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.

From structure topology to chemical composition. XI. Titanium silicates: crystal structures of innelite-1T and innelite-2M from the Inagli massif, Yakutia, Russia, and the crystal chemistry of innelite

2011 ◽  
Vol 75 (4) ◽  
pp. 2495-2518 ◽  
Author(s):  
E. Sokolova ◽  
F. Cámara ◽  
F. C. Hawthorne
Keyword(s):  
Crystal Structure ◽  
Crystal Structures ◽  
Microprobe Analysis ◽  
Electron Microprobe Analysis ◽  
Structure Refinement ◽  
Titanium Silicate ◽  
Space Group ◽  
Group Iii ◽  
Structure Topology ◽  
Titanium Silicates

AbstractThe crystal structures of two polytypes of innelite, ideally Ba4Ti2Na2M2+Ti(Si2O7)2[(SO4) (PO4)]O2[O(OH)] where M2+ = Mn, Fe2+, Mg, Ca: innelite-1T, a 5.4234(9), b 7.131(1), c 14.785(3) Å, α 98.442(4), β 94.579(3), γ 90.009(4)°, V 563.7(3) Å3, space group P1̄, Dcalc = 4.028 g/cm3, Z = 1; and innelite-2M, a 5.4206(8), b 7.125(1), c 29.314(4) Å, 0 94.698(3)°, V 1128.3(2) Å3, space group P2/c, Dcalc.= 4.024 g/cm3, Z = 2, from the Inagli massif, Yakutia, Russia, have been refined to R values of 8.99 and 7.60%, respectively. Electron-microprobe analysis gave the empirical formula for innelite as (Ba3.94Sr0.06)Σ4.00(Na2.16Mn0.382+Fe2+0.17Mg0.15Ca0.10☐0.04)Σ3(Ti2.97Nb0.02Al0.02)Σ3.01Si4.01 (S1.02P0.81☐0.17)Σ2H1.84O25.79F0.21 which is equivalent to (Ba3.94Sr0.06)Σ4.00(Ti1.97Nb0.02Al0.02)Σ2.01 [(OH0.99F0.21)Σ1.20O0.80], calculated on the basis of 26 (O + F) anions, with H2O calculated from structure refinement. The crystal structure of innelite 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) and exhibits linkage and stereochemistry typical for Ti-disilicate minerals of Group III (Ti = 3 a.p.f.u.): 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 I block contains T sites, statistically occupied by S and P, and Ba atoms. In the structures of innelite-1T and innelite-2M, TS blocks are related by an inversion centre and a cy glide plane, respectively. HRTEM images show a coherent intergrowth of the two polytypes, together with an as-yet unidentified ∼10 Å phase.

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 >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.

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.

From structure topology to chemical composition.VIII. Titanium silicates: the crystal chemistry of mosandrite from type locality of Låven (Skådön), Langesundsfjorden, Larvik, Vestfold, Norway

2008 ◽  
Vol 72 (4) ◽  
pp. 887-897 ◽  
Author(s):  
E. Sokolova ◽  
F. Cámara
Keyword(s):  
Crystal Structure ◽  
Electron Microprobe ◽  
Microprobe Analysis ◽  
Electron Microprobe Analysis ◽  
Type Locality ◽  
Titanium Silicate ◽  
Structure Topology ◽  
Titanium Silicates ◽  
And Topology ◽  
Group I

