I. V. Pekov

Crystal Structure of Chabazite K

AbstractThe crystal structure of the chabazite K with the formula (K1.33Na1.02Ca0.84)[Al4Si8O24] · 12.17H2O from late hydrothermalites in the Khibiny alkaline massif (Kola Peninsula) is established by X-ray diffraction analysis (CAD4 four-circle diffractometer, λMoKα radiation, graphite monochromator, T=193 K, 2θmax = 70°, R1 = 0.047 for 4745 reflections) on the basis of experimental data (6265 reflections) obtained from a twin (twinning parameter 0.535(1)): a = 13.831(3) Å, c = 15.023(5) Å, sp. gr.

Crystal Structure of the Na-, Ca-, Be-Cordierite and Crystallochemical Regularities in the Cordierite-Sekaninaite Series

R\bar 3m

Crystal structure of natrite, gamma-Na2CO3

, Z = 3, ρcalcd = 2.016 g/cm3. It is shown that cations occupy five independent positions in large cavities of the tetrahedral Al,Si,O anionic framework in potassium-rich chabazite. A comparative crystallochemical analysis of chabazites of different composition and origin is performed.

Césarferreiraite, Fe2+Fe23+(AsO4)2(OH)2·8H2O, from Eduardo mine, Conselheiro Pena, Minas Gerais, Brazil: Second arsenate in the laueite mineral group

Abstract The composition, structure, X-ray powder diffraction pattern, optical properties, density, infrared, Raman and Mössbauer spectra, and thermal properties of a homogeneous sample of metavivianite from the Boa Vista pegmatite, near Galiléia, Minas Gerais, Brazil are reported for the first time. Metavivianite is biaxial (+) with α = 1.600(3), β = 1.640(3), γ = 1.685(3) and 2Vmeas = 85(5)°. The measured and calculated densities are D meas = 2.56(2) and D calc = 2.579 g cm-3. The chemical composition, based on electronmicroprobe analyses, Mössbauer spectroscopy (to determine the Fe2+:Fe3+ ratio) and gas chromatography (to determine H2O) is MgO 0.70, MnO 0.92, FeO 17.98, Fe2O3 26.60, P2O5 28.62, H2O 26.5; total 101.32 wt.%. The empirical formula is (Fe3+1.64Fe2+1.23Mg0.085Mn0.06)Σ3.015(PO4)1.98(OH)1.72·6.36H2O. Metavivianite is triclinic, P1, a = 7.989(1), b = 9.321(2), c = 4.629(1) Å, α = 97.34(1), β = 95.96(1), γ = 108.59(2)°, V = 320.18(11) Å3 and Z = 1. The crystal structure was solved using a single-crystal techniques to an agreement index R = 6.0%. The dominant cations in the independent sites are Fe2+ and Fe3+, with multiplicities of 1 and 2, respectively. The simplified crystal-chemical formula for metavivianite is Fe2+ (Fe3+, Fe2+)2(PO4)2(OH,H2O)2·6H2O; the endmember formula is Fe2+Fe3+2(PO4)2(OH)2·6H2O, which is dimorphous with ferrostrunzite.

Crystal structure of strontium hilgardite

The crystal structure of the beryllium-rich cordierite [(Na0.28Ca0.19)(H2O)0.92](Mg1.86Fe0.1422−) · { Al3.39Be0.61Si5O18} was established by X-ray diffraction analysis (IPDS Stoe diffractometer, λMoKα radiation, graphite monochromator, 2θmax = 65°, R = 0.0186 for 1378 reflections): a = 16.850(3), b = 9.729(2), and c = 9.298(2) Å; V = 1524.3(4) Å3, sp. gr. Cccm, Z = 4, and ρcalcd = 2.655 g/cm3. The numbers of Mg and Fe atoms isomorphously occupying the octahedral positions, Al and Be atoms in tetrahedra, and Na and Ca atoms and H2O molecules in the framework cavities are refined. The hydrogen atom is localized and its coordinates and thermal displacement parameters are refined. Based on the comparative crystallochemical analysis of cordierites from different locations and origins, the regularities relating the unit-cell parameters b and c and the distortion index to the features of the chemical composition of the minerals under study are shown.

