400 QUICKSILVEK DEPOSITS OF THE rAClFlO SLOPE. 



taken place. Microscopical examinations of the ore are mucli more con- 

 clusive. 1 have twenty thin sections of the ores, and these show that, ex- 

 cepting in the rare eases in which the cinnabar is deposited with barite, 

 the sulphide has crystallized simultaneously with quartz even in the inter- 

 stices of the sandstones, themselves almost exclusively composed of quartz 

 Macroscopically, too, it may be seen throughout this mine that veinlets of 

 ore constantly contain quartz as a gangue mineral. This would be im- 

 possible were the cinnabar deposited by substitution for quartz, for, evi- 

 dently, if solution of quartz be a condition of the precipitation of cinna- 

 bar, the simultaneous precipitation of the two minerals cannot occur. The 

 two processes are mutually exclusive. 



Lipoid speaks of the replacement of constituents of the Lagerschiefer of 

 Idria by cinnabar, but he attributes to this reaction only a subordinate part 

 in the formation of the deposit and does not enlarge upon the theor}-. These 

 slates are carbonaceous and may possibly have had some effect upon j)recipi- 

 tation, but I saw no definite evidence of it and Lipoid mentions none. 



Professor von Groddeck, in his interesting memoir on the new Avala 

 mine in Servia,' describes the deposits as consisting of vein-like zones of meta- 

 morphosed rocks impregnated with quicksilver ore. The wall rock which 

 has been metamorphosed or altered is chiefly serpentine, and the process is 

 one of silicification accompaiiied by the formation or deposition of carbo- 

 nates. Most of the cinnabar occurs in stringers or impregnations which seem 

 later than the silicification, but the silicified serpentine also contains cinna- 

 bar, deposited, in von Groddeck's opinion, at the time of the alteration of the 

 serpentine. Though he speaks of the vein matter as pseudomorphic after 

 serpentine and as consisting in part of cinnabar, he does not state explicitly 

 that he regards the cinnabar as pseudomorphic after serpentine. It. is evi- 

 dently conceivable that while silicification of the serpentine was in progress 

 cinnabar should have been deposited by relief of pressure and temperature, 

 as was suggd'sted in a preceding paragraph. Other explanations also seem 

 possible, and I can see in this occurrence no sufficient proof that cinnabar 

 has been substituted for serpentine molecule for molecule. 



Professor von Groddeck also describes a specimen from New Almaden. 

 He regards the ore as having replaced serpentine, because it shows the net 



' See Zeitscbr. fUi Berg-, Hutten- ami S.iliueuwe.seu, vol. 153, 1^85, ji. 188. 



