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X-ray Diffraction Reveals Two Structural Transitions in Szomolnokite

Pardo, Olivia S. and Dobrosavljevic, Vasilije V. and Perez, Tyler and Sturhahn, Wolfgang and Liu, Zhenxian and Rossman, George R. and Jackson, Jennifer M. (2022) X-ray Diffraction Reveals Two Structural Transitions in Szomolnokite. American Mineralogist . ISSN 0003-004X. doi:10.2138/am-2022-8147. (In Press)

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Hydrated sulfates have been identified and studied in a wide variety of environments on Earth, Mars, and the icy satellites of the solar system. The subsurface presence of hydrous sulfur-bearing phases to any extent necessitates a better understanding of their thermodynamic and elastic properties at pressure. Endmember experimental and computational data are lacking and are needed to accurately model hydrous, sulfur-bearing planetary interiors. In this work, high-pressure X-ray diffraction and synchrotron Fourier-transform infrared (FTIR) measurements were conducted on szomolnokite (FeSO₄•H₂O) and up to ~83 and 24 Gpa, respectively. This study finds a monoclinic-triclinic (C2/c to P-1) structural phase transition occurring in szomolnokite between 5.0(1) and 6.6(1) Gpa and a previously unknown triclinic-monoclinic (P-1 to P2₁) structural transition occurring between 12.7(3) and 16.8(3) Gpa. The high-pressure transition was identified by the appearance of distinct reflections in the XRD patterns that cannot be attributed to a second phase related to dissocation of the P-1 phase and is further characterized by increased H₂O-bonding within the structure. We fit 3rd order Birch-Murnaghan equations of state for each of the three phases identified in our data and refit published data to compare the elastic parameters of szomolnokite, kieserite (MgSO₄•H₂O), and blödite (Na₂Mg(SO₄)2•₄HO). At ambient pressure, szomolnokite is less compressible than blödite and more than kieserite, but by 7 Gpa both szomolnokite and kieserite have approximately the same bulk modulus, while blödite’s remains lower than both phases up to 20 Gpa. These results indicate that stability of szomolnokite’s high-pressure monoclinic phase and the retention of water within the unit cell up to pressures found in planetary deep interiors.

Item Type:Article
Related URLs:
URLURL TypeDescription
Pardo, Olivia S.0000-0003-3964-9272
Dobrosavljevic, Vasilije V.0000-0002-3710-2188
Sturhahn, Wolfgang0000-0002-9606-4740
Liu, Zhenxian0000-0003-2617-7077
Rossman, George R.0000-0002-4571-6884
Jackson, Jennifer M.0000-0002-8256-6336
Additional Information:We thank the W.M. Keck Foundation and the National Science Foundation (NSF-CSEDI-EAR-1600956, 2009935) for supporting this work. O.P. acknowledges the support of DOE-NNSA SSGF (DE-NA0003960). Work at the National Synchrotron Light Source II at Brookhaven National Laboratory was funded by the Department of Energy (DEAC98-06CH10886). The use of the 22-IR-1 beamline was supported by COMPRES under NSF Cooperative Agreement EAR 11-57758 and CDAC (DE-FC03-03N00144).
Group:Division of Geological and Planetary Sciences, Seismological Laboratory
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
Department of Energy (DOE)DE-NA0003960
Department of Energy (DOE)DE-AC98-06CH10886
NSFEAR 11-57758
Department of Energy (DOE)DE-FC03-03N00144
Record Number:CaltechAUTHORS:20221205-211550925
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:118226
Deposited By: Tony Diaz
Deposited On:07 Dec 2022 19:02
Last Modified:07 Dec 2022 19:02

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