V. N. Yakovenchuk

Crystal structures of lamprophyllite-2M and lamprophyllite-2O from the Lovozero alkaline massif, Kola peninsula, Russia

The crystals of lamprophyllite-2 M and lamprophyllite-2 O were found coexisting in an ussingite-microcline-sodalite veins in the Alluaiv Mt., Lovozero alkaline massif, in association with ussingite, aegirine, microcline, sodalite, albite, mangan- neptunite, vuonnemite, sphalerite, lomonosovite and betalomonosovite. The chemical composition of the polytypes corresponds to the formula (Sr 1.18Na0.66Ca0.12)S1.96Na (Na1.30Mn0.36Fe0.22Mg0.12)S2.00Ti3O2(Si2O7)2(OH)2. The structures of lamprophyllite-2 M (C2/m, a = 19.215(5), b = 7.061(2), c = 5.3719(15) A , b = 96.797(4) o, V = 723.7(4) A3) and lamprophyllite-2 O (Pnmn, a = 19.128(4), b = 7.0799(14), c = 5.3824(11) A , V = 728.9(3) A3) have been refined to R = 0.040 for 688 reflections (| Fo| ‡ 4sF) and to R = 0.084 for 571 reflections (| Fo| ‡ 4sF), respectively. The structures of both polytypes are based on the HOH layer consisting of a central O sheet of edge-sharing Na(1)O 6, Na(2)O6 and Ti(2)O6 octahedra sandwiched between two heterophyllosilicate H sheets. The H sheet is built by corner-sharing of Ti(1)O 5 square pyramids and Si 2O7 groups and consists of two types of rings of polyhedra: (i) six-membered rings (6 R) formed by two Si 2O7 groups and two TiO 5 square pyramids and (ii) four-membered rings (4R) formed by two silicate tetrahedra and two TiO 5 square pyramids. The Sr atom is located in the interlayer and is coordinated by six anions from 6 R of the upper H sheet and four anions from 4 R of the lower H sheet. The difference between monoclinic and orthorhombic lamprophyllites can be described in terms of different orientations of HOH layers. Whereas in lamprophyllite-2 M, all HOH layers are in the same orientation, in lamprophyllite-2 O, two adjacent layers are in different orientations.

Crystal chemistry of natural layered double hydroxides. I. Quintinite-2H-3c from the Kovdor alkaline massif, Kola peninsula, Russia

Abstract The crystal structure of quintinite-2H-3c, [Mg4Al2(OH)12](CO3)(H2O)3, from the Kovdor alkaline massif, Kola peninsula, Russia, was solved by direct methods and refined to an agreement index (R1) of 0.055 for 484 unique reflections with |Fo| ≥ 4σF. The mineral is rhombohedral, R32, a = 5.2745(7), c = 45.36(1) Å. The diffraction pattern of the crystal has strong and sharp Bragg reflections having h-k = 3n and l = 3n and lines of weak superstructure reflections extended parallel to c* and centred at h-k ≠ 3n. The structure contains six layers within the unit cell with the layer stacking sequence of ...AC=CA=AC=CA=AC=CA... The Mg and Al atoms are ordered in metal hydroxide layers to form a honeycomb superstructure. The full superstructure is formed by the combination of two-layer stacking sequence and Mg-Al ordering. This is the first time that a long-range superstructure in carbonate-bearing layered double hydroxide (LDH) has been observed. Taking into account Mg-Al ordering, the unique layer sequence can be written as ...=Ab1C=Cb1A=Ab2C=Cb2A=Ab3C=Cb3A=... The use of an additional suffix is proposed in order to distinguish between LDH polytypes having the same general stacking sequence but with different c parameters compared with the ‘standard’ polytype. According to this notation, the quintinite studied here can be described as quintinite-2H-3c or quintinite-2H-3c[6R], indicating the real symmetry.

Crystal chemistry of natural layered double hydroxides. 2. Quintinite-1M: first evidence of a monoclinic polytype in M2+-M3+ layered double hydroxides

