Ann Villers, age 17, of Austin, Tex., for her question:

WHAT IS ZEOLITE? .

Zeolite isthe name of a group of minerals that has its atoms

arranged in an open crystal framework. Zeolites can hold other atoms or molecules in this framework, much as a sponge holds water.

Scientists call zeolites "hydrous" because they contain up to 20 percent water. They release this water easily when heated. The name zeolite comes from two Greek words meaning boiling stone.

Zeolite cystals can be found in nature or they can be manufactured. They consist of aluminum, oxygen, silicon and one other metal, usually calcium, potassium or sodium.

Zeolites are widely used as water softeners. They exchange their water and sodium for almost all the metal ions or electrically charged atoms, such as those of calcium, that make water hard.