THE MINERALS OF IDAHO 



149 



Penfield's report. 25 Apparently the mineral has been abundant in 

 the ores of several of the mines, the ore of the Henrietta mine con- 

 taining more miargyrite than pyrargyrite and proustite. In color 

 the mineral is steel black with metallic luster and it gives a red streak. 

 An analysis or a crystallographic examination is necessary to dis- 

 tinguish it from pyrargyrite. In the Henrietta ores it occurred as 

 crusts of crystals on quartz often coated by white clay. The crystals 

 commonly average less than 3mm. in diameter and are usually not 

 well adapted for crystallographic measurement, since the majority 

 of them are either dull, appearing as though they had been slightly 

 corroded, or are striated. The habits are as shown in Figures 23 and 

 24 and the forms observed, which are the common and characteristic 

 ones for the species, are as follows: 



a(100) m(lOl) £(111) d(Sll) 

 c(001) o(T01) s(211) £(124) 



The basal plane c is generally striated parallel with its intersection 

 with the orthodome o. The pyramids d and s occur in oscillatory 



23 

 Figs. 23-24.— Miargyrite. Henrietta mine, Owyhee County. After Penfield 



combination, both with one another and with the orthopinacoid a 

 and the pyramid t, and consequently are striated to such an extent 

 that they appear as a rounding of the edges between a and t rather 

 than as distinct faces. The faces lettered & are dull and give no dis- 

 tinct reflections but from their position and the direction of their 

 intersection with adjoining faces it is assumed that the form has been 

 correctly identified as the pyramid £(124) which is one of the com- 

 mon forms of the species. 



« TJ. S. Geol. Survey, 20th Ann. Rept., pt. 3, pp. 168-916, 1900. 



