Mother-of-pearl, found in the lining of a special type of shell, is made of thin layers of chalk crystals held together by tiny layers of glue.
Neither of these materials work well alone but together they can protect the shellfish.
In textiles, a composite describes the combination of two or more materials.
Think of a quilt. There is a woven textile on top, a filler textile in the middle and a softer textile at the bottom. Alone, none of these textiles would make a good quilt but layered together they work.
Biology can teach us how layers combine materials in different ways for specific jobs.
The shimmering lining of the abalone shell also known as mother of pearl, is composed of 95% CaCO3 (chalk) and 5% protein.
Chalk is very brittle and easily turns to powder. Paradoxically, mother of pearl is three thousand time tougher than chalk. This is due to the layered structure of the shell lining where thin layers of protein (glue) hold together thin tiles of chalk crystals.
Either of these materials would be no good at protecting the shellfish, but the layered structure enables the combination of two different materials and their properties resulting in extraordinary toughness.