Preferential Orientation of Aragonite Crystals in Nacre of Mollusc Shells

The preferential orientations of aragonite crystals in nacre of shells are considered to be one of the most important reasons responsible for high mechanical performance of nacre. Based on the X-ray diffraction analysis, the preferential orientations of aragonite crystals in nacre from shells of main pearl-cultivating molluscs of China were systematically studied. It shows that 1): in nacre of Pinctada martensii (Dunker), Pinctada maxima (Jameson), Peteria penguin (Roding) the c axis of aragonite crystals is all perpendicular to nacreous layers; 2):in nacre of Hyriopsis cuningii (Lea) shell, there exist two kinds of orientation, one is the c axis of aragonite perpendicular to nacreous layers, the second is inclined to nacreous layers, i. e. (012) net of aragonite lattice is parallel to nacreous layers.