112 



minerals very exact they can perhaps be considered as iso- 

 morphous. 



The common combination of the zeophyllite, viz c(000l}, 

 rt{ll20} and s {0221} is represented on figure 4. 



The etching flgures 



/<j1____\^ ^ \ __i— -— --T^ '^^*^ described by Pe- 



/ J- -Ж -7 s Y ^ a Y"''"^ /-0 LiKAN and show that 



^- ' the zeophyllite is te- 



Fig. 4. Zeophyllite; Alter Berg, Bohemia. т i • i • 



tartohedral; I think it 

 most probable that it belongs to the same class as gyrolite, 

 viz. the rhombohedral. 



The aggregations, the cleavage and the common habit of 

 the two minerals are quite similar; the optical properties are 

 almost the same too, the zeophyllite being negative but exhi- 

 biting more optical anomalies than the gyrolite; the index of 

 refraction is for the zeophyllite somewhat smaller the со being 

 determined by Cornu at Г545. 



The specific gravity is for the pure zeophyllite 2*748 — 

 2"766 while it for the gyrolite from Niakornat is 2"578. 



The composition is given by Pelikan for the zeophyllite: 

 Si,0,, Ca, H, F, 

 for the gyrolite from Niakornat it is : 



<Sïg O^Q Ca, ifg 

 so that we find in that respect a great difference between the 

 two minerals. 



Although there are many similarities between the zeo- 

 phyllite and the gyrolite they must be considered, as two well 

 defined minerals which are, most probably, isomorphous and 

 form a very interesting group of the calcium zeolites; un- 

 fortunately these are, with the exception of apophyllite, very 

 imperfectly known and consequently it is difficult if not quite 

 impossible to point out the relations between them. Some of 

 them come very near to gyrolite in composition and are, per- 

 haps, only a very fine grained form of that mineral. The most 



