THE MINERALS OF IDAHO 



247 



this district (Cat. No. 56532, U.S.N.M.) contains crusts and druses 

 of grayish cerusite crystals lining cavities in ocherous limonite. 



In the Texas district the Pittsburg-Idaho and Latest Out mines in 

 particular have produced large quantities of ore in which cerusite 

 constituted the valuable mineral, mainly in the incoherent granular 

 form mixed with iron and manganese oxides. The lead carbonate is 

 also known to occur in numerous other mines and prospects of this 

 district. 67 Specimens of ore from the Pittsburg-Idaho mine consist 

 of massive cerusite containing cavities lined with simple prismatic 

 and twinned crystals, the prismatic untwinned crystals being elonga- 

 ted, as is usual in cerusite, on the a axis. One such, which is illustrated 

 in the drawing, Figure 56, gave the following measurements: 



Measurements of simple cerusite crystal from Pittsburg-Idaho mine, normal -position 



A twinned crystal which was measured is shown in the drawing, 

 Figure 57. The relation between the two individuals of the twin is 

 shown by the following angular relations: 



v (vOo 



V for crystal 1 = 3G8°3S' v 

 v for crystal 2 = 245°50' (v,) D 



= 307° 14' -90° = 217° 14' =v angle for the twinning plane, 



<p for which is then 28° 36' showing the twinning plane to be r (130) 

 calculated <p for which is 28° 39'. Of all of the twinned cerusite 

 crystals from Idaho examined during the present work, those of this 

 specimen are the only ones in which the twinning plane is other than 

 m(110). A specimen from the bottom of the stope between the 300 

 and 400 levels, east vein, Pittsburg-Idaho mine is unusual in that it 

 consists of pure compact gray massive cerusite containing abundant 

 disseminated crystals of pyrite. Cerusite containing some iron oxide 

 and residual galena from the Latest Out mine is black in color. 



OWYHEE COUNTY 



The rich oxidized ores formerly mined in the South Mountain dis- 

 trict owed their value largely to cerusite as shown by old specimens 



«' J. B. Umpleby. U. S. Geol. Survey, Bull. 528, pp. 99-109; 1913! 