Abstract Quintinite-1M, [Mg4Al2(OH)12](CO3)(H2O)3, is the first monoclinic representative of both synthetic and natural layered double hydroxides (LDHs) based on octahedrally coordinated di- and trivalent metal cations. It occurs in hydrothermal veins in the Kovdor alkaline massif, Kola peninsula, Russia. The structure was solved by direct methods and refined to R1 = 0.031 on the basis of 304 unique reflections. It is monoclinic, space group C2/m, a = 5.266(2), b = 9.114(2), c = 7.766(3) Å, β = 103.17(3)º, V = 362.9(2) Å3. The diffraction pattern of quintinite-1M contains sharp reflections corresponding to the layer stacking sequence characteristic of the 3R rhombohedral polytype, and rows of weak superlattice reflections superimposed upon a background of streaks of modulated diffuse intensity parallel to c*. These superlattice reflections indicate the formation of a 2-D superstructure due to Mg-Al ordering. The structure consists of ordered metal hydroxide layers and a disordered interlayer. As the unit cell contains exactly one layer, the polytype nomenclature dictates that the mineral be called quintinite-1M. The complete layer stacking sequence can be described as ...=Ac1B=Ba1C=Cb1A=... Quintinite-1M is isostructural with the monoclinic polytype of [Li2Al4(OH)12](CO3)(H2O)3.

Crystal chemistry of natural layered double hydroxides. 3. The crystal structure of Mg,Al-disordered quintinite-2H

Abstract Two crystals of Mg, Al-disordered quintinite-2H (Q1 and Q2), [Mg4Al2(OH)12](CO3)(H2O)3, from the Kovdor alkaline massif, Kola peninsula, Russia, have been characterized chemically and structurally. Both crystals have hexagonal symmetry, P63/mcm, a = 3.0455(10)/3.0446(9), c = 15.125(7)/15.178(5) Å, V = 121.49(8)/121.84(6) Å3. The structures of the two crystals have been solved by direct methods and refined to R1 = 0.046 and 0.035 on the basis of 76 and 82 unique observed reflections for Q1 and Q2, respectively. Diffraction patterns obtained using an image-plate area detector showed the almost complete absence of superstructure reflections which would be indicative of the Mg-Al ordering in metal hydroxide layers, as has been observed recently for other quintinite polytypes. The crystal structures are based on double hydroxide layers [M(OH)2] with an average disordered distribution of Mg2+ and Al3+ cations. Average bond lengths for the metal site are 2.017 and 2.020 Å for Q1 and Q2, respectively, and are consistent with a highly Mg-Al disordered, average occupancy. The layer stacking sequence can be expressed as ...=AC=CA=..., corresponding to a Mg-Al-disordered 2H polytype of quintinite. The observed disorder is probably the result of a relatively high temperature of formation for the Q1 and Q2 crystals compared to ordered polytypes. This suggestion is in general agreement with the previous observations which demonstrated, for the Mg-Al system, a higher-temperature regime of formation of the hexagonal (or pseudo-hexagonal in the case of quintinite-2H-3c) 2H polytype in comparison to the rhombohedral (or pseudo-rhombohedral in the case of quintinite-1M) 3R polytype.

Trap formation of the Kola peninsula

The nepheline syenites and foidolites of the world’s largest Lovozero and Khibiny allkaline massifs contain numerous xenoliths of intercalating olivine basalts, their tuffs, tuffites, and quartzitosandstones that experienced more (in the Khibiny Massif) or less (in the Lovozero Massif) intense thermal-metasomatic transformation. In terms of geological, petrographical, and petrochemical features, the unaltered rocks of the Lovozero Formation can be ascribed to the rocks of the trap formation, while all wealth of the rocks formed during their contact-metasomatic alteration (sekaninaite-anorthoclase, annite-anorthoclase, fayalite-anorthoclase, rutile-freudenbergite-anorthoclase, topaz-andalusite-anorthoclase, and others) was formed due to alkaline metasomatism. The Fourier analysis of the color variation curves for the volcanogenic-sedimentary rocks revealed the identity between bedding of initial tuffs (tuffites) and banding of their fenitized analogues.

Crystal structure of rimkorolgite, Ba[Mg5(H2O)7(PO4)4](H2O), and its comparison with bakhchisaraitsevite

The crystal structure of rimkorolgite, ideally Ba[Mg 5 (H 2 O) 7 (PO 4 ) 4 ](H 2 O), (monoclinic, P 2 1 / c, a = 8.3354(9), b = 12.8304(13), c = 18.313(2) A, β = 90.025(2)°, V = 1958.5(4) A 3 , Z = 4) has been solved by direct methods and refined to R 1 = 0.052 using X-ray diffraction data collected from a crystal twinned on (001). There are five symmetrically independent Mg 2+ cations that are each octahedrally coordinated by four O atoms and two H 2 O groups. One symmetrically independent Ba 2+ cation is coordinated by eight O atoms and two H 2 O groups. The Mgϕ 6 octahedra (ϕ = O, H 2 O) and PO 4 tetrahedra form sheets parallel to (001). Their main elements are zigzag chains of the Mgϕ 6 edge-sharing octahedra. The chains are linked via common vertices to form an octahedral sheet in which Mg atoms are located at the vertices of the 6 3 hexagonal net. The PO 4 tetrahedra are above and below hexagonal rings of Mg octahedra and are linked to them by sharing common O vertices. The Ba atoms and H 2 O(1) and H 2 O(22) groups are located between the sheets providing their linkage into three-dimensional structure. The structure of rimkorolgite is closely related to that of bakhchisaraitsevite, Na 2 Mg 5 (PO 4 ) 4 7H 2 O. Both structures are based on the octahedral-tetrahedral sheets of the same type. In bakhchisaraitsevite, the sheets are linked into three-dimensional framework by edge-sharing between the Mgϕ 6 octahedra from two adjacent sheets, whereas in rimkorolgite, there is no linkage between adjacent sheets. The structure of rimkorolgite can be considered as bakhchisaraitsevite-like framework interrupted by the presence of large Ba 2+ cations.

