FORMATION OF ZEOLITES IN SOILS. 



165 



products of hydrometamorphism and not those of weathering, as limited 

 above. It is even questionable if the processes involved in weathering 

 are not entirely opposed to zeolitic formation, and destructive rather 

 than otherwise. The processes which result in the breaking up of such 

 minerals as the feldspars, micas, amphiboles, and pyroxenes would cer- 

 tainly quickly destroy a compound of the zeolitic type, even if once 

 existing. Again, the close juxtaposition of mineral particles, such as is 

 favorable to the production of " reaction rims," is quite obliterated in the 

 process of weathering and soil formation. In weathering, the amount of 

 interstitial space is continually augmented, until it amounts to practically 

 50 per cent, by bulk, of that of the soil itself, as shown by Dr Whitney 

 and by the present writer.* 



The fact, moreover, that zeolites are met with in the finest stages of 

 development in cavities of basic eruptive rocks where there are no signs 

 of such decomposition products as are incidental to weathering, and al- 

 most wholly lacking in secondary rocks, are facts which should not be 

 overlooked in this connection. f 



If formed in soils, why should they not be found in secondary rocks 

 resulting from the reconsolidation of materials derived by the same pro- 

 cesses and from similar rocks ? 



Efficacy of Zeolites as Conservators of Potash. 



Third, can zeolites, even if occurring in soils, be considered as of prac- 

 tical value as conservators of potash ? 



Among the twenty-three known species of zeolites (including apophyl- 

 lite), in but five is potash considered an essential constituent. These 

 five are enumerated below in tabular form : 



Name. 







Composition. 







Si0 2 . 



A1A. 



CaO. 



K 2 0. 



Na.,0. 



H 2 0. 



A poph vllite 



53.7 

 70.0 

 67.2 



48.8 



47.1 



11.9 

 11.4 

 20.7 



16.3 



25.0 



4.4 



2.1 



7.6 



BaO. 



20.6 



5.2 



2.4 

 3.5 



6.4 



2.1 



0.8 

 2.3 



16.1 



Ptilolite 



20.5 



Mordenite 



13.5 



Phillipsite 



16.5 



Harmotome 



14.1 







♦Bull. Geol. Soc. Am., vol. 6, p. 332. 



fThe formation of zeolitic compounds in amygdaloidal cavities of basic eruptives is commonly 

 regarded as due to the action of waters heated by the hot lavas into which they were infiltrated 

 or by water supplied from volcanic sources. See Geikie : Basalt Plateau of Xorthwestern Europe, 

 Quar. Jour. Geol. Soc. of London, May, 1896, and authorities there quoted. 



XXIV— Bull. Geol. Soc. Am.. Vol. 8, 1896 



