ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The antiferroelectric phase transition in titanite characterised by a collinear displacement of Ti-atoms from their central octahedral position is investigated using linear optical birefringence and X-ray diffraction techniques. Both methods indicate a continuous transition near 496 K and extra contributions to δΔn and X-ray intensity signals at higher temperatures. The critical exponent of the macroscopic order parameter is found to be β = 0.14 ± 0.02 and the transformation is interpreted in terms of a two-dimensional quasi-spin model. Topological features of the structure agree well with the spatial distribution of the diffuse scattering of the superstructure reflection 40 $$\bar 3$$ .
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Publication Date: 2012-02-01
    Description: Three samples from the dumortierite group of minerals were examined with magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR): a dumortierite [c. (Al,?)Al6(BO3)Si3O13(O,OH)2] consisting of dark blue euhedral crystals from Madagascar (D34); a fine-grained pale blue dumortierite from Island Copper mine, British Columbia, Canada (D12); and a creamy white holtite [c. (Ta,Nb,?,Al)Al6(BO3)(Si,Sb,As)3O12(O,OH,?)3] from Szklary, Lower Silesia, Poland (WPH). Restricted Hartree-Fock ab initio electronic structure calculations were performed on model clusters with the goal of matching local environments of Si atoms to peaks in the 29Si MAS NMR spectra. The spectrum of D34 showed five resolved peaks at -95.2, -92.6, -91.3, -89.1, and -86.5 ppm with deconvoluted peak area contributions of 57, 19, 7, 10, and 7%. Electronic structure calculations, cross-polarization MAS NMR measurements and relative intensities support assigning the peaks at -95.2 and -92.6 ppm to Si2 and Si1 sites, respectively, adjacent to fully occupied Al1 sites (i.e., Q4 Si sites), and assigning the three remaining peaks to Si sites adjacent to vacant Al1 sites (i.e., Q3 Si sites). Due to the complexity of the dumortierite structure, clusters composed of at least the first four shells of nearest neighbor atoms to the target Si atom are necessary to model Q4 sites. The spectrum of D12 showed two main peaks at -93 and -95 ppm, with minor peaks below -90 ppm and above -100 ppm. The spectrum of WPH showed one broad peak at -93 ppm, likely containing both Si1 and Si2 signals, and two minor peaks below -90 ppm.Single-crystal X-ray diffraction and structure refinement on D34 shows orthorhombic symmetry, Pnma, Z = 4, a = 4.6882(1), b = 11.7924(2), c = 20.1856(3) Å, and V = 1115.97(4) Å3 with R1 = 0.0124. Three distinct sub-sites of the face-sharing octahedral chain site Al1 were distinguished corresponding to sites with one vacancy above, with one vacancy below, and between two occupied sites; the vacancy-adjacent sites have the cation displaced to increase the Al3+-Al3+ distance. Each sub-site is approximately ¼ occupied, suggesting that Al3+ cations in individual face-sharing octahedral chains are ordered as ?-Al-Al-Al, although cations from chain to chain are disordered, preserving Pnma symmetry.Powder X-ray diffraction measurements were performed on both D34 and D12. The unit cell of D12 was found to be a = 4.7001(7), b = 11.785(2), c = 20.277(3) Å.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Publication Date: 2011-08-01
    Description: We have measured the elastic response of radiation-damaged titanite, CaTiSiO5, as a function of thermal annealing. We estimate the bulk modulus of the damaged samples (~24% amorphous) to be 85 GPa, which is much softer than for undamaged crystalline titanite [131.4 GPa; Angel et al. (1999)]. Conversely, the lowest shear modulus of the radiation-damaged material is 52-58 GPa, which is harder that of the undamaged titanite, 46-52 GPa. The bulk and shear moduli of the radiation-damaged materials are close to those of thermal titanite glass, Bglass {approx} 75 GPa and Gglass {approx} 47 GPa, and are much smaller than expected based on other radiation-damaged materials such as zircon (ZrSiO4). Surprisingly, annealing of the damaged titanite in the range 600 〈 T 〈 1000 K leads to additional massive softening of the shear moduli. During annealing the shear modulus of titanite sample 1 softened from 58 to 29 GPa, and sample 2 softened from 52 to 19 GPa. The temperature range for the softening coincides with that found for crystallization of the amorphous regions, as measured previously by diffraction and spectroscopic methods. In contrast to the huge softening of the ultrasonically measured shear modulus, the calorimetrically measured Debye temperature {theta}D increases by ~5%, suggesting a small intrinsic hardening of the acoustic shear modes. Additional heating to 1473 K leads, in one titanite sample, to a steep increase of the shear modulus to values much larger than that of the initial, radiation-damaged material. Theoretical models are discussed to rationalize the massive softening due to both radiation damage and subsequent anneal.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
