William G. Mumme

The crystal structure of the molybdenum bronze CsxMoO3 (x ≈ 0.25)

Cs0.25MoO3 crystallizes in the monoclinic system, space group P21m with unit cell dimensions a = 6.425, b = 7.543, c = 8.169, β = 96°30′. Its structure was determined from two-dimensional Patterson projections and refined by three-dimensional Fourier methods and also by least squares. It has a layer structure built up from subunits of six distorted octahedra sharing edges; the subunits are joined by corners to form layers. Cesium ions occupy irregular eight-coordinated interlayer sites. The bronze structure is compared with those of the related bronzes K0.26MoO3 and K0.28MoO3.

Jahnsite–whiteite solid solutions and associated minerals in the phosphate pegmatite at Hagendorf-Süd, Bavaria, Germany

Abstract Secondary phosphate assemblages from the Hagendorf Süd granitic pegmatite, containing the new Mn- Al phosphate mineral, nordgauite, have been characterized using scanning electron microscopy and electron microprobe analysis. Nordgauite nodules enclose crystals of the jahnsite−whiteite group of minerals, showing pronounced compositional zoning, spanning the full range of Fe/Al ratios between jahnsite and whiteite. The whiteite-rich members are F-bearing, whereas the jahnsite-rich members contain no F. Associated minerals include sphalerite, apatite, parascholzite, zwieselite-triplite solid solutions and a kingsmountite-related mineral. The average compositions of whiteite and jahnsite from different zoned regions correspond to jahnsite-(CaMnMn), whiteite-(CaMnMn) and the previously undescribed whiteite-(CaMnFe) end-members. Mo-Kα CCD intensity data were collected on a twinned crystal of the (CaMnMn)-dominant whiteite and refined in P2/a to wRobs = 0.064 for 1015 observed reflections.

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

Abstract The crystal structure of kassite, ideally Ca[Ti2O4(OH)2], containing 2 wt% Cr2O3, from the Saranovskoye chromite deposit, Perm’ district, Northern Urals, has been determined and refined to R1 = 0.06 using single crystal X-ray diffraction data. The crystals have monoclinic symmetry, P21/a, with a = 5.275(1), b = 9.009 (2), c = 9.557 (2) Å, β = 90.43∞. A pronounced sub-structure for the mineral, conforming to space group I2/a, is related to the I2/a structure for lucasite-(Ce), Ce[Ti2O5(OH)]. It comprises (001) layers of gibbsite-like fused hexagonal rings of edge-shared Ti(O,OH)6 octahedra with the Ca atoms sandwiched between pairs of opposing rings and displaced from the center of the rings along [010]. Ordering of the protons in chromian kassite lowers the symmetry to P21/a. Kassite, CaTi2O4(OH)2, and cafetite, CaTi2O5(H2O), are identical chemically but significantly different in their crystal structures

The structure of CrFeTi2O7

Abstract The phase CrFeTi 2 O 7 has been synthesized and is monoclinic, P2 1 a , a = 7.032(3) A, b = 5.000(2)A, c = 14.425(6)A, β = 116.59(4)°. It is isostructural with the compound Cr 2 Ti 2 O 7 . The structure is based on distorted hexagonal close packing of oxygen atoms, with the metal atoms occupying particular octahedral interstices to give a complex arrangement of octahedra joined by the sharing of corners, edges and faces. For one of the metal atom sites in the structure there is a 15% disorder for which possible origins are discussed. CrFeTi 2 O 7 is a member of the homologous series of compounds A 2 B n −2 O 2 n −1 (A = Cr, Fe; B = Ti, Zr) whose structures are closely related to that of α-PbO 2 , and may be considered to derive from it by the application of crystallographic shear.

