The glass transition of biologically secreted amorphous calcium carbonate

Amorphous carbonates are key phases in bio-geological processes. They also possess considerable unexplored potential for technological applications. We recovered a glass transition in biogenic amorphous calcium carbonate (ACC), extracted from the soft tissue of the sea slug Baptodoris cinnabarina, using novel fast differential scanning calorimetry (FDSC) (heating/cooling rates of 2000-5000 °C s^-1). Similar to synthetic ACC and ACMC, biogenic ACC, as demonstrated here, is a structural glass. Thus, synthetic and biogenic ACC likely share the same vitrification route - dehydration-driven glass formation. Experimental strategies employed here reveal that biogenic ACC exhibits an enhanced stability compared to synthetic ACC. This is interpreted as a crystallization-inhibiting role of Mg, P, and organics, initially present in biogenic ACC as has been previously inferred.