t>2 NEW YORK STATE MUSEUM 



Pyrargyrite is found in several German localities, in Mexico 

 and Chile; also in Idaho, Nevada, Colorado and other silver 

 bearing regions of the western states. 



It is mined for silver. 



Proustite (light ruby silver ore) Ag 3 AsS 3 



Proustite is a sulfarsenite of silver and contains 19.4$ sulfur, 

 15.2$ arsenic and 65.1$ silver. 



Proustite closely resembles pyrargyrite in crystallization as 

 well as in translucency. Its luster is adamantine rather than 

 metallic and it differs from pyrargyrite in the color, which 

 shades more toward scarlet. The streak is scarlet. 



Proustite is found associated with pyrargyrite, the localities 

 being essentially the same as for that species. 



It is a source of silver. 



Tetrahedrite (gray copper ore) Cu s Sb 2 S 7 

 Tetrahedrite is a sulfantimonite of copper and contains 23.1$ 



sulfur, 24.8$ antimony and 52.1$ copper. Some of the antimony 



is usually replaced by arsenic, which causes it to merge gradually 



into tennantite, the sulfarsenite of silver. 



Tetrahedrite crystallizes in the tetrahedral group of the 



isometric system. The crystals, two of the commonest types 



Fig. 174 Fig. 175 



Tetrahedrite 



of which are shown in fig. 174, 175, are tetrahedral in habit. 

 Massive forms are frequent. The color varies from a light 

 steel-gray to an iron-black; the luster is metallic. 



Tetrahedrite is commonly associated with chalcopyrite, 

 massive varieties frequently forming intimate mechanical 

 mixtures; crystals of tetrahedrite are often incrusted with 

 chalcopyrite. It is also associated with several other metallic 

 sulfids. It is found in Europe, South America, Mexico, Nevada 

 and Colorado. 