Chiral edge-shared octahedral chains in liskeardite, [(Al,Fe)32(AsO4)18(OH)42(H2O)22]·52H2O, an open framework mineral with a pharmacoalumite-related structure

Abstract The type specimen of liskeardite, (Al,Fe)3AsO4(OH)6·5H2O, from the Marke Valley Mine, Liskeard District, Cornwall, has been reinvestigated. The revised composition from electron microprobe analyses and structure refinement is [Al29.2Fe2.8(AsO4)18(OH)42(H2O)22]·52H2O. The crystal structure was determined using synchrotron data collected on a 2 μm diameter fibre at 100 K. Liskeardite has monoclinic symmetry, space group I2, with the unit-cell parameters a = 24.576(5), b = 7.754(2) Å, c = 24.641(5) Å, and β = 90.19(1)°. The structure was refined to R = 0.059 for 9769 reflections with I > 3σ(I). It is of an open framework type in which intersecting polyhedral slabs parallel to (101) and (101̅) form 17.4 Å × 17.4 Å channels along [010], with water molecules occupying the channels. Small amounts (<1 wt.%) of Na, K and Cu are probably adsorbed at the channel walls The framework comprises columns of pharmacoalumite-type, intergrown with chiral chains of six cis edge-shared octahedra. It can be described in terms of cubic close packing, with vacancies at both the anion and cation sites. The compositional and structural relationships between liskeardite and pharmacoalumite are discussed and a possible mechanism for liskeardite formation is presented

The crystal structure of ramdohrite, Pb5.9Fe0.1Mn0.1In0.1Cd0.2Ag2.8Sb10.8S24: A new refinement

Abstract The crystal structure of ramdohrite, Pb5.9Fe0.1Mn0.1In0.1Cd0.2Ag2.8Sb10.8S24, from the Chocaya mine, Potosí, Bolivia, determined by Makovicky and Mumme from film data in 1983, was refined from single-crystal diffractometer data to the R value 0.060, based on 5230 reflections [I > 2σ(I)] from a twinned crystal. Lattice parameters are a = 8.7348(3), b = 13.0543(4), c = 19.3117(6) Å, and β = 90.179(2)°, space group P21/n. Two bicapped trigonal prismatic sites of lead bridge and unite adjacent (311)PbS slabs. These slabs contain five distinct coordination pyramids of Sb with trapezoidal cross sections, a mixed and disordered Sb-Ag-Cd-(Pb) site, refined as 0.39 Sb + 0.61 Ag, a pure Ag site with a very open, irregular tetrahedral coordination, and an octahedral site occupied by Pb. The (311)PbS slabs contain large lone electron pair micelles formed by four distinct antimony sites in alternation with small such micelles formed by a single Sb site. The geometric arrangement of these slabs is not based on crankshaft chains of short, strong Me-S bonds but on a chess-board arrangement of (predominantly) Sb pairs that share two common S atoms via short bonds. Relationships to, and differenced from, fizelyite and uchucchacuaite are described and discussed.

The crystal structure of reduced cesium vanadate, CsV2O5

Abstract Electrolysis of a 44 mole% Cs2O, 56 mole% V2O5 melt at 585°C has has resulted in the formation of CsV2O5 in single crystal form. This compound is monoclinic, space group P 2 1 c , with a = 7.008 A (5), b = 9.977 A (5), and c = 7.729 A (5), β = 90.98° (5), and the structure analysis has shown it to contain vanadium V in tetrahedral and vanadium IV in distorted trigonal bipyramidal coordination. A sheet structure results from the formation of pairs of edge shared trigonal bipyramids crosslinked by the tetrahedra, with layers of Cs atoms separating the sheets.

Flurlite, Zn3Mn2+Fe3+(PO4)3(OH)2·9H2O, a new mineral from the Hagendorf Süd pegmatite, Bavaria, with a schoonerite-related structure

