Hydrogen bonding, thermal expansion, and phase transition of cranswickite (MgSO4 · 4H2O)
5 affiliations
- 1Tremough Campus
- 2University of Exeter
- 3Harwell Science and Innovation Campus, Fermi Avenue, Didcot, UK, OX11 0DE
- 4ISIS Neutron and Muon Source
- 5STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus
Abstract
Cranswickite, the rarer of the two natural polymorphs of MgSO4·4H2O, has until now been known only from its type locality and characterized solely by X-ray powder methods, leaving its hydrogen-atom positions undetermined. The crystal structure of perdeuterated cranswickite, MgSO4·4D2O, prepared by controlled-humidity dehydration of the heptahydrate, has been refined by Rietveld analysis of time-of-flight neutron powder diffraction data at 10 K and 295 K, with all deuteron positions and displacement parameters refined without restraints, yielding the first complete hydrogen-bond geometry for this phase. Variable-temperature measurements (10–340 K) reveal strongly anisotropic thermal expansion: one principal axis of the expansion tensor is negative over the entire temperature range, reaching α1 = −3.7(3) × 10-5 K-1 at 335 K, which is balanced by positive expansion of similar magnitude within the ac plane, such that the principal expansivities [α1:α2:α3 = −1.04(4):2.90(4):1.00(5) at 295 K] yield zero area expansion of the ac plane. At 330 K cranswickite’s transformation to starkeyite accompanied by a volume reduction of 4.72% was observed, which is among the largest known density increases associated with a phase transition. The relevance of these findings to MgSO4 hydrates as candidate rock-forming minerals on Mars and the icy Galilean satellites is discussed.
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BibTeX
@misc{meusburger2026hydrogen,
title = {{Hydrogen bonding, thermal expansion, and phase transition of cranswickite (MgSO4 · 4H2O)}},
author = {Johannes M. Meusburger and Karen A. Hudson-Edwards and Eamonn T. Connolly and Rich A. Crane and A. Dominic Fortes},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15011185/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15011185/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Hydrogen bonding, thermal expansion, and phase transition of cranswickite (MgSO4 · 4H2O)
AU - Johannes M. Meusburger
AU - Karen A. Hudson-Edwards
AU - Eamonn T. Connolly
AU - Rich A. Crane
AU - A. Dominic Fortes
PY - 2026
DA - 2026/10/28
PB - ChemRxiv
DO - 10.26434/chemrxiv.15011185/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15011185/v1
AB - Cranswickite, the rarer of the two natural polymorphs of MgSO4·4H2O, has until now been known only from its type locality and characterized solely by X-ray powder methods, leaving its hydrogen-atom positions undetermined. The crystal structure of perdeuterated cranswickite, MgSO4·4D2O, prepared by controlled-humidity dehydration of the heptahydrate, has been refined by Rietveld analysis of time-of-flight neutron powder diffraction data at 10 K and 295 K, with all deuteron positions and displacement parameters refined without restraints, yielding the first complete hydrogen-bond geometry for this phase. Variable-temperature measurements (10–340 K) reveal strongly anisotropic thermal expansion: one principal axis of the expansion tensor is negative over the entire temperature range, reaching α1 = −3.7(3) × 10-5 K-1 at 335 K, which is balanced by positive expansion of similar magnitude within the ac plane, such that the principal expansivities [α1:α2:α3 = −1.04(4):2.90(4):1.00(5) at 295 K] yield zero area expansion of the ac plane. At 330 K cranswickite’s transformation to starkeyite accompanied by a volume reduction of 4.72% was observed, which is among the largest known density increases associated with a phase transition. The relevance of these findings to MgSO4 hydrates as candidate rock-forming minerals on Mars and the icy Galilean satellites is discussed.
ER -