SULPHIDES, LRSENIDE8, .\\TI.\K )M I )i, < 



319 



iron is usually replaced l>y cobalt as the corresponding siilphar- 

 senide of cobalt, glaucodot (CoFe)SAs, is an isomorphous com- 

 pound. 



Ar-enopyrite occurs as a constituent of pegmatite-, in thedeep- 

 sratcd and intermediate veins, especially those in metamorphic 

 schists and serpentine, where it is associated with chalcopyrite, 

 pyrite, sphalerite, and the aix-nides of cobalt and nickel, as well us 

 with gold or silver minerals. By oxidation it yields arsenates which 



Fio. 403. Arsenopyrite from Freiberg, Saxony. 



form a series of minerals characteristic of the zone of oxidation ; or, 

 being soluble in this form, the arsenic may be carried away in solu- 

 tion; some mine waters and indeed the waters of some natural 

 springs contain arsenic in such quantities as to be highly poisonous. 

 Complex crystals occur at Franconia, New Hampshire ; simple 

 combinations at Tavistock, Devonshire. Arsenopyrite is mined 

 commercially, for the arsenic it contains, at several places in Vir- 

 ginia and in the state of Washington ; but as it is associated with 

 gold, silver, and copper ores, most of the commercial arsenic is 

 recovered from the flue dust of smelters using such ores. 



