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Article

Structural Modifications of Single-Crystal Aragonite CaCO3 Beginning at ~15 GPa: In Situ Vibrational Spectroscopy and X-Ray Diffraction Evidence

1
State Key Laboratory of Lithospheric Evolution and Institutions of Earth Science, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
2
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China
3
MNR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China
4
School of Gemmology, China University of Geosciences, Beijing 100083, China
*
Author to whom correspondence should be addressed.
Minerals 2020, 10(10), 924; https://doi.org/10.3390/min10100924
Received: 22 August 2020 / Revised: 8 October 2020 / Accepted: 13 October 2020 / Published: 19 October 2020
(This article belongs to the Special Issue Vibrational (Infrared and Raman) Spectroscopy of Minerals)
The structural chemistry of carbonates under mantle conditions facilitates our understanding of carbon recycling pathways in the earth’s interior. It also has impacts on the dynamics of mantle–slab interactions. Aragonite is a common calcium carbonate mineral in pelagic marine sediments. The structural chemistry of single-crystal aragonite during successive compression and the behavior of a structural H+ have been investigated by micro-vibrational spectroscopy and synchrotron X-ray diffraction techniques in diamond anvil cells. We describe a reduction of the b-axial compressibility beginning at ~15 GPa, and the related discontinuities in the first-order derivatives of the vibrational modes. The structural modifications of aragonite are manifested by mutations occurring in the pressure relations of the wavenumbers of the O-C-O bending modes, and of the bandwidth and band intensities of the measured internal and external modes. These anomalies are indicative of changes occurring in the force constant of the C-O bonds, and possibly a second-order phase transition. Besides, the [CaO9] polyhedra begin to deform, possibly with some Ca-O bonds becoming elongated and the others shortening. An increase in the co-ordination number for the Ca2+ sites could be expected under higher pressures. Additionally, the weakening of the OH modes may imply H+-loss from the aragonite lattice above 11.5 GPa. View Full-Text
Keywords: calcium carbonate; crystal chemistry; OH bands; diamond anvil cell calcium carbonate; crystal chemistry; OH bands; diamond anvil cell
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MDPI and ACS Style

Gao, J.; Liu, Y.; Wu, X.; Yuan, X.; Liu, Y.; Su, W. Structural Modifications of Single-Crystal Aragonite CaCO3 Beginning at ~15 GPa: In Situ Vibrational Spectroscopy and X-Ray Diffraction Evidence. Minerals 2020, 10, 924. https://doi.org/10.3390/min10100924

AMA Style

Gao J, Liu Y, Wu X, Yuan X, Liu Y, Su W. Structural Modifications of Single-Crystal Aragonite CaCO3 Beginning at ~15 GPa: In Situ Vibrational Spectroscopy and X-Ray Diffraction Evidence. Minerals. 2020; 10(10):924. https://doi.org/10.3390/min10100924

Chicago/Turabian Style

Gao, Jing, Yungui Liu, Xiang Wu, Xueyin Yuan, Yingxin Liu, and Wen Su. 2020. "Structural Modifications of Single-Crystal Aragonite CaCO3 Beginning at ~15 GPa: In Situ Vibrational Spectroscopy and X-Ray Diffraction Evidence" Minerals 10, no. 10: 924. https://doi.org/10.3390/min10100924

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