B. J. Harrington — Formula of Bornite. 153 



I. II. III. IV. V. CusFeSa 



Copper 56-76 58-20 57*89 57'7l 57*68 55-58 



Iron 14-84 14-85 14-94 13-89 ]5-ll 16-36 



Sulphur ...... 28-24 26-98 26-84 27*17 26*46 28-06 



99-84 100-03 99-67 98-77 99-25 100-00 

 I. Condorra Mine, Cornwall. Analysis by Plattner. 

 II. No locality is given, but the description makes it practi- 

 cally certain that the specimen was from Cornwall. 

 Analysis by Varrentrapp. 



III. Redruth, Cornwall. Analysis by Chodney. 



IV. and V. Cornwall. Exact locality not known. Analyses 



by the writer. 



It is obvious that none of these analyses agrees well with 

 the formula CiigFeSg, nor could it be expected that satisfactory 

 results would be obtained from the analysis of the Cornish 

 crystals, all of which, so far as the writer has had an oppor- 

 tunity of observing, are very impure." Nut only have they 

 generally been altered by oxidation, but they almost always 

 contain a yellow sulphide with the characters of chalcopyrite. 

 In some specimens nearly every crystal when broken shows a 

 yellow nucleus of chalcopyrite and the writer found it impos- 

 sible to obtain material which could be regarded as pure. The 

 early analysts, too, evidently found difficulty, if we are to judge 

 from their descriptions. Plattner, for example, tells how he 

 broke up the crystals and picked out the pieces which he con- 

 sidered to be free from copper pyrites. He further trusted to 

 washing with distilled water in order "as far as possible" to 

 remove the superficial portion of the crystals which appeared 

 to be somewhat oxidized. Yarrentrapp, again, states that the 

 small cubical crystals examined by him all contained a nucleus 

 (kern) of chalcopyrite and had their surfaces covered with a 

 laj'er of copper oxide. He admits also that his results do not 

 agree well with those of Plattner. 



There is then good reason for believing that the formula 

 CUgFeSj was deduced from analyses of impure material, and, 

 as we have seen, it does not apply to the crystallized mineral as 

 found at Bristol, Connecticut. If a mineral having this for- 

 mula really exists, then we have two distinct species — bornite 

 and something else. Artificial products agreeing well with 

 the formula CugFeSg are said to have been prepared,! and there 



* Professor Penfield lias kindly sent me a number of crystals broken from 

 specimens of Cornish bornite in the Brush collection and these are also very 

 impure. 



t See Hintze, " Handbuch der Mineralogie," 1901, p. 914. 



Doelter states that by heating a mixture of CuOjCuoO and FeaOs in a 

 current of H2S at a temperature not above 200° he obtained the "normal 

 bornite CusS + CuS + FeS " in aggregates of little cubes. He, however, gives 

 no analysis of these (Zeitschr. f. Kryst., xi, 1886, 36). 



