Repository logo
HARVEST

Geological Sciences

Permanent URI for this collection

https://hdl.handle.net/10388/11983

Browse

Browsing Geological Sciences by Subject "Biogeochemical tracer"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Discovery of Ge2+ in quartz: Evidence from EPR/XAS experiments and DFT calculations, and implications for Ge/Si systematics
    (Geochimica et Cosmochimica Acta, 2025-01) Mashkovtsev, Rudolf I.; Botis, Sanda M.; Lin, Jinru; Deevsalar, Reza; Cheung, Leo Ka Long; Wiens, Eli; Tunc, Ayetullah; Chen, Ning; Chernikov, Roman; Pan, Yuanming
    The Ge/Si systematics as a biogeochemical tracer with diverse applications from paleo-climatic reconstructions to discrimination of magma sources and elucidation of Earth’s early evolution hinges on the coherent behavior of these elements in the tetravalent state. However, determination of Ge speciation in quartz and other silicate minerals is technically challenging because this element almost invariably occurs at several parts per million or lower concentrations. This contribution reports a detailed study of Ge speciation in quartz by combining single-crystal electron paramagnetic resonance spectroscopy, synchrotron X-ray absorption spectroscopy, and ab initio theoretical calculations. Our single-crystal and powder electron paramagnetic resonance spectra of artificially irradiated quartz reveal a suite of previously reported Ge electron centers (GECs) such as [GeHLi2]0 and [GeHH2]0 centers as well as a new GeHLi center. These multiply-compensated GECs in artificially irradiated quartz suggest that their precursors before irradiation involve the diamagnetic Ge2+ state. Ge K-edge X-ray absorption spectroscopic data of selected quartz samples further support the presence of Ge2+. Theoretical calculations reproduce the experimental 1H and 7Li hyperfine constants of the [GeHLi2]0 center and suggest the new GeHLi center to be a new variant of the multiply-compensated GECs with the second monovalent cation in a distant c-axis channel, again supporting the Ge2+ state. The presence of Ge2+ in sedimentary-diagenetic quartz, in particular, challenges existing thermodynamic data that Ge4+ is the only stable oxidation state in aqueous solutions under near-surface conditions. Incorporation of Ge2+ in quartz and other silicates can significantly affect Ge/Si fractionations, with important implications for their applications as a biogeochemical tracer from surficial environments to magmatic-hydrothermal systems, Earth’s core-mantle differentiation, and other planetary processes.
  • Thumbnail Image
    Item
    Discovery of Ge2+ in quartz: Evidence from EPR/XAS experiments and DFT calculations, and implications for Ge/Si systematics
    (Elsevier, 2025-03-15) Mashkovtsev, Rudolf I.; Botis, Sanda M.; Lin, Jinru; Deevsalar, Reza; Cheung, Leo Ka Long; Wiens, Eli; Tunc, Ayetullah; Chen, Ning; Chernikov, Roman; Pan, Yuanming
    The Ge/Si systematics as a biogeochemical tracer with diverse applications from paleo-climatic reconstructions to discrimination of magma sources and elucidation of Earth’s early evolution hinges on the coherent behavior of these elements in the tetravalent state. However, determination of Ge speciation in quartz and other silicate minerals is technically challenging because this element almost invariably occurs at several parts per million or lower concentrations. This contribution reports a detailed study of Ge speciation in quartz by combining single-crystal electron paramagnetic resonance spectroscopy, synchrotron X-ray absorption spectroscopy, and ab initio theoretical calculations. Our single-crystal and powder electron paramagnetic resonance spectra of artificially irradiated quartz reveal a suite of previously reported Ge electron centers (GECs) such as [GeHLi2]0 and [GeHH2]0 centers as well as a new GeHLi center. These multiply-compensated GECs in artificially irradiated quartz suggest that their precursors before irradiation involve the diamagnetic Ge2+ state. Ge K-edge X-ray absorption spectroscopic data of selected quartz samples further support the presence of Ge2+. Theoretical calculations reproduce the experimental 1H and 7Li hyperfine constants of the [GeHLi2]0 center and suggest the new GeHLi center to be a new variant of the multiply-compensated GECs with the second monovalent cation in a distant c-axis channel, again supporting the Ge2+ state. The presence of Ge2+ in sedimentary-diagenetic quartz, in particular, challenges existing thermodynamic data that Ge4+ is the only stable oxidation state in aqueous solutions under near-surface conditions. Incorporation of Ge2+ in quartz and other silicates can significantly affect Ge/Si fractionations, with important implications for their applications as a biogeochemical tracer from surficial environments to magmatic-hydrothermal systems, Earth’s core-mantle differentiation, and other planetary processes.