NOTES ON METALLIC MINERALS— SHANNON. 



607 



Column two of the above table yields the following ratios 

 Ratios of naumannite. 



The mineral thus agrees reasonably well with the formula usually 

 assigned to naumannite, Ag2Se, the selenium (Se) being replaced to 

 a slight extent by sulphur (S). Aside from this replacement and 

 from the mechanical impurities mentioned, the material is remark- 

 ably pure silver selenide, careful determinations having proven that 

 lead, copper, gold, zinc, arsenic, antimony, bismuth, and tellurium 

 were either absent or present in minute traces. 



The ratio of selenium to sulphur is so great (17 : 2) that the mineral 

 must be designated naumannite, AgjSe, rather than aguilarite, 

 AgjS.AgjSe, in which sulphur and selenium are present in molecu- 

 larh' equal amounts. 



