Geiith.] ^ [Oct. 2, 



not that appearance, but it is more probably replacing some of the silver, 

 the analysis nearly agrees with the formula : (Ag 2 Pb) S. Bi 2 S s . 

 The pure Ag 2 S. Bi 2 S 3 would have the composition : 



Ag = 28.27 



Bi = 54.97 



S = 16.76 



5. Cosalite. 



The name rezbanyite was given, in 1858, by R. Hermann, to a mtxture of 

 a sulphobismutite of lead, silver and copper and sulphate of lead ; the 

 unoxidizod mineral was not analyzed, although he states that the interior 

 mass of his specimen was quite fresh, and of a lead-gray color. 



A sulphobismutite of the formula 2(PbAg 2 ) S. Bi 2 S 3 from Cosala in the 

 Province of Sinaloa, Mexico, was described by me in 1868 as cosalite. 



In 1874, A. Frenzel reexamined the rezbanyite and proved its identity 

 with cosalite. For another mineral 4PbS. 5Bi 2 S 3 , also found at Rez- 

 banya, he now adopts the name rezbanyite. 



In 1877 A. E. Nordenskiold distinguished as bjelkite a mineral from the 

 Bjelke Mine in Nordmark, Sweden, of which Nilson Lundstrom gave the 

 formula : FePb 2 Bi 2 S 6 . H. Sjogren, however, showed, in 1879, that the iron 

 in Lundstrotn's analysis was owing to an admixture of pyrrhotite, and 

 that the pure mineral was identical with cosalite. 



About two years ago I received, through the kindness of Mr. F. M. 

 Shideler, of Lake City, Colorado, a mineral from the Gladiator Mine in 

 Ouray county, Col., which contained, besides bismuth, lead and silver, a 

 considerable quantity of copper, but gave the atomic ratio of cosalite ; a 

 similar mineral was described at the meeting of the Colorado Scientific So- 

 ciety of Dec. 3, 1883, by W. F. Hillebrand, as coming from the Comstock 

 Mine, near Parrott City, La Plata Co., Col., and finally G. A. Koenig, 

 Proc. Am. Phil. Soc. xxii, 211, made an analysis of that which occurs 

 associated with his alaskaite (galenobismutite) from the Alaska Mine- 

 about six or eight miles above the Gladiator Mine. 



The cosalite of the Gladiator Mine occurs associated with galenite, bis- 

 muthinite, chalcopyrite and pyrite in quartz. It forms small irregular 

 masses more or less mixed with its associates, the largest which I have 

 seen was not over 25 mm in diameter. It is compact, without any apparent 

 crystalline structure ; where it appears to be fibrous it is mixed with bis- 

 muthinite. Some portions have a fringe of crystalline galenite, surround- 

 ing the whole patch of the cosalite. The bismuthinite is present in small 

 particles of a few millimeters in size, and frequently occupies the centre 

 of the cosalite (one fragment of about 4 mm long was examined and found 

 to be perfectly pure Bi 2 S 3 ). 



The cosalite is between lead gray and iron black, fracture uneven. For 

 the analysis I selected material which was perfectly free from bismuthi- 

 nite, galenite and chalcopyrite, but I was not able to obtain any which 



