Refinement of the crystal structure of the aragonite phase of CaCO3
- 1 January 1971
- journal article
- Published by National Institute of Standards and Technology (NIST) in Journal of Research of the National Bureau of Standards Section A: Physics and Chemistry
- Vol. 75A (1) , 27-32
- https://doi.org/10.6028/jres.075a.004
Abstract
Aragonite (CaCO3) crystallizes in the unit cell a = 4.9598(5) Å, b = 7.9641(9) Å, and c = 5.7379(6) Å at 25 °C with four formula weights in space-group Pmcn. The structure has been refined to Rw = 0.024, R = 0.040 using 765 x-ray reflections from a single crystal. The Ca ion is coordinated to nine oxygens with Ca … O distances in the range 2.414(2) Å to 2.653(1) Å. The two unique C—O distances in the CO3 group are 1.288(2) Å (on the mirror plane) and 1.283(1) Å. The two unique O—C—O angles are 119.6(2)° (across the mirror plane) and 120.13(8)°. The distances and angles in the CO3 group are not significantly different at the 95 percent confidence level.Keywords
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