84 Mr HAIDINGER on the Parasitic Formation 



the mineral kingdom, is shewn to be perfectly correct, by the 

 facts collected in this paper. In the native copper, I never 

 could observe any such changes, though I have examined a 

 great number of specimens with the view of discovering them; 

 probably we have to attribute to the admixture of tin, and the 

 electro-chemical action dependent upon the contact of the two 

 metals, the greater disposition of bronze, to form new compounds 

 with the elements contained in the atmosphere, and in water. 



There are several species into the composition of which sul- 

 phuretof copper enters as one of the most important ingredients, 

 such as the prismatic copper-glance, or vitreous copper, and the 

 octahedral and pyramidal copper-pyrites, or the variegated cop- 

 per and copper-pyrites. All of them are more or less subject to 

 successive changes in their chemical constitution, while the form 

 in some cases remains, and in others is entirely lost. Mr ALLAN 

 is in possession of a very interesting and numerous series of 

 copper ores, which he collected chiefly in the summer of 1 824, 

 on a journey in Cornwall, in which I had the pleasure of accom- 

 panying him. This series has given me an opportunity of noti- 

 cing several peculiarities, which had not been mentioned before 

 by mineralogists. 



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

 lustre, are often deposited on low six-sided prisms, which have a 

 tarnished surface. These, in respect to form, entirely agree with 

 the crystals of the other species ; their surface, however, is never 

 perfectly smooth, and on breaking them, they do not present 

 throughout a uniform appearance. Generally the portions near- 

 est the surface consist of the reddish metallic substance of varie- 

 gated 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 shews 

 the appearance of variegated copper, whereas in large crystals, 

 the two species are more or less irregularly mixed up with each 



