Mineralogy of South America. 9 



Arsenic 46*95 



Sulphur 18-12 



Iron 34-93 



Cobalt, nickel, bismuth, silver, and gold . traces 



10000 



which conforms to the usual formula for mispickel, FeS 2 + FeAs. 



I may mention that I examined the Danaite which is asso- 

 ciated with this mineral, and found in various specimens a per- 

 centage of cobalt (with trace of nickel) which varied from 1*81 

 to 3'9 per cent, metallic cobalt. 



Antimonial Galena. — Considerable veins of antimonial galena 

 are worked between La Paz and Yungas on the eastern slope of 

 the Andes, chiefly for the amount of silver contained in them. 

 The mines are situated in veins which cut at very high angles 

 through the lower Silurian slates, containing abundant fossils of 

 the genus Crusiana and Boliviana, as well as others not yet 

 determined. Their geological relations are otherwise similar to 

 the veins hitherto treated of in this paper. A specimen from 

 the Mina Pilar was examined by Mr. Philip Kroeber, who has 

 communicated the results to me. The mineral which was ana- 

 lyzed was quite free from gangue, but contained some minute 

 specks of iron pyrites and chalcopyrite ; compact but foliated in 

 structure, and in colour of a light steel-grey tint and very lus- 

 trous. Its analysis afforded him — 



Lead 62-510 



Antimony 

 Copper . 

 Iron . 

 Silver . 

 Arsenic . 

 Sulphur . 



15-379 

 2-461 

 0-853 

 0-190 

 trace 



18-807 

 100-200 



The associated minerals are quartz, calcspar, carbonate of iron, 

 iron pyrites, chalcopyrite, zincblende, cubic galena, Fahlerz, and 

 a new mineral, in strongly magnetic, copper-coloured crystals, 

 which I have called Kroeberite, and which, though not yet ana- 

 lyzed, appears to be principally a subsulphide of iron. In some 

 specimens also there occurs some mineral containing cobalt, 

 most probably " Selenkobaltblei," as the ore was found to con- 

 tain on analysis more than 2 per cent, of cobalt. 



If we look upon the iron and copper as combined with a 

 portion of the sulphur, forming iron or copper pyrites, we may 

 suppose the mineral here analyzed to pertain to the mineral 

 species Geokronite. I add a tabulated statement of the various 