Whiteite-(CaMnMn), CaMnMn2Al2[PO4]4(OH)2·8H2O, a new mineral from the Hagendorf-Süd granitic pegmatite, Germany

Abstract Whiteite-(CaMnMn), CaMnMn2Al2[PO4]4(OH)2·8H2O, is a new hydrous phosphate of Ca, Mn and Al, which is closely related to both jahnsite-(CaMnMn) and the minerals of the whiteite group. It is monoclinic, P2/a, with a = 15.02(2), b = 6.95(1), c =10.13(3) Å, β = 111.6(1)º, V = 983.3(6) Å3, Z = 2 (from powder diffraction data) or a = 15.020(5), b = 6.959(2), c = 10.237(3) Å, β = 111.740(4)º, V = 984.3(5) Å3, Z = 2 (from single-crystal diffraction data). The mineral was found in the Hagendorf Süd granitic pegmatite (Germany) as small (up to 0.5 mm in size) crystals elongated on a and tabular on {010}. The crystals are either simply or polysynthetically twinned on {001}. They crystallize on the walls of voids within altered zwieselite crystals or form coronas (up to 1 mm in diameter) around cubic crystals of uraninite. The mineral is transparent, colourless to pale yellow (depending on Al-Fe3+ substitution), with a vitreous lustre and a white streak. The cleavage is perfect on {001}, the fracture is stepped and the Mohs hardness is 3½. In transmitted light, the mineral is colourless; dispersion was not observed. Whiteite-(CaMnMn) is biaxial (+), α = 1.589(2), β = 1.592(2), γ = 1.601(2) (589 nm), 2Vmeas = 60(10)º, 2Vcalc = 60.3º. The optical orientation is X = b, Z^a = 5º. The calculated and measured densities are Dcalc = 2.768 and Dmeas = 2.70(3) g cm-3, respectively. The mean chemical composition determined by electron microprobe is Na2O 0.53, MgO 0.88, Al2O3 11.66, P2O5 34.58, CaO 4.29, MnO 17.32, FeO 8.32, ZnO 2.60 wt.%, with H2O 19.50 wt.% (determined by the Penfield method), giving a total of 99.68 wt.%. The empirical formula calculated on the basis of four phosphorus atoms per formula unit, with ferric iron calculated to maintain charge balance, is (Ca0.63Zn0.26Na0.14)∑1.03(Mn0.60Fe0.402+)∑1.00(Mn1.40Fe0.372+Mg0.18Fe0.063+)∑2.01(Al1.88Fe0.123+)∑2.00[PO4]4(OH)2·7.89H2O. The simplified formula is CaMnMn2Al2[PO4]4(OH)2·8H2O. The mineral is easily soluble in 10% HCl at room temperature. The strongest X-ray powder-diffraction lines [listed as d in Å (I) (hkl)] are as follows: 9.443(65)(001), 5.596(25)(011), 4.929(80)(210), 4.719(47)(002), 3.494(46)(400), 2.7958(100)(022). The crystal structure of whiteite-(CaMnMn) was refined for a single crystal twinned on (001) to R1 = 0.068 on the basis of 5702 unique observed reflections. It is similar to the structures of other members of the whiteite group. The mineral is named for the chemical composition, in accordance with whiteitegroup nomenclature.

