570 Washington — Constitution of Some Salic Silicates. 



Ciiabazite Subgroup, trigonal. 



Gmelinite, (NaSi) 2 (Na Al)(AlSi 2 8 ) 3 + 1211,0 

 Chabazite, (NaSi) 2 (CaAl)(AlSi 2 O fl ). 4- 12ll 2 

 Levynite, (CaSi 2 )(CaAl)(AlSi 2 8 ) 3 + 12H 2 U 



Gmelinite is here regarded as the purely sodic, and levynite 

 as the purely calcic, member of an isomorphous series like that 

 of the feldspars and scapolites. The commonly occurring 

 intermediate chabazites are mixed crystals of variable composi- 

 tion, and the one chosen for illustration is that midway 

 between the extremes. The ratios here given are exactly stoi- 

 chiometric, but not necessarily found in nature, though the 

 tendency would be to approximate to such ratios, as is also the 

 case with the sodi-calcic feldspars. It will be remarked that 

 the formula of gmelinite is that of a dodeca-hydrate of sodium 

 leucite and that of levynite of a similar hydrate of calcium 

 leucite. 



Similarly, analcite is the tetrahydrate of sodium leucite. 



Natrolite Subgroup, orthorhombic and monoclinic. 



Natrolite, (NaSi) 2 (Na 2 Al) 3 (AlSi 2 8 ) 6 + 8H 2 

 Scolecite, (CaSi 9 )(CaAl),(AlSi a O„) 4 + 12H.O 

 Mesolite, (NaSi) m (CaAl) D (AlSi 2 8 ) ra+n + pH 2 



Owing to the difference in crystal form and in water content 

 there is some doubt as to whether these minerals form a group 

 or series in the sense here suggested, but it is probable that 

 such is the case. It is interesting to note that the formula of 

 natrolite corresponds exactly, apart from the water, with that 

 of Rammelsberg's sigterite given above, while that of a meso- 

 lite, with J^a,0 : CaO = 1:2, and also minus the water, is that 

 of the anemousite of Linosa, as has been previously pointed 

 out.* 



Ungrouped Zeolites. 



Lauraontite, (CaSi 2 )(CaAl)(AlSi O 8 ) 3 + 12H 9 O 

 Analcite, (NaSi) 2 (Na 2 Al)(AlSi 2 O e ) 3 + 4H 2 

 Faujasite, (NaSi),(CaSiJ(CaAl)(AISi,O e ) 1 + 40lI 2 O 

 Edingtonite, (BaSi 2 )(BaAl) 3 (AISi 2 8 ) 6 + I2H,0 

 Thomsonite, (Na 2 ,Ca)(Al) 3 (AlSi 2 O s ) 2 4-5H 2 

 Hydronephelite, (Na 2 Al)(HSi)(AlSi 2 O fl ) 2 + 3H 2 



As regards the action of acids the zeolites, being hydrated 

 salts and of somewhat "loose" structure, as shown by the 

 behavior of their water content, are naturally more readily 

 attacked than the anhydrous minerals discussed previously. 



* Washington and Wright, this Journal, xxix, p. 57, 1910. 