AbstractThe crystal structure of mosandrite, ideally Na2Ca4REETi(Si2O7)2OF3, a = 7.4184(8), b = 5.6789(6), c = 18.873(2) Å, β = 101.410(2)°, V = 779.35(5) Å3, space group P21/c, Z = 2, Dcalc = 3.363 g.cm-3, from the type locality, Låven (Skådön), Langesundsfjorden, Larvik, Vestfold, Norway, has been refined to Ri = 6.33% on the basis of 1113 unique reflections F°≥4σF. Electron microprobe analysis gave the empirical formula Na1.99(Ca3.93Sr0.02)Σ3.95(Ce0.41La0.16Nd0.13Pr0.04Sm0.02Dy0.01Y0.13)Σ0.90 (Ti0.864+Nb0.08Zr0.05)Σ0.99(Si207)2(F1.20O0.80)Σ2.00F2, Z = 2, calculated on the basis of 18 (O + F) a.p.f.u.. The crystal structure of mosandrite is a framework of TS (titanium silicate) blocks. The TS block consists of HOH sheets (H-heteropolyhedral, O-octahedral). The TS block in mosandrite exhibits linkage and stereochemistry typical for Group I (Ti = 1 a.p.f.u.) Ti-disilicate minerals: two H sheets connect to the O sheet such that two (Si2O7) groups link to the trans edges of a Na polyhedron of the O sheet. The O sheet cations give Na(NaCa)Ti (4 a.p.f.u.). The TS blocks link via common vertices of (Si2O7) groups and common vertices and edges of Ca-dominant MH and Ap polyhedra. Two adjacent TS blocks are related by the glide plane cy. Composition and topology of the TS block in mosandrite and rinkite are identical. The crystal structure of mosandrite from the type locality is topologically and chemically identical to that of rinkite from the type locality of Kangerdluarssuk, Greenland.

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. 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.

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.

From structure topology to chemical composition. XIV. Titanium silicates: refinement of the crystal structure and revision of the chemical formula of mosandrite, (Ca3REE)[(H2O)2Ca0.5□0.5]Ti(Si2O7)2(OH)2(H2O)2, a Group-I mineral from the Saga mine, Morje, Porsgrunn, Norway

2013 ◽  
Vol 77 (6) ◽  
pp. 2753-2771 ◽  
Author(s):  
E. Sokolova ◽  
F. C. Hawthorne
Keyword(s):  
Crystal Structure ◽  
Long Range ◽  
Structure Refinement ◽  
Alkali Cations ◽  
Oh Groups ◽  
Structure Topology ◽  
Titanium Silicates ◽  
Group I ◽  
Ideal Composition ◽  
Cation Sites

AbstractThe crystal structure of mosandrite, ideally (Ca3REE)[(H2O)2Ca0.5☐0.5]Ti(Si2O7)2(OH)2(H2O)2, from the Saga mine, Morje, Porsgrunn, Norway, has been refined as two components related by the TWIN matrix ( 0 0, 0 0, 1 0 1): a 7.4222(3), b 5.6178(2), c 18.7232(7) Å, β 101.4226(6)°, V = 765.23(9) Å3, space group P21/c, Dcalc. = 3.361 g.cm–3, R1 = 3.69% using 1347 observed (Fo > 4σF) reflections. The empirical formula of mosandrite (EMPA) was calculated on the basis of 4 Si a.p.f.u., with H2O determined from structure refinement: [(Ca2.89Ba0.01)Σ2.90(Ce0.39La0.18Nd0.14Sm0.02Gd0.03Y0.16Th0.03)Σ1.01Zr0.09]Σ4 [(H2O)2.00Ca0.32Na0.17Al0.10Mn0.04Fe2+0.02☐0.35]Σ3(Ti0.87Nb0.09Zr0.04)Σ1(Si2O7)2[(OH)1.54F0.46]Σ2[(H2O)1.50F0.50]Σ2, Z = 2. The crystal structure of mosandrite is a framework of TS (titanium silicate) blocks; each TS block consists of HOH sheets (H-heteropolyhedral, O-octahedral). In the TS block, there are five fully occupied cation sites, two [4]-coordinated Si sites with <Si–O> 1.623 Å , [7]-coordinated MH and AP sites occupied by Ca and REE in the ratio ∼3:1, and one [6]-coordinated Ti-dominant MO(1) site. There are two H2O-dominant H2O-alkali-cation sites. The partly occupied MO(2) site has composition [(H2O)0.5☐0.33Na0.17], ideally [(H2O)0.5☐0.5] p.f.u. The MO(3) site has ideal composition [(H2O)1.5Ca0.5] p.f.u. In the O sheet, the XOM and XOA anion sites have compositions [(OH)1.54F0.46] (XOM) and [(H2O)1.50F0.50] (XOA), ideally (OH)2 and (H2O)2 p.f.u. The MH and AP polyhedra and Si2O7 groups constitute the H sheet that is completely ordered. In the O sheet, MO(1) octahedra are long-range ordered whereas H2O and OH groups and alkali cations Na and Ca are long-range disordered. Two SRO (short-range ordered) arrangements have been proposed for the O sheet: (1) Na [MO(2)], Ca2 [MO(3)] and F4[XOM and XOA anion sites]; (2) 2 H2O [MO(2)] and MO(3)] and (OH)2 and (H2O)2 [XOM and XOA]. Linkage of H and O sheets occurs mainly via common vertices of MH polyhedra and Si2O7 groups and MO(1) octahedra. Two adjacent TS blocks are related by the glide plane cy. Mosandrite is an H2O- and OH-bearing Na- and Ca-depleted analogue of rinkite, ideally (Ca3REE)Na(NaCa) Ti(Si2O7)2(OF)F2. Mosandrite and rinkite are related by the following substitution at the MO(2,3) and XO(M,A) sites in the O sheet: M[(H2O)2 + ☐0.5] + X[(OH)–2 + (H2O)2] ↔ M[Na+2 + Ca2+0.5] + X[(OF)3– + (F2)2–].

