Fernando Cámara

From structure topology to chemical composition. IX. Titanium silicates : revision of the crystal chemistry of lomonosovite and murmanite, Group-IV minerals

Abstract The crystal structures of lomonosovite, ideally Na10Ti4(Si2O7)2(PO4)2 O4, a = 5.4170(7) Å, b = 7.1190(9) Å, c = 14.487(2) Å, α = 99.957(3)º, β = 96.711(3)º, γ = 90.360(3)º, V = 546.28(4) Å3, Dcalc. = 3.175 g cm-3, and murmanite, ideally Na4Ti4(Si2O7)2O4(H2O)4, a = 5.3875(6) Å, b = 7.0579(7) Å, c = 12.176(1) Å, α = 93.511(2)º, β = 107.943(4)º, γ = 90.093(2)º, V = 439.55(2) Å3, Dcalc. = 2.956 g.cm-3, from the Lovozero alkaline massif, Kola Peninsula, Russia, have been refined in the space group P1̅ (Z = 1) to R values of 2.64 and 4.47%, respectively, using 4572 and 2222 observed |Fo ≥ 4σF| reflections collected with a single-crystal Bruker AXS SMART APEX diffractometer with a CCD detector and Mo-Kα radiation. Electron microprobe analysis gave empirical formulae for lomonosovite (Na9.50Mn0.16Ca0.11)∑9.77(Ti2.834+Nb0.51Mn0.272+Zr0.11Mg0.11Fe0.102+Fe0.063+Ta0.01)∑4.00(Si2.02O7)2 (P0.98O4)2(O3.50F0.50)∑4, Z = 1, calculated on the basis of 26(O+F) a.p.f.u., and murmanite (Na3.32Mn0.15Ca0.21K0.05)∑3.73(Ti3.084+Nb0.51Mn0.182+Fe0.153+Mg0.07Zr0.01)∑4.00(Si1.98O7)2(O3.76F0.24)∑4 (H2O)4, Z = 1, calculated onthe basis of 22(O+F) a.p.f.u., with H2O determined from structure refinement and Fe3+/(Fe2++Fe3+) ratios obtained by Mössbauer spectroscopy. The crystal structures of lomonosovite and murmanite are a combination of a titanium silicate (TS) block and an intermediate (I) block. The TS block consists of HOH sheets (H-heteropolyhedral, O-octahedral), and is characterized by a planar cell based on translation vectors, t1 and t2, with t1 ~5.5 and t2 ~7 Å and t1 ^ t2 close to 90º. The TS block exhibits linkage and stereochemistry typical for Group IV (Ti = 4 a.p.f.u.) of the Ti disilicate minerals: two H sheets connect to the O sheet such that two (Si2O7) groups link to Ti polyhedra of the O sheet adjacent along t1. In murmanite and lomonosovite, the invariant part of the TS block is of composition Na4Ti4(Si2O7)2O4. There is no evidence of vacancydominant cation sites or (OH) groups in the O sheet of lomonosovite or murmanite. In lomonosovite, the I block is a framework of Na polyhedra and P tetrahedra which gives 2[Na3 (PO)4] p.f.u. In murmanite, there are four (H2O) groups in the intermediate space between TS blocks. In lomonosovite, TS and I blocks alternate along c. In murmanite, TS blocks are connected via hydrogen bonding. The H atoms were located and details of the hydrogen bonding are discussed.

Kazanskyite, Ba□TiNbNa3Ti(Si2O7)2O2(OH)2(H2O)4, a Group-III Ti-disilicate mineral from the Khibiny alkaline massif, Kola Peninsula, Russia: description and crystal structure

