Till. NATIV1-; I. U. Ml. NTS 



291 



I'nited States alloys of silver and copper are found in the copper 

 mine> of the Lake Superior region, the Poor M:m'.- Lode, Idaho, anrl 

 many localities through the West. Mexico is the largest producer 

 of silver, with 72,000,000 l ounces, while* the United States 

 produced 57,796,117 ounces, and Canada, 31,500,000 ounces, in 

 1911. 



GOLD 



Gold. Native gold, Au ; Isometric ; Type, Ditesseral Cen- 

 tral: Common forms, o(lll), d(110); Malleable and din-tile; 

 Fracture, hackly; H. =2.5-3; G. = 15.8-19.3 ; Color and streak, 

 ^ old-yellow; Luster, metallic; Opaque. 



B.B. Fuses easily (1065). Insoluble in acids except aqua 

 regia, also in nascent chlorine, and in potassium cyanide in pres- 

 ence of oxygen. For other tests see page 582. 



General description. When crystalline, usually in octahedrons 

 elongated parallel to one axis or flattened parallel to a face. Also 

 in arborescent and reticular 

 shapes, or sheets, dissemi- 

 nated scales, and rolled water- 

 worn masses, known as 

 nuggets. 



The purest native gold is 

 said to be that of Mount 

 Morgan, Queensland, 99.7 

 per cent. gold. Most gold 

 contains silver ; electrum 

 from Hungary is a pale yel- 

 low natural alloy containing 30 per cent, silver. Gold may also 

 contain copper, iron, lead, bismuth, platinum, or mercury, most 

 of which reduce its specific gravity and modify its color. 



Gold is nearly world-wide in occurrence, though in very small 

 quantities except where it has been concentrated by secondary 

 causes. Most of the world's gold, until recent years, was recovered 

 from river sand and alluvial deposits, where, owing to its high 

 specific gravity and insolubility, it has remained behind unchanged 

 for centuries. Such gold is recovered by the simplest of all min- 

 ing, placer, which consists of washing the lighter sands away, in 

 sluices or pans. All placers of the world are worked by modifica- 



' 1010. 



Fia. 395. Crystals of Gold . Australia. 



