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  • 1990-1994  (33)
  • 1
    Monograph available for loan
    Monograph available for loan
    Cambridge : Cambridge Univ. Pr.
    Associated volumes
    Call number: M 95.0470 ; 11/M 93.0961
    In: Cambridge topics in mineral physics and chemistry
    Type of Medium: Monograph available for loan
    Pages: XXIII, 551 S. : graph. Darst.
    Edition: 2nd ed.
    ISBN: 0521430771
    Series Statement: Cambridge topics in mineral physics and chemistry 5
    Classification: A.3.6.
    Language: English
    Location: Upper compact magazine
    Location: Reading room
    Branch Library: GFZ Library
    Branch Library: GFZ Library
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  • 2
    Publication Date: 2019-01-25
    Description: Altitude-dependent, high radar-reflectivity surfaces on Venus are observed on most mountainous volcanic terranes above a planetary radius of about 6054 km. However, high radar-reflectivity areas also occur at lower altitudes in some impact craters and plain terranes. Pyrite (FeS2) is commonly believed to be responsible for the high radar reflectivities at high elevations on Venus, on account of large dielectric constants measured for sulfide-bearing rocks that were erroneously attributed to pyrite instead of pyrrhotite. Pentlandite-pyrrhotite assemblages may be responsible for high reflectivities associated with impact craters on the Venusian surface, by analogy with Fe-Ni sulfide deposits occurring in terrestrial astroblemes. Mixed-valence Fe(2+)-Fe(3+) silicates, including oxyhornblende, oxybiotite, and ilvaite, may contribute to high radar reflecting surfaces on mountain-tops of Venus.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Twenty-fourth Lunar and Planetary Science Conference. Part 1: A-F; p 233-234
    Format: text
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  • 3
    Publication Date: 2019-01-25
    Description: Salts believed to occur in Martian regolith imply that brines occur on Mars, which may have facilitated the oxidation of dissolved Fe(2+) ions after they were released during chemical weathering of basaltic ferromagnesian silicate and iron sulfide minerals. Calculations show that the rate of oxidation of Fe(2+) ions at -35 C in a 6M chloride-sulfate brine that might exist on Mars is about 10(exp 6) times slower that the oxidation rate of iron in ice-cold terrestrial seawater.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Twenty-fourth Lunar and Planetary Science Conference. Part 1: A-F; p 231-232
    Format: text
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  • 4
    Publication Date: 2013-08-31
    Description: In previous Mossbauer spectral studies of many of the Shergotite Nakhlite Chassignite (SNC) meteorites, attention was drawn to the close similarities of spectrum profiles between Lafayette and Nakhla, which were once suggested to be identical meteorites. These observations led to the acquisition of Governador Valadares and another specimen of Nakhla, as well as Zagami and Shergotty, for Mossbauer spectral measurements at 4.2K. Results reported here demonstrate that there are subtle differences between the three nakhlites (Nakhla, Lafayette, and Governador Valadares), as there are for three of the shergottites (Shergotty, Zagami, EETA 79001/lithologies A and B) and olivine-dominated Chassigny and ALHA 77005, indicating that all eight of the SNC meteorites discovered to data fell independently to Earth.
    Keywords: ASTROPHYSICS
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1990; p 259-261
    Format: application/pdf
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  • 5
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Determination of oxidation states and the crystal chemistry of iron-bearing minerals in carbonaceous chondrites by Mössbauer spectroscopy is complicated by thermally-induced electron-hopping in cronstedtite, superparamagnetism of hydrous ferric oxides and ill-defined contributions from an incommensurate layered iron sulfide phase believed to be tochilinite. Mössbauer spectra measurements at 30 K of several terrestrial cronstedtite and tochilinite specimens have enables modal proportions of these minerals, as well as Fe3+/Fe2+ ratios, to be determined quantitatively in a suite of CM-type meteorites.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The variety of coordination numbers, symmetries, distortions and ligand environments in thermally-stable iron-bearing minerals provide wide ranges of chemical shift (δ) and quadrupole splitting (δ) parameters, which serve to characterize the crystal chemistries and site occupancies of Fe2+ and Fe3+ ions in minerals of terrestrial and extraterrestrial origins. Correlations between ferrous and ferric chemical shifts enable thermally-induced electron delocalization behavior in mixed-valence Fe2+-Fe3+ minerals to be identified, while chemical shift versus quadrupole splitting correlations serve to identify nanophase ferric oxides and oxyhydroxides in oxidized minerals and in meteorites subjected to aqueous oxidation before and after they arrived on Earth.
