| Summary: | The superimposed layers of the true oyster shell have distinct morphology. The shells are mainly calcitic, comprising an outer prismatic region and inner foliated structure that is frequently interrupted by lenses of chalky calcitic deposits. Aragonite is restricted to the myostracum and ligament. Electron backscatter diffraction (EBSD) analysis has shown that despite the variations in structural morphology, the mineralized layers of the oyster shell maintain a single crystallographic orientation with the crystallographic c-axis orientated perpendicular to outer and inner shell surfaces. Varying crystal morphology, while maintaining crystallographic unity, may be an evolutionary trait that forms a crack-resistant shell with optimum strength and flexibility.
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