TY - JOUR

T1 - Low- and high-temperature evolution of löweite, Na12Mg7(SO4)13⸱15H2O

AU - Nazarchuk, E.V.

AU - Siidra, O.I.

AU - Baikina, A.S.

N1 - Export Date: 09 February 2026; Cited By: 0; Correspondence Address: O.I. Siidra; Department of Crystallography, Saint-Petersburg State University, Petersburg, University emb. 7/9, St., 199034, Russian Federation; email: o.siidra@spbu.ru

PY - 2026/6

Y1 - 2026/6

N2 - Hydrated sodium and magnesium sulfates are fairly common minerals. This study is focused on löweite from the fumaroles of the Tolbachik volcano in Kamchatka. The crystal structure of löweite was refined using single-crystal X-ray diffraction, and the hydrogen atoms were localized for the first time. In situ single-crystal (temperature range –173 to 227°C) and powder (temperature range –173 to 900°C) X-ray studies were performed. Both techniques show that löweite remains stable up to ∼220°C without showing any signs of potential phase transitions. The mineral is also stable under a vacuum of ∼600 Pa. The following transformation sequence for löweite was observed upon heating: löweite → metathénardite + vanthoffite + ‘x-phase’ → metathénardite + periclase. The thermal expansion of löweite demonstrates two distinct patterns in two temperature ranges. There is virtually no expansion in the structure until –93°C. Following this, the structure rapidly expands, exhibiting a highly anisotropic behaviour. Shear deformations of the soft S–O–Mg and S–O–Na hinges explain the structural flexibility and adaptability of löweite to changes in physicochemical environments.

AB - Hydrated sodium and magnesium sulfates are fairly common minerals. This study is focused on löweite from the fumaroles of the Tolbachik volcano in Kamchatka. The crystal structure of löweite was refined using single-crystal X-ray diffraction, and the hydrogen atoms were localized for the first time. In situ single-crystal (temperature range –173 to 227°C) and powder (temperature range –173 to 900°C) X-ray studies were performed. Both techniques show that löweite remains stable up to ∼220°C without showing any signs of potential phase transitions. The mineral is also stable under a vacuum of ∼600 Pa. The following transformation sequence for löweite was observed upon heating: löweite → metathénardite + vanthoffite + ‘x-phase’ → metathénardite + periclase. The thermal expansion of löweite demonstrates two distinct patterns in two temperature ranges. There is virtually no expansion in the structure until –93°C. Following this, the structure rapidly expands, exhibiting a highly anisotropic behaviour. Shear deformations of the soft S–O–Mg and S–O–Na hinges explain the structural flexibility and adaptability of löweite to changes in physicochemical environments.

UR - https://www.mendeley.com/catalogue/aa5234d7-6511-3dd2-a5b9-420c64c6f402/

U2 - 10.1180/mgm.2026.10192

DO - 10.1180/mgm.2026.10192

M3 - Article

VL - 90

SP - 565

EP - 573

JO - Mineralogical Magazine

JF - Mineralogical Magazine

SN - 0026-461X

IS - 3

ER -