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  • 1
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Olivine inclusions in diamonds from kimberlites originating from the deep Upper Mantle contain significant amounts of chromium. It has been suggested that divalent chromium occurs in these olivines. This hypothesis is supported by recent Mössbauer and electronic spectral measurements at high pressures, which demonstrate that pressure-induced reduction takes place in compounds and minerals initially containing Fe3+, Mn3+, and Cu2+ ions. The process is facilitated at high temperatures. Low oxidation states of other metals such as Cr(II) are expected to be stabilized under the very high pressures and elevated temperature conditions in the Mantle. Since Cr2+ ions are susceptible to the Jahn-Teller effect, they are predicted by crystal field theory to be stabilized in certain distorted coordination sites, such as the olivine Ml site, all three sites of the β-spinel phase, and the 7-coordinated site of the strontium plumbate structure-type. The Cr2+ ions in olivines are stabilized in kimberlites intruded into the Crust by the high confining pressures in the diamond inclusions.
    Type of Medium: Electronic Resource
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