THE MINERALS OF IDAHO 



143 



The tetrahedrite associated with the arsenopyrite from the Hypo- 

 theek mine is free from silver and arsenic. The arsenopyrite gives 

 the usual closed tube reactions and gave negative results when tested 

 for antimony. 



It is interesting to note that in many of its occurrences in the State 

 the arsenopyrite is intimately associated with antimonial minerals, 

 either boulangerite, jamesonite, stibnite, or tetrahedrite, yet in no 

 case is the arsenopyrite antimonial 

 nor do the associated antimony min- 

 erals contain any arsenic. 



The variability in color of this min- 

 eral deserves mention. Although 

 commonly tin white, varieties were 

 noted from several localities where 

 the color, even on fresh fracture, is 

 dull gray or reddish-gray. Such 

 occurrences were carefully tested and 

 all found to be of normal composition. 



DANAITE 



Cobaltiferous arsenopyrite. 



LEMHI COUNTY 



Arsenopyrite is probably a more 

 or less common constituent of the 

 cobalt ores of the Blackbird district 

 where it is cobalt bearing and asso- 

 ciated with cobaltite. It was found 

 by chemical tests to be a microscopic 

 constituent of a chlorite-chloritoid 

 rock from the Nickel Plate mine. 

 Polished specimens of typical ore from 

 the Haynes Stellite Co.'s mine on 

 Blackbird Creek 2 miles above the 

 mouth of the creek, collected by 

 Frank L. Hess show silver- white fig. 22.— danaite. white crystals em- 

 crystals up to 5 mm. in diameter 

 sparingly disseminated in a quartz 

 tourmaline rock containing finely disseminated cobaltite. The 

 large crystals are of the cobaltiferous variety of arsenopyrite which 

 has been given the varietal name danaite. By carefully cracking 

 away the surrounding gangue it was found possible to secure one 

 of these crystals which was suitable for goniometric measurement. 

 These crystals are stout prismatic by elongation of the a axis and 

 have the habit shown in the drawing figure 22, the dominant forms 



BEDDED IN ORE. HAYNES-StELLITE MINE,. 



Blackbird district, Lemhi County 



