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High-pressure polymorphs of ferroan dolomite; possible host structures for carbon in the lower mantle

Naira S. Martirosyan, Ilias Efthimiopoulos, Sandro Jahn, Sergey S. Lobanov, Richard Wirth, Hans-Josef Reichmann and Monika Koch-Mueller
High-pressure polymorphs of ferroan dolomite; possible host structures for carbon in the lower mantle
American Mineralogist (April 2024) 109 (4): 701-708

Abstract

In this study, we investigated four different ferroan dolomite samples using in situ Raman spectroscopy and powder X-ray diffraction (XRD) at pressures up to 48 GPa and room temperature. Our results show that the transition from Dolomite-I (Dol-I) to Dolomite-II (Dol-II) occurs above 13-16 GPa, and the transition pressure depends on the composition of the solid solution. Compression above 32-35 GPa results in the appearance of Dolomite-IIIc (Dol-IIIc) or Dolomite-IIIb (Dol-IIIb). In the high-pressure XRD study, we found that the XRD patterns of Ca (sub 0.97) (Mg (sub 0.77) Fe (sub 0.23) Mn (sub 0.03) )(CO (sub 3) ) (sub 2) (xFe = 0.23, Ank23) can be indexed as Dol-IIIc at 44 GPa, while the rhombohedral Dol-IIIb structure matches better with the XRD patterns of the xFe = 0.40 (Ank40) and 0.64 (Ank64) solid solutions. Additionally, in the Raman spectra of the Fe-richest sample (Ank64), we observed an abrupt frequency downshift of the CO (sub 3) -stretching vibrations between 40-42 GPa, which may reflect a pressure-induced Fe (super 2+) spin transition. We further investigated two samples with xFe = 0.19 (Ank19) and 0.23 (Ank23) at high pressure and high temperatures, up to at least 2600 K. The experiments revealed that the unquenchable Dol-IIIc structure could be a stable high-pressure/high-temperature polymorph in ferroan dolomite up to at least 2600 K.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 109
Serial Issue: 4
Title: High-pressure polymorphs of ferroan dolomite; possible host structures for carbon in the lower mantle
Affiliation: GFZ German Research Centre for Geosciences, Potsdam, Germany
Pages: 701-708
Published: 202404
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 37
Accession Number: 2024-032085
Categories: Geophysics of minerals and rocks
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
Secondary Affiliation: University of Cologne, DEU, Germany
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2024, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 2024
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