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  • 1
    Electronic Resource
    Electronic Resource
    Determination of the centroid or `the best centre' of a coordination polyhedron (1996)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 52 (1996), S. 78-81 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The geometric parameters related to the point in the coordination polyhedron having the minimum variation of distances to the vertices (`the centroid of the coordination polyhedron') are proposed as a measure of polyhedral irregularity or deformation. The numerical method for the determination of the centroid coordinates is described. Knowing these coordinates, the radius of the sphere circumscribed to the coordination polyhedron, the degree of sphericity of coordination, the principal axes of the ellipsoid fitted to the polyhedron and the displacement of the central atom from the centroid are calculated. These quantities are measures for various aspects of irregularity in the coordination polyhedron. The centroid calculation has been applied to the family of ABS2-type sulfides with cations in slightly to highly deformed octahedral coordinations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768195008251
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  • 2
    Electronic Resource
    Electronic Resource
    Nomenclature of inorganic structure types. Report of the International Union of Crystallography Commission on Crystallographic Nomenclature Subcommittee on the Nomenclature of Inorganic Structure Types (1990)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 46 (1990), S. 1-11 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Different degrees of similarity between inorganic crystal structures are defined concisely and examples are presented that illustrate their practical application. A notation giving the coordination of atoms is presented together with some basic rules for developing crystal-chemical formulae and the Bauverband description of inorganic structure types. Typical examples of the nomenclature are: pyrite Fe[6°]{g}[S2(3;1)t], [F(□2l) + F′FeS2Pa\bar 3; spinel Mg[4]AI2[6]O4, ∞3[Mg[4t]lAl2[6o]O4[l,3;12co]], Fm222 + D, T′ MgAI2O4 Fd\bar 3m.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767389008834
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  • 3
    Electronic Resource
    Electronic Resource
    New Measure of Distortion for Coordination Polyhedra (1998)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 54 (1998), S. 766-773 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A new global measure of distortion for coordination polyhedra is proposed, based on a comparison of the ratios Vs(circumscribed sphere)/Vp(polyhedron) calculated, respectively, for the real and ideal polyhedra of the same number of coordinated atoms which have the same circumscribed sphere. This formula can be simplified to υ (%) = 100[Vi(ideal) − Vr(real)]/Vi, where Vi and Vr are the volumes of the above-defined polyhedra. The global distortion can be combined with other polyhedral characteristics, e.g. with the eccentricity of the central atom in the polyhedron or with the degree of sphericity of the coordination sphere [Balic Zõunic & Makovicky (1996). Acta Cryst. B52, 78–81].Vs/Vp ratios are given for a number of ideal polyhedra, including several types of trigonal coordination prisms, with the aim of facilitating the distortion calculations. The application examples included in the paper are: complex sulfides based on PbS and SnS archetypes, coordination polyhedra of large cations in feldspars, a phase transformation in a monoclinic amphibole and the subdivision of structures isopointal to ilmenite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768198003905
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  • 4
    Electronic Resource
    Electronic Resource
    The role of Fe2+ and Fe3+ in synthetic Fe-substituted tetrahedrite (1990)
    Springer
    Mineralogy and petrology 43 (1990), S. 73-81 
    Details
    ISSN: 1438-1168
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Zusammenfassung Die Rolle von Fe2+ und Fe3+ in synthetischen Tetraedriten mit Fe-Substitution Tetraedrite mit einer Zusammensetzung zwischen Cu12Sb4S13 and Cu10Fe2Sb4S13 wurden bei 457 °C und 500 °C aus den Elementen synthetisiert und sorgfdltig mit Mössbauer-Spektroskopie von57Fe untersucht. Zwischen Cu12Sb4S13 and Cu11Fe1Sb4S13 ist Eisen überwiegend dreiwertig. Zwischen Cu11Fe1Sb4S13 and Cu11Fe2Sb4S13 ist Eisen überwiegend zweiwertig und besetzt die tetraedrisch koordinierten M1-Plätze.
