THE MINERALS OF IDAHO 115 



the characteristic brown streak of sphalerite. Polished cross sections 

 show that the blue color is due to partial replacement of the sphal- 

 erite by covellite along all seams and fractures, the material varying 

 from very thin films to almost complete replacements. Such 

 coveliite was seen in specimens from the stope between the upper 

 levels of the Mohawk mine and from the Coon Dog No. 1 mine, 

 Summit Flat district and also from the lower tunnel of the Carroll- 

 Driscoll group, Quartzburg district. In the latter specimen the 

 associated chalcopyrite is also similarly replaced by covellite. 



CUSTER COUNT* 



Covellite occurs as indigo blue films on other sulphides in various 

 parts of the Empire mine at Mackay. Some very fine specimens 

 of this mineral from the Hearst tunnel, a small tunnel west of the 

 dump of the 300-foot tunnel of the Empire mine consist of fine blue 

 covellite mixed with chalcopyrite, the covellite forming about 60 

 per cent of the masses. Polished surfaces show the two minerals 

 to form a very beautiful intergrowth of plates which has been inter- 

 preted as originating through the replacement of the chalcopyrite 

 by the covellite along cleavage lines. It is, however, possible that 

 the two minerals have deposited simultaneously in graphic inter- 

 growth. 



LEMHI COUNTY 



Covellite has been noted in specimens from the Blackbird district. 

 It occurs as beautiful indigo crusts surrounding cores of chalcopy- 

 rite which are in turn surrounded by iron oxide. 86 



SHOSHONE COUNTY 



Sooty covellite has been observed in several mines in the Coeur 

 d' Alene district. In a stope above the first level of the Last Chance 

 mine at Wardner some rich oxidized ore was accompanied by streaks 

 of soft black sooty material. The deep indigo color of freshly 

 broken lumps and characteristic blowpipe reactions proved this to 

 be covellite. Most of the lumps inclosed small specks of chalcopy- 

 rite showing this, perhaps with some tetrahedrite, to be the original 

 mineral from which the covellite was derived in the process of general 

 oxidation. 87 In the Caledonia mine covellite was common near the 

 base of the oxidized zone as a deep blue to black powder in cavities 

 and as compact lusterless masses. The mineral seemed in most cases 

 to replace galena and masses of galena were commonly incrusted with 

 layers of covellite 2 to 10 centimeters thick. This covellite was 

 deep indigo blue on fresh fracture but became dull black on short 

 exposure. It contained disseminated masses of pyrite and glassy 



8« J. B. Umpleby. U. S. Qeol. Survey, Bull. 528, p. 76, 1913. 



* : F. L. Ransonie. U. S. Qeol. Survey, Prof. Paper 62, p. 92, 1908. 



