600 MINERALS/Zeolites occurring in large quantities is clinoptilolite, so most applications involve this mineral The cation-exchange capacity, cation selectivity, and molecular-sieve property of bulk zeolites are being applied to various aspects of agriculture Some of the beneficial effects of using clinoptilolite are improved growth and feed utilization, improved eggshell quality in chickens, reduced free ammonia in the rumens of sheep and cattle, and reduced exposures to ammonia and odours in feed lots Zeolites are used in soil conditioning to improve plant productivity, increase fertilizer efficiency, and aid remediation of soils For example, clinoptilolite-bearing tuff is used to increase the yield of wheat in Azerbaijan Zeoponics is a new method of plant growth, using artificial soil with zeolite as a major component As in other agricultural applications, the zeolite helps to control soil solutions The selectivity of clinoptilolite for certain heavy metals is the basis for many applications in water and wastewater treatment Examples are the removal of 137Cs from contaminated waters resulting from the Chernobyl accident and the removal of copper from electroplating effluents The molecular-sieve property of many zeolites is used to separate gases Phillipsite has been shown to have adsorption selectivity of ammonia over methane in gases from coal gasification In Japan activated mordenite is used to increase the oxygen in air for steel making, and in the USA chabazite is used to separate carbon dioxide from methane in gas from a landfill site in southern California Where zeolitic tuff is abundant it has been used as a dimension stone at least since Roman times to construct castles and cathedrals in Italy and other countries of Europe These tuffs are also used as a constituent of lightweight aggregate, as in the production of pozzolanic cement Although most zeolites used as catalysts are synthetic and made for specific applications, a few natural zeolites have also been tried Natural ferrierite has been shown to be an effective material as a Claus tail-gas catalyst, to remove elemental sulphur from gas streams, and natural mordenite is effective in the hydroisomerization of n-hexane, with results similar to those of synthetic mordenite Glossary Hydrothermal alteration Alteration of a host rock by hot water percolating through fractures, generally where the water-to-rock ratio is very large Metastable zeolites Those zeolites that crystallize quickly but are later replaced by more stable phases (zeolites or feldspars) Oxygen bridge The oxygen anion between two tetrahedral sites Tetrahedral sites The space between four tightly held oxygen anions See Also Analytical Methods: Geochemical Analysis (Including XRay); Mineral Analysis Diagenesis, Overview Lava Metamorphic Rocks: Facies and Zones Minerals: Definition and Classification; Feldspars; Quartz Pyroclastics Tectonics: Hydrothermal Activity Further Reading Bargar KE and Beeson MH (1985) Hydrothermal alteration in Research Drill Hole Y 3, Lower Geyser Basin, Yellow stone National Park, Wyoming Professional Paper 1054 C Washington, DC: US Geological Survey Bish DL and Ming DW (2001) Natural Zeolites: Occur rence, Properties, Applications Reviews in Mineralogy and Geochemistry 45 Washington, DC: Mineralogical Society of America Coombs DS, Alberti A, Armbuster T, et al (1997) Recom mended nomenclature for zeolite minerals: report of the subcommittee on zeolites of the International Mineral ogical Association, Commission on New Minerals and Mineral Names Canadian Mineralogist 35: 1571 1606 Deer WA, Howie RA, Wise WS, and Zussman J (2004) Rock Forming Minerals, Volume 4B Framework Sili cates: Silica Minerals, Feldspathoids and the Zeolites London: The Geological Society Dibble WE Jr and Tiller WA (1981) Kinetic model of zeolite paragenesis in tuffaceous sediments Clays and Clay Mineralogy 29: 323 330 Gottardi G (1989) The genesis of zeolites European Jour nal of Mineralogy 1: 479 487 Gottardi G and Galli E (1985) Natural Zeolites Berlin: Springer Verlag Hay RL (1966) Zeolites and Zeolitic Reactions in Sedi mentary Rocks Special Paper 85 Boulder: Geological Society of America Neuhoff PS, Fridriksson T, and Bird DK (2000) Zeolite para geneses in the North Atlantic Igneous Province: implica tions for geotectonics and groundwater quality of basaltic crust International Geological Review 42: 15 44 Sand LB and Mumpton FA (1978) Natural Zeolites: Occurrence, Properties, Use Elmsford, New York State: Pergamon Press Sheppard RA and Gude AJ III (1973) Zeolites and Associ ated Authigenic Silicate Minerals in the Tuffaceous Rocks of the Big Sandy Formation, Mohave County, Arizona Professional Paper 830 Washington, DC: US Geological Survey Sheppard RA, Gude AJ III, and Fitzpatrick JJ (1988) Distri bution, Characterization, and Genesis of Mordenite in Miocene Silicic Tuffs at Yucca Mountain, Nye County, Nevada Bulletin 1777 Washington, DC: US Geological Survey