Work

High-pressure phase transition in groutite, MnO(OH)

Year: 2025

Type: article

Abstract: Groutite, α-Mn 3 ⁺O(OH), is a mineral that belongs to the diaspore group. We used X-ray synchrotron radiation in the pressure range from 0.65(6) GPa to 39.85(8) GPa to collect diffraction data for three single crystals of groutite placed in a diamond anvil cell. Groutite is orthorhombic, space group Pbnm . Analysis of the reciprocal lattice planes and the intensities of the measured reflections revealed that above 30 GPa, a phase transformation begins in the structure. This transition is gradual, with observable changes in the intensity of specific reflections, particularly those that are forbidden in the Cmcm space group. Although we see significant decreases in the intensities of these reflections, many of them still have intensities significantly greater than zero after the beginning of transformation. This is accompanied by a smooth, continuous shrinkage in the unit cell volume, symmetrization of hydrogen positions, and distortion of the MnO 6 octahedra. Analysis of the reflection intensities confirms that the observed changes are due to structural transformations and not experimental or sample effects. This means that the starting Pbnm symmetry is preserved although the mineral transforms as a function of pressure close to the Cmcm space-group symmetry. We propose a mechanism for this phase transition in the Pbnm space group.

Source: Mineralogical Magazine

DOI: 10.1180/mgm.2025.10161

Authors: Roman Gajda, Agnieszka Huć, Piotr Rejnhardt, Jan Parafiniuk, Pierre Fertey, Krzysztof Woźniak

Institutions: University of Warsaw, Synchrotron SOLEIL

Language: English

Topic: High-pressure geophysics and materials

Subfield: Geophysics

Field: Earth and Planetary Sciences

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $3,550