MINERALS OF CHILE. 75 



These are the general features of these famous silver-mines, 

 and as here described some general idea can doubtless be formed 

 of their geological character. Although the general character 

 of the mines resembles those just described, still the minerals 

 and the containing rock frequently differ. Thus in the San 

 Antonio mine, in the valley of Potrero Grande, the rock of the 

 country is porphyry, regularly stratified, and the gangue rock 

 of the veins a dark ashy-gray argillaceous rock of an earthy 

 fracture. It is oftener found impregnated with calcareous and 

 pearl spars, which form veins and nodules in the midst of the 

 gangue. The iron found in these veins is in the form of pro- 

 toxide, while that at Chanarcillo is in the form of hydrated 

 peroxide. Again, the mines of this latter locality abound in 

 chloride and chloro-bromide of silver, while on the sulphuret 

 of the San Antonio mine there is arseniuret and native silver. 

 Taking the chloride and chloro-bromide as a distinguishing 

 mark between the mines, they maybe divided into two classes ; 

 those like Chanarcillo and Agua Amarga abounding in these 

 two minerals, and those like San Antonio, San Lorenzo, San 

 Pedro Nolasco, etc., the prominent minerals of which are the 

 sulphuret and arseniuret of silver, with barely traces of the 

 chloride. 



CINNABAR. 



This mineral of mercury occurs in no great masses in Chile. 

 It is usually found in the granite formation near veins of gold 

 and copper, as in Coquimbo and Aconcagua ; also in a vein of 

 quartz, in some stratified porphyry, near the gold mines of 

 Andacollo. The gangue accompanying cinnabar is quartz, 

 with micaceous and hydrated oxide of iron. The composition 

 of the cinnabar is 



Mercury 86.2 



Sulphur 13.8 



The formula is Hg S. 100 -° 



GALENA. 



It is found in some parts of Chile, commonly associated 

 with the sulphur ets of other metals. Composition : 



Lead 86.66 



Sulphur 13.34 



Formula, Pb S. 