Abstract Kazanskyite, Ba⃞TiNbNa3Ti(Si2O7)2O2(OH)2(H2O)4, is a Group-III TS-block mineral from the Kirovskii mine, Mount Kukisvumchorr, Khibiny alkaline massif, Kola Peninsula, Russia. The mineral occurs as flexible and commonly bent flakes 2-15 μm thick and up to 330 μm across. It is colourless to pale tan, with a white streak and a vitreous lustre. The mineral formed in a pegmatite as a result of hydrothermal activity. Associated minerals are natrolite, barytolamprophyllite, nechelyustovite, hydroxylapatite, belovite-(La), belovite-(Ce), gaidonnayite, nenadkevichite, epididymite, apophyllite-(KF) and sphalerite. Kazanskyite has perfect cleavage on {001}, splintery fracture and a Mohs hardness of 3. Its calculated density is 2.930 g cm-3. Kazanskyite is biaxial positive with α = 1.695, β = 1.703, γ = 1.733 (λ = 590 nm), 2Vmeas = 64.8(7)°, 2Vcalc = 55.4°, with no discernible dispersion. It is not pleochroic. Kazanskyite is triclinic, space group P1̅, a = 5.4260(9), b = 7.135(1), c = 25.514(4) Å, α = 90.172(4), β = 90.916(4), γ = 89.964(3)°, V = 977.61(3) Å3. The strongest lines in the X-ray powder-diffraction pattern [d(Å)(I)(hkl)] are: 2.813(100)(124̅,12̅2̅̅), 2.149(82)(222̅,22̅0,207,220,22̅2), 3.938(70)(11̅3,112), 4.288(44)(111̅,11̅0,110,11̅1), 2.128(44)(223̅,22̅1,13̅4,221,13̅4,221,22̅3), 3.127(39)(11̅6,115), 3.690(36)(11̅4), 2.895(33)(12̅3,121) and 2.955(32)(12̅0,120,12̅2). Chemical analysis by electron microprobe gave Nb2O59.70, TiO219.41, SiO228.21, Al2O30.13, FeO 0.28, MnO 4.65, BaO 12.50, SrO 3.41, CaO 0.89, K2O 1.12, Na2O 9.15, H2O 9.87, F 1.29, O = F -0.54, sum 100.07 wt.%; H2O was determined from structure refinement. The empirical formula is (Na2.55Mn0.31Ca0.11Fe2+0.03)Σ3(Ba0.70Sr0.28K0.21Ca0.03)Σ1.22(Ti2.09Nb0.63Mn0.26Al0.02)Σ3Si4.05O21.42H9.45F0.59, calculated on 22 (O + F) a.p.f.u., Z = 2. The structural formula of the form AP2MH2MO4(Si2O7)2XO4XPMXPA(H2O)n is (Ba0.56Sr0.22K0.15Ca0.03⃞0.04)Σ1(⃞0.74Ba0.14Sr0.06K0.06)Σ1(Ti0.98Al0.0 2)Σ1(Nb0.63Ti0.37)Σ1(Na2.55Mn0.31Ca0.11Fe2+0.03)Σ3(Ti0.74Mn0.26)Σ1(Si2O7)2O2(OH1.41F0.59)Σ2(H2O)(⃞0.74H2O0.26)Σ1(H2O)2.74. Simplified and ideal formulae are as follows: Ba(⃞,Ba)Ti(Nb,Ti)(Na,Mn)3(Ti,Mn)(Si2O7)2O2(OH,F)2(H2O)4 and Ba⃞TiNbNa3Ti(Si2O7)2O2(OH)2(H2O)4. The Raman spectrum of the mineral contains the following bands: 3462 cm-1 (broad) and 3545 and 3628 cm-1(sharp). The crystal structure was solved by direct methods and refined to an R1 index of 8.09%. The crystal structure of kazanskyite is a combination of a TS (titanium silicate) block and an I (intermediate) block. The TS block consists of HOH sheets (H is heteropolyhedral and O is octahedral). The TS block exhibits linkage and stereochemistry typical for Group-III (Ti = 3 a.p.f.u.) Ti-disilicate minerals. The TS block has two different H sheets where (Si2O7) groups link to [5]-coordinated Ti and [6]-coordinated Nb polyhedra, respectively. There are two peripheral sites, AP(1,2), occupied mainly by Ba (less Sr and K) at 96% and 26%. There are two I blocks: the I1 block is a layer of Ba atoms; the I2 block consists of H2O groups and AP(2) atoms. The TS and I blocks are topologically identical to those in the nechelyustovite structure. The mineral is named in honour of Professor Vadim Ivanovich Kazansky, a prominent Russian ore geologist and an expert in Precambrian metallogeny.

