%0 Journal Article %T Synchrotron high-resolution XRD and thermal expansion of synthetic Mg calcites %+ Centre Interdisciplinaire de Nanoscience de Marseille (CINaM) %+ Laboratoire Magmas et Volcans (LMV) %+ Synchrotron SOLEIL (SSOLEIL) %A Floquet, Nicole %A Vielzeuf, Daniel %A Heresanu, Vasile %A Laporte, Didier %A Perrin, Jonathan %< avec comité de lecture %@ 0342-1791 %J Physics and Chemistry of Minerals %I Springer Verlag %V 47 %N 48 %8 2020-10-20 %D 2020 %R 10.1007/s00269-020-01115-5 %Z Sciences of the Universe [physics]/Earth Sciences/PetrographyJournal articles %X The structural parameters and the thermal behavior of a complete series of Ca–Mg carbonates synthesized at high pressure and temperature (1–1.5 GPa, 1273–1373 K) in the range 0–50 mol% MgCO3 have been investigated by in situ powder synchrotron high-resolution X-ray diffraction at ambient and up to 1073 K under self-controlled CO2 partial pressure. The crystal structures are disordered Mg calcite in the range 1–41 mol% MgCO3, and Ca dolomite at 49 mol% MgCO3. New calibration curves of the cell parameters for the Mg content and thermal expansion from ambient to 1073 K are given. Short-range structural effects of cation substitution and ordering and their thermal behavior as a function of Mg content were identified from three sets of data: the peak broadening, the cell parameter strains and the Raman band enlargements. Both intra- and inter-crystalline levels of compositional heterogeneity are identified and allow splitting the Mg calcites into two groups: low- and high-Mg calcites. The low-Mg calcites (up to 22 mol% MgCO3) are homogeneous in Mg content with short-range ordering. High-Mg calcite (up to 41 mol% MgCO3) displays domains with different local ordering configurations and similar or slightly different Mg contents, and to which is added a compositional variation between crystals, as determined by EMP, of the order of  ± 0.8 mol% MgCO3. The cation ordering in Ca-rich dolomites similarly occurs in high-Mg synthetic calcites. The role of (CO3)2− group ordering is shown to be an important factor in the formation of Ca–Mg carbonates. %G English %2 https://hal.uca.fr/hal-02975828/document %2 https://hal.uca.fr/hal-02975828/file/Floquet-PhysChemMin-10-2020-corrected%20proof.pdf %L hal-02975828 %U https://hal.uca.fr/hal-02975828 %~ UNIV-ST-ETIENNE %~ IRD %~ INSU %~ PRES_CLERMONT %~ CNRS %~ UNIV-AMU %~ LMV %~ GIP-BE %~ ACL-SF %~ UNIV-PARIS-SACLAY %~ CINAM %~ SYNCHROTRON-SOLEIL %~ OPGC %~ UDL %~ GS-PHYSIQUE %~ INSTITUT-SCIENCES-LUMIERE %~ TEST3-HALCNRS