602 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.58. 



the sulphantimonite occurs in free needles of very minute size, which 

 are entirely too small for goniometric measurement. Upon exam- 

 ination these needles were found to be exceedingly brittle, breaking 

 across the elongation at the slightest touch, in a manner indicating a 

 rather perfect cleavage in this direction. Upon exposure the mineral 

 assumes a faintly yellow color. The hardness is about 2.5, When 

 rubbed upon paper the mineral gives a gray mark like that made by 

 hard graphite, but its streak upon unglazed porcelain is reddish 

 brown. 



I'TROGNOSTICS. 



The blowpipe characteristics of the mineral are the usual ones for 

 sulphantimonites of lead. In the open tube it yields sulphur dioxide 

 and a heavy sublimate of white antimony oxide. In the closed tube 

 fragments melt and yield a faint upper ring of antimony oxide, suc- 

 ceeded downward by a yellow ring of sulphur, a red band of anti- 

 mony oxysulphide, and a black coating of antimony sulphide. 



CHEMICAL PROPERTIES. 



The mineral is completely soluble in hot concentrated hydro- 

 chloric acid. Selected fragments of the mineral when separated 

 from quartz were analyzed with the results given in the following 

 column : 



Analysis of silver jamesonite. 



Lead (Pb) 40.77 



Copper (Cu) .75 



Iron (Fe) ,46 



Sliver (Ag) 7.40 



Antimony (Sb) 30.61 



Sulpliur (S) 20.81 



Total 100. 80 



This analysis yields the ratios given in the following table : 



Ratios of silver jamesonite. 



PbS.. 

 FeS.. 



Sb.,S3 



2X1.00 

 1X1.04 



The amount of sulphur given in the analysis is somewhat higher 

 than required by the bases present, a fact possibly traceable to an 

 error in the analysis. From the above ratios it is evident that the 



