Genth.] 38 [Oct. 2, 



Only a very small quantity, not over 0.0312 grm., could be taken for 

 analysis, in which the metals were determined, and the sulphur required 

 by them calculated. It gave : 



100.00 

 This seems to indicate that the mineral from the Treasury Vault Mine 

 agrees with the formula of argentiferous beegerite : 



(A gi! Pb) 6 . Bi 2 S 3 . 



Dr. Kcenig described, in 1881, Am. Chem. Journ., ii, 379, under the 

 name of beegerite, a mineral from the Baltic vein, Park county, Colorado, 

 which, however, he found to be entirely free from silver. Lately he 

 described another variety from the Old Lout Mine near Lake City, Colo- 

 rado, containing about 10 per cent of silver. Proc. Am. Phil. Soc. xxii, 



211. 



7. Tetrahedrite. Sylmnite. 



Already about eleven years ago I have received from Mr. Schirmer 

 specimens of a variety of tetrahedrite in quartz, associated with crystal- 

 lized gypsum and a yellowish waxy oxidation product containing largely 

 oxide of antimony, which came from the Hotchkiss Mine in the San Juan 

 District, Colorado. 



Almost identical in appearance and associations in the tetrahedrite from 

 Governor Pitkins' Mine near Lake City, of which Mr. F. M. Shideler sent 

 me a number of specimens. 



The tetrahedrite does not show any signs of crystallization, but is mas- 

 sive, compact, disseminated through quartz ; in the cavities are small 

 crystals of gypsum. 



Iron black. Its specific gravity = 4.885. 



The material for analysis was slightly contaminated with quartz which 

 was deducted, in I, 2.46 per cent ; in II, 3 per cent. 



101.24 



