144 / 2025-04-08 19:31:03

Thermal-induced crystallographic transformation in bivalve shells

Aragonite and calcite, Electron Back-Scattered Diffraction (EBSD), crystallographic textures, High-angle boundary (HAB)

Theme 5: Life-Mineral Interaction and Evolutions > Session 5b: Mineralization of Organisms in Extreme Environments

Biominerals in hard parts are commonly used as paleoenvironmental archives. However, the crystallographic transformations they undergo during diagenesis in geological processes remain poorly understood. In this study, we investigated these processes through controlled experiments on bivalves, which are widely used in paleoenvironmental reconstructions. We utilized cultured Mytilus galloprovincialis specimens at five different temperatures to examine the effects of elevated temperatures on the mineralogical and crystallographic changes in both aragonitic and calcitic components of the same shell. Elevated temperatures first induced a transformation in the mineral phase of aragonite, followed by changes in the grain size of aragonite crystals and their crystallographic textures. Despite aragonite’s susceptibility to temperature, the grain size and texture of calcitic crystals remained unaffected, demonstrating significantly higher resilience. Interestingly, we observed an intermediate stage where the crystallographic transformation of aragonite into calcite was not immediately complete. During this state, we detected calcite minerals, but the crystal textures still resembled the original aragonite. Moreover, the high-angle boundary (HAB) content, including twin boundaries, was significantly elevated in this state, which may serve as a useful marker for distinguishing altered aragonite from the calcitic component in fossilized biominerals.