    Notes: Summary Tetrahedrites with the composition between Cu12Sb4S13 and Cu10Fe2Sb4S13 were synthesized at 457 °C and 500 °C from the elements and carefully studied by Mössbauer spectroscopy of57Fe. Between Cu12Sb4S13 and Cu11Fe1Sb4S13 iron is predominantly ferric. Between Cu11Fe1Sb4S13 and Cu10Fe2Sb4S13 iron is predominantly ferrous and occupies the tetrahedral M1-sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01164223
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  • 5
    Electronic Resource
    Electronic Resource
    Mineralogical data on a sulphosalt from the Rhodope mountains, Bulgaria (1969)
    Springer
    Mineralogy and petrology 13 (1969), S. 149-156 
    Details
    ISSN: 1438-1168
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Zusammenfassung Bei dem Versuch, die Kristallstruktur von Bonchevit zu bestimmen, stellte sich heraus, daß dieses Mineral—bis dahin PbBi4S7—aus zwei Phasen besteht. Der Hauptanteil wurde eindeutig als Galenobismutit identifiziert. Der Rest wies nach den Gitterkonstanten (a0=13,58±0,02 Å, b0=20,51±0,07 Å, c0=4,09±0,07 Å) auf ein bisher unbekanntes Mineral hin. Die Raumgruppe ist Bbmm. Ein indiziertes Pulverdiagramm und die dazugehörigen d-Werte werden angegeben. Die Emissionsspektralanalyse zeigt Pb und Bi als Hauptkomponenten, Cu und Ag als Nebenkomponenten und Spuren von Zn und Sn. Die Strukturanalyse führte zu der Formel Me5S6, wobei die Me-Atome etwa gleich schwer sind, so daß als chemischo Formel nur Pb3Bi2S6 mit Z=4 in Frage kommt. Strukturell gehört das Mineral in die Gruppe Andorit-Ramdohrit-Fizelyit. Die Verwandtschaft bzw. Identität des Minerals mit anderen Mineralen und synthetischen Verbindungen wird diskutiert.
    Notes: Summary During an attempt to determine the crystal structure of bonchevite, this mineral was found to consist of two phases. Previously it was thought to have the composition PbBi4S7. The main constituent could unambiguously be identified as galenobismutite. For the rest the lattice constants (a0=13.58±0,02 Å, b0=20.51±0,07 Å, c0=4.09±0.07 Å), indicated a new mineral. Space group is Bbmm. An indexed powder diagram (with d-values) is given. The emission spectrographic analysis shows Pb and Bi to be main components, Cu and Ag to be minor components, and traces only of Zn and Sn. The structure analysis has led to the formula Me5S6, with Me-atoms of approximately the same atomic number; therefore, the chemical formula has to be Pb3Bi2S6, with Z=4. In a structural classification the mineral belongs to the andoriteramdohrite-fizelyite-group. The relationships to or the identity with other minerals and synthetic compounds are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01088019
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  • 6
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    SINNERITE, Cu6As4S9, FROM THE LENGENBACH QUARRY, BINN VALLEY, SWITZERLAND: DESCRIPTION AND RE-INVESTIGATION OF THE CRYSTAL STRUCTURE (2014)
    Mineralogical Association of Canada
    Details
    Publication Date: 2014-03-25
    Description: We have characterized the crystal structure of sinnerite, Cu 6 As 4 S 9 , a rare sulfosalt mineral from the ores of the Lengenbach quarry, Binn Valley, Canton Valais, Switzerland, by single-crystal X-ray diffraction and chemical analysis. We found sinnerite to be structurally identical to synthetic Cu 6 As 4 S 9 . It is triclinic, space group P 1, with cell parameters: a 9.103(2), b 9.860(3), c 9.111(2) Å, α 90.27(2), β 109.53(2), 107.58(2)°, V 729.6(4) Å 3 , and Z = 2. Semi-quantitative SEM-EDS analyses confirmed the Cu 6 As 4 S 9 stoichiometry. The crystal structure of an untwinned crystal has been refined to R 1 = 5.45%. It consists of a sphalerite substructure with 2/5 of the tetrahedra replaced by AsS 3 pyramids; four pyramids form As 4 S 12 clusters around the vacant anion positions of the sphalerite archetype. These pyramids are linked into twisted and branched chain-like structures with compositions As 3 S 7 and As 5 S 11 . The chains are linked by CuS 4 tetrahedra. Packing of these chains results in the OD (order-disorder) character of the sinnerite structure.
