High-pressure and high-temperature vibrational properties and anharmonicity of carbonate minerals up to 6 GPa and 500 ˚C by Raman spectroscopy

Farsang, Stefan and Widmer, Remo N. and Redfern, Simon A. T. (2020) High-pressure and high-temperature vibrational properties and anharmonicity of carbonate minerals up to 6 GPa and 500 ˚C by Raman spectroscopy. American Mineralogist. ISSN 0003-004X DOI https://doi.org/10.2138/am-2020-7404 (In Press)

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Abstract

Carbonate minerals play a dominant role in the deep carbon cycle. Determining the high-pressure and high-temperature vibrational properties of carbonates is essential to understand their anharmonicityand their thermodynamic properties under crustal and upper mantle conditions. Building on our previous study on aragonite, calcite (both CaCO3 polymorphs), dolomite [CaMg(CO3)2], magnesite (MgCO3), rhodochrosite (MnCO3), and siderite (FeCO3) (Farsang et al. 2018), we have measured pressure- and temperature-induced frequency shifts of Raman-active vibrational modes up to 6 GPa and 500 ̊C for all naturally occurring aragonite- and calcite-group carbonate minerals, including cerussite (PbCO3), strontianite (SrCO3), witherite(BaCO3), gaspeite (NiCO3), otavite (CdCO3), smithsonite (ZnCO3), and spherocobaltite(CoCO3). Our Raman and XRD measurements show that cerussite decomposes to a mixture of 2Pb2O3 and tetragonal PbO between 225 and 250 ̊C, smithsonite breaks down to hexagonal ZnO between 325 and 400 ̊C, and gaspeite to NiO between 375 and 400 ̊C. Spherocobaltite breaks down between 425 and 450 ̊C and otavite between 375 and 400 ̊C. Due to their thermal 26stability, carbonates may serve as potential reservoirs for a number of metals (e.g., Co, Ni, Zn, Cd) in a range of crustal and upper mantle environments (e.g., subduction zones). We have determined the isobaric and isothermal equivalents of the mode Grüneisen parameter and the anharmonic parameter for each Raman mode , and compare trends in vibrational properties as a function of pressure, temperature, and chemical composition with concomitant changes in structural properties. Finally, we use the anharmonic parameter to calculate the thermal contribution to the internal energy and entropy, and isochoric and isobaric heat capacity of certain carbonates.

Item Type: Article
Uncontrolled Keywords: 2020AREP; IA76
Subjects: 03 - Mineral Sciences
Divisions: 03 - Mineral Sciences
08 - Green Open Access
12 - PhD
Journal or Publication Title: American Mineralogist
Identification Number: https://doi.org/10.2138/am-2020-7404
Depositing User: Sarah Humbert
Date Deposited: 12 Aug 2020 22:12
Last Modified: 12 Aug 2020 22:12
URI: http://eprints.esc.cam.ac.uk/id/eprint/4861

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