Journal
AMERICAN MINERALOGIST
Volume 106, Issue 3, Pages 367-373Publisher
MINERALOGICAL SOC AMER
DOI: 10.2138/am-2020-7490
Keywords
Carbonate; high pressure; Raman spectroscopy; lattice distortion
Categories
Funding
- National Key Research and Development Program of China [2019YFA0708502]
- National Natural Science Foundation of China (NSFC) [U1930401]
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This study investigated the Raman modes of natural magnesite under high pressure and found changes in lattice structure, indicating the significant impact of hydrostatic conditions on the structural evolution of MgCO3. The findings provide important insights for modeling the carbon cycle in the Earth's lower mantle.
Knowledge of the stability of carbonate minerals at high pressure is essential to better understand the carbon cycle deep inside the Earth. The evolution of Raman modes of carbonates with increasing pressure can straightforwardly illustrate lattice softening and stiffening. Here, we report Raman modes of natural magnesite MgCO3 up to 75 GPa at room temperature using helium as a pressure-transmitting medium (PTM). Our Raman spectra of MgCO3 show the splitting of T and v(4) modes initiated at approximate 30 and 50 GPa, respectively, which may be associated with its lattice distortions. The MgCO3 structure was referred to as MgCO3-Ib at 30-50 GPa and as MgCO3-Ic at 50-75 GPa. Intriguingly, at 75.4 GPa some new vibrational signatures appeared around 250-350 and similar to 800 cm(-1). The emergence of these Raman bands in MgCO3 under relatively hydrostatic conditions is consistent with the onset pressure of structural transition to MgCO3-II revealed by theoretical predictions and high-pressure and high-temperature experiments. This study suggests that hydrostatic conditions may significantly affect the structural evolution of MgCO3 with increasing pressure, which shall be considered for modeling the carbon cycle in the Earth's lower mantle.
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