ZEOLITES 



691 



Table 148. — Zeolites reported from sedimentary rocks 



Zeolite Formula 



Analcime NaAlSi^Oa-H^O 



Chabazite (Ca.Na™) Al.Si.Oi-'eH^O 



Clinoptilolite (Na.,K=,Ca),Al„Si3<,0T2'24H=0 



Epistilbite (Ca,Na,)3AlaShsO,,-16H:0 



Erionite (Na=,K:,Ca)..5Al„Si2rOv2'27H,0 



Faujasite (Na,,Ca),.vr,Al3.5Si8.=0=.'16HoO 



Ferrierite (K,Na)-(Mg,Ca)2Al„Si3,,0,.'18HoO 



Gismondine (Ca,Na:,K2)4AUSisO.E'16H,0 



Gonnardite Na,CaAhSi„02„'5H,0 



Harmotome (Ba,Na=)=Al,Sii«03='12H.O 



Heulandite (Ca,Na=),AlsSi2,Ov:'24H:0 



Laumontite Ca,Al.Si,.;0„'16H=0 



Mordenite (Na.,K.,Ca) Al2Si,„O.M'7HoO 



Natrolite Na,Al,Si„0o„«4H=0 



Phillipsite (K,,Na«,Ca)2Al.Sii:032'12H:0 



Scolecite Ca=Al,Si„02o'6H20 



Stilbite (Ca,Na2),AlsSi280T2'28H20 



Thomsonite NaCa.AlsSisO.o-eHoO 



Wairakite CaAl2Si40i2'2H20 



Yugawaralite CaAl2SieOi6«4H20 



heulandite, laumontite, mordenite, and phillipsite. 

 Analcime and clinoptilolite are by far the most 

 abundant zeolites in the sedimentary rocks. All nine 

 of these common zeolites in sedimentary rocks show 

 a considerable range in Si : Al ratios and cation con- 

 tents. Except for heulandite and laumontite, they 

 are generally alkalic and more siliceous than their 

 counterparts that occur in mafic igneous rocks. Sum- 

 maries of their chemistry are given by Deer, Howie, 

 and Zussman (1963), Hay (1966), Sheppard (1971), 

 andUtada (1970). 



Most zeolites in sedimentary deposits formed after 

 burial of the enclosing sediments by the reaction of 

 aluminosilicate materials with the pore water. Silicic 

 volcanic glass is the aluminosilicate material that 

 most commonly served as a precursor for the zeo- 

 lites, although materials such as clay minerals, feld- 

 spars, feldspathoids, nad gels also have reacted 

 locally to form zeolites. Hay (1966) showed that 

 authigenic zeolites and associated silicate minerals 

 can be correlated with the following factors: (1) 

 composition, grain size, permeability, and age of the 

 host rocks, (2) composition of the pore water includ- 

 ing pH, salinity, and proportion of dissolved ions, and 

 (3) depth of burial of the host rock. Except for 

 laumontite and possibly some heulandite, the com- 

 mon zeolites generally occur in tuffaceous sedi- 

 mentary rocks that have not been deeply buried or 

 exposed to hydrothermal solutions. 



Classification of the diverse zeolitic sedimentary 

 rocks is difficult, but the following tenuous classifi- 

 cation is based on geologic setting and is offered as 

 a basis for further discussion: (1) hydrothermal, 

 (2) burial metamorphic, (3) weathering, (4) open 

 system, and (5) closed system. The hydrothermal 

 type includes those zeolites associated with metallic 



deposits such as those at the East Tintic district, 

 Utah (Levering and Shepard, 1960), and especially 

 with hot-spring deposits. Well-known examples of 

 the latter are at Yellowstone National Park, Wyo. 

 (Fenner, 1936; Honda and Muffler, 1970), Wairakei, 

 New Zealand (Steiner, 1953, 1955), and Onikobe, 

 Japan (Seki and others, 1969). Zeolites of geother- 

 mal areas commonly show a vertical zonation, and 

 the downward succession of mineral assemblages 

 seems to correlate with an increase in temperature. 

 At Wairakei and Onikobe, for example, the down- 

 ward succession is characterized by mordenite, lau- 

 montite, and then wairakite. 



Zeolites of the burial metamorphic type were 

 originally recognized by Coombs (1954) in Triassic 

 sedimentary rocks of the Southland syncline. New 

 Zealand. Coombs, Ellis, Fyfe, and Taylor (1959) 

 demonstrated a vertical zonation of mineral assem- 

 blages that is characterized by a downward succes- 

 sion of clinoptilolite-heulandite-analcime, laumon- 

 tite-albite, and then prehnite-pumpellyite-albite. 

 Rocks rich in prehnite and pumpellyite commonly 

 grade downward into rocks typical of the green- 

 schist metamorphic facies. Locally, a zone rich in 

 wairakite occurs between the laumontite-albite and 

 prehnite-pumpellyite-albite zones or overlaps these 

 zones. The zeolites and associated silicate minerals 

 of the burial metamorphic type commonly occur in 

 marine volcaniclastic strata that are more than 

 10,000 feet thick and locally are as much as 40,000 

 feet thick. The vertical succession of mineral assem- 

 blages is one of decreasing hydration with depth and 

 is generally thought to be temperature dependent; 

 however, chemical variables may prove to be equally 

 important. Besides occurrences in New Zealand, zeo- 

 litic rocks of the burial metamorphic type have been 

 recognized in Australia (Packham and Crook, 1960), 

 Puerto Rico (Otalora, 1964), U.S.S.R. (Kossovskaya 

 and Shutov, 1963), Japan (Seki, 1969; Utada, 1970), 

 British Columbia, Canada (Surdam, 1968), and the 

 United States. Laumontite-bearing rocks of the 

 burial metamorphic type occur in central Oregon 

 (Dickinson, 1962; Brown and Thayer, 1963), in 

 Mount Rainier National Park, Wash. (Fiske and 

 others, 1963), and near Cache Creek, Calif. (Dick- 

 inson and others, 1969). 



Zeolites of the weathering type are volumetrically 

 rather minor, but many deposits have probably been 

 overlooked. Analcime was recently reported from 

 alkaline, saline soils of the eastern San Joaquin 

 Valley, Cailf. (Baldar and Whittig, 1968). The anal- 

 cime was detected to a depth of about 4 feet, and 

 its abundance decreased with depth. Hay (1963a) 

 recognized analcime, chabazite, natrolite, and phil- 



