152 



BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



district in Shoshone County. A generalization, derived from the 

 study of a large series of specimens of ores seems to be that stibnite 

 is not stable in association with galena, the antimony sulphide 

 tending to enter into combination in the form of a sulphosalt, and 

 under the conditions obtaining in most ore deposits boulangerite is 

 the most stable compound. The mineral often closely resembles 

 stibnite and the various Idaho occurrences have usually been con- 

 sidered to be stibnite. 



BLAINE COUNTY 



Boulangerite has been identified in ores from the North Star, 

 Independence, and Minnie Moore mines in the Hailey (Wood River, 

 Mineral Hill, Ketchum) district. The ores of the North Star mine 

 consist of an intimate mixture of galena, pyrite, sphalerite, chal- 

 copyrite, pyrrhotite, and arsenopyrite in a gangue of quartz. Most 

 of the specimens which the writer has examined show galena, dark 

 brown rather coarsely crystalline sphalerite, pyrite, arsenopyrite, 



and boulangerite in a gangue of quartz or a 

 carbonate of the ankerite group. The gray 

 mineral which has heretofore been mistaken 

 for stibnite is all boulangerite. This boulang- 

 erite seems to be a constant constituent of the 

 ores. It has the usual steel gray color and 

 metallic luster and exhibits the characteristic 

 brownish rubbed streak. It occurs as com- 

 pact parallel fibrous masses, as slender needles 

 lining cavities, as tufted wool-like aggregates 

 in cavities and as compact and slightly schis- 

 tose massive forms with other sulphides, the 

 massive variety evidently having been subjected to pressure. The 

 boulangerite is commonly the youngest mineral in the veins and 

 it often lines cavities or occurs between the crystals making up 

 quartz combs. Upon analysis a sample containing some adhering 

 quartz gav results tabulated in column 1 below. In column 2 the 

 analysis is recalculated to 100 per cent after deducting gangue: 



Analysis oj boulangerite from North Star mine 



Fig. 25.— Boulangerite. In- 

 dependence mine, Blaine 

 County 



Constituent 



Original 



Recal- 

 culated 



Lead (Pb) _ 

 Silver (Ag). 



Iron (Fe). 



Antimony (Sb) 



Arsenic (As) _. 



Sulphur (S) 



Insoluble (quartz) _ 



Total 



