massif ◽  
The Ideal

ABSTRACTThe crystal structure of vigrishinite, ideally NaZnTi4(Si2O7)2O3(OH)(H2O)4, a murmanite-group mineral of the seidozerite supergroup from the type locality, Mt. Malyi Punkaruaiv, Lovozero alkaline massif, Kola Peninsula, Russia, was refined in space group C$\bar 1$, a = 10.530(2), b = 13.833(3), c = 11.659(2) Å, α = 94.34(3), β = 98.30(3), γ = 89.80(3)°, V = 1675.5(2.1) Å3 and R1 = 12.52%. Based on electron-microprobe analysis, the empirical formula calculated on 22 (O + F), with two constraints derived from structure refinement, OH + F = 1.96 pfu and H2O = 3.44 pfu, is: (Na0.67Zn0.21Ca0.05□1.07)Σ2 (Zn0.86□1.14)Σ2(Zn0.14□0.36)Σ0.5(Ti2.60Nb0.62Mn0.30${\rm Fe}_{{\rm 0}{\rm. 23}}^{{\rm 2 +}} $Mg0.10Zr0.06Zn0.05Al0.03Ta0.01)Σ4(Si4.02O14) [O2.60(OH)1.21F0.19]Σ4[(H2O)3.44(OH)0.56]Σ4{Zn0.24P0.03K0.03Ba0.02} with Z = 4. It seems unlikely that constituents in the {} belong to vigrishinite itself. The crystal structure of vigrishinite is an array of TS blocks (Titanium Silicate) connected via hydrogen bonds. The TS block consists of HOH sheets (H = heteropolyhedral and O = octahedral) parallel to (001). In the O sheet, the Ti-dominant MO(1,2) sites, Na-dominant MO(3) and □-dominant MO(4) sites give ideally Na□Ti2 pfu. In the H sheet, the Ti-dominant MH(1,2) sites, Zn-dominant AP(1) and vacant AP(2) sites give ideally Zn□Ti2 pfu. The MH and AP(1) polyhedra and Si2O7 groups constitute the H sheet. The ideal structural formula of vigrishinite of the form ${\rm A}_{\rm 2}^{P} {\rm M}_{\rm 2}^{\rm H} {\rm M}_{\rm 4}^{\rm O} $(Si2O7)2(${\rm X}_{\rm M}^{\rm O} $)2(${\rm X}_{\rm A}^{\rm O} $)2(${\rm X}_{{\rm M,A}}^{P} $)4 is Zn□Ti2Na□Ti2(Si2O7)2O2O(OH)(H2O)4. Vigrishinite is a Zn-bearing, Na-poor and OH-rich analogue of murmanite, ideally Na2Ti2Na2Ti2(Si2O7)2O2O2(H2O)4. Murmanite and vigrishinite are related by the following substitution: H(${\rm Na}_{\rm 2}^{\rm +} $)mur + O(Na+)mur + O(O2–)mur ↔ H(Zn2+)vig + H(□)vig + O(□)vig + O[(OH)–]vig. The doubling of the t1 and t2 translations of vigrishinite compared to those of murmanite is due to the order of Zn and □ in the H sheet and Na and □ in the O sheet of vigrishinite.

scholarly journals 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

2017 ◽  
Vol 81 (6) ◽  
pp. 1533-1550 ◽  
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.

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

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).

scholarly journals From structure topology to chemical composition. X. Titanium silicates: the crystal structure and crystal chemistry of nechelyustovite, a group III Ti-disilicate mineral

2009 ◽  
Vol 73 (5) ◽  
pp. 753-775 ◽  
Author(s):  
F. Cámaraite ◽  
E. Sokolova
Keyword(s):  
Crystal Structure ◽  
Microprobe Analysis ◽  
Electron Microprobe Analysis ◽  
Structure Refinement ◽  
Titanium Silicate ◽  
Group Iii ◽  
Structure Topology ◽  
Titanium Silicates ◽  
Peripheral Site ◽  
Alkaline Massif

