New Crystallographic Relationships in Biogenic Aragonite: The Crossed-Lamellar Microstructures of Mollusks

Crossed-lamellar microstructures are the most common shell-forming biomaterials in mollusks. Because of their complex hierarchical 3D arrangement and small crystallite size, previous crystallographic studies are scarce and have centered on particular species with no comprehensive analysis available. To evaluate the crystallographic diversity of the crossed-lamellar microstructures, we have studied a large set of bivalve and gastropod species with crossed-lamellar layers using X-ray diffraction and electron backscatter diffraction. From the number, distribution, and relationships of maxima, we have classified pole figures into nine different recurring crystallographic patterns. According to their crystallographic equivalences, these patterns can be grouped into five groups. A first division is established according to whether there is one or two main orientations for the c-axis of aragonite. In the latter case, each orientation corresponds to one of the two sets of alternating first-order lamellae. The two...