446 W. F. Foshag — Relations of Siilphosalts. 



Andorite AgPbSb.So 



Alaskaite Ag.Pb Bi^S^, 



Schirrxierite Ag^PbBi^S., 



Owylieeite Ag.Pb-ISb,.Si5 



Brougniarcltite Ag-.Pb SboSg 



Schapbachite Ag.PbBi.S^ 



Freieslebenite Ag.PboSbgSs 



Diapliorite Ag^boSb.Sg 



Seligmanite CuPbAsSo 



Bournoiiite CuPbSbS., 



Aikinite CuPbEiS^ 



Ag.,S-2PbS;3Sb.,S, 



Ag.,S-PbS-2BioS, 



2Ag,S-PbS-2BLS3 



Ag.,S-5PbSoSboS3 



Ag:,S-PbS-Sb..S; 



Ag.S-PbS-Bi..S, 



3Ag„S-4PbS-3Sb.S3 



3Ag.S-4PbS-3Sb.,S., 



CuoS-2PbS-As.S3 



Cu.,S-2PbS-SboS3 



Cu.S-2PbS-Bi:S., 



The above formulas show the shiiple ratios of the 

 constituent sulphides. This, together with the constancy 

 of composition, even in specimens from widely differing 

 localities and occurrences, places these minerals definitely 

 as double salts. 



There are no simple silver analogues of the lead salts. 

 AVliere a silver-bearing mineral falls into a grouiD with a 

 number of lead minerals it is one of the double compounds 

 given above.^ In the case of the copper salts there are a 

 few cases in which they are similar to the lead salts in 

 type of compound but there seems to be evidence that they 

 also are not isomorphous. 



The conclusions arrived at from a critical survey of 

 the best analytical data are : (1) that lead on the one hand 

 and silver and copper on the other hand are not isomor- 

 phous and that they do not form mixed crystals ; (2) that 

 the silver-lead or the copper-lead sulphosalts are double 

 salts. 



^ See Wheriy and Foshasr, A new Classification of the sulfo-salt Minerals, 

 Jour. Wash. Acad. Sei. ll/l, 1921. 



