Sulphosalts of Lead, Silver and Copper. 4^1:5 



almost all cases hardly adequate to determine how free 

 of admixture the particular sample was. Only in a few 

 cases were any mineralographic examinations attempted 

 and these invariably showed small amounts of admixture 

 even Avhere crystals were used. In many cases copper 

 and silver have not been determined in lead salts or lead 

 sought for in copper or silver salts. The sums, however, 

 indicate that their amounts, if present at all, are negli- 

 gible. Because of this unsatisfactory character of the 

 analyses they are not included here and only the general 

 results Avill be noted. Of 32 analyses of lead minerals, 

 made mainly upon crystallized material and embracing all 

 the species, none showed a copper or silver content of over 

 1 percent and in most cases hardly more that 0.5 percent. 

 Of 21 copper salts only one showed a percentage of more 

 than 1 percent of lead. Of the silver salts tAvo analyses 

 from the same locality made upon ^'excellent" material 

 showed over 1 percent of lead. Twenty-three showed less 

 than 1 percent or none at all. These analyses were picked 

 only to the extent that the material was crystallized or 

 apparently homogenous as far as determinable. 



It is evident that the miscibility between lead on the one 

 hand and silver and copper on the other is very slight 

 if it takes place at all. It is difficult to determine from the 

 existing analyses whether the small amounts of lead, or 

 of the silver and copper, are due to slight miscibility or 

 to admixture. Since mineralographic examination has 

 shown the presence of foreign material even in the best 

 crystallized samples it is safe to assume that the small 

 percent of these constituents are foreign to the mineral 

 proper. 



We have another t^^pe of compound in which lead, silver 

 and copper do occur together in considerable amounts. 

 These include such minerals as diaphorite, bournonite, 

 ■Preieslebenite, etc. A survey of the analyses of these 

 minerals shows them to have a remarkably constant com- 

 position. They are in fact double salts. In some cases 

 the minerals have been recognized as double salts, in 

 some this has been suggested, but in a large number of 

 cases they are regarded as isomorphous mixtures. In 

 all cases the ratios of the constituent sulphides to each 

 other are simple and definite. These minerals are as 

 follows : 



Am. Jour. Sci. — Fifth Series, Vol. I, No. 5.— May, 1921. 

 30 