AbstractThe crystal structure of nechelyustovite, ideally Na4Ba2Mn1.5☐2.5Ti5Nb(Si2O7)4O4(OH)3F(H2O)6, a 5.447(1) Å, b 7.157(1) Å, c 47.259(9) Å, α 95.759(4)°, β 92.136(4)°, γ 89.978(4)°, V 1831.7(4) Å3, space group P, Z = 2, Dcalc. 3.041 g cm–3, from Lovozero alkaline massif, Kola Peninsula, Russia, has been solved and refined to R1 = 13.9% on the basis of 1745 unique reflections (Fo > 15σF). Electron microprobe analysis yielded the empirical formula (H20)6.01, Z = 2, calculated on the basis of 42 (O + F) a.p.f.u., H2O and OH are calculated from structure refinement (H2O = 6 p.f.u.; F + OH = 4 p.f.u.). The crystal structure of nechelyustovite 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. There are two distinct TS blocks of the same topology, TS1 and TS2, that differ in the cations of the O sheet, [(Na1.5Mn1☐0.5)Ti] and [(Na2Mn0.5☐0.5)Ti] (4 a.p.f.u.) respectively. The TS1 and TS2 blocks have two different H sheets, H1,2 and H3,4, where (Si2O7) groups link to [5]- and [6]-coordinated (Ti,Nb) polyhedra respectively. There are three peripheral sites, AP(1—3), occupied mainly by Ba (less Sr and K) at 96, 86 and 26% and one peripheral site AP(4) occupied by Na at 50%. There are two I blocks: the I1 block is a layer of Ba atoms; the I2 block consists of H2O groups and AP(3) atoms. TS blocks alternate with I blocks or link through hydrogen bonds (as in epistolite). There is a sequence of four TS blocks and three I blocks per the c cell parameter: TS2 — I1 — TS1 — I2 — TS1 — I1 — TS2.

scholarly journals From structure topology to chemical composition. XX. Titanium silicates: the crystal structure of hejtmanite, Ba2Mn4Ti2(Si2O7)2O2(OH)2F2, a Group-II TS-block mineral

2016 ◽  
Vol 80 (5) ◽  
pp. 841-853 ◽  
Author(s):  
E. Sokolova ◽  
F. Cámara ◽  
F. C. Hawthorne ◽  
L. A. Pautov
Keyword(s):  
Crystal Structure ◽  
Chemical Composition ◽  
Structure Refinement ◽  
Central Province ◽  
Crystal Structure Refinement ◽  
Titanium Silicate ◽  
Oh Groups ◽  
Structure Topology ◽  
Titanium Silicates ◽  
Group Ii

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.

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

2007 ◽  
Vol 71 (06) ◽  
pp. 593-610 ◽  
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 &gt;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.

scholarly journals Fogoite-(Y), Na3Ca2Y2Ti(Si2O7)2OF3, a Group I TS-block mineral from the Lagoa do Fogo, the Fogo volcano, São Miguel Island, the Azores: Description and crystal structure

2017 ◽  
Vol 81 (2) ◽  
pp. 369-381 ◽  
Author(s):  
F. Cámara ◽  
E. Sokolova ◽  
Y. A. Abdu ◽  
F. C. Hawthorne ◽  
T. Charrier ◽  
...  
Keyword(s):  
Crystal Structure ◽  
New Mineral ◽  
X Ray Diffraction ◽  
Titanium Silicate ◽  
Triclinic Space Group ◽  
X Ray ◽  
Group I ◽  
Mohs Hardness ◽  
Fogo Volcano ◽  
The Ideal

