South Mountain Mining District, Idaho. 



123 



tion and hydration. Frequently a crystal seems to have 

 been split longitudinally and the two halves slightly dis- 

 placed, this discrepancy in one case reaching five 

 degrees. The fracture was parallel to b, the most prom- 



FlG. 1. 



Fig. 2. 



Fig. 3. 



Pi 



m 



Fig. 6. 



inent cleavage, and was not visible on the crystal, being 

 located on a deeply striated face. Its location was clearly 

 shown when the angles measured on the crystal were 

 plotted on a Penfield stereographic circle. 



The terminated crystals show exactly the same forms 

 in the prism zone as were observed on the embedded 

 crystals. On the whole, the faces in this zone on the 

 terminated crystals are not as good as they are on some 

 of the embedded crystals. The crystals are frequently 

 unsymmetrical as shown in fig. 5, where a form may be 

 present as a broad face on one side of the crystal, and 

 be absent or represented by a very narrow line on the 



