162 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



The ratios indicate the formula Pb 5 Ag 2 Sb e S l5 or 5PbS.Ag 2 S.3Sb 2 S 3 . 

 A mineral described as an argentiferous jamesonite from Nevada 

 by Burton is probably also owyheeite and Foshag has recently 

 found the mineral in a specimen from a third locality in Nevada, 

 so that its occurrence is not confined to Idaho. It may be found in 

 other specimens of the rich silver ores from the Poorman mine. 



JAMESONITE (130) 



Lead iron sulphantimonite, 4PbS.FeS.3Sb 2 S 3 . Orthorhombic 



For some years it has been the practice of many mineralogists to 

 call all fibrous lead sulphantimonites not otherwise identified jame- 

 sonite. Recent investigations by Spencer and Schaller have shown 

 that jamesonite, which contains iron as an essential ingredient and 

 possesses a cleavage across the needles rendering them brittle, is a 

 comparatively uncommon mineral. As mentioned above, much of 

 what has heretofore been called jamesonite is really boulangerite. 

 Most of the occurrences of jamesonite mentioned in Idaho are not 

 certainly correct, the identification of the mineral being only tentative. 



BLAINE COUNTY 



Jamesonite has been reported to occur in the Reliance mine, Era 

 district, associated with pyrite, galena, sphalerite, and chalcopyrite 

 in a fine-grained quartz-chalcedony gangue. 47 



OWYHEE COUNTY 



Specimens of altered rhyolite from the dump of the 800 foot level 

 of the De Lamar mine have open cavities which contain radiating 

 prismatic fibers up to 1 cm. long of a steel gray sulphantimonite. 

 The fact that the fibers are brittle and break sharply across the 

 elongation indicates that the mineral is either jamesonite or owyhee- 

 ite. Similar needles occur imbedded in quartz crystals or projecting 

 into open cavities of quartz of ore from the Rising Star mine, Flint 

 district. These are associated with argentiferous tetrahedrite. 



SHOSHONE COUNTY 



A specimen of a fibrous sulphantimonite from the stopes above the 

 2,000-foot level of the Standard-Mammoth mine contained a fibrous 

 sulphantimonite of lead which, upon partial analysis, yielded only 

 36.4 per cent of lead. This is probably jamesonite although boul- 

 angerite was common in this ore body. 



« J. B. Umpleby. U. S. Qeol. Survey, Prof. Paper 97, p. 122, 1917. 



