X-ray diffraction reveals two structural transitions in szomolnokite

Abstract

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 sulfurbearing 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, highpressure X-ray diffraction and synchrotron Fourier-transform infrared (FTIR) measurements were conducted on szomolnokite (FeSO 4 H 2 O) 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 P2 1 ) 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 dissociation of the P-1 phase and is further characterized by increased H 2 O-bonding within the structure. We fit 3 rd order Birch-Murnaghan equations of This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.