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Zeolites are among the most common authigenic silicate minerals in sedimentary deposits. Zeolites occur in rocks that are diverse in age, lithology, and depositional environment, but they are most common in sedimentary rocks that originally contained abundant vitric material. Of the more than 30 naturally occurring zeolites, 6 commonly occur in bedded deposits that have not been subjected to deep burial or hydrothermal activity. These are analcime, chabazite, clinoptilolite, erionite, mordenite, and phillipsite. They are generally more siliceous and more alkalic than their counterparts that occur in mafic volcanic rocks. Most zeolites in sedimentary rocks formed during diagenesis mainly by reaction of vitric material with interstitial water, which may have originated as e ther meteoric water or connate water of a saline, alkaline lake. Formation of zeolites is favored by a relatively high pH and high activities of alkali ions in the interstitial water. Most zeolitic sedimentary rocks consist of 2 or more zeolites with authigenic clay minerals, silica minerals, or feldspars, and relict glass and crystal and rock fragments. Extensive and relatively pure beds of zeolite, however, occur in upper Cenozoic lacustrine deposits of the western United States.
The ion exchange, adsorption, and molecular sieve properties of zeolites, coupled with a seemingly low cost of mining, suggest a variety of industrial applications. Potential uses include purification and drying of gases and liquids, chemical separations, catalysis, decontamination of radioactive wastes, removal of ammonia from wastewater, and numerous other uses in agriculture and animal husbandry. Potential uses of these zeolites could be considerably increased by chemical and structural modifications of the natural materials.
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