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  • Springer  (14)
  • Mineralogical Society of Great Britain and Ireland  (9)
  • American Association for the Advancement of Science  (4)
  • 1
    Electronic Resource
    Electronic Resource
    Bond length and radii variations in fluoride and oxide molecules and crystals (1994)
    Springer
    Physics and chemistry of minerals 20 (1994), S. 617-624 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Molecular orbital calculations completed on fluoride molecules containing first and second row cations have generated bond lengths, R, that match those observed for coordinated polyhedra in crystals to within ∼0.04 Å, on average. The calculated bond lengths and those observed for fluoride crystals can be ranked with the expression R=Kp −0.22, where p=s/r, s is the Pauling strength of the bond, r is the row number of the cation and K=1.34. The exponent -0.22 (≈ -2/9) is the same as that observed for oxide, nitride and sulfide molecules and crystals. Bonded radii for the fluoride anion, obtained from theoretical electron density maps, increase linearly with bond length. Those calculated for the cations as well as for the fluoride anion match calculated promolecule radii to within ∼0.03 Å, on average, suggesting that the electron density distributions in the vicinity of the minima along the bond paths possess a significant atomic component despite bond type. Bonded radii for Si and O ions provided by experimental electron density maps measured for the oxides coesite, danburite and stishovite match those calculated for a series of monosilicic acid molecules. The resulting radii increase with bond length and coordination number with the radius of the oxide ion increasing at a faster rate than that of the Si cation. The oxide ion within danburite exhibits several distinct radii, ranging between 0.9 and 1.2 Å, rather than a single radius with each exhibiting a different radius along each of the nonequivalent bonds with B, Si and Ca. Promolecule radii calculated for the coordinated polyhedra in danburite match procrystal radii obtained in a structure analysis to within 0.002 Å. The close agreement between these two sets of radii and experimentally determined bonded radii lends credence to Slater's statement that the difference between the electron density distribution observed for a crystal and that calculated for a procrystal (IAM) model of the crystal “would be small and subtle, and very hard to determine by examination of the total charge density.”
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00211857
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  • 2
    Electronic Resource
    Electronic Resource
    Compression of witherite to 8 GPa and the crystal structure of BaCO3II (2000)
    Springer
    Physics and chemistry of minerals 27 (2000), S. 467-473 
    Details
    ISSN: 1432-2021
    Keywords: Key words Witherite ; High pressure ; Aragonite ; Crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Natural witherite (Ba0.99Sr0.01CO3) has been studied by single-crystal X-ray diffraction in the diamond anvil cell at eight pressures up to 8 GPa. At ambient pressure, cell dimensions are a = 5.3164(12) Å, b = 8.8921(19) Å, c = 6.4279(16) Å, and the structure was refined in space group Pmcn to R(F) = 0.020 from 2972 intensity data. The unit cell and atom position parameters for the orthorhombic cell were refined at pressures of 1.2, 2.0, 2.9, 3.9, 4.6, 5.5, 6.2, and 7.0 GPa. The volume-pressure data are used to calculate equation of state parameters K T0 = 50.4(12) GPa and K′ = 1.9(4). At approximately 7.2 GPa, a first-order transformation to space group P3¯1c was observed. Cell dimensions of the high-pressure phase at 7.2 GPa are a = 5.258(6) Å, c = 5.64(1) Å. The high pressure structure was determined and refined to R(F) = 0.06 using 83 intensity data, of which 15 were unique. This high-pressure phase appears to be more compressible than the orthorhombic phase with an estimated initial bulk modulus (K 7.2GPa) of 10 GPa.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690000087
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  • 3
    Electronic Resource
    Electronic Resource
    Comparative compressibilities of majorite-type garnets (1994)
    Springer
