THE MINERALS OF IDAHO 



137 



ADA COUNTY 



Arsenopyrite is mentioned as a prominent accessory constituent of 

 gold ores, especially of the Black Hornet district. 



BLAINE COUNTY 



Arsenopyrite occurs commonly in the gold ores of the Hailey gold 

 belt at the Red Cloud, Croesus, and other mines and also in many of 

 the lead-silver mines of the Wood River region, including the Minnie 

 Moore, Independence, North Star, etc. A specimen from the Red 

 Cloud mine shows prismatic crystals and granular aggregates of 





14 15 16 17 



Figs. 14-17.— 14-16, Arsenopyrite. Star mine, Wood River district, Blaine County. 17, Arseno- 

 pyrite. Crystal from vug in siderite, Ramshorn mine, Custer County 



arsenopyrite with pyrite and galena. Arsenopyrite is especially 

 prominent in the complex ores of the North Star mine, where it is 

 associated in quartz and carbonate gangue with galena, dark brown 

 sphalerite and boulangerite. Much of the arsenopyrite from this 

 mine has a pale yellow color like that of pyrite, which is rather per- 

 sistent, but which disappears when the mineral is inmersed in hydro- 

 chloric acid. The mineral sometimes occurs in a rather spectacular 

 form as slender prisms embedded in sphalerite. Crystals for exami- 

 nation were obtained by dissolving out ankerite occurring as gangue. 

 These are prismatic by elongation of the vertical axis, the most promi- 

 nent form being the unit prism to(110). The prisms taper somewhat 

 and where terminated show the forms Z(011), s(012), and <?(013), 

 either singly or together. The forms and relative proportions of the 