From structure topology to chemical composition. XII. Titanium silicates: the crystal chemistry of rinkite, Na2Ca4REETi(Si2O7)2OF3

Abstract Rinkite, ideally Na2Ca4 REETi(Si2O7)2OF3, is a common mineral in alkaline and peralkaline rocks. The crystal structures of five rinkite crystals from three alkaline massifs: Ilimaussaq, Greenland; Khibiny, Kola Peninsula, Russia and Mont Saint-Hilaire, Canada, have been refinedas two components related by the TWIN matrix (-1 0 0, 0 -1 0, 1 0 1) (Mo-Kα radiation). The crystals, a = 7.4132-7.4414, b = 5.6595-5.6816, c = 18.8181-18.9431 Å, β = 101.353-101.424(2)º, V = 776.1-786.7 Å3, space group P21/c, Z = 2, Dcalc = 3.376-3.502 g cm3, were analysedusing an electron microprobe subsequent to collection of the X-ray intensity data. Transmission electron microscopy confirmed the presence of pseudomerohedral twinning in rinkite crystals. The crystal structure of rinkite is a framework of TS (titanium silicate) blocks. The TS block consists of HOH sheets (H-heteropolyhedral, O-octahedral). The TS block in rinkite exhibits linkage and stereochemistry typical for Group I (Ti = 1 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 Na polyhedron of the O sheet. The crystal chemistry of rinkite and nacareniobsite-(Ce) is discussed.

Sveinbergeite, Ca(Fe2+6 Fe3+)Ti2(Si4O12)2O2(OH)5(H2O)4, a newastrophyllite-group mineral from the Larvik Plutonic Complex, Oslo Region, Norway: description and crystal structure

Abstract Sveinbergeite, Ca(Fe62+Fe3+)Ti2(Si4O12)2O2(OH)5(H2O)4, is a new astrophyllite-group mineral discovered in a syenite pegmatite at Buer on the Vesterøya peninsula, Sandefjord, Oslo Region, Norway. The mineral occurs in pegmatite cavities as 0.01-0.05 mm thick lamellar (0.2-0.5 × 5-10 mm) crystals forming rosette-like divergent groups and spherical aggregates, which are covered by brown coatings of iron (and possibly manganese) oxides, associated with magnesiokatophorite, aegirine, microcline, albite, calcite, fluorapatite, molybdenite, galena and a hochelagaite-like mineral. Crystals of sveinbergeite are deep green with a pale green streak and a vitreous and pearly lustre. Sveinbergeite has perfect cleavage on {001} and a Mohs hardness of 3. Its calculated density is 3.152 g/cm3. It is biaxial positive with α 1.745(2), β 1.746(2), γ 1.753(2), 2V(meas.) = 20(3)º. The mineral is pleochroic according to the scheme Z > X ~ Y : Z is deep green, X and Y are brownish green. Orientation is as follows: X ⊥ (001), Y ^ b = 12º, Z = a, elongation positive. Sveinbergeite is triclinic, space group P1̄, a = 5.329(4), b = 11.803(8), c = 11.822(8) Å; α = 101.140(8)º, β = 98.224(8)º, γ = 102.442(8)º; V = 699.0(8) Å3; Z = 1. The nine strongest lines in the X-ray powder diffraction pattern [d in Å (I)(hkl)] are: 11.395(100)(001,010), 2.880(38)(004), 2.640(31)(2̄10,1̄41), 1.643(24)(07̄1,07̄2), 2.492(20)(21̄1), 1.616(15)(070), 1.573(14)(3̄2̄2), 2.270(13)(1̄3̄4) and 2.757(12)(1̄40,1̄32). Chemical analysis by electron microprobe gave Nb2O5 0.55, TiO2 10.76, ZrO2 0.48, SiO2 34.41, Al2O3 0.34, Fe2O3 5.57, FeO 29.39, MnO 1.27, CaO 3.87, MgO 0.52, K2O 0.49, Na2O 0.27, F 0.24, H2O 8.05, O=F -0.10, sum 96.11 wt.%, the amount of H2O was determined from structure refinement, and the valence state of Fe was calculated from structure refinement in accord with Mössbauer spectroscopy. The empirical formula, calculated on the basis of eight (Si + Al) p.f.u., is (Ca0.95Na0.12K0.14)∑1.21(Fe5.652+Fe0.933+Mn0.25Mg0.18)∑7.01(Ti1.86Nb0.06Zr0.05Fe0.033+)∑2(Si7.91Al0.09)∑8O34.61H12.34F0.17, Z = 1. The infrared spectrum of the mineral contains the following absorption frequencies: 3588, ~3398 (broad), ~3204 (broad), 1628, 1069, 1009, 942, 702, 655 and 560 cm-1. The crystal structure of the mineral was solved by direct methods and refined to an R1 index of 21.81%. The main structural unit in the sveinbergeite structure is an HOH layer which is topologically identical to that in the astrophyllite structure. Sveinbergeite differs from all other minerals of the astrophyllite group in the composition and topology of the interstitial A and B sites and linkage of adjacent HOH layers. The mineral is named in honour of Svein Arne Berge (b. 1949), a noted Norwegian amateur mineralogist and collector who was the first to observe and record this mineral from its type locality as a potential new species.

