358 W. M. Thornton, Jr. — Enargite, Covellite, and Pyrite. 



Art. XXXI. — An Association of Enargite, Covellite, and 

 Pyrite from Ouray Co., Colorado; by William M. 

 Thornton, Jr. 



In October, 1906, Professor William H. Echols received a 

 curious sample of copper ore from the Grenesse Yanderbilt 

 mine in the Red Mountain district, Ouray county, Colorado. 

 The specimen was seen to consist of three distinct metallic 

 minerals, which were subsequently identified by physical 

 properties, behavior before the blowpipe, and quantitative 

 analysis as enargite, covellite, and pyrite. 



General Description. 



The enargite is closely interlocked with pyrite — both grow- 

 ing out from a quartz gangue. The color of the enargite is 

 dark grey ; and the luster metallic. The structure is columnar. 

 The cleavage is easy in one direction. Specific gravity =4*49. 

 A few crystals are present but badly crushed and distorted. 

 The covellite joins the other two minerals, and includes here 

 and there a little pyrite or gangue. The color is indigo-blue 

 and the luster sub-metallic. The structure is foliated, and the 

 mineral can be easily cleaved into thin plates. 



Analysis of enargite by Wm. M. Thornton, Jr. 



Copper 50*82 per cent. 



Zinc . 0-83 " 



Arsenic . _ 17-28 " 



Sulphur _ . . 32-53 " 



Silver .__ _. None " 



Iron _.. Trace " 



100-96 



Corresponds approximately to the formula : Cu 3 AsS 4 ^3Cu 2 S, 

 As 2 S 5 . 



Analysis of covellite by John M Seabright. 



Copper 68 # 38 per cent. 



Sulphur 32-51 



100-89 

 Corresponds to the formula: CuS. 



Methods of Analysis. — The enargite was first treated with 

 nitric acid and the resulting mass thoroughly dried. A fusion 

 was then made with sodium carbonate and potassium carbonate 



