Theresa Hagerty, age 9 of Sioux City, Iowa for her question:

What is mother‑of‑pearl?

Certain shellfish, such as oysters arid clams, use mother‑of‑pearl to line the walls of their homes. It is a hard smooth substance for the little creatures have soft sensitive bodies. The inside walls of their homes must be smooth or the shellfish bodies would be scratched and bruised.

The job of lining those walls is never finished. The material used is made mostly from calcium carbonate, or lime. This and other chemicals are plentifully dissolved in the water. Certain cells in the shellfish's body turn the right chemicals into a kind of paint. The paint oozes out and covers the walls. It dries with a hard, glossy finish. Then another layer is applied and another and another. The older the shellfish is, the more layers of mother‑of‑pearl line his shells.

This mother‑of‑pearl is also called nacre. It is built up in layers, one upon the other. And nacre plays tricks with the light. It bends or refracts it. This makes the nacre glow with soft rainbow colors or gleam with pearly tints. And this beautiful nacre, or mother‑of‑pearly is the very same material which a pearl oyster uses to build up a pearl.