bio

Nacre

The iridescent inner lining of bivalve and gastropod shells, 95% aragonite by volume — a form of calcium carbonate, essentially chalk — and 5% elastomeric organic matrix. Bulk aragonite has a fracture toughness around 0.2-0.4 MPa·m^0.5, which is to say almost none; nacre, built from that same mineral, reaches 3.5-5.8 and absorbs on the order of a thousand times more energy before it breaks. The entire gain comes from where the mineral is put: tiles roughly 0.5 µm thick laid in offset courses like brickwork, with 20-30 nm of matrix between them that shears instead of letting the mineral crack, plus mineral bridges, corrugated tile faces that jam as they slide, and sacrificial protein bonds that unravel in sequence. It is the cleanest teaching example of architecture beating ingredient.