Twin density of aragonite in molluscan shells characterized using X-ray diffraction and transmission electron microscopy

• Published in: Journal of crystal growth Vol. 397; pp. 39 - 46
• Main Authors: Kogure, Toshihiro, Suzuki, Michio, Kim, Hyejin, Mukai, Hiroki, Checa, Antonio G., Sasaki, Takenori, Nagasawa, Hiromichi
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.07.2014; Elsevier
• Subjects: A1. Biocrystallization; A1. Defects; A1. X-ray diffraction; A1. {110} twin; Aragonite; B1. Aragonite; B1. Calcium compounds; Condensed matter: structure, mechanical and thermal properties; Crystal structure; Deformation and plasticity (including yield, ductility, and superplasticity); Density; Diffraction; Exact sciences and technology; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Microstructure; Physics; Planes; Shells; Transmission electron microscopy; B1. Calcium compounds; A1. Biocrystallization; A1. X-ray diffraction; A1. {110} twin; B1. Aragonite; A1. Defects; Crystal defects; Crystallographic direction; Crystal orientation; Calcium compounds; XRD; Preferred orientation; Fibers; Interfaces; Lamellar structure; Transmission electron microscopy; Microstructure
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2014.03.029

{110} twin density in aragonites constituting various microstructures of molluscan shells has been characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM), to find the factors that determine the density in the shells. Several aragonite crystals of geological origin were also investigated for comparison. The twin density is strongly dependent on the microstructures and species of the shells. The nacreous structure has a very low twin density regardless of the shell classes. On the other hand, the twin density in the crossed-lamellar (CL) structure has large variation among classes or subclasses, which is mainly related to the crystallographic direction of the constituting aragonite fibers. TEM observation suggests two types of twin structures in aragonite crystals with dense {110} twins: rather regulated polysynthetic twins with parallel twin planes, and unregulated polycyclic ones with two or three directions for the twin planes. The former is probably characteristic in the CL structures of specific subclasses of Gastropoda. The latter type is probably related to the crystal boundaries dominated by (hk0) interfaces in the microstructures with preferred orientation of the c-axis, and the twin density is mainly correlated to the crystal size in the microstructures. •The method using XRD revealed {110} twin density of aragonite crystals.•{110} twin density of the CL microstructure varied greatly depending on the species.•TEM observations showed the validity of the results from XRD measurements.•{110} twin density is mainly correlated to the crystal size in the microstructures.