Chris Kosmider, age 12, of Milwaukee, Wisconsin, for his question:

What are zeolites?

The word "zeolite" means a boiling stone, which refers to its bubbly reaction with water. Actually, more than a dozen whitish minerals are classified as zeolites and several similar minerals often are called zeolites. Basically they are a group of hydrous aluminum silicates, containing ions of sodium and calcium. Their open crystal formations are riddled with channels that readily hold water.

Heat can be used to drive out the water without changing the crystal structure and the channels can be re-saturated. This process causes ion exchanges between the water and the mineral. These and other chemical activities make the various zeolites useful in many ways. For example, natrolite is a zeolite mineral often used as a water softener. Hard water contains calcium ions. These are neutralized when the water filters through a bed of natrolite grains. The chemical is reversed to make the natrolite  reuseable.