Bornite and its Relation to Other Sulpho-Minerals. 511 







Observed 



Calculated 



(110) 



: (101) 



60°15' 



60° 



(110) 



: (112) 



30 2 



30 



(110) 



: (221) 



19 40 



19 28' 



(211) 



(121) 



33 43 



33 34 



(322) 



(232) 



19 41 



19 45 



(411) 



• (141) 



60 23 



60 



(433) 



(343) 



13 45 



15 56 



(522) 



(252) 



43 15 



43 21 



(533) 



(353) 



25 4 



24 55 



Of the new forms for bornite (221), (133), (411), (522), and 

 (833), only (111) should be considered as doubtful. The iden- 

 tification of this form is based upon only one measurement, the 

 observed angle differing from the calculated by 28 minutes. 

 The values for all the other angles, given in the table, are the 

 averages of from two to eight readings. 



Earlier Interpretations of the Chemical Composition* 



For over one hundred years the chemical composition of 

 bornite has been the subject of much discussion among min- 

 eralogists. Based upon the results of the earliest analyses of 

 this mineral, Hisinger, Phillips, and Berzelins assumed bornite 

 to be a mixture of the sulphides of copper and iron, as follows : 

 2Cu 2 S + FeS. Plattner in 1839 analyzed specimens of bornite 

 from five different localities and concluded that the composi- 

 tion of ciwstallized bornite should be expressed by the formula 

 3Cti„S + Fe 2 S 3 . He, however, considered massive bornite as 

 being variable in character, that is, a mixture of bornite of the 

 above composition with chalcopyrite and chalcocite. In 1810 

 Schaffgotsch concluded that the composition of massive bornite 

 could be best indicated by varying combinations of Fe 2 S 3 and 

 Cu 2 S, thus one Fe 2 S 3 with either 3, 5 or 9Cn„S. A little later, 

 in 1811, Rammelsberg considered Fe„S 3 .3Cu 2 S as the correct 

 formula, but assumed the admixture of varying amounts of 

 Cu 2 S in some varieties. In 1851 Forbes thought the com- 

 position of bornite should be represented by the following- 

 three mixtures : CuS + 2Cu 2 S, CuS + Cu 2 S, or 2CuS + Cu 2 S. 

 Forbes, however, assumed that iron partially replaced copper. 



By heating varying quantities of Cu 2 0, CuO, and Fe 2 3 in 

 a current of H 2 S at a temperature of about 200° C, Doelter,f 

 in 1885, obtained small cubical crystals which he thought were 

 bornite. The analyses, however, did not lead to any of the 



* This summary is based largely upon Hintze's resume, Hand buck der 

 Mineralogie, I, p. 905, where references to the original contributions may be 

 found. 



fZeitschr. Kryst., xi, 36, 1886. 



