of Mineral Species. 87 



specimen of variegated copper from Ireland, this species is com- 

 posed of one atom of protosulphuret of iron, and four atoms of 

 sulphuret of copper, or Fe S* + 4 Cu S. The three ingredients, 

 copper, iron, and sulphur, are in the ratio of 62-67, 13-44, and 



23-89. 



The composition of copper-pyrites, from the analysis of Pro- 

 fessor HENRY ROSE, might be considered as being essentially one 

 atom of protosulphuret of iron, and one atom of a sulphuret of 

 copper, containing twice as much sulphur as the native sulphu- 

 ret, which forms the species of prismatic copper-glance. Pro- 

 fessor ROSE is of opinion, however, that the copper contained in 

 the mineral is in combination only with one atom of sulphur, 

 as in other species, and that the whole mixture should be consi- 

 dered as a compound of one atom of protosulphuret of iron, one 

 of persulphuret of iron, and two of the sulphuret of copper. 

 The chemical formula is Fe S 8 + Fe S* + 2 Cu S, and the ra- 

 tio among the ingredients, copper, iron and sulphur, is 34.80, 

 29.83, and 35.37. 



The changes, therefore, can be explained, upon the supposi- 

 tion that the copper contained in the original species has been 

 replaced by iron, in a smaller quantity, however, as every par- 

 ticle of iron required twice the quantity of sulphur to be convert- 

 ed into protosulphuret, in the variegated copper, and four times 

 the quantity for that portion of it in the copper-pyrites, which is 

 in the state of persulphuret. The compound of protosulphuret 

 and persulphuret of iron, which, in the last species, is joined to 

 the sulphuret of copper, is one of those forming the chemical con- 

 stitution of magnetic pyrites. 



When the sulphur is entirely driven off, and the copper at- 

 tracts so much oxygen as to be converted into the peroxide, 

 black copper remains. During this process, also, some of the 

 carbonate is frequently formed. 



