Articles | Volume 38, issue 4
https://doi.org/10.5194/ejm-38-461-2026
https://doi.org/10.5194/ejm-38-461-2026
Research article
 | 
22 Jul 2026
Research article |  | 22 Jul 2026

Thermally activated multistep alteration of Fe2+-bearing fluorophlogopite revealed by in situ Raman spectroscopy

Christian Reinberg, Stylianos Aspiotis, Thomas Malcherek, Stefan T. M. Peters, and Boriana Mihailova

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Cited articles

Aspiotis, S., Schlüter, J., Redhammer, G. J., and Mihailova, B.: Non-destructive determination of the biotite crystal chemistry using Raman spectroscopy: how far we can go?, Eur. J. Mineral., 34, 573–590, https://doi.org/10.5194/ejm-34-573-2022, 2022. 
Bernardini, S., Della Ventura, G., Schlüter, J., and Mihailova, M.: Thermally-activated electron hopping in Fe-rich amphiboles: Implications for the high-conductivity anomalies in subduction zones, Geochem., 83, 125942, https://doi.org/10.1016/j.chemer.2022.125942, 2023. 
Bernardini, S., Della Ventura, G., Schlüter, J., Hawthorne, F. C., and Mihailova, B.: The effect of the A-site cations on the charge-carrier mobility in amphiboles, Am. Mineral., 109, 1545–1553, https://doi.org/10.2138/am-2023-9138, 2024. 
Bernardini, S., Della Ventura, G., Hawthorne, F. C., Marcelli, A., Salvini, F., and Mihailova, B.: The effect of anisotropic electrical conductivity of amphiboles on geophysical anomalies observed in subduction zones, Sci. Rep., 15, 14244, https://doi.org/10.1038/s41598-025-98025-9, 2025. 
Chon, C.-M., Lee, C.-K., Song, Y., and Kim S. A.: Structural changes and oxidation of ferroan phlogopite with increasing temperature: in situ neutron powder diffraction and Fourier transform infrared spectroscopy, Phys. Chem. Miner., 33, 289–299, https://doi.org/10.1007/s00269-005-0045-y, 2006. 
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Short summary
By applying in situ high-temperature Raman spectroscopy to (OH)-- and Fe2+-bearing fluorophlogopite we show that a phonon-driven structural instability near 600 K triggers the mobilization of interlayer K+ cations, which can act as charge carriers. Above 1100 K all H+ cations delocalize and can also contribute to transport processes. Above 1300 K oxidation of Fe takes place, along with limited dehydrogenation and dehydroxylation, facilitating partial K+ leakage and structural decomposition.
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