EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Ikaite (CaCO3*6H2O) -> ACC (amorphous calcium carbonate) -> calcite transformation and its paleoclimatological implication

Anett Lázár1, Máté Karlik1, Zsombor Molnár2, Attila Demény1, and Péter Németh1,2
Anett Lázár et al.
  • 1Research Centre For Astronomy and Earth Sciences, Institute for Geological and Geochemical Research, Hungary (
  • 2University of Pannonia - Eötvös Loránd Research Network, Research Institute of Biomolecular and Chemical Engineering,Environmental Mineralogy Research Group, Hungary, Egyetem út 10, 8200 Veszprém, Hungary (

Ikaite (CaCO3*6H2O) is a cryogenic calcium carbonate phase, which forms below about 5°C. If the temperature increases above 5-7 °C ikaite transforms to calcite. Understanding the transformation process is important to interpret paleoclimatological data from glendonites, i.e., calcite pseudomorphs after ikaite in sediments. Tollefsen et al. (2020) suggested that the transformation occurs via a coupled dissolution–reprecipitation mechanism at the ikaite–calcite interface (1). In contrast, Vickers et al. (2022) proposed a quasi-solid state ikaite to calcite transformation mechanismand suggested that stable isotope data of glendonite can be used for reconstructing paleotemperatures(2). However, in sediments the majority of the ikaite to calcite transformation occurs in diagenetic environments, where ambient solutions interact with the transforming mineral.

We synthesized ikaite at 2 °C in alkaline environment in order to study its transformation using organic solvents, vacuum pumping and rapid (1 min) heating from 5 to 30 °C. These experiments indicated the formation of amorphous calcium carbonate (ACC) during the ikaite to calcite transition. We also monitored the ikaite transformation by letting the 2 °C parent solution to reach room temperature (25 °C) within ~5 hours. We observed ACC and calcite formations depending on the alkalinity of the parent solution. Our experiments suggest that the ikaite to calcite transition is a two-step process consisting of the solid-state ikaite → ACC transformation and the ACC → calcite dissolution–reprecipitation mechanisms. During these transitions ikaite lost all its water but preserved its original morphology. We hypothesize that the occurrence of a transient amorphous phase during the ikaite to calcite transition implies the alteration of the isotopic data, similar to what was reported for the ACC to calcite transition (3).

We acknowledge the financial support of NKFIH ANN141894 grant.



(1) E. Tollefsen, T. Balic-Zunic, C. M. Mörth, V. Brüchert, C. C. Lee and A. Skelton, Scientific Reports, 2020, 10, 8141.

(2) M. L.Vickers, M. Vickers, R. E. M. Rickaby, H. Wu, S. M. Bernasconi, C. V. Ullmann, G. Bohrmann, R. F. Spielhagen, H. Kassens, B. P. Schultz, C. Alwmark, N. Thibault and C. Korte, Geochimica et Cosmochimica Acta, 2022, 334, 201-216.

(3) A. Demény, Gy. Czuppon, Z. Kern, Sz. Leél-Őssy, A. Németh, M. Z. Szabó M. Tóth, C.-C. Wu, C.-C. Shen, M. Molnár, T. Németh, P. Németh and M. Óvári, Quaternary International, 2016, 415, 25-32.

How to cite: Lázár, A., Karlik, M., Molnár, Z., Demény, A., and Németh, P.: Ikaite (CaCO3*6H2O) -> ACC (amorphous calcium carbonate) -> calcite transformation and its paleoclimatological implication, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-1133,, 2023.

Supplementary materials

Supplementary material file