U"oJ^3SCf-^\^AVv 



328 



METALS. 



Obs. ^ A very common ore and extensively worked in the 

 mines of South America and Mexico, where it occurs with 

 native silver. It also«occurs at the mines of Saxony, Sibe 

 ria, Norway, the Hartz, and in Cornwall-. 



Iodic Silver. Bromic Silver. Silver also occurs in nature united 

 with iodine and bromine. These rare ores occur with the preceding 

 in Mexico, and the latter in Chile, and at Huelgoet, in Brittany. 



Embolite. A chlorobromid of silver, resembling the/mlorid or horn 

 silver. Color asparagus to olive green. Contains 51 of chlorid of silver 

 to 49 of bromid. This ore is not less common in Chili than the chlorid 

 It has also been found in Chihuahua, Mexico. 



REMARKS ON SILVER AND ITS ORES. 



The ores from which the silver of commerce is mostly obtained are 

 the vitreovs silver, brittle or black silver ore, red silver ore and horn 

 silver, in addition to native silver. Besides these, silver is obtained in 

 large quantities from galena, (lead ore,) and from different ores of cop- 

 per : and soma galenas are so rich in silver that the lea'd is neglected 

 for the more precious metal. This metal occurs in rocks of various 

 ages, in gneiss, and allied rocks, in porphyry, trap, sandstone, lime- 

 stone, and shales ; and the sandstone and shales may be as recent as the 

 middle secondary, as is the case in Prussia, and probably also in our 

 own Michigan mining region. The silver ores are associated often 

 with ores of lead, zinc, copper, cobalt, and antimony, and the usual 

 gangue is calc spar or quartz, with frequently fluor spar, pearl spar, or 

 heavy spar. 



The silver of South America is derived principally from the horn sil- 

 ver, brittle silver ores, including arseniuretted silver ore, vitreous silver 

 ore, and native silver. Those of Mexico are of nearly the same charac- 

 ter. Besides, there are earthy ores called colorados, and in Peru pacos, 

 which are mostly earthy oxyd of iron, with a little disseminated silver ; 

 they are found near the surface where the rock has undergone partial 

 decomposition. The sulphurets of lead, iron, and copper, of the mining 

 regions, generally contain silver, and are also worked. 



The mines of Mexico are most abundant between 18° and 24° north 

 latitude, on the back or sides of the Cordilleras and especially the west 

 side ; and the principal are those of the districts of Guanaxuato, Zaca- 

 tecas, Fresnillo, Sombrerete, Catorce, Oaxaca, Pachuca, Real del Monte, 

 Moran, and Pasco. The veins traverse very different rocks in these 

 regions. The vein of Guanaxuato, the most productive in Mexico, in- 

 tersects argillaceous and chloritic shale, and porphyry ; it affords one- 

 fourth oi aH the Mexican silver. The Valencian mine is the richest in 

 Guanaxuato, and has yielded for many years, from one to two millions 

 uf dollars annually. In the district of Zacatecas the veins are in gray- 



Where is horn silver a common ore ? From what ores is the silver 

 A commerce mostly obtained I How do they occur ? What are the 

 common ores of South America ? 



