Silica transforms through solid-state processes

PUBLICATION — Andrzej Pisera, Sylvie Masse, Mohamed Selmane, Magdalena Łukowiak 2026. Diagenesis of siliceous sponge spicules: microstructural and mineralogical modifications of biosilica with time. Annales Societatis Geologorum Poloniae, 96. https://doi.org/10.14241/asgp.2026.03

Figure: Secondary silica structures in an Eocene sponge spicule from Australia under a scanning electron microscope.

We compared fossil sponge spicules up to 150 million years old with modern specimens. Using scanning electron microscopy and mineralogical analyses, we found that their silica gradually transforms from an amorphous state to quartz through solid-state processes, not only by dissolution and reprecipitation. The nature of these changes preserve parts of the original structure, and makes such  fossil spicules suitable for silicon isotope studies used to reconstruct ancient ocean chemistry and past climate change.