( 467 ) 



Fig. 1. 

 (Diplienylhydiazine). 



Tr icUno-pinaco ida I. 



a :b:c = 0,7698 : 1 : 0,5986. 

 A= 89"J3|' a=: 89°24' 

 ^=i37°28' ^?=:137°28i' 



C= 89°29' v== 90° M' 



The approach to iiwnoclinic symmetry is 

 very phiiii. 



Forms observed: />=i|010|, broad and 

 lustrous; //i = |J'iOj, somewhat narrower ami 

 reflecting less sharply; p = |il0|, very lustrous 

 and broad; c = jOOij, well developed and 

 yielding fairly sharp reflexes; o = |lIl|, very 

 lustrous and well developed. The crystals are 

 mostly flattened towards p, or they may be 

 developed isometrically with a slight elongation 

 along the c-axis. It is peculiar that in the 

 vertical zone the co-related parallel planes of 

 the forms 7/?, /> and h are generally very 

 unevenly developed. Perhaps we may have 

 here a new example of the presence of an 

 acentric crystal; the nature of the surface of 

 the parallel planes is also often different on 

 a plane and its corresponding contreplane. 

 Etched figures could not be obtained. 



No distinct plane of cleavage. 



Measured : 

 // : p = (010) : (ifO) =* 62°6' 

 h : m = (010) : (110) =:* 62 54V, 

 // : c = (010) : (001) =* 89 137, 

 p:c =: (110) : (001) =* 48 53 

 : m! = (111) : (TfO) =* 73 38 

 m : c = (110) : (001) = 49 24 



0:C = (111) : (001) rr: 56 54 



p:o = (1Ï0) : (111) = 7842 

 0:b' = (ïïl) : (010) = 58 45\/, 

 p:m =r (110): (110)= 54597, 



Calcidated : 



49°28' 

 56 54 

 78 36 

 58 43 



54 597, 



In the vertical zone the situation of the optical elasticity axes was 

 almost parallel to the direclion of the r-axis ; bul on h the angle of 

 inclination amounted to about 10°, on in oidy about 1°. An axial 

 image could not be observed. 