  • 5
    Publication Date: 2018-12-11
    Description: Kristiansenite, ideally Ca2ScSn(Si2O7)(Si2O6OH), a rare late-stage hydrothermal Sc-bearing sorosilicate mineral, was found in a gadolinite-fergusonite-type pegmatite of the MI-REE subclass related to the Karkonosze granite, exposed in a quarry at Szklarska Poręba, Lower Silesia, Poland. Kristiansenite occurs in an association with andradite, epidote, allanite-(Ce), titanite, fersmite, scheelite, Sc-bearing columbite-(Fe), a YNbO4 mineral as fergusonite-(Y) or fergusonite-(Y)-beta, silesiaite and wolframite. Single-crystal study of the mineral (R1 of 4.96%), with composition Ca2.00(Sn0.97Sc0.69Fe3+0.17Mn0.05Ti0.04Zr0.03Nb0.02Al0.02Ta0.01)Σ2(Si2O7)[(Si1.98Al0.02)Σ2O6.03(OH)0.97], corroborates its triclinic structure with space group-symmetry C1, Z = 2, and unit-cell parameters a = 10.0304(5), b = 8.4056(4), c = 13.3228(6) Å, α = 90.001(3), β = 109.105(3), γ = 89.997(3)° and V = 1061.40(9) Å3. In the structure of the mineral, the Ca and Si sites are dominantly occupied with Ca and Si, whereas the M1–M4 sites are disordered. The M3 and M4 sites are occupied dominantly by Sn and subordinately Sc, whereas the M1 and M2 sites are occupied dominantly by Sc and subordinately by remaining occupants, including Sn.
    Electronic ISSN: 2075-163X
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Publication Date: 2019-02-13
    Description: Although emerald deposits are relatively rare, they can be formed in several different, butspecific geologic settings and the classification systems and models currently used to describeemerald precipitation and predict its occurrence are too restrictive, leading to confusion as to theexact mode of formation for some emerald deposits. Generally speaking, emerald is beryl withsufficient concentrations of the chromophores, chromium and vanadium, to result in green andsometimes bluish green or yellowish green crystals. The limiting factor in the formation of emeraldis geological conditions resulting in an environment rich in both beryllium and chromium orvanadium. Historically, emerald deposits have been classified into three broad types. The first andmost abundant deposit type, in terms of production, is the desilicated pegmatite related type thatformed via the interaction of metasomatic fluids with beryllium-rich pegmatites, or similar graniticbodies, that intruded into chromium- or vanadium-rich rocks, such as ultramafic and volcanic rocks,or shales derived from those rocks. A second deposit type, accounting for most of the emerald ofgem quality, is the sedimentary type, which generally involves the interaction, along faults andfractures, of upper level crustal brines rich in Be from evaporite interaction with shales and otherCr- and/or V-bearing sedimentary rocks. The third, and comparatively most rare, deposit type is themetamorphic-metasomatic deposit. In this deposit model, deeper crustal fluids circulate along faultsor shear zones and interact with metamorphosed shales, carbonates, and ultramafic rocks, and Beand Cr (±V) may either be transported to the deposition site via the fluids or already be present inthe host metamorphic rocks intersected by the faults or shear zones. All three emerald depositmodels require some level of tectonic activity and often continued tectonic activity can result in themetamorphism of an existing sedimentary or magmatic type deposit. In the extreme, at deepercrustal levels, high-grade metamorphism can result in the partial melting of metamorphic rocks,blurring the distinction between metamorphic and magmatic deposit types. In the present paper,we propose an enhanced classification for emerald deposits based on the geological environment,i.e., magmatic or metamorphic; host-rocks type, i.e., mafic-ultramafic rocks, sedimentary rocks, andgranitoids; degree of metamorphism; styles of minerlization, i.e., veins, pods, metasomatites, shearzone; type of fluids and their temperature, pressure, composition. The new classification accountsfor multi-stage formation of the deposits and ages of formation, as well as probable remobilizationof previous beryllium mineralization, such as pegmatite intrusions in mafic-ultramafic rocks. Suchnew considerations use the concept of genetic models based on studies employing chemical,geochemical, radiogenic, and stable isotope, and fluid and solid inclusion fingerprints. The emerald occurrences and deposits are classified into two main types: (Type I) Tectonic magmatic-relatedwith sub-types hosted in: (IA) Mafic-ultramafic rocks (Brazil, Zambia, Russia, and others); (IB)Sedimentary rocks (China, Canada, Norway, Kazakhstan, Australia); (IC) Granitic rocks (Nigeria).(Type II) Tectonic metamorphic-related with sub-types hosted in: (IIA) Mafic-ultramafic rocks(Brazil, Austria); (IIB) Sedimentary rocks-black shale (Colombia, Canada, USA); (IIC) Metamorphicrocks (China, Afghanistan, USA); (IID) Metamorphosed and remobilized either type I deposits orhidden granitic intrusion-related (Austria, Egypt, Australia, Pakistan), and some unclassifieddeposits.