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

Abstract The 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 P1̅, Dcalc. = 4.028 g/cm3, Z = 1; and innelite-2M, a = 5.4206(8), b = 7.125(1), c = 29.314(4) Å, β = 94.698(3)°, V = 1128.3(2) Å3, space group P2/c, D calc. = 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(Na2.16Mn2+0.38Fe2+0.17Mg0.15Ca0.10⃞0.04)Σ3(Ti2.97Nb0.02Al0.02)Σ3.01Si4.01(S1.02P0.81⃞0.17)Σ2H1.84O25.79F0.21 which is equivalent to(Ba3.94Sr0.06)Σ4.00(Ti1.97Nb0.02Al0.02)Σ2.01(Na2.16Mn2+0.38Fe2+0.17Mg0.15Ca0.10⃞0.04)Σ3Ti(Si4.01O14)[(SO4)1.02(PO4)0.81(OH)0.51H2O0.17]O2[(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.): twoH sheets co nnect tothe 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.

The seidozerite supergroup of TS-block minerals: nomenclature and classification, with change of the following names: rinkite to rinkite-(Ce), mosandrite to mosandrite-(Ce), hainite to hainite-(Y) and innelite-1T to innelite-1A

Abstract Here we report a nomenclature and classification for the seidozerite-supergroup minerals. The TS (Titanium-Silicate) block is the main structural unit in all seidozerite-supergroup structures; it consists of a central O (O = Octahedral) sheet and two adjacent H (H = Heteropolyhedral) sheets where Si2O7 groups occur in the H sheets. The TS block is characterized by a planar minimal cell based on translation vectors, t1 and t2, the lengths of these vectors are t1 ≈ 5.5 and t2 ≈ 7 Å, and t1 ^ t2 is close to 90°. The forty-five minerals of the sedozerite supergroup are divided into four groups based on the content of Ti and topology and stereochemistry of the TS block: in rinkite, bafertisite, lamprophyllite and murmanite groups, Ti (+ Nb + Zr + Fe3+ +Mg + Mn) = 1, 2, 3 and 4 apfu (atoms per formula unit), respectively. All TS-block structures consist either solely of TS blocks or of two types of block: the TS block and an I (Intermediate) block that comprises atoms between two TS blocks. Usually, the I block consists of alkali and alkaline-earth cations, H2O groups and oxyanions (PO4)3-, (SO4)2- and (CO3)2-.The general formula of the TS block is as follows AP2 BP2 MH2 MO4 (Si2O7)2X4+n, where MH2 and MO4 = cations of the H and O sheets; MH = Ti, Nb, Zr, Y, Mn, Ca + REE, Ca;MO = Ti, Zr, Nb, Fe3+, Fe2+, Mg, Mn, Zn, Ca, Na; AP and BP = cations at the peripheral (P) sites = Na, Ca + REE, Ca, Zn, Ba, Sr, K; X = anions = O, OH, F, H2O; X4+n=XO4 +XPn , n = 0, 1, 1.5, 2, 4; XP = XP M and XP A = apical anions of MH and AP cations at the periphery of the TS block .

