412 Koenig — New Species Melanochalcite and Keneenawite. 



This result was communicated to Superintendent Smith at my 

 visit to the mine on July 6, 1901. The material had come 

 from the sixth level. I collected material at the vein crossing 

 on the fifth level. In appearance it was identical with the one 

 just described. The analysis made with O'S gram samples gave 

 the following data : 



0-3379 Cu^S 



00487 Ni 



0-0047 Co 



0-3560 Mg^ASjO, 



0-0039 quartz. 



63 = 0-856 

 58-6 = 0-182 

 75 = 0-456 



99-60 



The ratio (Cu,Ni,Co) : As = 2-27 : 1, is not so close to 2 : 1 

 as that of the first material, but still sufficiently so. The 

 material, though freer from quartz, was not so faultless through- 

 out as the first. There appeared certain pseudocleavages 

 along which a thin olive-green film could be seen. Just to 

 what extent this condition has to do with preponderance of the 

 metals over the arsenic, I am not prepared to sa3^ But on the 

 other hand, this analysis shows unmistakably the replacement 

 of copper by nickel, and vice versa. 



A third analysis was made with another sample, the arsenic 

 not determined. 



The percentages are : 





Cu 



= 53-96 



Ni 



= 9-74 



Co 



= 0-94 



As 



= 34-18 



Quartz 



0-78 



Quartz 



= 060 



Cu 



= 40-72 



Ni 



= 19-42 



Co 



= 0-82 



Fe 



— trace 



(diff) As 



= 38-42 



63 = 0-646 

 58-6 = 0-346 



0-992 



75 = . . 0-515 



100-00 

 (Cu, Ni, Co) : As = 1-128 : 1 



In my paper on mohawkite (this Journal, December, 1900) 

 I showed how an arsenide CiijAs forms very easily when the 

 vapors of arsenic act upon copper at red heat. This artificial 

 CujAs shows the color and crystalline structure of chalcocite. 

 The difference in color in keweenawite must, therefore, be 

 owing to the nickel. 