    Electronic ISSN: 2075-163X
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Publication Date: 2018-01-01
    Description: Sakhaite, ca. Ca48Mg16(BO3)32(CO3)16(HCl,H2O)2, is a rare rock-forming borate-carbonate mineral typically occurring in high-temperature, low-pressure calcareous skarns. It forms a complete solid solution with harkerite, ca. Ca48Mg16[AlSi4(O,OH)16]4(BO3)16(CO3)16(HCl,H2O)2. The solid solution can be described with the general formula Ca48(Mg,Fe,Mn)16(CO3)16[AlaSi5−a(O,OH)16]y(BO3)32−4y(HCl,H2O)n where ymax = 8 and nmax = 16 – y. In this study, we examine samples of sakhaite and harkerite from four localities worldwide: Titovskoye deposit, Sakha Republic, Russia (type locality for sakhaite); Solongo B deposit, Buryatia Republic, Russia; Camas Malag, Skye, Scotland (type locality for harkerite); as well as a sakhaite-like mineral from the Kombat Mine, Tsumeb. The Si:B ratios of the samples ranged from that of end-member sakhaite (containing B only) to that of end-member harkerite (Si:B = 1:1), with several intermediate compositions. All samples were deficient in B relative to the ideal composition, implying significant substitution for borate groups. The Si:Al ratio of silicate-containing samples ranged from the ideal 4:1 to 4:1.5, implying substitution of Al at the Si site. The cubic unit-cell parameter was found to increase linearly with increasing Si content, except for the sakhaite-like mineral from Tsumeb. This mineral was found to have significant substitution of Pb for Ca (0.4–0.5 apfu) and was poor in Cl, which in most sakhaite and harkerite samples occupies the interstitial site surrounded by four borate groups. This interstitial site in the Tsumeb samples appears to be, instead, mainly occupied by H2O, which may qualify the mineral as a distinct species.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Publication Date: 2014-06-01
    Print ISSN: 0024-4937
    Electronic ISSN: 1872-6143
    Topics: Geosciences
    Published by Elsevier
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Publication Date: 1994-06-01
    Description: Detailed examination of ‘staringite’ by X-ray precession photography and high-resolution transmission electron microscopy shows it to consist of a sub-microscopic intergrowth of cassiterite and tapiolite. ‘Staringite’ is discredited as a valid mineral species.
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Publication Date: 1996-08-01
    Description: Leisingite, ideally Cu(Mg,Cu,Fe,Zn)2Te6+O6·6H2O, is hexagonal, P3 (143), with unit-cell parameters refined from powder data: a = 5.305(1), c = 9.693(6) Å, V = 236.2(2) Å3, c/a = 1.8271, Z = 1. The strongest six reflections of the X-ray powder-diffraction pattern [d in Å (I) (hkl)] are: 9.70 (100) (001), 4.834 (80) (002), 4.604 (60) (100), 2.655 (60) (110), 2.556 (70) (111) and 2.326 (70) (112). The mineral is found on the dumps of the Centennial Eureka mine, Juab County, Utah U.S.A. where it occurs as isolated, or rarely as clusters of, hexagonal-shaped very thin plates or foliated masses in small vugs of crumbly to drusy white to colourless quartz. Associated minerals are jensenite, cesbronite and hematite. Individual crystals are subhedral to euhedral and average less than 0.1 mm in size. Cleavage {001} perfect. Forms are: {001} major; {100}, {110} minute. The mineral is transparent to somewhat translucent, pale yellow to pale orange-yellow, with a pale yellow streak and an uneven fracture. Leisingite is vitreous with a somewhat satiny to frosted appearance, brittle to somewhat flexible and nonfluorescent; H(Mohs) 3–4; D(calc.) 3.41 for the idealized formula; uniaxial negative, ω = 1.803(3), ɛ = 1.581 (calc.). Averaged electron-microprobe analyses yielded CuO 24.71, FeO 6.86, MgO 6.19, ZnO 0.45, TeO3 36.94, H2O (calc.) [21.55], total [96.70] wt.%, leading to the empirical formula based on O = 12. The infrared absorption spectrum shows definite bands for structural H2O with an O-H stretching frequency centered at 3253 cm−1 and a H-O-H flexing frequency centered at 1670 cm−l. The mineral name honours Joseph F. Leising, Reno, Nevada, who helped collect the discovery specimens.
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...