Dictionary.net

Zeolites. A group of crystalline, hydrated alkali-aluminum silicates. They occur naturally in sedimentary and volcanic rocks, altered basalts, ores, and clay deposits. Some 40 known zeolite minerals and a great number of synthetic zeolites are available commercially. (From Merck Index, 11th ed)

A mineral, or rather a family of minerals, being hydrous silicates of alumina, with some of the earths or alkalies, so named from their intumescence before the blow-pipe.

An extensive family of minerals, so called from their forthing or intumescing into a whitish spongy enamel under the blow-pipe.