338 



MINEEALOGY 



General description. Crystals are octahedrons, rhombic 

 dodecahedrons, and cubes, or combinations of these three forms. 

 Other forms occur, but are rare. The pentagonal didodecahedron 



FIG. 411. Crystalline Cuprite. Cornwall, England. 



(986) has been described as occurring on crystals from Cornwall, 

 England. It is never twinned. Occurs in compact, granular, 



massive, and also 

 earthy forms . Tile ore 

 is an impure cuprite 

 mixed with limonite 

 and hematite. 



Cuprite is found in 

 connection with all 

 copper deposits, as a 

 secondary oxidation 

 product in the surface 

 or upper levels of the 

 workings. It is formed 

 as the result of oxi- 

 dation of the sulphur 

 of sulphides, reducing 

 some of the copper to 

 the metallic state, 



FIG. 412.-Cuprite Coated with Malachite. 

 Cnessy, France. 





. 



dized to cuprite. Quite 

 often masses of cuprite are found which still inclose a core of 

 metallic copper that has as yet not been oxidized to cuprite. 



