154 B, J. Harrington — Formula of B or rate. 



is no evident reason why such a mineral should not occur in 

 nature. 



Many of the published analyses of so-called bornite show a 

 composition which could be easily explained by the presence 

 of chalcopyrite, which would reduce the proportion of copper 

 and increase the proportions of iron and sul^Dliur. In other 

 cases chalcocite would appear to be present. In this connec- 

 tion it is interesting to note that a mixture of one molecule of 

 bornite with one of chalcopyrite would give the old formula, 

 thus : 



Bornite Cu^FeS, 



Chalcopyrite CuFeS^ 



Cu^Fe^S, = 2Cu,FeS3. 



Such a mixture would contain 73*20 per cent of bornite and 

 26*8 per cent of chalcopyrite. 



The range for the specific gravity of bornite is sometimes 

 stated to be 4*9 to 5*4 ; but a substance with as definite a com- 

 position as pure bornite evidently possesses should not show 

 so great variation, and it will probably be found that when 

 the material is carefully selected the range will be more like 

 5*05 to 5*10. As we have seen, the crystallized mineral from 

 Bristol gave 5-072. 



Department of Chemistiy and Mineralogy, 

 McGill University, May, 1903. 



