Lindgren and Hillebrand — Minerals from Arizona. 455 



A rough preliminary analysis of selected pitch black material 

 from the Detroit mine gave 



CuO _ 28-6 



ZnO 8-4 



Mn0 2 .-_ 21-2 



Fe 2 3 + Al 2 0,-fP 2 5 4-0 



Insoluble in H,Cl __ 22*8 



Ignition loss 16'3, less oxygen due 



to conversion of Mn0 2 to Mn s 4 .. 13'7 



98-7 



Similar material surmounted by crusts of chrysocolla from 

 the Modoc open cut contained much Mn0 2 , with a good deal of 

 CuO and ZnO, and is thus evidently the same substance. Man- 

 ganese is largely but not certainly wholly present as Mn0 2 . 

 The insoluble portion consists of silica, is wholly separated by 

 acid without need of evaporation, and is nearly all soluble in 

 dilute potassium hydroxide. It is not possible to say whether 

 silica is in combination or as opal, but it cannot be present in 

 any other form. 



Most of these copper pitch ores, known from many districts, 

 have been described as impure chrysocolla. As shown by the 

 optical characteristics, they are not however a mixture and they 

 certainly do not contain any chrysocolla, the characteristics of 

 which are very different. They probably represent a series of 

 closely related compounds, the chemistry of which has not yet 

 been fully elucidated. Prof. G-. A. Koenig* describes a similar 

 mineral with the same isotropic character from Bisbee, and 

 names it melanochalcite. Its composition is different, contain- 

 ing 



CuO 76-88 



Si0 2 ._ 7-80 



C0 2 7-17 



H 2 _ 771 



ZnO 0-41 



FeS 0-07 



100-04 



Prof. Koenig considers it as most probably a basic salt of an 

 ortho-silico-carbonic acid. No carbon dioxide was found in the 

 Morenci minerals. In conclusion, it would seem that the 

 chemistry of these copper pitch ores would bear further 

 examination. 



Morencite. — In a lime shale on the intermediate level of the 

 Arizona Central mine, Morenci, 200 feet below the surface, 



* This Journal, xiv, p. 404, Dec. 1902. 



