Palache and Wood — Crystallograjphic Study of Millerite. 351 



12 

 13 



14 

 15 



16 

 17 

 18 

 19 

 20 

 21 

 22 

 23 

 24 

 25 

 26 

 27 

 30 

 31 



3 





; 



3 



X 



X 



3 



3 



3 



3 



3 



3 



3 



1 



3 



3 



3 



3 



3 





1 





1 



3 



2 



1* 



1 





1* 





3 





X* 



. 



(The star indicates that the crystal was doubly terminated, but 

 the faces on one end only are given.V^ 



The forms may be characterized as follows : 



Prisms. 



The prisms usually show a triangular cross-section with 

 rounded corners, but sometimes the cross-section is nearly cir- 

 cular. This is due in part to the development of three or four 

 prisms, partly or completely, and in part to the oscillatory 

 combination of these prisms. The prism zone is badly striated 

 in its length from this cause and in measurement yields signals 

 every fe_w degrees. 



o, (1010). Twenty-four out of the twenty-eight crystals 

 which were measured systematically showed faces of the first 

 order prisms, and eleven of these showed all its faces. It is 

 easily the dominant form on the mineral, and it is the least 

 striated of any prism. In most cases it was developed 

 trigonally. 



a, (1120). The second order prism was also undoubtedly 

 present on nine crystals, although but one had every face. 

 Its faces when large were considerably striated. 



/j, (2130). This known prism was found developed incom- 

 pletely, but none the less surely on four crystals. Its faces 

 were narrow and poorly characterized. 



tZ, (7290). This new prism was found developed incom- 

 pletely on seven crystals, and the data establishing it are given 

 in full in the following table : 



