280 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



Pyrite and niarcasite accompany the ore of the Reclington. The pyr- 

 ite was tested for gold in my Uihoratory and unmistakable reactions for it 

 were obtained. Millerite occurs in microscopic crystals in slides of the ore, 

 but not, so far as known, in masses recognizable macroscopically. The 

 gangue minerals are quartz and carbonates, and vast quantities of opal, 

 usuall3' dark brown or black, but sometimes of lighter colors, are closely 

 associated with cinnabar. Microscopical examination shows that, while 

 pyrite is frequently directly embedded in the opal, cinnabar is as a rule de- 

 posited with crystalline silica; indeed no case was found in which the cin- 

 nabar was directly embedded in opal. 



The black opal, locally known as quicksilver rock, is manifestly a re- 

 sult of silicification, which formed a part of the series of cliemical changes 

 attending the deposition of ore. It was not a phase of the regional meta- 

 morphism of the country, but a local phenomenon. It seems here and else- 

 where to have preceded ore deposition by a short interval. The opal was 

 certainly not deposited in open cavities to any considerable extent, and for 

 the most part has replaced constituents of rock masses particularly, but not 

 exclusively, serpentine. In the Redington mine, ore is sometimes found 

 with the quicksilver rock and sometimes at short distances from it, but the 

 two substances are never far apart. 



Although the occurrence of opal in this and other mines, as well as 

 microscopical examinations of tlie material which will be described in Chap- 

 ter XIV, shows that hydrated silica replaced rocks, cinnabar seemed to me 

 to be confined to fissures, sometimes formed in opalized rocks and some- 

 times in other materials. Cinnabar occurs in contact with serpentine, but 

 only where there lias been disturbance prior to its deposition, and, so far as 

 I know, never under conditions indicating replacement. The ore is not 

 more usually found in contact with one rock than with another, but the 

 larger ore bodies seem most often associated witli brittle rocks. 



Bituminous matter is not infrequent in this mine, and Dr. E. F. Durand 

 has described a volatile substance which occurs here and at New Almaden 

 as aragotite, a substance which he thinks allied to idrialite.^ 



■ Proc. Califoruia Acad. Nat, Sci., vol. 4, 1872, p. 218. 



