On the Paragenetxc Relations of Minerals. 149 



zinc formation, it is to be regarded as terminated, and the 

 same may perhaps be said of the second generation of quartz ; 

 therefore quartz and iron spar are frequently found to sup- 

 port the clinoedritic formation. Since, however, iron rose 

 and manganese spars possess a close mineralogical relation, 

 and protoxides of iron, manganese, &c, replace each other 

 chemically, they are frequently found alone or associated in 

 the lodes. When pearl spar occurs, it is the oldest of the car- 

 bonates. It is remarkable that the galena implanted upon 

 rose spar presents imperfect crystal forms, rounded edges, 

 broken planes, &c. While all these carbonates appear as the 

 supporters of this formation, still they are tolerably contem- 

 poraneous in formation with galena, zinc-blende, and the 

 clinoedrites, although these minerals are obviously the more 

 recent, from their distinct superposition. Arsenical pyrites 

 are no longer found, nor indeed in any more recent formation. 

 Magnetic pyrites is likewise wanting. Pyritic minerals, on 

 the whole, are less abundant, and the smaller their quantity 

 the greater the amount of silver in the galena and clinoedrites. 

 When copper pyrites is altogether wanting, weissgultigerz 

 occurs, with thirty-one per cent, of silver. The minerals are 

 likewise more argentiferous when the formation occurs alone, 

 and when the lodes ramify. In this case, even antimonial 

 silver-blende and eugenite occur. When the formation lies 

 over the pyritic, it is poorer in clinoedrites, and the per- 

 centage of silver is smaller. 



In this formation, as in most others, one or other of its sup- 

 porting minerals, and sometimes all of them, are wanting, 

 the mineral then being implanted upon the adjoining rock. 

 Sometimes this deficiency is owing to subsequent decompo- 

 sition, with production of quartz pseudomorphs ; thus, at 

 Kapnik the whole of the manganese spar, and at Freiberg the 

 rose spar, have been removed, while the other associated 

 minerals are well preserved. 



The formation has sometimes heavy spar superposed, but 

 belonging to more recent formation. At the contact of the 

 clinoedritic with the heavy spar and ccelestine formation, the 

 galena and fahlerz of the former have a large amount of 

 silver. 



