Mineralogy of South America. 7 



The formula FeS 2 + FeAs would require — 



Arsenic, 1 atom . . . 75-0 or percentage 46*02 

 Sulphur, 2 atoms . . . 32'0 „ 1963 



Iron, 2 atoms .... _560 „ 3435 



163-0 100-00 



Danaite. — In the analysis of the mispickel above given, I had 

 fully expected to find considerably more cobalt than actually 

 was found ; for it must be remembered that this mispickel had 

 crystallized out of the Danaite, to which it bears a proportion 

 quite insignificant, as the Danaite forms the entire mass of the 

 vein, which occasionally has presented a solid mass of the mineral 

 having a breadth of more than ten feet between the walls. 



The Danaite was never found crystallized, but formed a com- 

 pact mass, possessing a granular, fibrous, or foliated structure, 

 and more or less crystalline appearance. The specific gravity of 

 the fibrous variety, which probably is the most pure, was found 

 to be 6*94 at 60° Fahr., of the granular variety 5*86; but this 

 was invariably intermixed with more or less quartz or gangue in 

 a very fine state of dissemination. Several analyses were made 

 by the methods described under mispickel, and the following 

 percentages show the average composition derived from their 

 results : — 



Arsenic . . . 



. 42-83 



Sulphur . . 

 Iron . . . 



. 18-27 

 . 29-22 



Manganese 

 Cobalt . . . 



. 5-]2 

 . . 311 



Nickel . . . 



; . o-8i 



Bismuth . . 



. . 0-64 



10000 



which corresponds to the same formula as for mispickel, allowing 

 a portion of the iron to have been replaced by the cobalt, nickel, 

 and manganese here present. 



Nickeliferous Mispickel. — From Mr. Philip Kroeber I received 

 a specimen of this mineral which I have not before seen described 

 in any of the published works upon mineralogy. The mineral 

 occurs as a vein in the lower Silurian slates in the Cordilleras 

 between La Paz and Yungas in Bolivia, about 5 leagues from 

 Unduavi, at a place called by the Indians Chacaltaya. The 

 geological relations of this vein are very similar to those described 

 in the case of the vein of San Baldomero, and it has doubtless 

 originated from the same cause, the outburst of the same granite. 



More or less distinct crystals occur, and pertain to the trimetric 



