THE MINERALS OP IDAHO 



335 



them, when removed from the inclosing quartz, are suitable for 

 measurement on the reflecting goniometer. Only the prismatic 

 zone is represented, these embedded crystals, so far as observed, 

 being unterminated by crystal faces. The most common habits of 

 the embedded crystals are like the prism zones of Figures 97 to 100, 

 although all the forms observed in this zone on the terminated crystals 

 were also found on the embedded crystals. The crystals are often 



or 



m 



7)1 



Stfltfl 



97 



98 



s tfiav l s 



vLU' 



100 101 102 



Figs. 97-102.— Ilvaite crystals from Oolconda mine, South Mountain mine, Owyhee County 



deeply striated and rounded, apparently by oscillation between the 

 prisms m(110) and s(120). They greatly resemble black tourmaline 

 and upon casual examination might be mistaken for that mineral. 

 The forms present on one of the best of these crystals were identi- 

 fied as: a(100), &(010), m(110), fc(210), s(120), and <Z(140). 



The measurements obtained on one of the crystals occurring em- 

 bedded in quartz are compared with the angles given by Dana for 

 the species as follows: 