Abstract Flurlite, ideally Zn3Mn2+Fe3+(PO4)3(OH)2·9H2O, is a new mineral from the Hagendorf-Süd pegmatite, Hagendorf, Oberpfalz, Bavaria, Germany. Flurlite occurs as ultrathin (<1 μm) translucent platelets that form characteristic twisted accordion-like aggregates. The colour varies from bright orange red to dark maroon red. Cleavage is perfect parallel to (001). The mineral occurs on mitridatite and is closely associated with plimerite. Other associated minerals are beraunite, schoonerite, parascholzite, robertsite and altered phosphophyllite. The calculated density of flurlite is 2.84 g cm-3. It is optically biaxial (-), α = 1.60(1), β = 1.65(1) and γ = 1.68(1), with weak dispersion and parallel extinction, X ≈c, Y ≈ a, Z ≈ b. Pleochroism is weak, with colours: X = pale yellow, Y = pale orange, Z = orange brown. Electron microprobe analyses (average of seven) with FeO and Fe2O3 apportioned and H2O calculated on structural grounds, gave ZnO 25.4, MnO 5.28, MgO 0.52, FeO 7.40, Fe2O3 10.3, P2O5 27.2, H2O 23.1, total 99.2 wt.%. The empirical formula, based on 3 P a.p.f.u. is Zn2.5Mn2+ 0.6Fe2+ 0.8Mg0.1Fe3+(PO4)3(OH)2·9H2O. Flurlite is monoclinic, P21/m, with the unit-cell parameters (at 100 K) of a = 6.3710(13), b = 11.020(2), c = 13.016(3) Å, β = 99.34 (3)°. The strongest lines in the X-ray powder diffraction pattern are [dobs in Å(I) (hkl)] 12.900(100)(001); 8.375(10)(011); 6.072(14)( 1̅01); 5.567(8)(012); 4.297(21)(003); 2.763(35)(040). Flurlite (R1 = 0.057 for 995 F > 4σ(F)) has a heteropolyhedral layer structure, with layers parallel to (001) and with water molecules packing between the layers. The slab-like layers contain two types of polyhedral chains running parallel to [100]: (a) chains of edge-sharing octahedra containing predominantly Zn and (b) chains in which Fe3+-centred octahedra share their apices with dimers comprising Zn-centred trigonal bipyramids sharing an edge with PO4 tetrahedra. The two types of chains are interconnected by corner-sharing along [010]. A second type of PO4 tetrahedron connects the chains to MnO2(H2O)4 octahedra along [010] to complete the structure of the (001) slabs. Flurlite has the same stoichiometry as schoonerite, but with dominant Zn rather than Fe2+ in the edge-shared chains. Schoonerite has a similar heteropolyhedral layer structure with the same layer dimensions 6.4 × 11.1 Å. The different symmetry (orthorhombic, Pmab) for schoonerite reflects a different topology of the layers.

Carbon incorporation in plumbogummite-group minerals

Abstract Non-stoichiometric, carbon-containing crandallite from Guatemala and plumbogummite from Cumbria have been characterized using electron microprobe (EMPA) and wet-chemical analyses, Rietveld analysis of powder X-ray diffraction (PXRD) patterns, and infrared (IR), Raman and cathodoluminescence (CL) spectroscopies. The samples contain 11.0 and 4.8 wt.% CO2, respectively. The IR spectra for both samples show a doublet in the range 1410-1470 cm-1, corresponding to CO3 vibrations. Direct confirmation of CO3 replacing PO4 was obtained from difference Fourier maps in the Rietveld analysis. Carbonate accounts for 67% of the C in the plumbogummite and 20% of the C in the Guatemalan crandallite, the remainder being present as nano-scale organic carbon. The CO3 substitution for PO4 is manifested in a large contraction of the tetrahedral volume (14-19%) and by a contraction of the a axis, analogous to observations for carbonate-containing fluorapatites. Stoichiometric crandallite from Utah was characterized using the same methods, for comparison with the non-stoichiometric, carbon-bearing phases.

Ba–Cu ordering in bariopharmacoalumite-Q2a2b2c from Cap Garonne, France

Abstract Bariopharmacoalumite-Q2a2b2c, Ba0.5(Cu,ZnO)0.1H0.6[Al4(OH)4(As0.9Al0.1O4)3]·5.5H2O, from the south mine of the old copper mine at Cap Garonne, France, has a 2 × 2 × 2 I-centred tetragonal superstructure of the basic pharmacosiderite-type structure. Cell parameters are a = 15.405(2) Å and c = 15.553(3) Å . The structure was determined and refined in I4̅2m to R1= 0.057 for 2697 reflections with I > 2σ(I), using synchrotron X-ray data on a twinned crystal. The origin of the superlattice cell doubling was determined to be due predominantly to the ordering of Ba atoms in half of the [0 0 1] channels, centred at (0, 0, 0) and (½, ½, 0). The other channels, centred at (½, 0, 0) and (0, ½, 0), were found to be occupied by corner-connected chains of Cu/Zn-centred square planar units.