Magnesio-riebeckite from the Varenche mine (Aosta Valley, Italy): crystal-chemical characterization of a grandfathered end-member

2017 ◽  
Vol 81 (6) ◽  
pp. 1431-1437 ◽  
Author(s):  
Roberta Oberti ◽  
Massimo Boiocchi ◽  
Frank C. Hawthorne ◽  
Marco E. Ciriotti
Keyword(s):  
Crystal Structure ◽  
Microprobe Analysis ◽  
Electron Microprobe Analysis ◽  
Structure Refinement ◽  
Chemical Characterization ◽  
Unit Cell Parameters ◽  
X Ray ◽  
Cell Parameters ◽  
D Values

AbstractMagnesio-riebeckite from the dumps of the abandoned mine of Varenche (45°47’22’’ N, 7°29’17’’ E), Saint-Barthélemy, Nus, Aosta Valley (Italy), was studied to provide the complete mineral description (including crystal structure) and insights into the crystal-chemistry of riebeckite. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement is A(Na0.09K0.01)Σ=0.10B(Na1.77Ca0.11Mg0.08Mn2+ 0:04)Σ=2.00C(Mg2.93Mn2+0:13Fe2+0:07Zn0.01Ni0.12Fe3+1:25Al0.48Ti0.01)Σ=5.00T(Si7.92Al0.08)Σ=8.00 O22W(OH1.88F0.12)Σ=2.00. Magnesio-riebeckite is biaxial (+), with α = 1.678(2), β = 1.682(2), γ = 1.688(2) and 2V (meas.) = 80.2(1.7)°, 2V (calc.) = 78.7°. The unit-cell parameters are a = 9.6481(14), b = 17.873(3), c = 5.3013(7) Å, β = 103.630(2)°, V = 888.4 (2)Å3, Z = 2, space group C2/m. The strongest ten reflections in the powder X-ray pattern [d values (in Å), I, (hkl)] are: 2.701, 100, (151); 8.303, 83, (110); 3.079, 62, (310); 3.391, 53, (131); 4.467, 50, (040,021); 2.522, 50, (̅202); 2.578, 35, (061); 2.155, 30, (261), 4.855, 30, (̅111), 2.300, 29, (̅351).

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