Articles | Volume 38, issue 4
https://doi.org/10.5194/ejm-38-461-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/ejm-38-461-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Thermally activated multistep alteration of Fe2+-bearing fluorophlogopite revealed by in situ Raman spectroscopy
Christian Reinberg
Department of Earth System Sciences, University of Hamburg, Grindelallee 48, 20146 Hamburg, Germany
Stylianos Aspiotis
CORRESPONDING AUTHOR
Institute for Materials and X-ray Physics, Hamburg University of Technology, Denickestrasse 15, 21073 Hamburg, Germany
Centre for the Study of Manuscript Cultures (CSMC), Cluster of Excellence “Understanding Written Artefacts”, University of Hamburg, Warburgstrasse 28, 20354 Hamburg, Germany
Thomas Malcherek
Department of Earth System Sciences, University of Hamburg, Grindelallee 48, 20146 Hamburg, Germany
Stefan T. M. Peters
Museum of Nature Hamburg – Mineralogy, Leibniz Institute for the Analysis of Biodiversity Change (LIB), Grindelallee 48, 20146 Hamburg, Germany
Boriana Mihailova
CORRESPONDING AUTHOR
Department of Earth System Sciences, University of Hamburg, Grindelallee 48, 20146 Hamburg, Germany
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We provide a tool for fast preparation-free estimation of the Fe3+ content in Al–Fe3+ series epidotes by Raman spectroscopy. The peaks near 570, 600, and 1090 cm−1, originating from Si2O7 vibrations, strongly correlated with Fe content, and all three signals are well resolved in a random orientation. Among them, the 570 cm−1 peak is the sharpest and easily recognized. Hence, the linear trend, ω570 = 577.1(3) − 12.7(4)x, gives highly reliable Fe content, x, with accuracy ± 0.04 Fe3+ apfu.
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Combined Raman-scattering and wavelength-dispersive electron microprobe (WD-EMP) analyses of natural biotites expanding over the whole biotite solid-solution series demonstrate that the chemical composition of the MO6 octahedra, TO4 tetrahedra, and interlayer space can be non-destructively determined by Raman spectroscopy with relative uncertainties below 8 %. The content of critical minor elements such as Ti at the octahedral site can be quantified as well with a relative error of ~ 20 %.
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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.
By applying in situ high-temperature Raman spectroscopy to (OH)-- and Fe2+-bearing...