    Physics and chemistry of minerals 21 (1994), S. 344-349 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Relative compressibilities of five silicate garnets were determined by single-crystal x-ray diffraction on crystals grouped in the same high-pressure mount. The specimens include a natural pyrope [(Mg2.84Fe0.10Ca0,06) Al2Si3O12], and four synthetic specimens with octahedrally-coordinated silicon: majorite [Mg3(MgSi)Si3O12], calcium-bearing majorite [(Ca0.49Mg2.51)(MgSi)Si3012], sodium majorite [(Na1.88Mgp0.12)(Mg0.06Si1.94)Si3O12], and an intermediate composition [(Na0.37Mg2.48)(Mg0.13Al1.07 Si080) Si3O12]. Small differences in the compressibilities of these crystals are revealed because they are subjected simultaneously to the same pressure. Bulk-moduli of the garnets range from 164.8 ± 2.3 GPa for calcium majorite to 191.5 ± 2.5 GPa for sodium majorite, assuming K′=4. Two factors, molar volume and octahedral cation valence, appear to control garnet compression.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202099
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  • 4
    Electronic Resource
    Electronic Resource
    SiO and GeO bonded interactions as inferred from the bond critical point properties of electron density distributions (1998)
    Springer
    Physics and chemistry of minerals 25 (1998), S. 574-584 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  The topological properties of the electron density distributions for more than 20 hydroxyacid, geometry optimized molecules with SiO and GeO bonds with 3-, 4-, 6- and 8-coordinate Si and Ge cations were calculated. Electronegativities calculated with the bond critical point (bcp) properties of the distributions indicate, for a given coordination number, that the electronegativity of Ge (∼1.85) is slightly larger than that of Si (∼1.80) with the electronegativities of both atoms increasing with decreasing bond length. With an increase in the electron density, the curvatures and the Laplacian of the electron density at the critical point of each bond increase with decreasing bond length. The covalent character of the bonds are assessed, using bond critical point properties and electronegativity values calculated from the electron density distributions. A mapping of the (3, −3) critical points of the valence shell concentrations of the oxide anions for bridging SiOSi and GeOGe dimers reveals a location and disposition of localized nonbonding electron pairs that is consistent with the bridging angles observed for silicates and germanates. The bcp properties of electron density distributions of the SiO bonds calculated for representative molecular models of the coesite structure agree with average values obtained in X-ray diffraction studies of coesite and danburite to within ∼5%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050150
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  • 5
    Electronic Resource
    Electronic Resource
    Compressibility and crystal structure of sillimanite, Al2SiO5, at high pressure (1997)
    Springer
    Physics and chemistry of minerals 25 (1997), S. 39-47 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  The unit-cell dimensions and crystal structure of sillimanite at various pressures up to 5.29 GPa have been refined from single-crystal X-ray diffraction data. As pressure increases, a and b decrease linearly, whereas c decreases nonlinearly with a slightly positive curvature. The axial compression ratios at room pressure are βa:βb:βc=1.22:1.63:1.00. Sillimanite exhibits the least compressibility along c, but the least thermal expansivity along a (Skinner et al. 1961; Winter and Ghose 1979). The bulk modulus of sillimanite is 171(1) GPa with K′=4 (3), larger than that of andalusite (151 GPa), but smaller than that of kyanite (193 GPa). The bulk moduli of the [Al1O6], [Al2O4], and [SiO4] polyhedra are 162(8), 269(33), and 367(89) GPa, respectively. Comparison of high-pressure data for Al2SiO5 polymorphs reveals that the [SiO4] tetrahedra are the most rigid units in all these polymorphic structures, whereas the [AlO6] octahedra are most compressible. Furthermore, [AlO6] octahedral compressibilities decrease from kyanite to sillimanite, to andalusite, the same order as their bulk moduli, suggesting that [AlO6] octahedra control the compression of the Al2SiO5 polymorphs. The compression of the [Al1O6] octahedron in sillimanite is anisotropic with the longest Al1-OD bond shortening by ∼1.9% between room pressure and 5.29 GPa and the shortest Al1-OB bond by only 0.3%. The compression anisotropy of sillimanite is primarily a consequence of its topological anisotropy, coupled with the compression anisotropy of the Al-O bonds within the [Al1O6] octahedron.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050084
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  • 6
    Electronic Resource
    Electronic Resource
    Power law relationships between bond length, bond strength and electron density distributions (1998)
    Springer
