Chemical and Structural Insights of the Nano Organo–Mineral Interfaces in Growing Abalone Nacre

Characterizing the nano organo–mineral interfaces in nacre is of primary importance to understand the processes of nucleation, growth, orientation, and organization of the aragonite tablets. Here, we investigated these different interfaces in growing nacre of abalone Haliotis tuberculata shell using a combination of advanced techniques, i.e., focused ion beam milling coupled with field emission gun scanning electron microscopy, high-resolution transmission electron microscopy, scanning transmission X-ray microscopy, and electron energy loss spectroscopy. We show the presence of “globules”-like organic-rich inclusions within the center of each tablet that extend from one tablet to another through mineral bridges surrounded by organics. These structures may control the growth of the columnar stacking of tablets supporting different findings from the literature. In the lateral growing surface of the tablets, we reveal the presence of a thick organic domain rich in calcium but deficient in carbonate ions strengthening the idea that calcium-binding acidic proteins are involved in tablet’s lateral growth. Overall, this work emphasizes the importance of nanoscale chemical and structural analysis of the organo–mineral interfaces in growing nacre, allowing in particular for the discrimination between organic and inorganic carbons.