AbstractFogoite-(Y), Na3Ca2Y2Ti(Si2O7)2OF3, is a new mineral from the Lagoa do Fogo, São Miguel Island, the Azores. It occurs in cavities as highly elongated (on [001]) prisms, up to 2000 μm long and 50 μm× 50 μm in cross-section, associated with sanidine, astrophyllite, fluornatropyrochlore, ferrokentbrooksite, quartz and ferro-katophorite. Crystals are generally transparent and colourless, with vitreous lustre, occasionally creamy white. Fogoite-(Y) has a white streak, splintery fracture and very good {100} cleavage. Mohs hardness is ∼5. Dcalc. = 3.523 g/cm3. It is biaxial (+) with refractive indices (λ = 590 nm) α = 1.686(2), β = 1.690(2), γ = 1.702(5); 2Vmeas. = 57(1)° and 2Vcalc. = 60°. It is nonpleochroic. Fogoite-(Y) is triclinic, space group P1, a = 9.575(6), b = 5.685(4), c = 7.279(5) Å, α = 89.985(6), β = 100.933(4), γ = 101.300(5)°, V = 381.2 (7) Å3. The six strongest reflections in the powder X-ray diffraction data [d (Å), I, (hkl)] are: 2.954, 100, (1̄1̄2, 3̄10); 3.069, 42, (300, 01̄2); 2.486, 24, (310, 21̄2); 3.960, 23, (1̄1̄1, 2̄10); 2.626, 21, (2̄20); 1.820, 20, (1̄04). Electron microprobe analysis gave the following empirical formula calculated on 18 (O + F) (Na2.74Mn0.15)∑2.89Ca2[Y1.21(La0.01Ce0.03Nd0.03Sm0.02Gd0.08Dy0.08Er0.05Yb0.04Lu0.01)∑0.35Mn0.16Zr0.11Na0.09Fe0.072+Ca0.01]∑2(Ti0.76Nb0.23Ta0.01)∑1(Si4.03O14)O1.12F2.88, Z = 1. The crystal structure was refined on a twinnedcrystal to R1 = 2.81% on the basis of 2157 unique reflections (Fo > 4σFo) and is a framework of TS (Titanium Silicate) blocks, which consist of HOH sheets (H – heteropolyhedral, O – octahedral) parallel to (100). In the O sheet, the the [6]MO(1) site is occupied mainly by Ti, <MO(1)–ϕ> = 1.980 Å, and the [6]MO(2) and [6]MO(3) sites are occupied by Na and Na plus minor Mn, <MO(2)–ϕ>= 2.490 Å and <MO(3)–ϕ> = 2.378 Å. In the H sheet, the two [4]Si sites are occupied by Si, with <Si–O> = 1.623 Å; the [6]MH site is occupied by Y and rare-earth elements (Y > REE), with minor Mn, Zr, Na, Fe2+ and Ca, <MH–ϕ> = 2.271 Å and the [6]AP site is occupied by Ca, <AP–ϕ> = 2.416 Å. The MH and AP octahedra and Si2O7 groups constitute the H sheet. The ideal compositions of the O and two H sheets are Na3Ti(OF)F2 and Y2Ca2(Si2O7)2 apfu. Fogoite-(Y) is isostructural with götzenite and hainite. The mineral is named after the type locality, the Fogo volcano in the Azores.

Alumoåkermanite, (Ca,Na)2(Al,Mg,Fe2+)(Si2O7), a new mineral from the active carbonatite-nephelinite-phonolite volcano Oldoinyo Lengai, northern Tanzania

2009 ◽  
Vol 73 (3) ◽  
pp. 373-384 ◽  
Author(s):  
D. Wiedenmann ◽  
A. N. Zaitsev ◽  
S. N. Britvin ◽  
S. V. Krivovichev ◽  
J. Keller
Keyword(s):  
Crystal Structure ◽  
Structure Refinement ◽  
New Mineral ◽  
Crystal Structure Refinement ◽  
Chemical Formula ◽  
Oldoinyo Lengai ◽  
Structure Topology ◽  
Northern Tanzania ◽  
Mohs Hardness ◽  
Measured Density

AbstractAlumoåkermanite, (Ca,Na)2(Al,Mg,Fe2+)(Si2O7), is a new mineral member of the melilite group from the active carbonatite-nephelinite-phonolite volcano Oldoinyo Lengai, Tanzania. The mineral occurs as tabular phenocrysts and microphenocrysts in melilite-nephelinitic ashes and lapilli-tuffs. Alumoåkermanite is light brown in colour; it is transparent, with a vitreous lustre and the streak is white. Cleavages or partings are not observed. The mineral is brittle with an uneven fracture. The measured density is 2.96(2) g/cm3. The Mohs hardness is ~4.5–6. Alumoåkermanite is uniaxial (–) with ω = 1.635(1) and ε = 1.624–1.626(1). In a 30 mm thin section (+N), the mineral has a yellow to orange interference colour, straight extinction and positive elongation, and is nonpleochroic. The average chemical formula of the mineral derived from electron microprobe analyses is: (Ca1.48Na0.50Sr0.02 K0.01)(Si1.99Al0.01O7). Alumoåkermanite is tetragonal, space group P421m with a = 7.7661(4) Å, c = 5.0297(4) Å, V = 303.4(1) Å3 and Z = 2. The five strongest powder-diffraction lines [d in Å, (I/Io), hkl] are: 3.712, (13), (111); 3.075, (25), (201); 2.859, (100), (211); 2.456, (32), (311); 1.757, (19), (312). Single-crystal structure refinement (R1 = 0.018) revealed structure topology typical of the melilite-group minerals, i.e. tetrahedral [(Al,Mg)(Si2O7)] sheets interleaved with layers of (CaNa) cations. The name reflects the chemical composition of the mineral.

