Washington — Constitution of Some Salic Silicates. 569 



In most cases it is undoubtedly " water of crystallization " or 

 but loosely attached to the crystal molecule, as is shown by 

 its replaceability by NII 3 , H 2 S, CS„ C 2 H 6 0, etc. But in other 

 cases it certainly, or almost certainly, exists, at least in part, 

 as acidic hydrogen or basic hydroxy!. In view of this uncer- 

 tainty all the zeolitic water is regarded in the following formu- 

 las as "of crystallization," but were it constitutional, in part 

 or entirely, it could be introduced in the molecular formulas 

 without change of type and with only slight increase in com- 

 plexity. The chemical compositions of all the zeolite formulas 

 here given have been calculated and found to agree with the 

 results of analysis. It will be noted that the introduction of 

 the decivalent radical (CaSi 2 ), which would be present in a 

 calcium albite, is necessary in some cases. 



Heulandite Subgroup, monoclinic. 



Heulandite, (CaSi 2 ) (AlSi 2 8 ) 2 + 5H 5 

 JBrewsterite, (Ba,Sr)Si 2 (AlSi 2 8 ) 2 + 5H 2 3 



Heulandite is obviously the pentahydrate of calcium albite 

 and brewsterite the pentahydrate of a corresponding bari- 

 strontium salt. 



Phillipsite Series, monoclinic. 



Hypothetical, (CaAl) 4 (AlSi 2 8 ) 4 + 8lT 2 

 Website, (CaAl).(BaAl) (KSi) 2 (AlSi 2 8 ) 5 + 12H 2 

 Phillipsite, (CaAl) 2 (KSi) 4 (AlSi„O a )„ + 16H 2 

 Harmotome, (BaAl) (BaSi„) 3 (AlSi 2 O 8 ) 7 + 20H 2 O 

 Stilbite, (CaSi 2 ) 4 ( AlSi 2 8 ) 8 + 24H 2 G 



These minerals apparently represent a homologous series, as 

 was pointed out by Fresenius, cited by Pratt and Foote.* It 

 would seem that considerable isomorphous replacement is pos- 

 sible among the integrals, and several parallel pure series 

 might exist. The authors citsd suggest a hydrated calcium 

 anorthite and a hydrated calcium albite as the end members. 

 The first of these is shown above, though as yet unknown, and 

 the latter would have the composition of stilbite. The formu- 

 las are given in the form above so as to bring out the serial 

 relationship, but several of them can be simplified by division. 

 Thus reduced to their simplest terms, the hypothetical end 

 member would be an anorthite di-hydrate and stilbite a cal- 

 cium albite hexa-hydrate. 



* Pratt and Foote, this Journal, iii, p. 448, 1897. 



