128 Mr Haidinger on the changes which take place 



Haiiy does not consider the crystals formed by aggregated 

 masses of the green filamentous malachite as Epigenies of the 

 blue copper, as he unites the two species into one, and rejects 

 the slight difference in the results of the chemical analysis as 

 irrelevant. Beudant, I believe, is the first naturalist wlio en- 

 tertained a correct view of this subject. 



Not only the blue copper, but also the imbedded octahe- 

 drons and dodecahedrons of octahedral copper-ore, are found 

 in that locality in a state of incipient decomposition, resem- 

 bling it in so far as the form of the crystals is not altered. 

 There is one curious difference, however, in the progress of this 

 decomposition. In the octahedral copper-ore the surface first 

 turns green, by the absorption of oxygen and water, since 

 the protoxide is converted into a hydrate of the peroxide, 

 and then the change penetrates deeper into the mass, form- 

 ing a more or less considerable coating of compact mala- 

 chite; whereas the reverse takes place in blue copper, the 

 surface of the crystals being the last portion which is con- 

 verted into malachite, the decomposition beginning from the 

 point of support. There are crystals of an octahedral form, 

 consisting, at least near the surface, of fibrous malachite, of 

 the same kind as that which often constitutes the body of 

 crystals having the shape of blue copper, for the interior 

 of them generally consists of octahedral copper-ore not de- 

 composed. A dodecahedral crystal of octahedral copper-ore, 

 changed into blue copper on its surface, is preserved in Mr 

 Allan's cabinet, but such examples are rare. 



The cuivre hydro-silicieux of Haiiy, comprehending chry- 

 socolla, is a species not yet well established, as the crystals 

 usually observed in the collections are not in a determinable 

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

 chite, but their angles show that in their original state they 

 have not been blue copper. I have seen crystals in Mr Al- 

 lan'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 hemi-prisma- 

 tic or tetarto-prismatic system. There is an angle in Haviy's 



