A while back, I wrote an article about the teeth of sea urchins, which are extraordinary. The teeth, which are fairly standard calcium compounds, manage to chew through much harder rock as the urchins grind protective holes for themselves. The trick lay in both the macro-structure of the teeth (with a strong dense keel) and the micro-structure (with a cutting edge that fractured to expose new sharp cutting edges).
This related work on another calcium-based material shows how controlling fractures with microstructure can strengthen relatively brittle materials. Mother-of-pearl inspires super-strong material.