Jurkowska, Agata Anna, and Ewa Świerczewska-Gładysz. “Opoka – a Mysterious Carbonate-Siliceous Rock: An Overview of General Concepts”.
Geology, Geophysics and Environment, vol. 48, no. 3, Nov. 2022, pp. 257-78,
https://doi.org/10.7494/geol.2022.48.3.257.