COLLECTIONS IN ECONOMIC GEOLOGY AND METALLURGY. 76 



CHALCOCITE. (VITREOUS fJOPPER, SULPHURET OF COPPER, COPPER 



GLANCE.) 



Composition : CaiS- Subsuli)lii(le of copper, coutaining copper 70.8 

 per cent, and sulplmr 20.'J per cent. It crystallizes in the orthorliombic 

 system, showing especially the basal, unit prism, unit and several other 

 octahedrons, brachy pinacoid, and several brachy dome planes; twinning 

 is common. The crystals are quite complex. They are, however, some- 

 what rare. Its most common occurrence is massive. It varies in hard- 

 ness from 2.5 to 3 and in specific gravity from 5.5 to 5.8, has a lead- 

 gray color, and fall metallic luster. 



Chalcocite is a very valuable ore of copper and has supplied large 

 amounts of the metal. It generally occurs in the upper portions of a 

 mine, and in Tennessee and Montana large masses of very pure material 

 have' been found. It is very rich in metal, Avhicli is easily extracted. 

 Chalcocite is generally the result of the decomposition of the other sul- 

 phides of copper, and is intimately associated with them. To illustrate 

 the occurrence of chalcocite three specimens are shown : 



(1) Crystallized. Bristol, Hartford County, Connecticut. (65145.) 



('2) Crystalline, massive ; showing decomposition. New Mexico. (30140.) 



(3) Massive. Anaconda Mine, Butte, Silver Bow County, Montana. (56493.) 



CUPRITE. (RED OR RUBY COPPER ORE.) 



Composition: Cu^O. Suboxide of copper, containing copper 88.8 

 per cent, and oxygen 11.2 per cent. It crystallizes in the isometric 

 system, especially in cubes and octahedrons, and compounds of these; 

 a\so in other complicated forms. Cubes are sometimes elongated into 

 hair-like forms. It also occurs massive, and, when impure, earthy. It 

 varies in hardness from 3.5 to 4, and in specific gravity from 5.85 to 6.15. 

 The color is red of various shades and the luster is adamantine. 



Cuprite is a valuable source of copper, since, besides its high content 

 of metal, it is very easily reduced. It is, however, never found alone in 

 sufficient amounts to constitute an ore, but is always associated with 

 other copper minerals. It is easily affected by decomposing influences, 

 and may be either reduced to the metal or it may be changed to the 

 higher oxide, the carbonate, or silicate. To illustrate the occurrence 

 of cuprite two specimens are shown : 



(1) Crystallized in octahedrons, on limonite. Copper Queen Mine, Bisbee, Cochise 

 County, Arizona. (56046.) 



(•2) Massive, showing decomposition to carbonate and silicate. Longfellow Mine, 

 Clifton district, Arizona. (33873.) 



CHRYSOCOLLA. (SILICATE OF COPPER.) 



Composition very variable, as it generally contains an excess of silica, 

 besides other impurities. It contains from 22 to 30 per cent, of copper. 

 Occurs mostly as an incrustation or filling seams, looking very much 

 like an enamel. 



