Epistilbite from Heulandite. 237 



of printing a communication from Dr Gustavus Rose of Berlin, 

 " on Epistilbite, a new mineral species of the Zeolite family." 

 This distinguished chemist, whose crystallographic and chemi- 

 cal knowledge is well known, had separated the Epistilbite 

 from Heulandite on the authority of certain differences in 

 their chemical composition, their hardness and specific gra- 

 vity, and their crystallographic form. Professor Weiss too, in 

 whose practised eye and theoretic skill every confidence may 

 be placed, had previously regarded the Epistilbite as a new 

 variety of foliated Zeolite ; and Count Bournon, one of the fa- 

 thers of mineralogical science, had likewise considered it as 

 something new. 



With all this evidence in favour of the separation of these 

 two species, we were not a little surprised at an ingenious and 

 elaborate memoir, published by Mr Levy in the Philosophical 

 Magazine for January 1827, in which he considers the iden- 

 tity of the two minerals as almost demonstrated. In order 

 that the nature of his arguments may be understood, we shall 

 give the following comparative tables of the properties of the 

 two minerals. 



Heulandite. Epistilbite. 



Specific gravity, - 2.211 2.249 



Hardness, a little greater than Heulandite. 



Blowpipe, - - the same as Heulandite. 



In order to compare the crystallographic structure of the two 

 minerals, Mr Levy assumes that the crystals of Epistilbite 

 may be derived from the primitive form of Heulandite ; and 

 he then shows that this primitive form may be so modified 

 as to give a secondary form very like that of Epistilbite. In 

 this way he obtains the following angles : 



* In this comparison, taken from Dr Rose's paper, the soda is wanting 

 in the Heulandite. Dr Rose's second analysis of Epistilbite contains, how- 

 ever, no soda ; but we think it has been omitted in the manuscript by 

 mistake. 



