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Abstract

Active analcime having a chemical composition comprising 60 to 95% by weight of SiO.sub.2, 0.3 to 20% by weight of Al.sub.2 O.sub.3 and 0.02 to 11% by weight of Na.sub.2 O based on the three components, an X-ray diffraction pattern inherent to analcime and a moisture adsorption of 5 to 30% by weight as determined under conditions of a relative humidity of 90%, an ambient temperature of 25.degree. C. and a standing time of 24 hours, wherein individual particles have a tetracosahedral or angle-rounded tetracosahedral particulate shape and the primary particle size of 0.1 to 50 .mu.m as determined according to the electron microscope method. This active analcime is obtained by acid-treating a zeolite by using an acid in an amount of 0.1 to 1.2 molar equivalents per mole of the sum of Al.sub.2 O.sub.3 and Na.sub.2 O components in the zeolite so that the crystal structure of analcime is left. Amorphous silica which is obtained by an acid treatment of a zeolite and is X-ray diffractometrically substantially amorphous, wherein individual particles have a tetracosahedral or angle-rounded tetracosahedral particulate shape and the primary particle size is 0.1 to 50 .mu.m as determined according to the electron microscope method. This amorphous silica is obtained by acid-treating a zeolite so that Al.sub.2 O.sub.3 and Na.sub.2 O components are removed in amounts sufficient to render the zeolite amorphous.

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