F. W. Clarke — Constitution of the Zeolites. 191 



Faujasite. — Al 4 X 6 Na 2 CaH 8 . 15H 2 0. Si0 4 : Si 3 8 = 2:1. 

 Faujasite may also be represented as a salt of the acid H 6 Si 2 7 , 

 with the forimda Al 4 (Si 2 T ) 5 CaNa 2 H 14 . 12H 2 0. As the mine- 

 ral does not gelatinize when decomposed by hydrochloric acid, 

 it may not belong with the orthosilicates. 



Natrolite. — Al 2 (Si0 4 ) 3 JSTa 2 H 4 . Doubtful as regards the char- 

 acter of its water. Yields nepheline on fusion, the latter 

 mineral being Al 3 (Si0 4 ) 3 Na 3 , with occasional replacements of 

 Si0 4 by a very little Si 3 8 . 



A careful scrutiny of the foregoing formulae will show that, 

 so far as our present data go, they fulfill all the conditions laid 

 down at the beginning of this article. They agree with the 

 published analyses, and account fully for their variations, and 

 in type they correspond to the two feldspathic molecules of 

 which the configurations have been given. They differ chiefly 

 with respect to hydration, and these differences are now intel- 

 ligible. Furthermore, several of the species yield anorthite 

 when fused, which connects the formulae given with the types 

 assumed, and also with the probable genesis of zeolites from 

 feldspars. Their deficiencies correspond to deficiencies in 

 evidence, and they suggest the lines of investigation by which 

 they may be finally established or discarded. If the formulae 

 do no more than to perform the last named function, they have 

 a value which entitles them to consideration. Neglecting the 

 distinction between crystalline and constitutional water, and 

 omitting for sake of brevity the few barium-strontium salts, 

 the normal zeolites, if I may call them so, can be tabulated as 

 follows : 



First Group. 



Thomsonite .... Al 6 (Si0 4 ) 6 (CaNa o ) 3 . 7H„0 



Gismondite Al e (Si0 4 ) 6 (CaK s )„. 12^0 



Phillipsite. Al 6 X 6 CaR' 4 . 15H„0. 



Levynite.. Al 6 X 6 Ca 3 . 15H 2 



Chabazite. A... Al 6 X 6 Ca 3 . 18H„0 



B.._ Al 3 X 3 Na 3 . 9H 



Gmelinite Al 3 X 3 Na 3 . 9^0 



Hydronephelite . Al 3 (Si0 4 ) 3 Na o H. 3H 2 



Offretite . . A1 3 X 3 R' 3 . SH 2 



Second Croup. 



Foresite Al 4 (SiO 4 ) 6 CaH 10 . H„0 



Scolecite Al 4 (Si0 4 ) 6 Ca 2 H 8 . 2H 2 



Laumontite Al 4 X 6 Ca„H 8 . " 4H 2 



Heulandite Al 4 X 6 C a ;H 8 . 6H a 



Epistilbite Al 4 X 6 Ca 2 H 8 . 6H 2 



Stilbite Al 4 X 6 Ca„H b . 8H o 



Faujasite Al 4 X 6 Na 2 CaH e . 15H o 



Natrolite Al o (Si0 4 ) 3 Na 2 H 4 