    Physics and chemistry of minerals 25 (1998), S. 585-590 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  The strength of a bond, defined as p=s/r, where s is the Pauling bond strength and r is the row number of an M cation bonded to an oxide anion, is related to a build-up of electron density along the MO bonds in a relatively large number of oxide and hydroxyacid molecules, three oxide minerals and three molecular crystals. As p increases, the value of the electron density is observed to increase at the bond critical points with the lengths of the bonds shortening and the electronegativities of the M cations bonded to the oxide anion increasing. The assertion that the covalency of a bond is intrinsically connected to its bond strength is supported by the electron density distribution and its bond critical point properties. A connection also exists between the properties of the electron density distributions and the connectivity of the bond strength network formed by the bonded atoms of a structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050151
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  • 7
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    Anorpiment, As2S3, the triclinic dimorph of orpiment (2011)
    Mineralogical Society of Great Britain and Ireland
    Details
    Publication Date: 2011-12-01
    Description: The new mineral anorpiment, As2S3, the triclinic dimorph of orpiment, has space group P1I and cell parameters a = 5.7577(2), b = 8.7169(3), c = 10.2682(7) Å, a = 78.152(7), ß = 75.817(7), ? = 89.861(6)°, V = 488.38(4) Å3 and Z = 4. It occurs at the Palomo mine, Castrovirreyna Province, Huancavelica Department, Peru. It is a low-temperature hydrothermal mineral associated with dufrénoysite, muscovite, orpiment, pyrite and realgar. It occurs in drusy crusts of wedge-shaped, transparent, greenish yellow crystals. The streak is yellow. The lustre is resinous on crystal faces, but pearly on cleavage surfaces. The Mohs hardness is about 1. The mineral is sectile with an irregular fracture and one perfect and easy cleavage on {001}. The measured and calculated densities are 3.33 and 3.321 g cm-3, respectively. All indices of refraction are greater than 2. The mineral is optically biaxial (–) with 2V = 35–40° and no observed dispersion. The acute bisectrix (X) is approximately perpendicular to the {001} cleavage. Electron microprobe analyses yielded the averages and ranges in wt.%: As 58.21 (57.74–59.03), S 38.72 (38.33 39.00), total 96.94 (96.07 97.75), providing the empirical formula (based on 5 atoms) As1.96S3.04. The strongest powder X-ray diffraction lines are [d (hkl) I] 4.867(002) 97, 4.519 (110,11I1) 77, 3.702 (1I1I1) 46, 3.609 (022,11I2) 82, 2.880 (201,02I2,1I2I1,023) 75, 2.552 (1I13,1I31,132) 100, 2.469 (114,130,13I1) 96. The structure of anorpiment [R1 = 0.021 for 1484 reflections with Fo 〉 4s(F)] consists of layers of covalently bonded As and S atoms. Each S atom bonds to two As atoms at As–S–As angles between 100.45 and 104.15°. Each As atom is strongly bonded to three S atoms at S–As–S angles between 91.28 and 103.59°, forming an AsS3 pyramid with As at its apex. The As–S linkages within the layers form rings of six AsS3 pyramids. Interlayer bonding forces are interpreted as van der Waals. The structure of anorpiment is similar to that of orpiment in that it is composed of layers of As2S3 macromolecules, but arranged in a different stacking sequence.
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
    Published by Mineralogical Society of Great Britain and Ireland
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  • 8
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    Unknown
    A chemical and structural re-examination of fettelite samples from the type locality, Odenwald, southwest Germany (2012)
    Mineralogical Society of Great Britain and Ireland
    Details
    Publication Date: 2012-06-01
    Description: The crystal structure and chemical composition of two samples of fettelite from the type locality, including a portion of the holotype material, was investigated to verify if a previously proposed revision of the chemical formula was applicable, and to study the role of cation substitution for Hg that would suggest new members of the fettelite family. The crystal structure of fettelite from the type locality was found to be equivalent to that reported previously for the Chilean occurrence, and consists of an alternation of two kinds of layers along c: layer A with general composition [Ag6As2S7]2− and layer B with general composition [Ag10HgAs2S8]2+. In this structure, the Ag atoms occur in various coordination configurations, varying from quasi-linear to quasi-tetrahedral, the AsS3 groups form pyramids as are typically observed in sulfosalts, and Hg links two sulfur atoms in a linear coordination. The refined compositions for the crystals in this study, [Ag6As2S7][Ag10(Fe0.53Hg0.47)As2S8] (R100124) and [Ag6As2S7][Ag10(Hg0.79Cu0.21)As2S8] (R110042), clearly indicate that new mineral species related to fettelite are likely to be found in nature.
