Multiple deformation mechanisms in the stone of a sea urchin tooth†
Abstract
The sea urchin tooth is a biogenic grinding tool that exhibits unique mechanical properties during food biting and rock boring, while being almost entirely composed of intrinsically brittle CaCO3 (i.e., calcite). Revealing its underlying design can broaden the potential engineering applications of low-cost, brittle structural materials (e.g., ceramics). To this end, the present study investigated the deformed stone of a Glyptocidaris crenularis tooth using transmission electron microscopy. We observed multiple deformation mechanisms associated with its structural components, i.e., the single-crystalline microfiber, meso-crystalline matrix, and organic sheath. The fiber functioned via formation of e- and r-twins, with the matrix dissipating energy mainly by crack propagation; the organic sheath located between the fiber and matrix modulated the deformation of the mineral phases, contributing to energy dissipation and damage localization of the stone component of the tooth.