scholarly journals Lobanovite, K2Na(Fe42+Mg2Na)Ti2(Si4O12)2O2(OH)4, a new mineral of the astrophyllite supergroup and its relation to magnesioastrophyllite

2017 ◽  
Vol 81 (1) ◽  
pp. 175-181 ◽  
Author(s):  
Elena Sokolova ◽  
Fernando Cámara ◽  
Frank C. Hawthorne ◽  
Evgeny I. Semenov ◽  
Marco E. Ciriotti
Keyword(s):  
Kola Peninsula ◽  
Structure Refinement ◽  
New Mineral ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
International Mineralogical Association ◽  
Orange Colour ◽  
Alkaline Massif ◽  
Khibiny Alkaline Massif

AbstractLobanovite, K2Na(Fe42+Mg2Na)Ti2(Si4O12)2O2(OH)4, is a new mineral of the astrophyllite supergroup from Mt. Yukspor, the Khibiny alkaline massif, Kola Peninsula Russia. It has been known previously under the following names: monoclinic astrophyllite, magnesium astrophyllite, magnesiumastrophyllite and magnesioastrophyllite but has never been formally proposed and approved as a valid mineral species by the Commission on new Minerals, Nomenclature and Classification of the International Mineralogical Association. It has now been revalidated and named lobanovite after Dr. Konstantin V. Lobanov, a prominent Russian ore geologist who worked in the Kola Peninsula for more than forty years (Nomenclature voting proposal 15-B). Lobanovite has been described from pegmatitic cavities on Mt. Yukspor where it occurs as elongated bladed crystals, up to 0.04 mm wide and 0.2 mm long, with a straw yellow to orange colour. Associated minerals are shcherbakovite, lamprophyllite, delindeite, wadeite, umbite and kostylevite. Lobanovite is biaxial (–) with refractive indices (λ = 589 nm) α = 1.658, βcalc. = 1.687, γ = 1.710; 2Vmeas. = 81.5– 83°. Lobanovite is monoclinic, space group C2/m, a = 5.3327(2), b = 23.1535(9), c = 10.3775(4) Å, β = 99.615(1)°, V = 1263.3 (1) Å 3, Z = 2. The six strongest reflections in the powder X-ray diffraction data [d (Å), I, (hkl)] are: 3.38, 100, (003); 2.548, 90, (063); 10.1, 80, (001); 3.80, 60, (042,131); 3.079, 50, (132,062); 2.763, 90, (1̄71). The chemical composition of lobanovite was determined by electron-microprobe analysis and the empirical formula (K1.97Ba0.01)∑1.98(Na0.65Ca0.14)∑0.79 (Fe3.182+Mg2.02Na1.00Mn0.72)∑6.92(Ti1.99Nb0.06)∑2.05[(Si8.01Al0.06)∑8.07O24]O2(OH)4.03F0.19 was calculated on the basis of 30.2 (O + OH + F) anions, with H2O calculated from structure refinement, Dcalc. = 3.161 g cm–3. In the structure of lobanovite, the main structural unit is the HOH block, which consists of one close-packed O (Octahedral) and two H (Heteropolyhedral) sheets. The M(1–4) octahedra form the O sheet and the T4O12 astrophyllite ribbons and [5]-coordinated Ti-dominant D polyhedra link through common vertices to form the H sheet. The HOH blocks repeat along [001], and K and Na atoms occur at the interstitial A and B sites. The simplified and end-member formulae of lobanovite are K2Na [(Fe2+,Mn)4Mg2Na]Ti2(Si4O12)2O2(OH)4 and K2Na(Fe42+Mg2Na)Ti2(Si4O12)2O2(OH)4, respectively.

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