AET. 19. 



MORDENITE — ROSS AND SHANNON. 



11 



bulging, or parallel growth in the vertical zone rendering accurate 

 orientation on the goniometer very difficult. The average degree of 

 agreement may be shown by giving, in detail, the measurements 

 obtained upon two crystals, shown in figures 1 and 2, which were as 



follows : 



Measurements obtained on heulandite (fig. 1). 



Measurements on heulandite crystal (fig. 2). 



The agreement, while not satisfactory, is sufficiently close to show 

 the essential crystallographic identity of the mineral with heulandite. 

 The abrupt displacement of certain forms so that they give angles a 

 degree or more off is no doubt connected either with compound char- 

 acter or with the heterogeneous internal structure as seen in polarized 

 light. 



This material was analyzed, the material for analysis being se- 

 lected small red nodules and the analyzed powder was shown to be 

 20183— 25— Proc.N.M.voI.64 30 



