Bornite and, its Relation to Other Sulpho-Minerals. 549 



Schapbachite (Pb,Ag 2 ) 2 Bi 2 S 6 



Sychnodymite (Cu,Co,Ni) 2 Co 2 S 6 



Polydymite Ni 2 Ni 2 S 5 



Bornite Cu 6 Fe 2 S 6 



Proustite Ag B As 2 S 6 



Pyrargyrite Ag 6 Sb 2 S 6 



Xanthoconite Ag B As 2 S 6 



Pyrostilpnite Ag 6 Sb 2 S 6 



Seligmannite Pb 2 Cu 2 As 2 S 6 



Bournonite Pb„Cu 2 Sb 2 S 6 



Aikinite Pb 2 Cu 2 Bi 2 S 6 



Guitermanite Pb 3 As 2 S 6 



Lillianite Pb 3 Bi 2 S 6 



Bornite Cu e Fe 2 S 7 



Tetrahedrite M' s R'" a S T * 



M' = Cu,Ag,Hg 



M" = Fe,Zn 



R'"= As,Sb 



Jordanite Pb 4 As 2 S 7 



Meneghinite Pb 4 Sb 2 S 7 



Bornite Cu ]0 Fe 2 S 8 



Stepbanite Ag 10 Sb 2 S 8 



Geocronite Pb 5 Sb 2 S 8 



Bornite Cu 12 Fe 2 S 9 



Kilbrickenite Pb 6 Sb 2 S 9 



Beegerite Pb^Bi 2 S 9 



Bornite Cu 14 Fe 2 S ]0 



Bornite Cu 16 Fe 2 S„ 



Pearceitef (Ag,Cu) ]6 As 2 S u 



Polybasitef (Ag,Cu) ]6 Sb 2 S u 



PlumbostanniteJ Pb 2 (Fe,Zn) 2 Sn 2 Sb 2 S u 



Bornite Cu 18 Fe 2 S 12 



Pearceitef (Ag,Cu) 18 As 2 S 12 



Polybasitef (Ag,Cu) 18 Sb 2 S ]2 



FranckeiteJ Pb 6 Sn 2 Sb„S 12 



Polyargyrite Ag 24 Sb 2 S 1 " 6 



Bornite Cu 34 Fe 2 S 20 



CylindriteJ Pb 6 Sn 6 Sb„S 21 



Bornite Cu 40 Fe 2 S 23 



* This older, simpler, and generally accepted formula is retained for the 

 present classification, even though Kretschmer has recently (Zeitsclir. Kryst., 

 xlviii, 484-513, 1910) suggested a more complex one, namely xM' 9 R'" 3 S9 +- 

 M" 6 R'"2S 9 . If M' 9 R'" 3 S9 be written in its simpler form, M' 8 R'" 2 S6, it will 

 be noted that both of these components correspond to well-known minerals 

 in the above list. 



f Penfield (this Journal, xliv, 17, 1892) gave Ag 18 R'" 2 S 12 as the general 

 formula for these minerals. Van Horn and Cook have, however, recently sug- 

 gested Agi 6 R'" 2 Sii (ibid., xxxi, 518, 1911, and xxxii, 40). Unquestionably both 

 formulas hold good, the conditions being analogous to what is now shown to 

 be the case for bornite with its varying composition, belonging as it does to 

 the Fe 2 S 3 -Cu 2 S series. Pearceite and polybasite are accordingly to be inter- 

 preted as being members of two similar series, namely, As 2 S 3 -Ag 2 S and 

 Sb 2 S 3 -A g2 S. 



% In these minerals tin is considered as being basic in character. 



