In situ Raman vibrational spectra of siderite (FeCO3) and rhodochrosite (MnCO3) up to 47 GPa and 1100 K

Abstract

Siderite (FeCO 3 ) and rhodochrosite (MnCO 3 ) are two interesting carbonate minerals, which normally occur in hydrothermal deposits on deep-sea altered oceanic crust. Despite the ubiquity of carbonates in the slab, little is known of the physicochemical behavior of siderite and rhodochrosite at high-pressure (P) and high-temperature (T) conditions during slab subduction. In this study, we characterized the Raman vibrational spectra of natural siderite and rhodochrosite up to 47 GPa and 1100 K in an externally-heated diamond-anvil cell (DAC). Experimental results show that the Raman frequency shifts ( i ) for siderite and rhodochrosite are a function of both P and T, and the effect of the P-T cross derivative term cannot be neglected, especially at high-P and high-T conditions.Based on the functional relationship of  i -P-T, the P-T calibrants of siderite and rhodochrosite are developed, respectively. This is significant for studying the water-carbonate interaction at high P-T conditions in a DAC because the undesired change of the experimental system from traditional pressure sensors (e.g., ruby, quartz) in a reaction chamber can be avoided. Like previous studies, we observed a sharp spin transition at ~ 45 GPa in siderite and a phase transition from MnCO 3 -I to MnCO 3 -II at ~ 46 GPa for rhodochrosite at room temperature. Furthermore, we determined the isobaric and isothermal equivalents of the mode Grüneisen parameter ( iT ,  iP ) and the anharmonic parameter (a i ) for each Raman mode of siderite and rhodochrosite. The  i /P,  i /T,  iT, 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.

Revisiting the Raman Spectra of Carbonate Minerals

“…The 1086 cm −1 Raman band is slightly shifted to 1085 cm −1 ; the 1 cm −1 spectral resolution allows that observation. The presence of the half-filled d orbital for the transition metal ions can create a different influence by their additional and concentrated negative charge, since they are cations with a smaller radius than calcium and are leading to the opposite effect [26,28,31,34,38,39,42]. Such changes were studied previously by Zhang and collaborators, showing that the substitution of calcium ions by a transition metal cation leads to differences in the vibrational properties [42], such as shifts to lower wavenumbers for the symmetrical vibrational modes.…”

“…the literature: the small Fe atom allows distortion that leads to the appearance of an u sual mode that is only infrared allowed [11,28,39,48]. Interestingly, until this moment derite (FeCO3) is expected to have a more flexible crystalline lattice than rhodochro (MnCO3) because of the appearance in the Raman spectrum of the active modes in the This flexibility-temperature relationship is not seen in the Raman spectrum at differ temperatures for these two minerals.…”

“…Rhodochrosite shows T and L modes that are very similar to calcite, but this is not observed in the siderite spectrum. It is known that the siderite Raman spectrum has a strong temperature dependence and the shoulder observed in the bending mode for siderite corresponds to a vibrational mode that is shown to be infrared active in the vibrational analysis, but the flexibility of the structure of this mineral allows that this mode also becomes Raman active depending on the temperature [11,28,39,48].…”

“…Interestingly, until this moment derite (FeCO3) is expected to have a more flexible crystalline lattice than rhodochro (MnCO3) because of the appearance in the Raman spectrum of the active modes in the This flexibility-temperature relationship is not seen in the Raman spectrum at differ temperatures for these two minerals. Rhodochrosite presents a variation of the Ram bands, both in displacement and intensity, that is much greater than siderite, that is, r dochrosite would be more flexible if this justification were considered [11,36,39]. The c tradiction exists in the literature [11,28,36,39,48] and the interaction of the carbonate an with the transition metal is unique in each system, making these structures not comp ble to each other.…”

Deciphering the Origin of Abiotic Organic Compounds on Earth: Review and Future Prospects

“…(3) Water-driven disproportionation reactions with carbonates Thermal decomposition of FeCO 3 (siderite) is observed between 350°C and 400°C at 1 bar with magnetite and scarce graphite formed as reaction products. Such experiments indicate the potential for disproportionation of carbon to different valence states (Wang et al, 2023). In an H 2 O-rich environment, some fascinating chemical reactions are generated.…”