458 



walker: crystal form of spencerite 



The crystals are very small, few exceeding 2 or 3 mm. in 

 length. They are tabular in habit and in color, luster, and 

 habit closely resemble small, bright crystals of calamine. The 

 crystals, though small, are admirably suited for accurate measure- 

 ments. The conclusions regarding the crystal form contained in 

 the original contribution are confirmed, since the mineral is 



TABLE l 



found to be mono clinic, with polysynthetic twinning on the pina- 

 coid (100). 



There are two types of crystals, the first of which is represented 

 in figure 1. The peculiarity of this type is the prominence of 

 the pyramid 221 with relatively small terminal faces of the ortho- 

 diagonal zone. Crystals of the second type are terminated by 



