This Natural Treasure Contains the Secret to Stronger Armor

Keshi pearls, sourced from Akoya pearl oysters, can exhibit up to 2,615 layers of nacre, built up over a span of 548 days.

-  LEILA SLOMAN

WHEN IT COMES TO BUILDING tough, resilient materials without wasting energy, few human manufacturers can compete with Mother Nature. One of her most intriguing achievements is nacre, commonly known as mother-of-pearl, a material that is much stronger than the sum of its parts. “[Nacre] is effectively chalk, but it doesn't break like chalk. When I think of chalk, I think of a very brittle, delicate material," says Robert Hovden, a professor of materials science at the University of Michigan and one of the researchers on a study involving nacre. Last year, his team uncovered new information about the nano-level structure of nacre that could open new frontiers in the world of human-made supermaterials.

The study, published in Proceedings of the National Academy of Sciences, focuses on nacre's structure at the nanoscale level-lengths of a billionth of a meter, even smaller than a wavelength of light. Using an electron microscope, the researchers noticed that inconsistencies in the nacre's brick-and-mortar structure led to "corrections" in future layers. When an asymmetrical nacreous layer corrupted the pearl's symmetry, future layers "adjusted” their thicknesses to make the pearl more spherical.

Clams and other mollusks construct pearls by blanketing a “bead nucleus," or a small object inside the pearl sac, with tiny alternating layers of calcium carbonate and organic protein. These layers make up nacre. “It's sometimes referred to as brick and mortar,” explains Neil H. Landman, curator emeritus at New York City's American Museum of Natural History. "The bricks are the nacreous [calcium carbonate] tablets; the mortar are the organic sheets between the tablets."

Hovden and seven other researchers analyzed the “periodicity of this brick-and-mortar structure, or how uniform the layers of nacre were.