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.