332 



5CLFHURET 0? I/EATJ, COPfER, AND AVTTMOIvr. 



more liable to decomposition than either of the preceding, 

 particularly when crystallized. 

 Copper pyrites. 4th, The double combination of copper and iron with 

 sulphur, which is shining and of a deep yellow colour. 

 We have no analysis of this species, except that of Lam. 

 padius, who gives for its component parts 41 copper, 17 

 iron, and 45 sulphur : but it is very probable, that the 

 specimen analysed by him contained a superabundance of 

 sulphur interposed in its substance; and besides, the pro- 

 portion of iron given by this analysis is certainly too small*. 

 From several assays of this copper ore made with Mr. 

 Chcnevix, it always appeared to us, that it differed very 

 little, either in its component parts, or in their proportions 

 to each other, from the gray species, which I have said 

 should bear the name of gray sulphuret of copper and iron. 

 The form of its primitive crystal is a regular tetraedron, 

 modifications of which it sometimes admits, though much 

 fewer than the gray sulphuret of copper and iron ; and 

 among which we chiefly find the regular octaedron, and the 

 dodecaedron with rhombic faces ; but the latter variety, 

 "which occurs in Cornwall, is very rare. The specific 

 gravity of this sulphuret is 4 058 + . It is not so hard as the 

 fahlerlz. Its fracture is very brilliant, ragged, and as if it 

 were composed of small laminae intersecting each other in 

 various directions. In decomposition it assumes the most 



* Additional note. I have lately seen in the Journal des Mines, 

 No. 122, that Mr. Gueniveau, engineer of mines in France, has 

 analysed two varieties of yellow sulphuret of copper and iron: One, 

 from St. Bel near Lyons, afforded him metallic copper 30, metallic 

 iron 33, and sulphur 36. The other, from Baigorry, yielded me- 

 tallic copper 27 - 5, metallic iron 29*5, sulphur 3 1*5 §. 



% This specific gravity is a mean of those of four tetraedral 

 crystals, either perfect, or with their solid angles truncated. Authors 

 i have hitherto carried this specific gravity to 4-315: but I presume, 

 that it was not taken from crystals, and that the pieces weighed were 

 mingled with sulphuret of iron, which frequently happens. I 

 have found yel low sulphurets of copper and iron, thus mingled, 

 weighing as high as 4*6. 



§ See Journal, vol. xxi, p. 148. 



lively 



