404 



Decomposition of Iron Pyrites. 



ical intermixture or of chemical combination, are exceedingly 

 varied. In regard to the usual composition of chalcopyrite, for 

 example, Dana states that "some analyses give other propor- 

 tions, but probably from mixture with pyrite. These are in- 

 definite mixtures of the two, and with the increase of the latter 

 the color becomes paler. . . In Cornwall, . . its richness may 

 in general be judged of by the color ; if of a fine yellow hue, and 

 readily yielding to the hammer, it may be considered a good ore ; 

 but if hard and pale yellow, it is poor from admixture with py- 

 rite." Taking then as materials the simple arsenide and the 

 protosulphide of iron, and the four minerals, pyrite (Fe S 2 . 

 S.G.=5.), marcasite (Fe S 2 . S.G.=4.85), chalcocite (Cu 2 S. 

 S.G.=5.7), and lollingite (Fe As 2 . S.G.=8.6), the constitution 

 of the minerals mentioned in the first column is found to present 

 the replacements stated in the last. 



Mineral. 



Sp. Gr 



Leucopyrite. 

 Arsenopyrite. 

 Pacite. 

 Lonchidite. 

 Bornite, Killarney. 



" Corsica. 



" Cornwall. 



Bristol, Ct. r 



" Lauterberg 



Ramos, 

 Mex. 



Chalcopyrite. 



Cubanite, 



Barnhardtite. 



7.1 

 6.0 

 6.3 

 4.9 



4.2 

 4.1 

 4.5 



Formula. 



Molecular Consti- 

 tution. 



Fe As + Fe As 2 

 Fe As 8 + Fe S 2 

 4 Fe As 2 -f Fe S 2 



1 iron arsenide -f- 1 



lollingite. 

 1 lollingite -f-1 pyrite. 



4 lollingite + 1 pyrite. 



Fe As 2 +Fe S 2 +23 to 25 1 arsenopvrite + 23 to 



Fe S a 25 marcasite. 



Fe S -f- 2 Cu 2 S 1 iron monosulphide-f 



2 chalcocite. 

 Cu 2 S -f Fe S 2 1 chalcocite+1 pyrite. 



4 (Cu 2 , Fe) S + Fe S 2 4 bornite -f- 1 pyrite. 



6 (Cu 2 , Fe) S + Fe S 2 6 bornite -f 1 pyrite. 



10 (Cu 2 , Fe) S + Fe S 2 10 bornite -f- 1 pyrite. 



11 (Cu 2 , Fe) S + Fe S 2 11 bornite + 1 pyrite. 



Cu 2 S -f Fe S -f- Fe S 2 1 bornite + 1 pyrite. 



Cu 2 S + Fe S + 3 Fe S 8 il chalcopyrite + 2 py- 

 rite. 



2 Cu 2 S+Fe S + Fe S 2 1 chalcopyrite + 1 

 chalcocite. 



