1912] Eakle: The Minerals of Tonopah, Nevada 



13 



The best readings obtained for the several forms observed 



ave as averages : 





Measured 



Calculated 



(0001) 



(1011) 



43°27' 



43°25' 



(0001) 



(2021) 



62 13 



62 09 



(0001) 



(3051) 



70 31 



70 36 



(0001) 



(4041) 



75 52 



75 12 



(UUO) 



(1120) 



30 00 



30 00 



Twinning is on the usual twinning-plane (3034), but not many 

 of the crystals are twinned, comparatively. The twinned crys- 

 tals are generally flattened parallel to the prism faces in the 

 same zone with the twinning-plane. 



Some of the characteristic types of the crystals are illustrated 

 in figures 2 and 3 of plate 1. 



Oxides : Quartz, Opal, Cuprite, Hematite, Limonite, Man- 

 ganite, pyrolusite, psilomelane, and wad 



Quartz. — Massive white quartz constitutes the chief part of 

 the gangue. The fine granular silver minerals are always in it, 

 and the best of the crystals occur in its cavities and fissures. 

 Many of the cavities of the veins have been produced by the 

 alteration and leaching out of the feldspathic portion of the 

 gangue, and these pockets are often lined with a secondary 

 deposit of drusy quartz and quartz crystals, which are sometimes 

 corroded and stained yellowish brown. Trigonal development 

 of the quartz terminations are common, but none occur with 

 trapezohedrons. 



Opal. — In the Valley View vein a small amount of clear 

 colloidal silica has solidified into colorless hyalite and this has 

 spread as a thin coating over minute crystals of white apatite, 

 giving them a glassy glaze. The opal has taken up crystals of 

 yellow iodyrite and other fragments in its flow and it is one of 

 the latest secondary formations. 



Cuprite. — A few small masses of the red copper oxide have 

 been encountered in the oxidized zone, which have their source 

 originally in the chalcopyrite. 



Hematite and Limonite. — Naturally the common iron oxides 

 would be plentiful in the weathered zone as impure earthy 



