9-5 Oyster shell crystallographic parameters are linked to microstructural heterogeneity and geochemistry.

Session: Early Career Investigators in Mineralogy and Crystallography

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Eastern oysters, Crassostrea virginica, are important reef-building organisms to the Mid-Atlantic region of the United States. Oyster Reefs in the Chesapeake Bay protect coastlines from erosion, serve as natural water filters, provide habitats for marine life, and are essential to the aquaculture industry which supports local communities. Oyster shell growth is sensitive to environmental conditions and is negatively impacted by water chemistry, pollution, and stress. Although monomineralic, the adult oyster shell is composed of multiple calcite microstructures, each containing distinct material properties and biomineralization processes. This study investigates these microstructures and how they may shift under environmental stress. In a healthy oyster, the bulk of its shell is composed of dense, foliated ‘mother of pearl’-like microstructures interlayered with lenses of soft, chalky microstructures. Although the morphology, chemistry, and isotopic composition of these microstructures have been explored in the literature, this study is the first to add a detailed crystallographic and mineralogical characterization. Using classical mineralogical techniques like micro-X-ray diffraction and Raman spectroscopy, clear differences in crystallographic parameters and bonding environments are observed between foliated and chalky calcite. Compared to chalk, foliated calcite microstructures have larger unit cell volumes driven by an increase in c-axis lengths. However, chalk displays more crystallographic disorder, as evidenced by Raman spectroscopy targeting crystal bonding environments. These crystallographic perspectives are then coupled with trace element analyses and isotopic measurements to render a more complete analysis of these microstructures. For example, chalky calcite is richer in the smaller cation, Mg²⁺, than foliated calcite, which may drive its increased disorder and smaller unit cell volumes. These findings corroborate previous geochemical measurements and mirror morphological observations that chalk is more disordered on the micron scale—and now the atomic scale. This work has implications for mollusks in paleoclimate proxies, biomineral materials science, and aquaculture.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6956

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