550 Kraus and Goldsberry — Chemical Composition of 



It is thus seen that many of the rarer minerals with complex 

 molecules fall into this series. The chemical composition of 

 some of these has generally, heretofore, been considered rather 

 doubtful. Thus, to cite but one example, poly argy rite, 

 Ag 24 Sb 2 S ]6 , has always been placed in a class by itself, but it 

 now appears that its composition is such as to conform to the 

 general formula of this series. 



Other Series of Sutpho-Minerals. 

 (1) The klaprotholite group shows the general formula 



M'xE/'^Sy where y = — + 6. These minerals are : 



Klaprotholite Cu 6 Bi 4 S 9 



Rathite Pb„As,$ 



4 9 



(Binnite) 

 Warrenite Pb,Sb,S 



4 9 



Schirmerite (Ag 2 ,Pb) 3 Bi 4 S 9 



Boulangerite Pb 6 Sb 4 S 11 



Diaphorite (Pb,Ag 2 ) B Sb 4 S n 



Freieslebenite (Pb,AgJ 5 Sb 4 S n 



(2) Baumhauerite, Pb 4 As 6 S ]3 , has a composition which may be 

 expressed by the general formula M'JR/'^Sy, where y = +9. 



This is the only mineral of this type thus far noted. 



(3) The composition of plagionite, Pb 5 Sb 8 S 17 , may be written 



to conform to the formula M / x R /// 8 S y , where y = ~ + 12. 



Plagionite is the only member of this series thus far observed. 



(4) The series of sulpho-stannates possesses the general 



formula M' x R /v 2 S y , where y = — + 4. M. ; may be silver, 



univalent copper, or bivalent iron ; R/ v is either tin or ger- 

 manium. The minerals of this series are : 



Stannite Cu 4 Fe 2 Sn 2 S g 



Canfieldite Ag ]6 (Sn,Ge) 2 S 12 



Argyrodite Ag 16 Ge 2 S 12 



(5) The series of minerals in which arsenic, antimony, 

 vanadium are interpreted as having valencies of five con- 



form to the formnla M' x R v 2 Sy, where y = — + 5. The series 

 is as follows : 



