Astrid Holzheid

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Observations of martian surface morphology have been used to argue that an ancient ocean once existed on Mars. It has been thought that significant quantities of such water could have been supplied to the martian surface through volcanic outgassing, but this suggestion is contradicted by the low magmatic water content that is generally inferred from(More)
Experiments in sulfide-silicate systems demonstrate that two sulfide phases are stable in the asthenospheric upper mantle: a crystalline osmium-iridium-ruthenium-enriched monosulfide and a rhodium-platinum-palladium-enriched sulfide melt. During silicate melt segregation, monosulfide stays in the solid residue, dominating the noble metal spectrum of(More)
Metal–olivine Fe–Ni exchange distribution coefficients were determined at 1500 8C over the pressure range of 1 to 9 GPa for solid and liquid alloy compositions. The metal alloy composition was varied with respect to the Fe/Ni ratio and the amount of dissolved carbon and sulfur. The Fe/Ni ratio of the metal phase exercises an important control on the(More)
Introduction: In Table 1 we have compiled the chemical compositions, including Ni and Co, of representative basalts from Earth, Moon, Mars and Vesta. The SiO2 and MgO concentrations of all basalts cover only a small compositional range, suggesting a similar extent of fractionation. The Ni and Co contents increase with the radius of the planet, with very low(More)
Three new potassium uranyl borates, K12[(UO2)19(UO4)(B2O5)2(BO3)6(BO2OH)O10] ·nH2O (TPKBUO-1), K4[(UO2)5(BO3)2O4]·H2O (TPKBUO-2), and K15[(UO2)18(BO3)7O15] (TPKBUO-3), were synthesized under high-temperature/high-pressure conditions. In all three compounds, the U/B ratio exceeds 1. Boron exhibits BO3 coordination only, which is different from other uranyl(More)
A neodymium borosilicate, Mg(2)Nd(13)(BO(3))(8)(SiO(4))(4)(OH)(3) (MgNdBSi-1), was obtained from a high-temperature (1400 °C), solid-state reaction under high-pressure conditions (4.5 GPa). MgNdBSi-1 contains six different types of Nd(3+) coordination environments with three different ligands: BO(3), SiO(4), and OH groups. Mg(2+) cations are only bond to(More)
Introduction: The abundance of Cu in the Earth’s mantle normalized to C1 and Mg is similar to the abundances of Ni and Co [1, 2]. This is surprising as Cu is much less siderophile [2] than Ni and Co. Although a lower bulk Earth abundance of Cu is expected because of its lower condensation temperature, this is not sufficient to compensate for the much lower(More)