Amphiboles of the Khibiny alkaline pluton, Kola Peninsula, Russia

The rocks of the Khibiny pluton contain 25 amphibole varieties, including edenite, fluoredenite, kaersutite, pargasite, ferropargasite, hastingsite, magnesiohastingsite, katophorite, ferrikatophorite, magnesiokatophorite, magnesioferrikatophorite, magnesioferrifluorkatophorite, ferrimagnesiotaramite, ferrorichterite, potassium ferrorichterite, richterite, potassium richterite, potassium fluorrichterite, arfvedsonite, potassium arfvedsonite, magnesioarfvedsonite, magnesioriebeckite, ferriferronyboite, ferrinyboite, and ferroeckermannite. The composition of rock-forming amphiboles changes symmetrically relative to the Central Ring of the pluton; i.e., amphiboles enriched in K, Ca, Mg, and Si are typical of foyaite near and within the Central Ring. The Fe and Mn contents in amphiboles increase in the direction from marginal part of the pluton to its center. Foyaite of the marginal zone contains ferroeckermannite, richterite, arfvedsonite, and ferrorichterite; edenite is typical of foyaite and hornfels of the Minor Arc. Between the Minor Arc and the Central Ring, foyaite contains ferroeckermannite, arfvedsonite, and richterite; amphiboles in rischorrite, foidolite and hornfels of the Central Ring are (potassium) arfvedsonite, (potassium) richterite, magnesiokatophorite, magnesioarfvedsonite, ferroeckermannite, and ferriferronyboite; amphiboles in foyaite within the Central Ring, in the central part of the pluton, are arfvedsonite, magnesioarfvedsonite, ferriferronyboite, katophorite, and richterite. It is suggested that such zoning formed due to the alteration of foyaite by a foidolite melt intruded into the Main (Central) Ring Fault.

Porous titanosilicate nanorods in the structure of yuksporite, (Sr,Ba)2K4(Ca,Na)14(□,Mn,Fe) {(Ti,Nb)4(O,OH)4[Si6O17]2[Si2O7]3}(H2O,OH)n, resolved using synchrotron radiation

Abstract The crystal structure of yuksporite, (Sr,Ba)2K4(Ca,Na)14(⃞ ,Mn,Fe){(Ti,Nb)4(O,OH)4[Si6O17]2[Si2O7]3}(H2O,OH)n, where n ∼ 3 [monoclinic, P21/m, a = 7.126(3), b = 24.913(6), c = 17.075(7) Å, β = 101.89(3)°, V = 2966.4(17) Å3] has been solved using X-ray synchrotron radiation data collected from a needle-like crystal with dimensions of 6 × 6 × 50 µm3 at the Swiss-Norwegian beamline BM01 of the European Synchrotron Research Facility (ESRF, Grenoble, France). The structure was refined to R1 = 0.101 on the basis of 2359 unique observed reflections with |Fo| ≥ 4σF. The structure of yuksporite is based upon titanosilicate nanorods elongated along a and with an elliptical cross-section of ca. 16 × 19 Å = 1.6 × 1.9 nm. Silicate tetrahedra form double xonotlite-like chains 1∞[Si6O17] oriented parallel to (001). Two 1∞[Si6O17] chains are linked into a rod via TiO6 octahedra and Si2O7 double tetrahedra. The {(Ti,Nb)4(O,OH)4[Si6O17]2[Si2O7]3} nanorods are porous. The internal pores are defined by eight-membered rings (8MR) with open diameters of 3.2 Å. The interior of the titanosilicate nanorods is occupied by Sr, Ba, K, and Na cations and H2O molecules. The nanorods are separated by walls of Ca coordination polyhedra that are parallel to (010) and link the rods into a three-dimensional structure.

Crystal chemistry and nomenclature of the lovozerite group

The paper summarizes crystal-chemical data and describes the IMA-accepted nomenclature of lovozerite-group minerals (LGM). The lovozerite group includes nine zeolite-like cyclosilicates with the general formula A3B3C2MSi6O12O6� x(OH)xnH2O, with species-defining M ¼ Zr, Ti, Fe 3þ , Ca; C ¼ Ca, Mn 2þ , Na, &; A ¼ Na, Ca; B ¼ Na, & ;0 � x � 6; n ¼ 0-1. Their structures are based upon a heteropolyhedral framework consisting of rings of Si-centred tetrahedra and M-centred octahedra forming a 3D system of channels that host A, B, and C cations. The structures can be also considered as based upon pseudocubic modules centred at the midpoint of the Si tetrahedral ring. The M, A, and B cations are located at the borders of the module, whereas C cations are inside the module. The modules are stacked in three different arrangements in LGM allowing distinction of three subgroups: (1) zirsinalite-lovozerite subgroup (includes cation-saturated combeite, kapustinite, kazakovite and zirsinalite, and cation-deficient litvinskite, lovozerite and tisinalite), (2) koashvite subgroup (incl. koashvite) and (3) imandrite subgroup (incl. imandrite). The nature of cation-deficient LGM is discussed. The calculation scheme for empirical formulae of LGM and the criteria of definition of a mineral species (end-members) in the group are given.