Fluoro-aluminoleakeite, NaNa2(Mg2Al2Li)Si8O22F2, a new mineral of the amphibole group from Norra Kärr, Sweden: description and crystal structure

Abstract Fluoro-aluminoleakeite, ideally ANaBNa2C(Mg2Al2Li)TSi8O22WF2, is a new mineral of the amphibole group from Norra Kärr, Sweden (IMA-CNMMNC 2009-012). It occurs ina proterozoic alkaline intrusion that mainly comprises a fine-grained schistose agpaitic nepheline-syenite (grennaite). Fluoro-aluminoleakeite occurs as isolated prismatic crystals 0.10-2 mm long in a syenitic matrix. Crystals are light greenish-blue with a greenish-blue streak. It is brittle, has a Mohs hardness of 6 and a splintery fracture; it is non-fluorescent with perfect {110} cleavage, no observable parting, and has a calculated density of 3.14 g cm−3. In plane-polarized light, it is pleochroic, X = pale green, Y = dark green, Z = pale green; X ^ a = 62.9° (in β obtuse), Y ∥ b. Fluoro-aluminoleakeite is biaxial negative, α = 1.632(1), β = 1.638(1), γ = 1.643(1); 2Vobs. = 98.0(4)°, 2Vcalc. = 95.5°. Fluoro-aluminoleakeite is monoclinic, space group C2/m, a = 9.7043(5) Å, b = 17.7341(8) Å, c = 5.2833(3) Å, β = 104.067(4)°, V = 882.0(2) Å3, Z = 2. The eight strongest X-ray diffraction lines in the powder-diffraction pattern are [d in Å, (I), (hkl)]: 2.687, (100), (3̅31, 151); 4.435, (80), (021, 040); 3.377, (80), (131); 2.527, (60), (2̅02); 8.342, (50), (110); 3.096, (40), (310); 2.259, (40), (1̅71, 3̅12) and 2.557, (30), (002, 061). Analysis, by a combination of electron microprobe and crystal-structure refinement, gives SiO2 58.61, Al2O3 7.06, TiO2 0.32, FeO 3.27, Fe2O3 6.05, MgO 8.61, MnO 0.73, ZnO 0.43, CaO 0.05, Na2O 9.90, K2O 2.43, Li2O 1.62, F 3.37, H2Ocalc. 0.50, sum 101.08 wt.%. The formula unit, calculated on the basis of 24 (O,OH,F,Cl) p.f.u. with (OH) + F = 2 a.p.f.u., is A(Na0.65K0.43)Σ=1.09B(Na1.99Ca0.01)Σ=2.00C(Mg1.77Fe2+0.38Mn0.09Zn0.04Fe3+0.63Al1.16Ti0.03Li0.90)Σ=5.00TSi8.00O22W(F1.47OH0.53)Σ=2.00. Crystal-structure analysis shows CLi to be completely ordered at the M(3) site, and provided reliable site populations. Fluoro-aluminoleakeite is related to the end-member leakeite,ANaBNa2C(Mg2Fe3+2Li)TSi8O22W(OH)2, by the substitutions CFe3+ → CAl and WF → W(OH).

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

Abstract The crystal structure and chemical formula of zvyaginite, ideally Na2ZnTiNb2(Si2O2)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 (Nb1.68Ti1.25Al-)Σ3 (Si4.03O14)O2 [(OH)1.11F0.89]Σ4(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: (Na+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.