    Print ISSN: 0008-4476
    Topics: Geosciences
    Published by Mineralogical Association of Canada
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  • 7
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    The crystal structure of jasrouxite, a Pb-Ag-As-Sb member of the lillianite homologous series (2014)
    Schweizerbart
    Details
    Publication Date: 2014-03-11
    Description: Jasrouxite, Ag 16 Pb 4 (Sb 25 As 15 ) 40 S 72 , is triclinic, space group P- 1, lattice parameters a = 8.2917(5), b = 19.101(1), c = 19.487(1) Å, α = 89.731(1)°, β = 83.446(1)°, and = 89.944(1) °. Unit-cell volume is V = 3066.1(3) Å 3 , Z = 1 for the title formula. It is the N =4 member of the lillianite homologous series of modular structures created by unit-cell twinning of (311) slabs of the PbS archetype. The structure contains 30 independent cation sites, from which 12 are mixed sites, and 36 independent sulphur sites ( i.e . six times the sites of the lillianite-like subcell). Only the c parameter copies that of lillianite, a is doubled and b is about 3/2 of a diagonal to (001) of lillianite. In agreement with the "2Pb-〉 Ag + (Sb,As) oversubstitution" against ideal PbAgSb 3 S 6 , the trigonal prismatic sites on composition planes of twinning are occupied by two Pb-Sb rows and one Sb-Sb row, and the PbS-like slabs contain excess number of Ag sites. Unlike lillianite, the alternating (311) PbS slabs are non-equivalent and each of them has two types of differently occupied diagonal planes of atoms, always present in a 2:1 ratio. This results in triclinic symmetry with only small distortions from monoclinic metrics. In both slab types lone electron pairs of As and Sb congregate in large micelles with elliptic cross-section. Among lillianite homologues, jasrouxite exhibits hitherto unseen complications of cation ordering, resulting from the presence of two distinct metalloids in the structure, oversubstitution by (Ag + M 3+ ), and highly expressed lone electron pair activity of trivalent cations.
    Print ISSN: 0935-1221
    Electronic ISSN: 1617-4011
    Topics: Geosciences
    Published by Schweizerbart
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  • 8
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    Vaterite: Interpretation in terms of OD theory and its next of kin (2016)
    Mineralogical Society of America
    Details
    Publication Date: 2016-07-02
    Description: The polytypic structures of vaterite, CaCO 3 , described in recent literature, have been reinterpreted in terms of the order-disorder (OD) theory, which allows us to explain and systematize all the observed and predicted polytypes of the mineral in a unified fashion. In terms of this theory, the structure consists of OD layers that comprise a layer of calcium coordination polyhedra and the attached halves of the standing CO 3 groups. The two-sided layer group of symmetry of the OD layer is c 2/ m , whereas the interlayer symmetry operations are three twofold rotation axes at 120° to one another, as well as a mirror plane in the common layer boundaries and partial c glide planes perpendicular to the boundary. Depending on the orientation of the active twofold rotation axis with respect to the above-defined layer mesh, performed independently in each stacking step, maximally ordered simple stacking sequences P 6 1 22, P 6 5 22, C 2/ c , C 2/ c 2/ m 2 1 / m , and a more complicated sequence P 3 1 2 or P 3 2 2, as well as several complicated or disordered sequences is obtained (before eventual relaxation to a subgroup of a particular space group). A perfect copy of the vaterite OD layer occurs in the structures of the bastnäsite-synchysite polysomatic series of fluorocarbonates. In these structures, the REE layers, configurationally analogous to the Ca-based OD layer, have layer symmetry p 32 and their stacking does not lead to polytypism and OD phenomena; these are generated on the Ca-based OD layers.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Published by Mineralogical Society of America
