310 MINERALOGY 



and in diabase, with a gangue of calcite. The associated minerals 

 are niccolite, chloanthite, millerite, cobaltite, smaltite, argentite, 

 dyscrasite, pyrargyrite, arsenopyrite, with other oxidized ores and 

 native silver in the superficial areas. These minerals have either 

 been concentrated from the near-by diabase or carried up from 

 depths by warm solutions. In addition to the localities mentioned, 

 niccolite occurs at Chatham, Connecticut ; Franklin, New Jersey ; 

 Silver Cliff, Colorado; and Tilt Cove, Newfoundland. 



BORNITE 



Bornite. Purple copper ore; Horseflesh ore; CusFeSs; Cu = 

 55.5, Fe = 16.4, S = 28.1 ; Isometric ; Type, Ditesseral Central ; 

 Common forms, o (111), d (110), n(211); Twinning plane, 111; 

 Cleavage, octahedral in traces, slightly sectile; Fracture, con- 

 choidal ; H. = 3 ; G. = 4.9-5.4 ; Color, copper-red to brown, irides- 

 cent from tarnish ; Streak, grayish black ; Luster, metallic, opaque. 



B.B. Fuses easily on coal in the R. F. to a magnetic globule. 

 In the O. F. yields a sulphur dioxide odor; well roasted and reduced 

 with soda yields malleable copper buttons. Soluble in hot nitric 

 acid. 



General description. Crystals are very rare, cubic or octahe- 

 dral in habit, but are rough and irregular ; the usual occurrence is 

 massive, granular, or disseminated. 



Bornite occurs as a primary magmatic constituent of igneous 

 rocks, but more often in veins and fissures of contact zones, as well 

 as impregnations and replacements, associated with other metallic 

 sulphides. It oxidizes easily in the superficial areas, forming car- 

 bonates, etc., or is carried down in solution as sulphates. 



Bornite next to chalcopyrite and chalcocite is the most important 

 copper ore; it forms the greater bulk of the ore in the Copper 

 River region, Alaska ; also in quantity at Butte, Montana, and in 

 nearly all copper mining districts. 



CHALCOPYRITE 



Chalcopyrite. Copper pyrite, CuFeS- sulphide of copper 

 and iron ; Cu = 34.5, Fe = 30.5, S = 35.(f; Tetragonal ; Type, 

 Ditetragonal Alternating ; c = .9852; Common forms, P(111). 

 c(001), m(110) r(332), z (201) ; Twinning plane, 111 and 110; 

 Cleavage, at times distinct ; Brittle, fracture uneven ; H. = 3.5-4 ; 



