any of a group of hydrated silicates of aluminum with alkali metals, commonly occurring as secondary minerals in cavities in basic volcanic rocks: used for their molecular sieve properties because they undergo dehydration with little or no change in crystal structure.
Any of a family of hydrous aluminum silicate minerals, whose molecules enclose cations of sodium, potassium, calcium, strontium, or barium. Zeolites are usually white or colorless, but they can also be red or yellow. They are characterized by their easy and reversible loss of water of hydration. They usually occur within cavities in basalt.