Caratterizzazione della microstruttura e la consistenza dei cristalli di carbonato di calcio conchiglie bivalvi

In my Master Thesis study, I analyze the different organizations of calcium carbonate crystals secreted by mollusk organisms. In total, I investigate calcium carbonate crystal organization in the shell of seven mollusk species. I investigate more intensely three specimens, where I measure carbonate crystal arrangement in different parts of the shell. Calcium carbonate can have two crystalline forms: aragonite and calcite, these crystals form in mollusk shells in different microstructures, e.g., crossed lamellar, nacreous, and fibrous prismatic crystal arrangements. I characterize differences in carbonate crystal organization in specific parts of the shell: (i) the myostracum, the region where the muscles attach to the shell, and (ii) in other shell parts, where there is no muscle attachment. In my studies, I compare the microstructure and texture present in the myos- tracum with the microstructure and texture that prevails in other shell portions. Recent research Crippa et al. (2020a,b) based on the analysis of the shell of the bivalve, Glycymeris glycymeris, has shown that the microstructure and texture of the myostracum are significantly different from the structure of other shell portions. My work highlights these structural differences. I use structure and mate- rial property characterization techniques, such as electron backscatter diffraction (EBSD) and nanoindentation testing. EBSD characterization allows for visualiza- tion of the microstructure and texture of the bivalve shell material, such as the organization of the crystals within the shell. With nanoindentation testing, I can measure the hardness of the shell in several regions. The seven taxa that I inves- tigate live in different marine environments at different depths in the seawater and have slightly different habitats. I found that the myostracum has a different microstructure relative to the shell portion. Additionally, I observed different myostracum microstructures for the dif- ferent species. I found noticeable differences in mechanical properties between the myostracum and shell portion