258 Analysis of the Copper Ore of Franco nia. 



position of these varieties of pyritous copper, they do not pre- 

 sent any specific characters which will guide the mineralogist 

 in distinguishing them, except, indeed, it be possible that the 

 specific gravity may betaken as a sufficiently precise character 

 for this purpose. It does not appear probable that bodies having 

 exactly the same chemical constitution, will differ essentially in 

 their gravity. It would be desirable that some of the heavier 

 copper pyrites should be subjected to a chemical analysis, 

 with the express object of ascertaining whether they do or do 

 not agree in composition with that of the double sulphuret of 

 copper and iron, while the less heavy may be found to agree 

 with thai of the Franconia ore. 



The mineralogical characters of pyritous copper do not, 

 nor, so far as a careful inspection of the cleavage will warrant 

 the inference, do the crystallographical characters, present 

 any marks for making a subdivision of the species, and yet it 

 may he considered as sufficiently established, that there are 

 essential differences in the chemical constitution. 



