290 MINERALOGY 



rocks, but is now concentrated by solution and precipitation in the 

 conglomerate. 



Native copper is also found in the Copper Queen mine, Arizona ; 

 in sheets at Enid, Oklahoma, and associated with fossil bones in 

 Peru, evidently reduced by the organic matter of the bone. Small 

 amounts of copper are present, usually as a secondary product, in 

 nearly every copper region and mine; but only in the Lake Superior 

 region does it constitute nearly all the copper content of the ore. 



The United States produced, in 1911, 550,645 tons, nearly one 

 half of the world's product ; of this Lake Superior region contrib- 

 uted 110,700 tons; Montana, 141,250 tons, and Arizona, 110,500 

 tons. 



SILVER 



Silver. Native Silver, Ag; Isometric; Type, Ditesseral Cen- 

 tral; Common forms, a (100), o(lll), d (101) ; Twinning plane, 

 111; Malleable and ductile; Fracture, hackly; H. = 2.5-3; 

 G. = 10.1-11.1 ; Color and streak, silver- white ; Luster, metallic; 

 Opaque. 



B.B. Fuses easily (955), and in O. F. on coal yields a brown 

 coat of silver oxide. Soluble in nitric acid. Other tests for silver 

 are given on page 578. 



General description. Crystals are usually elongated or dis- 

 torted octahedrons. All seven forms of the type occur on silver 

 crystals, but others than the octahedron and cube are comparatively 

 rare. In occurrence it is more often, in dendritic or arborescent 

 growths, due to twinning and parallel positions ; sheets, wire, and 

 disseminated scales are also common. 



On exposure the bright surfaces become brown to black, from the 

 formation of sulphides. Owing to its solubility and the easily 

 formed sulphides, silver is not found in placer deposits, but it is 

 associated with gold and copper in vein deposits, where most of the 

 native silver is of secondary origin, being reduced from sulphides, 

 chlorides, and other compounds. 



Masses of native silver weighing from 500 to 1000 pounds have 

 been taken from the deposits of Cobalt, Ontario, where it is asso- 

 ciated with ores of cobalt and nickel. Masses weighing as much -as 

 800 pounds have been found at Huantaya, southern Peru, while 

 beautiful specimens of crystalline and wire silver are obtained in 

 the mines of Batopilas, Mexico ; and Kongsberg, Norway. In the 



