258 C. Palache — Mineralogical Notes. 



obtained, the relations of the group appear as in the following 

 table : 







a 



6 



c 



Chalcocite 



Cu„S 



0-5822 : 



1 



: 0-9701 



Stromeyerite 



(Ag,C.i) a S 



0-5822 



: 1 



: 0-9668 



Sternbergite 



Ag 9 S-Fe 4 S 6 



0-5832 : 



: 1 



: 0-8391 



Cbalmersite 



Cii>Fe 6 S 7 



0-5725 : 



: 1 



: 0-9637 



Pyrrhotite 



Fe ?l S„ + 1 



0-5760 



: 1 



: 0-9524 



The propriety of placing pyrrhotite in the Chalcocite Group, 

 long ago suggested by Streng and others, and confirmed by the 

 discovery of the intermediate chalmersite, seems no longer open 

 to question with the established orthorhombic nature of pyr- 

 rhotite. The discordant value for the c-axis of sternbergite 

 suggests the need of a revision of the crystals of that species. 



Harvard University, April, 1907. 



