a microporous structure composed of either crystalline aluminosilicates, chemically similar to clays and feldspars and belonging to a class of materials known as zeolites, or crystalline aluminophosphates derived from mixtures containing an organic amine or quaternary ammonium salt (whose) pore sizes range from 5 to 10 Å (and whose characteristic is its) ability to undergo dehydration with little or no change in crystalline structure, porous crystalline substances, especially aluminosilicates (see zeolite), that can be dehydrated with little change in crystal structure. As they form regularly spaced cavities, they provide a high surface area for the adsorption of smaller molecules.