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
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  • 9
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    New data on hemihedrite from Arizona (2017)
    Mineralogical Society of Great Britain and Ireland
    Details
    Publication Date: 2017-08-08
    Description: Hemihedrite from the Florence Lead-Silver mine in Pinal County, Arizona, USA was first described and assigned the ideal chemical formula Pb 10 Zn(CrO 4 ) 6 (SiO 4 ) 2 F 2 , based upon a variety of chemical and crystal-structure analyses. The primary methods used to determine the fluorine content for hemihedrite were colorimetry, which resulted in values of F that were too high and inconsistent with the structural data, and infrared (IR) spectroscopic analysis that failed to detect OH or H 2 O. Our reinvestigation using electron microprobe analysis of the type material, and additional samples from the type locality, the Rat Tail claim, Arizona, and Nevada, reveals the absence of fluorine, while the presence of OH is confirmed by Raman spectroscopy. These findings suggest that the colorimetric determination of fluorine in the original description of hemihedrite probably misidentified F due to the interferences from PO 4 and SO 4 , both found in our chemical analyses. As a consequence of these results, the study presented here proposes a redefinition of the chemical composition of hemihedrite to the ideal chemical formula Pb 10 Zn(CrO 4 ) 6 (SiO 4 ) 2 (OH) 2 . Hemihedrite is isotypic with iranite with substitution of Zn for Cu, and raygrantite with substitution of Cr for S. Structural data from a sample from the Rat Tail claim, Arizona, indicate that hemihedrite is triclinic in space group P 1 , a = 9.4891(7), b = 11.4242(8), c = 10.8155(7) Å, α = 120.368(2)°, β = 92.017(3)°, = 55.857(2)°, V = 784.88(9) Å 3 , Z = 1, consistent with previous investigations. The structure was refined from single-crystal X-ray diffraction data to R 1 = 0.022 for 5705 unique observed reflections, and the ideal chemical formula Pb 10 Zn(CrO 4 ) 6 (SiO 4 ) 2 (OH) 2 was assumed during the refinement. Electron microprobe analyses of this sample yielded the empirical chemical formula Pb 10.05 (Zn 0.91 Mg 0.02 ) = 0.93 (Cr 5.98 S 0.01 P 0.01 ) = 6.00 Si 1.97 O 34 H 2.16 based on 34 O atoms and six (Cr + S + P) per unit cell.
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
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  • 10
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    Hydroxycalciomicrolite, Ca1.5Ta2O6(OH), a new member of the microlite group from Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil (2017)
    Mineralogical Society of Great Britain and Ireland
    Details
    Publication Date: 2017-05-10
    Description: Hydroxycalciomicrolite, Ca 1.5 Ta 2 O 6 (OH) is a new microlite-group mineral found in the Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil. It occurs as isolated octahedral and as a combination of octahedral and rhombic dodecahedral crystals, up to 1.5 mm in size. The crystals are yellow and translucent, with a white streak and vitreous to resinous lustre. The mineral is brittle, with a Mohs hardness of 5–6. Cleavage is not observed and fracture is conchoidal. The calculated density is 6.176 g cm –3 . Hydroxycalciomicrolite is isotropic, n calc. = 2.010. The infrared and Raman spectra exhibit bands due to O–H stretching vibrations. The chemical composition determined from electron microprobe analysis ( n = 13) is (wt.%): Na 2 O 0.36(8), CaO 15.64(13), SnO 2 0.26(3), Nb 2 O 5 2.82(30), Ta 2 O 5 78.39(22), MnO 0.12(2), F 0.72(12) and H 2 O 1.30 (from the crystal structure data), O = F –0.30, total 99.31(32), yielding an empirical formula, (Ca 1.48 Na 0.06 Mn 0.01 ) 1.55 (Ta 1.88 Nb 0.11 Sn 0.01 ) 2.00 O 6.00 [(OH) 0.76 F 0.20 O 0.04 ]. Hydroxycalciomicrolite is cubic, with unit-cell parameters a = 10.4205(1) Å, V = 1131.53(2) Å 3 and Z = 8. It represents a pyrochlore supergroup, microlite-group mineral exhibiting P 4 3 32 symmetry, instead of Fd m . The reduction in symmetry is due to long-range ordering of Ca and vacancies on the A sites. This is the first example of such ordering in a natural pyrochlore, although it is known from synthetic compounds. This result is promising because it suggests that other species with P 4 3 32 or lower-symmetry space group can be discovered and characterized.
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    Electronic ISSN: 1471-8022
    Topics: Geosciences
    Published by Mineralogical Society of Great Britain and Ireland
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