1885.] 35 fGenth. 



Another specimen from the same locality, which was considered the 

 same mineral, gave very different results : 



T'his mineral, while it showed an eminent brachydiagonal cleavage, 

 was much whiter, and less brittle. It had the same associations, but there 

 appeared to be also some granular native bismuth in its immediate neigh- 

 borhood. The analysis, after deducting 3 per cent of impurities, gave : 



Sulphur = 11.87 % 



Selenium = 4.25 — 



Lead = 5.36 — 



Bismuth = 74.44 — 



95.92 



There is a loss of about 4 per cent, for which I cannot account, possibly 

 selenium. 



There was only a small quantity of the mineral obtainable for analysis, 

 which would indicate that it is a mixture of probably about 20 per cent 

 of the seleniferous galenobismutite with 63 per cent of bismuthinite and 

 about 17 per cent of the native bismuth. 



4. Argentobismutite (Silberwismuthglanz). 



Prof. C. Rammelsberg described, in 1876, under the name silberwis- 

 muthglanz, a compact gray mineral from the Matilda Mine, Peru, corres- 

 ponding to the formula : Ag 2 S, Bi 2 S 3 . 



Amongst the minerals which the late J. F. L. Schirmer presented me 

 about eleven years ago, was a specimen of granular quartz penetrated 

 by thin needle-shaped iron black crystals, about l mm in thickness and 

 10-25 mm in length, showing a deep longitudinal striation, apparently no 

 cleavage, but an uneven fracture. It came from Lake City, Colorado, 

 and was evidently a surface specimen. In vain I have endeavored since 

 to get the same mineral again from the mines near Lake City. 



I have made several rough tests and found in one about 24 per cent of 

 silver and 55 per cent of bismuth. I have sacrificed the greater portion of 

 my specimen, and by crushing and washing off the quartz and oxidized 

 portion of the mineral, I obtained a small quantity for analysis, consisting 

 of the nearly pure sulphide and quartz with ferric oxide, which latter 

 were left undissolved by nitric acid . 



The analysis gave : 



The lead may be an admixture of galenite, although the mineral had 



