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P-V-T behavior of FeO(OH) and MnO(OH)

Authors

Wiethoff,  Felix
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Grevel,  Klaus-Dieter
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Marler,  Bernd
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Herrmann,  Julia
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Majzlan,  Juraj
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Kirste,  Jens
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/persons/resource/lathe

Lathe,  Christian
6.3 Geological Storage, 6.0 Geotechnologies, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

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Citation

Wiethoff, F., Grevel, K.-D., Marler, B., Herrmann, J., Majzlan, J., Kirste, J., Lathe, C. (2017): P-V-T behavior of FeO(OH) and MnO(OH). - Physics and Chemistry of Minerals, 44, 8, 567-576.
https://doi.org/10.1007/s00269-017-0884-3


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_2730892
Abstract
The P-V-T behavior of FeO(OH) and MnO(OH) has been determined under high pressure and high temperature up to 7.5 GPa and 500 °C using a MAX 80 cubic anvil high-pressure apparatus. The samples, synthetic goethite, α-FeO(OH), respectively, a natural groutite/manganite, α-MnO(OH)/γ-MnO(OH), specimen were mixed with Vaseline to ensure hydrostatic pressure-transmitting conditions, and NaCl served as an internal standard for pressure calibration. Energy-dispersive diffraction patterns were collected at a fixed 2θ angle (θ ≈ 4.52°). At pressures >7.1 GPa and temperatures >310 °C, respectively, P > 6.3 GPa and T > 350 °C, the transformation goethite ↔ ε-FeO(OH) was observed. Between 400 and 450 °C, the sample dehydrated to magnetite due to the reducing conditions caused by the graphite-tube furnace. By fitting a Birch–Murnaghan equation of state to the data, the bulk modulus of goethite was determined as (112.26 ± 2.26) GPa, (K′ = 4), VT,0 = (138.79 ± 0.10) Å3·exp [∫(0.497 ± 0.103) × 10−4 dT], (∂KT/∂T)P = (–0.033 ± 0.020) GPa K−1. For ε-FeO(OH), the values K = (142.8 ± 15.1) GPa, V0 = (66.18 ± 0.16) Å3, (K′ = 4), were obtained. Groutite and manganite are more compressible than their Fe analogues. K(groutite) = (84.0 ± 2.9) GPa, V0 = (139.92 ± 0.13) Å3, (K′ = 4). K(manganite) = (82.2 ± 3.0) GPa, V0 = (135.37 ± 0.15) Å3, (K′ = 4). Groutite disappeared at P ≈ 5.5 GPa and T = 300 °C, only manganite remained. At T > 400 °C, the sample dehydrated first to Mn3O4 [II] and then to manganosite (MnO) again pointing to reducing conditions.