On the Paragenetic Relations of Minerals. 351 



stood for a long time in lodes. Its decomposition in contact 

 with sulphurets, especially iron pyrites, gives rise to the 

 formation of sulphuretted hydrogen, and hydrated or anhy- 

 drous peroxides of iron. Entire lodes of iron pyrites have 

 thus been converted into brown haematite. Copper pyrites, 

 and its associates, gray copper, variegated pyrites, redruthite, 

 &c, have been converted into red copper, copper pechertz, 

 tile ore, and, when carbonic acid had access, into malachite, 

 copper lazure, &c. 



It is not improbable that metallic silver may have been 

 produced from argentine, as well as from polybasite, by the 

 action of hot aqueous vapours. 



Fragments of spathose iron in the refuse heaps of mines 

 are often found to have become quite brown, and entirely 

 converted into hydrated peroxide. The same change is shewn 

 to take place in lodes by the pseudomorphous peroxide in 

 rhombohedrons. 



Partial abstraction of metal may frequently give rise to 

 the formation of higher sulphurets. Some of the lodes at 

 Freiberg not unfrequently bear pseudomorphous hepatic, 

 pyrites, iron pyrites, and mispickel, in the form of magnetic 

 pyrites, which is itself very rare in the same lodes. Analo- 

 gous lodes, however, at Drehbach, contain large masses of 

 magnetic pyrites, associated, as at other places, with galena 

 and calcite. Perfect crystals of magnetic pyrites, presenting 

 exactly the same characters as the pseudomorphs at Frei- 

 berg, occur in lodes of the same formation in Stranitza (Tran- 

 sylvania). When it is remembered that in some places con- 

 siderable quantities of magnetic pyrites occur in lodes, it is 

 not at all improbable that the greater part of the iron pyrites 

 in the Freiberg lodes was formerly magnetic pyrites. More- 

 over, iron pyrites, when associated with magnetic pyrites, is 

 always the more recent, and this view is likewise in accord- 

 ance with the fact that iron pyrites occurs upon copper pyrites. 



Exhalations of sulphuretted hydrogen have undoubtedly 

 caused a regeneration of altered minerals. The filamentous 

 silver is found reconverted into sulphuret of silver, and con- 

 taining a nucleus of this metal. Pyromorphite formed from 



