CHAPTER III 



PRECIOUS METALS 



GOLD, SILVER AND PLATINUM 



Properties of Gold. Gold, symbol Au, is a soft yellow metal 

 unaffected by either moist or dry air. It is insoluble in all single 

 acids save selenic. It surpasses all other metals in its malleability 

 and ductility. Its specific gravity is 19.3; melting-point, 1065 C. 

 and atomic weight, 197.2. 



Ores Containing Gold. Native gold: Pure Au is sometimes 

 found but most of the native gold contains a small amount of silver 

 platinum, etc. Petzite (Ag,Au) 2 ,Te: In ratio of 3 : 1 the gold 

 content would be 25.5 per cent. Hessite (Ag 2 Te) : Gold is often 

 present replacing a part of the silver. Sylvanite (Au,Ag)Te 2 : 

 If the ratio is 1:1 it would give 24.5 per cent. gold. Calaverite 

 (Au,Ag)Te 2 : with ratio 7:1 it would contain 39.5 per cent, 

 gold. Krennerite (Ag 2 Te,Au 2 Te3) : The per cent, of gold is 35.5. 

 Nagyagite (Au 2 ,Pbi4,Sb 3 ,Te 7 ,Si7). Some samples have given upon 

 analysis 12.75 per cent, of gold. 



Occurrence. Gold occurs native encased within quartz. 

 Sometimes in a finely divided state, sometimes in particles of 

 considerable size, as nuggets, grains, scales, plates, threads and 

 wires in quartz rock. It is often encased in pyrite, chalcopyrite, 

 arsenopyrite, magnetite and hematite. It occurs also in a finely 

 divided state in schistose rocks, often in too small quantity to pay 

 for profitable extraction. It has been observed in the process of 

 deposition at Steamboat Springs, Nevada. It is present in sea 

 water, especially along the coast of Norway. It has been detected 

 in many saline minerals, as sylvite, kainite, halite, and carnallite. 

 It has also been found in the ashes of sea weeds. An attempt was 

 made several years ago to reclaim the gold from the sea waters of 

 the northeastern coast of the United States, and although the 

 metal appeared in considerable quantity, the effort proved futile. 



The percentage of gold in sea water varies. It is present in 

 greatest abundance where meteoric waters, flowing freely through 



52 



