190 THE ROYAL SOCIETY OF CANADA 



SiOa 67-42 10 



AI2O3 11-46 1 



MgO 2-99 f 



NaaO 4-65 f 



"^^\ 1213 6 



100-00 



It is true that, in arriving at the above formula for ferrierite, an 

 entirely arbitrary assumption has been made with regard to the water 

 content of the mineral; but, in general, the same criticism might be 

 levelled at the formulae which have been assigned to practically all 

 the zeolites. These minerals without exception commence to lose 

 water at a relatively low temperature, and the percentage loss in- 

 creases at a fairly uniform rate as the temperature is raised to 300°. 

 Determinations which have been made of the loss of water at definite 

 temperatures seldom go beyond this point, at which the minerals still 

 retain several per cent of water. Moreover, with many zeolites, as 

 for example chabazite, scolecite, thomsonite, brewsterite, etc., it has 

 been found that after heating at this temperature the material regains 

 its original weight when exposed for some time to a moist atmosphere. 

 It is very probable that all these minerals continue to lose water at 

 the same gradual and uniform rate at temperatures considerably 

 higher than 300°, and that much of the water still retained by them 

 at the latter temperature is water of crystallization. Levynite, for 

 example, remains hygroscopic even after heating at 360 . 



There is thus no reason for supposing that the whole of the 5-71 

 per cent of water which ferrierite retains at 275° is constitutional, or 

 basic; on the other hand, a consideration of certain other related 

 zeolites indicates that some portion of it may well be present in the 

 mineral as water of constitution, and in the formula here suggested 

 for ferrierite, 1-35 per cent of water is assumed to be so combined. 



In the case of the ptilolite from Silver Cliff (Custer County, 

 Colorado), Cross and Eakins^ found that 3-10 per cent of the water 

 were stable at 300°. In the theoretical composition assigned to this 

 mineral by Clarke, a trifîe less than two per cent of the water is 

 basic, but this discrepancy is not considered an insuperable objection 

 to the formula proposed. 



Ferrierite is apparently not isomorphous with mordenite, which 

 is monoclinic. Ptilolite has only been observed in capillary needles; 

 these have parallel extinction, and a negative optical character^. 



^Amer. Jour. Set., 3rd. Series, Vol. 44, 1892, p. 96. 

 ^ Cross and Eakins, op. cit. 



