162 ECONOMIC GEOLOGY 



atmosphere, but when freshly cut its luster is very brilliant. It 

 is readily soluble in the mineral acids. Its specific gravity is 

 8.6, melting point, 321.7 C., and its atomic weight is 112.4. 



Ores of the Metal. Cadmium does not occur free and uncom- 

 bined in nature. It must, therefore, occur only in combination. 

 The one important mineral is the yellow sulphide, greenockite, 

 CdS. This ore occurs in association with sphalerite, ZnS, and 

 as an incrustation on calcite, CaCOg. The resinous luster of 

 cadmif erous sphalerite has often been attributed to the presence of 

 greenockite. Cadmium occurs also in combination with carbonic 

 acid as cadmium carbonate, CdCOa, and in smithsonite, ZnCOs. 



Origin of the Ores. Cadmium ores are always of secondary 

 origin. They are deposited from solution with the ores of zinc 

 by the action of alkaline sulphides upon ascending solutions of 

 the metal. The metal may also be precipitated as the sulphide 

 with the sulphide of zinc by the action of organic matter. By 

 the alteration of cadmiferous sphalerite in the upper level of 

 ore bodies, cadmiferous smithsonite would be formed as a surface 

 deposit. 



Geographical Distribution. Greenockite occurs in associa- 

 tion with zinc in Arkansas, Kansas and Missouri. It occurs also 

 in Pennsylvania where it is associated with the yellow zinc car- 

 bonate known by the miners as "turkey fat." 



Geological Horizon. The ores of cadmium are not confined 

 to any particular geological horizon. They are, in fact, the same 

 as that of zinc. 



Method of Extraction. The manufacture of metallic cadmium 

 was begun for the first time in the United States in 1907 by the 

 Grasselli Chemical Company, Cleveland, Ohio. The process is 

 fractional distillation in iron retorts. The brown fumes that 

 distill over in the first product from the refining of zinc are cad- 

 mium oxide, CdO. 



Uses of Cadmium. Cadmium is used to some extent in the 

 manufacture of yellow pigments. The iodide and bromide of 

 cadmium are used in photography. Cadmium is used extensively 

 in the manufacture of sterling silverware. In this industry 0.5 

 per cent, of cadmium imparts malleability to the alloy and pre- 

 vents the formation of blisters. Cadmium alloys all possess a 

 low melting point. Many of these alloys of cadmium, bismuth, 

 lead and tin in varying proportions melt between 60 and 100. 

 Stereotype metal consists of 50 per cent, lead, 27.5 per cent, tin 



