Non-Classical Crystallization in Moon-Milk Deposits in the Nerja Cave, Spain

The Nerja Cave is located in an alpine folding chain, specifically in the Inner Zone of the Betic Range (SE, Spain), and it is developed within middle Triassic dolomite marbles (Carrasco et al., 1998). Its mean annual temperature is 18.1 ± 0.1 °C (Jiménez de Cisneros et al., 2021). Moon-milk deposits, a white substance present inside caves. Samples were collected in the touristic part of the cave and were characterized using synchrotron high-resolution XRD (HR-XRD), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). We detected the presence of amorphous magnesium carbonate (AMC), huntite, and dolomite. Additionally, the AMC formation and the subsequent crystallization process were studied in laboratory conditions to gain a more comprehensive understanding of the processes occurring in the cave. We performed titration experiments using magnesium and calcium chloride solutions and potassium carbonate buffers to investigate nucleation and transformation processes at elapsed times (1, 2, 7, and 14 days). The filtered solids were characterized by XRD, SEM, FTIR, Raman, and TEM. The results of these analyses highlighted the critical role of AMC in the formation of Ca-Mg crystalline carbonates.

Acknowledgment to financial support is given by the Spanish Ministry of Science and Innovation through the research project PID2021-125305NB-I00 and the project from the Junta de Andalucía through the EMERGIA research program under the grant agreement EMERGIA20_38594.

Carrasco F, Durán JJ, Andreo B, Liñán C, Vadillo I (1998) Consideraciones sobre el karst de Nerja. Karst en Andalucía 173–181

Jiménez de Cisneros, C., Peña, A., Caballero, E., & Liñán, C. (2021). A multiparametric approach for evaluating the current carbonate precipitation and external soil of Nerja Cave (Málaga, Spain). International Journal of Environmental Research, 15, 231-243.