THE MINERALS OF IDAHO 167 



mens of argentiferous galena from the Bunker Hill mine showing 0.08 

 and 0.09 per cent of silver, upon assay, proved to contain microscopic 

 grains of tetrahedrite when polished and examined under a metallo- 

 graphic microscope as did a specimen from the Hercules mine con- 

 taining 0.108 per cent of silver. 52 The Caledonia mine at Wardner 

 contained bodies, often of considerable size, consisting almost entirely 

 of massive tetrahedrite, in quartzite, sometimes with included irregular 

 patches of chalcopyrite, although there was very little tetrahedrite 

 in the galena ore from other parts of the mine. Ore mined from 

 these silver-rich tetrahedrite bodies sometimes carried 3,000 ounces 

 to the ton. 



Tetrahedrite has been noted in the Hypotheek mine at Kingston 

 in a calcite gangue with pyrite and arsenopyrite and also as crystals 

 along cracks in quartz. The crystals reach 5 mm. in diameter and 

 show bright faces which yield excellent reflections of the signal. The 

 development is such, however, that the tetrahedral symmetry is not 

 apparent. A typically developed crystal is shown in Figure 29 and 

 the most completely developed and symmetrical crystal measured is 

 shown in somewhat idealized form in Figure 30. The forms recognized 

 are o (111), n (211), d (110), and r (332). This tetrahedrite was 

 analyzed, the analysis giving the following results and ratios, after 

 having been recalculated to 100 per cent after deducting quartz: 



Analysis and ratios of tetrahedrite from Hypotheek mine 

 (E. V. Shannon, analyst) 



The ratios agree fairly well with Wherry and Foshag's formula, 

 but, like the preceding, this formula is satisfied without assuming the 

 presence of any cupric copper and the analysis is best represented by 

 the formula derived for the mineral from the Ramshorn mine, 

 namely 10Cu 2 S.3FeS.2ZnS.4Sb 2 S 3 . The practical absence of silver 

 is noteworthy, as is the absence of more than a trace of arsenic, since 

 the mineral occurs in a vein containing abundant arsenopyrite. 



Tetrahedrite has been noted from other veins of the Pine Creek 

 Basin, as the Big 8, Lookout-Mountain, Carbonate, Northern Light, 



« F. N. Guild. A microscopic study of the silver ores and their associated minerals. Economic Geology 

 vol. 12, pp. 305-306, 1917. 



