568 Washington — Constitution of Some Salic Silicates. 



(NaSi) 4 Al a (AlCl)Si 6 94 (marialite), and (CaAl) 4 Al,SiSi t 94 



(meionite) 



It will be seen that this formula for marialite somewhat 

 resembles that of sodalite as proposed by Brogger and Bact- 

 strom, Ka 4 (AlCl)Al 2 Si 3 12 . 



It must be pointed out, however, that few of the analyses of 

 the scapolites are satisfactory. This is partly because of the 

 apparently great variability in composition, even at the same 

 locality, partly because of defects obvious in the analyzes them- 

 selves, and partly because of the unsatisfactory character of the 

 material, as the scapolites are very prone to alteration and the 

 purity and freshness of the mineral analyzed is often not 

 assured. A thorough, modern study of scapolites is highly 

 desirable, carried out on carefully selected material of un- 

 doubted homogeneity, purity, and freshness, and by modern 

 analytical methods. 



As regards the action of acids, we see in this series the same 

 relative resistance to attack induced by the presence of the 

 integrals (NaSi) and (CaAl) as was found to be the case with 

 the feldspars. According to both Dana and Hintze, marialite 

 and mizzonite are only slightly or not at all attacked by HC1, 

 wernerite is imperfectly decomposed, and meionite is wholly 

 decomposed but without gelatinization. 



Zeolite Group, polymorphous. 



The obviously very close relationship between the feldspars 

 and lenads and the zeolites can be explained, and the whole 

 group of " normal " zeolites (except apophyllite, mordenite, and 

 ptilolite), can be harmonized, if we regard them as hydrated 

 or sometimes acid or basic salts of the general fellenadic 

 acid (H 6 AlSi 2 8 ) n , in which the integrals (B'Si) and (B"A1) 

 replace the PL, and of which the feldspars and lenads are 

 regarded as anhydrous salts. With the exceptions noted, all 

 the well-defined zeolites proper can be reduced to this type of 

 formula. The polymorphism of the anhydrous salts of fellen- 

 adic acid, taken in connection with the different degrees of 

 hydration (since the different hydrates of a given salt show 

 different crystal forms), logically explains the great diversity 

 in crystal form of the zeolites, and the similarity in chemical 

 constitution suggested here gives a reason for the crystallo- 

 graphic similarities of the two large groups of anhydrous and 

 hydrated salts. 



The function of water in the zeolites is as yet uncertain, 

 although it has been the subject of much research and an 

 extensive literature, which cannot be cited adequately here. 