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  • 9
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    The Order-Disorder Character of Owyheeite (2016)
    Mineralogical Association of Canada
    Details
    Publication Date: 2016-09-16
    Description: Owyheeite, Ag 1.5 Pb 4.43 Sb 6.07 S 14 , monoclinic and pseudo-orthorhombic, is invariably intimately twinned, and its structure displays an alternation of two types of unit order-disorder (OD) layers, with layer symmetries P (2/ n ) 2(1)/ m 2(1)/ m for the thicker OD layer, and P (1) 1 2(1)/ m for the three-times thinner OD layer. These layers occur in two orientations, indexed as (021) and (0 2 1) of the owyheeite lattice. Ambiguity in the orientation of the thinner OD layer after the thicker one leads to intimate twinning (stacking disorder). Pseudohexagonality of the lattice ( b x 3/2 c ) with two alternative sets of OD layers further complicates the twinning situation, which also can be described using a rod representation of the structure.
    Print ISSN: 0008-4476
    Topics: Geosciences
    Published by Mineralogical Association of Canada
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  • 10
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    Exploratory Studies of Substitutions In the Tetrahedrite/Tennantite-Goldfieldite Solid Solution (2017)
    Mineralogical Association of Canada
    Details
    Publication Date: 2017-07-13
    Description: Phases on the Fe-tetrahedrite–goldfieldite and Fe-tennantite–goldfieldite joins were synthesized from high purity elements in evacuated silica glass tubes at 450 °C and analyzed using electron microprobe analysis and X-ray powder diffraction. The synthetic studies confirm that the compositions on these joins are determined by a (formal) interplay of the Fe 3+ + Cu + 2 Fe 2+ , Cu + + Te 4+ Fe 2+ + (Sb,As) 3+ , Cu + + 2Te 4+ Fe 3+ + 2(Sb,As) 3+ , and Cu + + Te 4+ Cu 2+ + (Sb,As) 3+ substitutions, and also for the region close to Te = 2 apfu by + Te 4+ Cu + + Sb 3+ . The latter exchange determines the Te-tennantite/tetrahedrite–goldfieldite join. For the region of goldfieldite just above and below 2 Te atoms pfu , the latter exchange is modified by the Fe n + n Cu + exchange. The 2Fe 2+ Fe 3+ + Cu + exchange causes an arc-like retreat of the composition field away from the linear Cu + + Te 4+ Fe 2+ + (Sb,As) 3+ boundary. Incomplete elimination of Fe, compensated by early onset of Cu vacancies, results in a gradual transition between the region of tellurian td/tn and goldfieldite sensu stricto . This variety of substitution and omission mechanisms determines the proportions of alternative endmembers and intermediate members: Cu 10 Fe 2+ 2 (Sb,As) 4 S 13 , Cu 11 Fe 3+ (Sb,As) 4 S 13 , Cu 12 (Sb,As) 4 S 13 , Cu 12 Te 2 (Sb,As) 2 S 13 , and Cu 10 Te 4 S 13 , plus a measure of the Fe n + n Cu + exchange. Natural goldfieldite conforms with the synthesis results in its compositional extent. The natural data are mostly not good or complete enough to examine the compositional details suggested here because the calculations described above are very sensitive to the quality of the analyses.
    Print ISSN: 0008-4476
    Topics: Geosciences
    Published by Mineralogical Association of Canada
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