19 12 J Eakle; The Minerals of Tonopah, Nevada 



3 



The origin of the silver haloids. — The most important second- 

 ary minerals in the zone of oxidation are the three silver salts, 

 cerargerite, embolite, and iodyrite. They have undoubtedly 

 crystallized out of descending solutions which obtained their 

 chlorides, bromides, and iodides from superficial deposits im- 

 pregnated with the alkaline salts, and their general arrangement, 

 as stated by Burgess, is in three zones with cerargerite above, 

 embolite intermediate, and iodyrite below. Since iodyrite is much 

 less soluble in water than cerargerite, this order of crystallization 

 may appear reversed, but in reality it is the natural order of 

 occurrence when the silver salts have been deposited from mixed 

 solutions such as undoubtedly obtained at Tonopah. 



The formation of good crystals of these difficultly soluble salts 

 generally indicates a slow growth by gradual evaporation of very 

 weak solutions, but the degree of solubility and of concentration 

 before crystallization depends upon the solvent, and crystals may 

 not form until the excess of certain salts have first been removed. 



In the cerargerite zone the crystals are quite perfectly formed 

 and have evidently grown from solutions dilute enough to pre- 

 vent the previous precipitation of manganese and iron hydrates. 

 "While the oxides of iron and manganese may be abundant in 

 this zone, their formation from the solutions was independent of, 

 and later than, the formation of the cerargerite. 



In the embolite zone the crystals are in general imperfectly ' 

 formed and segregated into bunches. They characteristically 

 rest upon coatings of psilomelane and limonite which have been 

 previously deposited from the solutions and therefore indicate a 

 growth from more concentrated solutions. 



In the iodyrite zone the imperfectly formed crystals have 

 grown rather rapidly from solutions concentrated sufficiently to 

 precipitate previously psilomelane, flaky hematite and flaky 

 jarosite in abundant coatings and masses. The evidence points 

 strongly to the conclusion that the crystallization of the iodyrite 

 depended upon the prior or simultaneous precipitation of these 

 iron and manganese minerals. 



It is manifestly impossible to form more than an approximate 

 idea of the character of the oxidizing solutions. The waters con- 

 tained essentially chlorides, bromides, iodides, carbonates, and 



