E. V. Shannon — Notes on Boulangerite. 425 



Since the latter form yielded the better reflections its 

 angles were taken as fundamental for calculating the 

 crystallographic constants yielding the following : 



a = .5038 log a = 9.70226 log po = 10.13386 po = 1.3620 

 c = .6862 log c = 9. 83645 log qo= 9.83645 qo= .6862 



The axial ratios thus derived may be compared with 

 those given for boulangerite by Sjogren and those of 

 diaphorite as follows : 



a 



Boulangerite (new) 5038 



Boulangerite (Sjogren) 5527 



Diaphorite 4919 



c 

 .6862 

 .7478 

 .7345 



The crystals from Idaho show a well-defined cleavage 

 parallel to a(lOO) while Sjogren does not mention any 

 such cleavage in the material from Sala nor is such a pina- 

 coidal cleavage given for diaphorite. The forms 

 observed on the crystals from Idaho are given with their 

 calculated and measured angles in the following table : 



Forms and angles of hoidangerite from Idaho. 









Measured 







Calculated 





ter 



Miller 



















/ 



) 



a 



100 



90^ 



^00' 



90^ 



00' 



90' 



^00' 



90^ 



00' 



N 



450 



58^ 



^15' 



90^ 



'00' 



57' 



'47' 



90^ 



'00' 



n 



120 



44c 



^23' 



90^ 



00' 



44' 



^47' 



90' 



'00' 



g 



130 



33 



^32' 



90^ 



00' 



33 



'24' 



90' 



'00' 



fi 



140 



27 



^50' 



90' 



^00' 



26 



'22' 



90' 



'00' 



k 



180 



13 



^33' 



90' 



=00' 



13 



'55' 



90 



'00' 



r 



210 



75 



'13' 



90' 



^00' 



75 



'51' 



90 



'00' 



t 



310 



79 



=44' 



90 



'00' 



80 



'28' 



90 



=00' 



? 



5.12.0 



38 



°11' 



90 



'00' 



39 



'34' 



90 



'00' 



z 



124 



44 



°47' 



25 



=48' 



44 



°47' 



25 



'48' 



Sjogren sought to show that boulangerite was the lead 

 extreme of a series having the general composition 

 expressed by the formula 5(Pb, Ag2)S.2Sb2S3 which is 

 the formula which has been accepted for some years for 

 diaphorite. . In a recent paper Wherry and Foshag^ have 

 recognized the fact that lead and silver are not isomor- 

 phous in minerals of this t}^e but that, when these bases 

 of unlike valence occur in the same mineral, their ratio to 

 each other is constant, the compound being essentially 

 a double salt. This principle is futher discussed in a 



* Wherry, E. T., and Foshag, W. F., Classification of the sulphosalt min- 

 erals, Jour. Wash. Acad. Sci., vol. 11, pp. 1-8, Jan., 1921. 



