F. W.Clarke — Constitution of the Zeolites. 189 



In the second group we find foresite, laumontite, heulandite, 

 epistilbite, brewsterite, scolecite, stilbite, faujasite, and natrolite. 

 The two groups remain in this form, however, only so long as 

 we ignore water, for when we begin to regard the latter as 

 partly constitutional, several members of the first series must 

 be transferred to the second. This point will be made clear 

 farther on. The species above named may be individually 

 considered as follows : 



Thomsonite. — Al 6 (Si0 4 ) 6 Ca 3 . TH 2 0. This is equivalent to 

 anorthite plus water, and according to Doelter thomsonite 

 yields anorthite upon fusion. Commonly a part of the lime is 

 replaced by soda, either one or two atoms being so replaceable. 

 Sometimes, as in " mesole," there is an excess of silica, which 

 is accounted for by small admixtures of trisilicate molecules, 

 or Si 3 8 groups. The dehydration experiments of Damour, 

 Hersch, etc., indicate that 4 of the water must be regarded as 

 constitutional. This may be represented as bringing about a 

 replacement of Al by — Al = (OH) 2 4-H 2 . Hence the final 

 formula should be written 



Al 4 (Si0 4 ) 6 Ca 3 (AlH 2 6 2 ) 2 H 4 .3H 2 0. 



Gismondite. — Uncertain, but probably Al 6 (Si0 4 ) 6 Ca. 12H 2 0, 

 with part of the lime replaced by potash, and perhaps in some 

 cases Si 3 8 replacing Si0 4 . It is stated that •§• of the water 

 goes off at 100°, if the remaining eight molecules are constitu- 

 tional, four aluminum atoms would be replaced by 4(A1H 2 2 ) 

 + H 8 , giving the formula 



Al 2 (Si0 4 ) 6 Ca 3 (AlH 2 2 ) 4 H 8 .4H 2 0. 



Edingtonite. — Probably Al 6 X 6 Ba 3 . 12H 2 0, with X about 

 |Si0 4 and ^Si 3 8 . Barium partly replaceable by other bases. 

 Mode of hydration undetermined. According to Lemberg 

 edingtonite, or a compound like it, is artificially derivable from 

 natrolite. Although edingtonite has the same total number of 

 water molecules as gismondite, its crystallization is totally dif- 

 ferent ; so that the ratio of crystalline to constitutional water 

 is probably not the same for the two species. 



Phillipsite. — Al 6 X 6 CaB/ 4 . 15H 2 0. R' may be either Ka or 

 K, and the ratio between Si0 4 and Si 3 8 is quite variable. 

 Little, if any of the water can be regarded as constitutional. 



Iiarmotome. — Al 6 X 6 Ba 3 . 15H 2 0. Ratio of Si 3 8 and Si0 4 

 commonly 1:1. A little Ba replaced ordinarily by H 2 or alka- 

 lies. Recognized generally as closely analogous to phillipsite. 



Levynite.—MX&z, . 15H 2 0. Si'0 4 : Si 3 6 8 : : 3 : 2. Slight 

 replacements of lime by alkalies. About -| of the water 

 appears to be constitutional, judging from Damour's experi- 

 ments. 



