in tile interior of Cupriferous Minerals. ISlr 



Dark grey crystals of copper-glance, with a bright metallic 

 lustre, are often deposited on low six-sided prisms, with a, tax- 

 nished surface, which, in respect to form, entirely agree wiljK. 

 that species. Their surface, however, is never perfectly 

 smooth. On breaking them they do not present a uniform, 

 appearance ; generally the portions nearest the surface coUm 

 sist of the reddish metallic substance of variegated copper 

 having an uneven fracture, while the rest possess the grey 

 colour and perfect conchoidal fracture of the copper-glance. 

 Often, and particularly in thin plates, the whole shows the 

 appearance of variegated copper, whereas in large crystals the 

 two species are more or less irregularly mixed up with each 

 other. These prisms are sometimes more than an inch in 

 diameter, but are usually smaller. The copper-glance, which 

 originally occupied the regularly limited space, has been suc- 

 ceeded by variegated copper. The arrangement of the por- 

 tions of both species in successive coats shows that the decom- 

 position proceeded from the surface. 



On breaking some of the six-sided prisms here alluded to, I 

 found a stratum of copper-pyrites of its usual bright yellow 

 colour contiguous to their surface, while the rest consisted of 

 variegated copper. The original form had here still been 

 preserved, but a new change in the chemical constitution had 

 converted the variegated copper into copper-pyrites,. The 

 peculiar twin-crystals discernible in groups of six-sided plates 

 crossing each other at nearly right angles, and the distinct 

 form of the six-sided plates themselves, leave no doubt that 

 two of Mr Allan's specimens, consisting entirely of copper- 

 pyrites, owe their origin to the decomposition of copper-glance. 

 One of them is covered with a black pulverulent oxide, but 

 the surface of the other is perfectly bright, and of a fine brass- 

 yellow colour. It presents to the observer the deceitful and 

 puzzlipg appearance of copper-pyrites crystallized in nearly 

 regular six-sided plates. No cleavage can be traced ; but as 

 this is not easily obtained in any of the species, it cannot form, 

 in the present instance, a sufficient distinctive character be- 

 tween the simple and compound minerals. 



The variegated copper itself occurs in distinct crystals, 

 mostly small, which are hexahedrons. Some larger ones, but 



