152 B. J. Harrington — Formula of Bornite. 



Nor are such concordant results likely to iiave been obtained 

 from mere mixtures of different sulpliides. Furthermore, 

 they are in close accord with a number of previously published 

 analyses of massive bornites. Out of fifty analyses cited by 

 Hintze* about one-iifth agree well with the formula Cu^FeS^ 

 and the average of eight of these gives : 



Copper. 62-85 



Iron. 11-57 



Sulphur 25-34 



99-V6 



We pass now to the consideration of crystallized bornite. 

 Through the kindness of Professors Dana and Peniield of 

 Yale University, the writer has been able to obtain a speci- 

 men of the crystallized mineral from Bristol, Connecticut, 

 which, though long known, had apparently never been anal- 

 yzed. f It came from the Brush collection (specimen No. 805) 

 and though partly massive showed at one end a group of fairly 

 distinct rhombic dodecahedrons, which, so far as could be ascer- 

 tained microscopically, were entirely free from other minerals 

 and were found to have a specific gravity of 5-072 at 15° C. 

 Their analysis gave : 



CusFeSi 



Copper 63-24 63-27 



Iron... 11-20 11-18 



Sulphur 25-54 25-55 



99-98 100-00 



Here then we have a crystallized bornite which does not 

 agree in composition w4th the commonly accepted formula 

 CugFeSg. As to this formula, which has so long been assigned 

 to the crystallized mineral, we find that it was based upon the 

 analysis of a Cornish specimen publislied by Flattner in 18394 

 This was followed in the same year by an analysis of another 

 Cornish specimen by Yarrentrapp,§ while a third analysis by 

 Chodney appeared in the same journal in 1844.1 These three 

 analyses, together with two others, also of Cornish specimens, 

 are given below : 



* Handbnch der Mineralogie, 1901, p. 915. 



f For an analysis of the massive mineral from Bristol see Dana, " System 

 of Mineralogy," 1892, p. 77. 



X Pogg. Ann. xlvii, p. 351, 1839. 



§ Ibid., p. 372. 



II Ibid., Ixi, p. 395, 1844. 



