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American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu / Swainson, Ian


IMPACT FACTOR 2017: 2.645

CiteScore 2018: 2.55

SCImago Journal Rank (SJR) 2018: 1.355
Source Normalized Impact per Paper (SNIP) 2018: 1.103

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1945-3027
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Volume 100, Issue 1

Issues

Applications of Hirshfeld surfaces to mineralogy: An example of alumohydrocalcite, and the classification of the dundasite group minerals

Marcin Stachowicz
  • College of Inter-Faculty Individual Studies in Mathematics and Natural Sciences (MISMaP), Żwirki and Wigury 93, 02-089 Warszawa, Poland
  • Biological and Chemical Research Centre, Chemistry Department, University of Warsaw, Żwirki i Wigury 101, 02-089 Warszawa, Poland
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/ Jan Parafiniuk
  • Institute of Mineralogy, Geochemistry, and Petrology, University of Warsaw, 02-089 Warszawa, Poland
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/ Claire Wilson
  • Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, U.K.
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/ Simon Coles
  • Faculty of Natural & Environmental Sciences, School of Chemistry, University of Southampton, Highfield, Southampton, SO17 1BJ, U.K.
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/ Krzysztof Woźniak
  • Corresponding author
  • Biological and Chemical Research Centre, Chemistry Department, University of Warsaw, Żwirki i Wigury 101, 02-089 Warszawa, Poland
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Published Online: 2015-01-10 | DOI: https://doi.org/10.2138/am-2015-4939

Abstract

The crystal structure of alumohydrocalcite was determined using synchrotron X-ray radiation. Alumohydrocalcite crystallizes in the triclinic P1̅ space group with unit-cell parameters: a = 5.71(5), b = 6.54(4), c = 14.6 (2) Å, α = 81.8(3)°, β = 83.9(3)°, γ = 86.5(7)°, and V = 537(7) Å3. This mineral has the formula CaAl2(CO3)2(OH)4·4H2O as opposed to the commonly accepted formula CaAl2(CO3)2(OH)4·3H2O. The fourth water molecule interacts with the strongly bonded polyhedral unit of the structure through hydrogen bonds and connects three adjacent units. This water molecule plays a major role in crystal stability. On heating the sample, this fourth water molecule escapes from the crystal structure as a first one at lower temperature (~105 °C) than the other water molecules in the crystal structure (~128 °C).

Analysis and description of the alumohydrocalcite crystal structure and particularly of the intermolecular interactions, together with a comparison to the crystal structures of other minerals with the analog formula M2+M3+2 (CO3)2(OH)4·nH2O, suggests that this mineral is an extension of the dundasite group that should, we propose, be formed for all minerals with the above formula (dundasite, dresserite, strontiodresserite, petterdite, kochsándorite, hydrodresserite, and alumohydrocalcite). They all exhibit very similar patterns on Hirshfeld surfaces. Hirshfeld surfaces appear to be a very useful tool in the analysis of interactions, classification, and validation of mineral crystal structures.

Keywords: Alumohydrocalcite; hydrate; crystal structure; X‑ray diffraction; synchrotron radiation

About the article

Received: 2014-02-17

Accepted: 2014-06-26

Published Online: 2015-01-10

Published in Print: 2015-01-01


Citation Information: American Mineralogist, Volume 100, Issue 1, Pages 110–119, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am-2015-4939.

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© 2015 by Walter de Gruyter Berlin/Boston.

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