82 Mr HAIDINGER on the Parasitic Formation 



usually observed in collections are not in a determinable 

 state. They are for the greater part converted into mala- 

 chite, but their angles shew, that, in their original state, 

 they have not been blue copper. I have seen crystals in 

 Mr ALLAN'S cabinet, pretty distinctly pronounced, in the shape 

 of compressed six-sided prisms, the narrow faces meeting at 

 angles of about 112 ; and the narrow with the broad faces at 

 angles of about 122 and 126 ; from which it appears that the 

 original substance, as to form, belongs to the hemiprismatic or 

 tetartoprismatic systems. There is an angle in HAUY'S description 

 of 122 19', situated like the one of 122 ; but the fundamental 

 prism being supposed to be a right rhombic one, the other two 

 angles of the derived six-sided prism follow to be 115 22', and 

 122 19'. Besides, HAUY gives a specific gravity of 2.733 to his 

 crystals, while the varieties of chrysocolla never go beyond 2.2. 

 I know only of one specimen, with crystals apparently homoge- 

 neous, and resembling chrysocolla, engaged in a pale-brown 

 clayey substance. It forms part of the magnificent collection 

 of Mr BERGEMANN of Berlin, who intended to subject it to a 

 chemical analysis, while Professor GUSTAVUS ROSE was to exa- 

 mine its miner alogical, and particularly its crystallographic cha- 

 racters. We have therefore to look to the ability and zeal of 

 the Berlin mineralogists and chemists, for more accurate infor- 

 mation regarding this remarkable substance. 



The blue copper, ground to an impalpable'powder, is employ- 

 ed as a blue paint, of a very bright tint, paler than the mineral 

 itself. It is not, however, highly valued, because it is apt to 

 lose its original colour, and to turn green. This is mentioned 

 by HAUY, who quotes authorities as old as WALLERIUS and BOE- 

 TIUS DE BOOT, for the colour obtained from the Armenian stone 

 of the ancients *. The decomposition of the blue pigment is a 



* Traite, 2de edit. t. iii. p. 503. 