The crystal structure of chromian kassite from the Saranovskoye deposit, Northern Urals, Russia

The crystal structures of K-and Cs-exchanged forms of zorite were studied by X-ray diffraction and IR spectroscopy: K4.75Na1.82[Ti(Ti0.79Nb0.20)4Si12O34(O,OH)5.2] × 10.62 H2O (sp. gr. Cmmm, R= 0.0481 for 516 independent reflections) and Cs4.34Na1.90[Ti(Ti0.80Nb0.18)4Si12O34(O,OH)5] × 5.37 H2O (sp. gr. Cmmm, R = 0.0285 for 621 independent reflections). Both structures retain the mixed polyhedral framework of zorite: Na6Ti(Ti,Nb)4(Si6O17)2(O,OH)5 × nH2O, where n ∼ 11. It is shown that the positions of the atoms located in the cavities of the frameworks of these compounds differ from those in the structures of zorite and its synthetic analogs.

New data on vlasovite: refinement of the crystal structure and the radiation damage of the crystal during the X-ray diffraction experiment

Abstract: A new occurrence of natrite,g-Na 2 (CO 3 ), was discovered as monominerallenses (more than 20cm in size) in pegmatites of Mt. Koashva, Khibiny alkalinemassif, Kola peninsula, Russia. Electron microprobe, XRD, IR and optical data fornatrite of this new occurrence are given. A single-crystal fragment isolated frompolysynthetic twinned material was used for collecting X-ray single-crystal data:l(Mo K a)=0.71073A, C 2/ m,a =8.905(4), b =5.237(3), c =6.045(2)A,b=101.32(3)E , 1290 reflections. Satellite reflections on oscillation photographs indicatethe presence of modulation in the structure of natrite. The average structure con-vergedto R =0.106; models with ( i ) all atomic positions split and ( ii ) anharmonicthermal displacement parameters applied to unsplit atoms converged to R =0.036and 0.029 respectively. The structure of natrite contains [001] columns formed byface sharing Na octahedra and further 7-fold coordinated Na polyhedra; the col-umns are connected by CO 3 groups.Key words: natrite, crystal structure, carbonate, modulated structure, Khibiny.

Refined crystal structure of lovozerite Na2CaZr[Si6O12(OH,O)6] · H2O

Abstract Césarferreiraite, Fe2+Fe23+(AsO4)2(OH)2·8H2O, is a new laueite-group mineral (IMA 2012-099) of triclinic symmetry, from Eduardo pegmatite mine, Conselheiro Pena municipality, Minas Gerais, Brazil. Intimately associated minerals are pharmacosiderite, scorodite, and earlier arsenopyrite, and probably césarferreiraite replaces the latter. It occurs as fibrous-to-tabular aggregates up to 2 mm. Single crystals, up to 10 μm long with a thickness of about 1-2 μm, are elongated along [001] and flattened on (100). The fibers have almost rectangular cross-section apparently bound by the {100} and {010} pinacoid forms. Color and streak are pale to greenish yellow. Luster is vitreous; individual crystals are transparent and masses are translucent. Cleavage is distinct, presumably on {010} and {100}. Calculated density is 2.934 g/cm3. The mineral is biaxial (+), n (min) = 1.747(3), n (max) = 1.754(3) (589 nm). IR spectrum of césarferreiraite is unique and can be used for the identification of the mineral. Chemical composition (n = 4, WDS, calculated for the condition Fe2+:Fe3+ = 1:2, H2O for the ideal structural formula, wt%) is: FeO 11.50, Fe2O3 25.56, CaO 15.41, As2O5 33.51, H2O 26.01, total 100.12. The empirical formula (based on 18 O apfu) is Fe2+0.98Fe3+1.96[(AsO4)1.79(PO4)0.31](OH)1.52·8.08H2O. The strongest eight X-ray powder-diffraction lines [d in Å(I)(hkl)] are: 9.85(95)(010), 6.35(100)(001), 3.671(29)(1̅21), 3.158(32)(13̅0), 2.960(39)(022̅), 2.884(35)(1̅31), 2.680(29)(2̅11), and 2.540(23)(2̅10). Unit-cell parameters refined from powder data indexed by analogy with related laueite-group minerals (space group: P1̅) are: a = 5.383(2), b = 10.363(3), c = 6.878(2) Å, α = 96.42(4), β = 109.19(3), γ = 102.30(2)°, V = 347.1(2) Å3, and Z = 1. Gladstone-Dale compatibility is -0.020 (excellent). Césarferreiraite is the arsenate analog of ferrolaueite.