G-enth.] ^^8 , [Aug. 21, 



Copper = trace — trace 



Bismuth = 0.41 — 



Lead =- 0.26 — 



Zinc = 0.05 — 0.21 



Iron = 0.78 — 1.28 



Tellurium = 33.49 by diff. 32.97 



100.44 100.00 



The above analyses, to which add for comparison those of Prof. Silli- 

 man and the petzite from Nagy-Ag, give the following atomic ratios 

 between gold, silver and tellurium 



32.7 



14 

 7 



4.7 

 3.1 



34.3 



8.2 

 5.9 

 4.2 



From which it will be seen that gold and silver appear to replace each 

 other in indefinite proportions, while the mixture of the two combines 

 atom for atom with tellurium. 



5. Sylvanitb. 



The Red Cloud Mine is the first American locality at which this mineral 

 has been fovmd. It was observed by Prof. Silliman, but his stock was 

 not sufficient for a more minute description. The specimens which I 

 have are massive, showing eminent cleavage in one direction, giving it a 

 plated appearance. In one piece it occurs in quartz, which is penetrated 

 by crystalline aggregations arranged in a line of i over one inch in length 

 and gV of an inch in thickness, resembling the real '■'■ grci'pMc tellurium " 

 from Transylvania. Its color is silver-white, with a strong gray tint : 

 brilliant metallic lustre. 



It is associated with pyrite, which, in very small crystals, is often so 

 thickly disseminated through the mass, that it is very difficult, if not 

 impossible, to obtain pure material for analysis. 



Sp. gr. ^ 7.943. 



100.29 100.00 100.00 



