NO. 2351. NOTES ON METALLIC MINERALS— SHANNON. 603 



mineral agrees very closely with the simple formula given in most 

 textbooks for jamesonite, namely, QPbS.SbaSs. Taking the silver 

 into account we have for the present mineral the formula : 



2(Pb,Ag,)S.Sb,S3, 



with lead and silver present in definite ratios as Pb:Ag2=4:l. 

 Expanding the above formula gives — 



8PbS.2Ag2S.5Sb2S3, 



with silver (Agj) in small measure replaced by copper (Cuo) and 

 iron (Fe). 



In a recent paper Spencer^ writes that jamesonite showing the 

 brittleness of the needles, which indicates transverse cleavage, does 

 not agree with the formula commonly given, but has the composition 

 expressed by the formula 7(Pb4/5Fei/5)S.4Sb2S3, and shows that the 

 more generally accepted formula 2PbS.Sb2S3 belongs riglitly to 

 plumosite, the needles of which are flexible and not brittle. Schaller,- 

 more recently still, proposes a different formula for jamesonite — 

 namely, 4PbS.FeS.3Sb2S3. The present mineral may be compared 

 with these two proposed formulas as follows : 



4PbS. FeS. SSbjSa Jamesonite (Schaller). 



4PbS. AgjS. 2iSb2S3 Idaho silver jamesonite. 



7(Pb4/5Fei/5)S.4Sb2S3 Jamesonite (Spencer). 



7(Pb</5( Ag2)i/5)S. 3.48Sb2S3 Silver jamesonite. 



Taking into account the perfect cleavage manfested by the brittle- 

 ness of the needles, and the fact that silver almost completely replaces 

 the iron which has been regarded as an essential constituent of jame- 

 sonite, the present mineral is designated silver jamesonite rather than 

 simply argentiferous jamesonite. Were it not for the stress laid by 

 recent writers on the value of the cleavage as a diagnostic charac- 

 teristic of jamesonite it might perhaps have been better to call the 

 Silver City mineral simply argentiferous plumosite. 



The mineral above described does not differ greatly in composition 

 from the argentiferous jamesonite from the Sheba mine, Star City, 

 Nevada, described by Burton.^ This mineral is described as silver- 

 white to bluish-white in color, massive to coarsely fibrous or columnar 

 in structure with a hardness of 2.5 and a specific gravity of 6.03. It 

 was associated in quartz with sphalerite and tetrahedrite. Selected 

 samples gave, upon analysis, the results in the following table . 



» Spencer, L. J., Mineraloglcal Magazine, vol. 14, p. 207, 1907. 

 > Schaller, W. T., U. S. Geological Survey Bull. 490, p. 26, 1911. 

 •Burton, B. S., Amer. Joum. Sci., vol. 4.5, p. 36, 1868. 



