ZEOLITES 



693 



facilitate the location of favorable targets and pro- 

 vide a guide for a meaningful sampling program. 



POTENTIAL RESOURCES 



Evaluation of zeolite resources is hampered by 

 the paucity of data on the extent and grade of the 

 identified deposits. Although more than 100 occur- 

 rences of zeolites in sedimentary rocks of the United 

 States have been recorded (Sheppard, 1971), infor- 

 mation such as the grade, mineralogy, and vertical 

 and lateral extent of the zeolitic rock and the thick- 

 ness of overburden are lacking except for several 

 deposits. The occurrence of zeolites in a certain sedi- 

 mentary unit is commonly recognized from the ex- 

 amination of only one sample. Nevertheless, very 

 large tonnages of zeolitic tuff of high purity are 

 known from the Cenozoic deposits of the Western 

 United States and the Gulf Coastal Plain. 



The only published estimate of zeolite resources 

 in the United States was made by Deffeyes (1968), 

 who estimated that about 120 million tons of clinop- 

 tilolite, chabazite, erionite, mordenite, and phillipsite 

 occur in near-surface deposits of the Basin and 

 Range province. This estimate is probably conserva- 

 tive for the zeolite deposits of the Basin and Range 

 province, and the potential zeolite resources of the 

 United States is probably several orders of magni- 

 tude greater. If the restraints of grade and depth 

 of overburden are ignored, the total of identified, 

 hypothetical, and speculative zeolite resources in the 

 United States is conservatively estimated at 10 tril- 

 lion tons. The nine common zeolites listed in ap- 

 proximate order of decreasing abundance are 

 clinoptilolite (including heulandite), analcime, mor- 

 denite, erionite, phillipsite, chabazite, laumontite, 

 and ferrierite. The United States probably has the 

 world's largest potential resources of high-grade 

 chabazite, erionite, and phillipsite. The only high- 

 grade deposits of ferrierite in the world have been 

 reported from central Nevada (Regis, 1970) . 



If an estimate of zeolite resources in the United 

 States is difficult to make, a meaningful estimate of 

 zeolite resources for the other countries of the world 

 is impossible to make. Zeolites have been reported in 

 sedimentary rocks from many other countries, and 

 their occurrences were summarized by Hay (1966) 

 and lijima and Utada (1966). However, no resource 

 estimates have been published. In addition to the 

 foreign zeolite deposits mentioned in these sum- 

 maries and those foreign deposits mentioned pre- 

 viously in this chapter, apparently extensive and 

 relatively high grade zeolite deposits occur in France 

 (Esteoule and others, 1971), Germany (F. A. Mump- 



ton, written commun., 1972), Italy (Sersale, 1960; 

 Alietti and Ferrarese, 1967; AHetti, 1970), Yugo- 

 slavia (Stojanovic, 1968), Hungary (Nemecz and 

 Varju, 1962), and Bulgaria (Alexiev, 1968). Most of 

 the occurrences are in Cenozoic tuffaceous rocks, 

 and the major zeolite is clinoptilolite. 



Additional deposits of zeolites will undoubtedly be 

 discovered in the Western United States and in other 

 countries of the world. Zeolites can form from a 

 variety of aluminosilicate materials during diagene- 

 sis, providing the interstitial water has a relatively 

 high pH and high concentration of alkalis. The 

 purest zeolite deposits, however, form from volcanic 

 ash that lacks crystal and rock fragments. In the 

 Western Hemisphere, zeolites have not been reported 

 from countries south of the United States except 

 Argentina. An examination of upper Mesozoic and 

 Cenozoic tuffaceous rocks will probably reveal large 

 zeolite deposits in Mexico and many of the countries 

 of Central America and western South America. 

 Future exploration will also probably identify bedded 

 zeolite deposits in the volcanic terranes of southern 

 Europe, eastern Africa, and southern Asia. 



RESEARCH NEEDED 



The genesis of zeolites in sedimentary rocks is 

 understood in general terms ; however, several prob- 

 lems merit additional study. Phillipsite and clinop- 

 tilolite are the chief zeolites in young deep-sea 

 deposits, but the relative importance of the pre- 

 cursor materials and the interstitial fluids in their 

 formation is unknown. Tuffs of originally rhyolitic 

 composition in deposits of alkaline, saline lakes char- 

 acteristically contain a variety of zeolite minerals, 

 but the factors that control which particular zeolite 

 forms are poorly understood. Low-temperature ex- 

 perimental studies combined with studies of the zeo- 

 lites and associated interstitial fluids in Holocene 

 tuffs presently undergoing alteration may provide 

 some answers. Another problem that warrants inves- 

 tigation is the relationship of the chemistry of a 

 certain zeolite species to the geologic setting of the 

 host rock. 



Other research of a technological nature that de- 

 serves consideration is (1) development of tech- 

 niques for the separation of zeolites from the gangue, 

 (2) development of techniques for the separation of 

 one zeolite from another, and (3) chemical or struc- 

 tural modifications of natural zeolites to increase 

 their usefulness. Natural zeolites or zeolitic rocks 

 will undoubtedly be used in many industrial and 

 agricultural processes ; however, additional applied 

 research is necessary to achieve these goals. 



