Nacre – Strong as Steel?
When walking along the beach, most people notice shells in the sand. People have come to understand that these shells are strong and they hurt when you step on them. But have you ever taken a deeper look? Have you ever wondered what makes these shells so strong? Even seagulls need to take certain mollusks and drop them over 25 feet onto sharp rocks just to get them to crack. By getting the shell to crack, the bird can then enjoy the tasty flesh inside the shell. The reason these shells are so strong is because they are lined with nacre. Nacre is the iridescent material thickly lining a shell (McGee). This material may look very simple, but it is amazingly complex.
Before going any further, I want to point out that not all shells are lined with nacre. I’m pretty certain I could take a crab with my bare hands and crack it pretty easily. Nacre is famous for lining the abalone shell. Nacre also strengthens the shells of other mollusks, bivalves, and cephalopods as well, such as the chambered nautilus. Under a microscope, we see what makes nacre so strong. Experts have found nacre to be extremely orderly, having layers of complexity arranging from large to small scale. This gives the material a hierarchical structure. “A microscopic cross-section resembles brickwork, with flat, hexagonal tablets of a crystalline, calcium carbonate mineral stacked in neat layers. (Petit)” Connecting the hexagonal tablets is a flexible protein-rich gum originally created by the shellfish.
Due to the shell comprising mostly of crystals and a water-soluble protein polymer that resembles white glue, the material is transparent, as strong as steel, yet lighter in weight. Engineering professor from the University of Michigan, Nicholas Kotov, almost dubbed the material, “plastic steel,” but the material didn’t stretch quite as much as steel (McGee). Like bones and teeth, nacre is a biomineral, a combination of organic molecules, made by...