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The crystal structure of calcite III

Smyth, Joseph R. and Ahrens, Thomas J. (1997) The crystal structure of calcite III. Geophysical Research Letters, 24 (13). pp. 1595-1598. ISSN 0094-8276. doi:10.1029/97GL01603.

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The crystal structure of calcite III has been deduced from existing high pressure powder X-ray diffraction patterns, based on the assumption that it is a displacive modification of the calcite I structure. The structure is monoclinic with space group C2 and a Z of 6. There are two Ca and two C positions, and five O positions, and atom coordinates have been refined by distance-least-squares methods to give reasonable octahedral coordination for Ca and parallel, planar CO_3 groups. Unit cell parameters refined from a published powder diffraction pattern at 4.1 GPa are: a = 8.746(8)Å; b = 4.685(5)Å; c = 8.275(8)Å; and β= 94.4°. The structure has a calculated density of 2.949 Mg/m³ at 4.1 GPa which is less than that of aragonite at this pressure and consistent with early piston cylinder studies. This implies that calcite III is indeed a metastable intermediary between calcite I and aragonite.

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Additional Information:© 1997 American Geophysical Union. Received March 7, 1997; accepted April 21, 1997. The authors with to thank W. A. Bassett, R. T. Downs, and one anonymous referee for helpful comments. The work was supported by National Science Foundation grant EAR-96-05935 to J. R. Smyth, and NASA grant NAGW 1941 to T. J. Ahrens.
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Issue or Number:13
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Official Citation:Smyth, J. R., & Ahrens, T. J. (1997). The crystal structure of calcite III. Geophysical Research Letters, 24(13), 1595-1598. doi: 10.1029/97gl01603
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:50723
Deposited On:23 Oct 2014 23:16
Last Modified:10 Nov 2021 18:59

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