6 



PROCEEDINGS OF THE NATIONAL MUSEUM 



VOL. 74 



All of the crystals are strongly striated in two zones. The most 

 prominent set of striations is parallel to the intersections of the faces 

 in the zone 100:011 and the faces of this zone are often rounded hj 



oscillation between the various 

 forms in this zone with many 

 vicinal forms. The striation 

 is more marked in the end of 

 the zone toward the front pina- 

 coid and diminishes toward the 

 opposite end, the form (Oil) 

 being usually brilliant. Another 

 less prominent series of striae 

 occurs in the zone (100) : (001). 

 These two sets of striations are 

 both present on the a (100) face 

 and this together with the tri- 

 angular or inverted keystone 

 shape of the face serves to 

 identify it and to orient the 

 crystal. 



The crystals implanted on 

 the druses of quartz are some- 

 wliat more highly modified and 

 vary from those which are thick 

 tabular parallel to the front 

 pinacoid to some which are 

 Every gradation exists between these 

 This crj^stal gave 



Fig. 



2.— Crystal of miargyrite thick tabular 

 ON (100) 



tabular parallel to the base. 



two types. The former is illustrated in Figure 2. 



the following measurements : 



Measuremenls of miargyrite crystal, Figure 2 