    Type of Medium: Electronic Resource
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  • 7
    Publication Date: 2013-08-31
    Description: The occurrence of ferric bearing assemblages, comprising phyllosilicates, oxide hydroxides and magnetite, in carbonaceous chondrites (CC) indicates that these meteorites underwent pre-terrestrial, sub-aqueous oxidation reactions. Reported here are results of a Mossbauer spectral study of a suite of CC demonstrating that a variety of ferrous and ferric bearing phases may be distinguished in different classes of this meteorite type.
    Keywords: ASTROPHYSICS
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1990; p 256-258
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  • 8
    Publication Date: 2013-08-31
    Description: The reflectance spectra of Fe(2+)-Mg(2+) disordered orthopyroxenes are relevant to surfaces of terrestrial planets onto which basaltic magma has been extruded. If cooling rates of basalt lava flows were fast, equilibrium iron intersite partitioning may not have been achieved so that abnormal enrichments of Fe(2+) ions in M1 sites would occur. The two intense pyroxene Fe(2+) site CF bands in the 1 micron and 2 micron regions would continue to dominate the the reflectance spectra so that the pyroxene composition and structure type would be readily identified in telescopic spectral profiles. However, abnormal intensification of the Fe(2+)/M1 site CF band at 1.20 microns could lead to the false identification of olivine in remote sensed spectra because in pyroxene-olivine mixtures the inflection around 1.20 microns is the only spectral feature for detecting the presence of olivine. The identification of iron-bearing plagioclase feldspars, too, would be obscured by the pyroxene Fe(2+)/M1 site CF band at 1.20 microns. Such interference would be a major problem if in situ reflectance spectra could be measured on the surface of Venus where ambient temperatures are as high as 475 C. Disordering of Fe(2+) and Mg(2+) ions comparable to that in the orthopyroxenes used in this spectral chemical study might be expected in low Ca pyroxenes occurring on the Venusian surface. Researchers conclude that Fe(2+)/M1 site spectral features need to be carefully assessed in remote-sensed spectra before deductions are made about the presence of olivine on planetary surfaces.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1990; p 253-255
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  • 9
    Publication Date: 2013-08-31
    Description: Experiments demonstrated that oxidation of ferromagnesian silicates and magnetite occurs when these minerals are heated at 800 C in 1 atmosphere of CO2, under which conditions hematite is thermodynamically stable. The 30 ppm oxygen impurity in CO2 presumably facilitates the oxidation of some of the ferrous iron initially present in the crystal structures of the minerals. Mossbauer spectral measurements reveal, however, that only CO2 degraded olivine and pigeonite is hematite formed as a magnetically ordered phase at ambient temperatures. In orthopyroxene, some of the ferric iron produced by oxidation is present as nanophase hematite which, because it remains superparamagnetic until 4.2 K, must exist as particles less than or equal to 4 nm in diameter. In the calcic pyroxenes much of the oxidized ferrous iron may still remain as structural Fe3(+) in the host silicates. Some ferric iron may also be present as unit cell sized Fe2O3 inclusions in the pyroxenes, or be segregated along cleavage planes, or be coating mineral grains. In these states of aggregation, the Fe2O3 is unidentifiable by x ray diffraction and in low temperature Mossbauer spectra. Applications of this research to the surface of Venus are discussed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1990; p 207-209
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  • 10
    Publication Date: 2013-08-31
    Description: Inferences from these investigations are that Fe(3+)-bearing minerals such as hematite magnesioferrite, acmite, and epidote are thermodynamically unstable, and that magnetite is the predominant mixed-valence iron oxide mineral on venus. Recently, the Fe(2+)-Fe(3+) silicate mineral laihunite was proposed to be a reaction product of olivine with the venusian atmosphere. This possibility is discussed further here. We suggest that other mixed-valence Fe(2+)-Fe(3+)-Oz-OH(-) silicates could also result from surface-atmosphere interactions on Venus. Topics discussed include the following: (1) conversion of hematite to magnetite; (2) stability of laihunite; (3) the possible existence of oxy-amphiboles and oxy-micas on Venus; and (4) other mixed-valence Fe(2+)-Fe(3+) silicates likely to exist on Venus.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Papers Presented to the International Colloquium on Venus; p 15-17
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