4 PROCEEDINGS OF THE NATIONAL, MUSEUM vol.72 



CANON DIABLO SHALE BALLS 



Among the most widely known and thoroughly studied examples 

 of oxides derived from the alteration of meteoric iron are the so- 

 called " iron shale " masses which are common around the rim of the 

 meteoric crater of Coon Butte near Canon Diablo, Ariz. These 

 masses of iron oxide are scattered concentrically around the crater 

 for a distance of several miles from the rim.' The origin of the 

 smaller masses of the " shale " is inferred from the fact that they all 

 contain nickel and cobalt and have similar form and occurrence to 

 larger masses which either include cores of unoxidized meteoric iron 

 or scattered plates of the nickel-iron phosphide schreibersite or show 

 on polished surface, even when completely oxidized, ghostlike out- 

 lines of the wiclmanstatten structure of octahedral meteoric iron. 



The oxides from this source have been described by Farrington,^ 

 Avho gives the following analysis, made by H, W. Nichols : 



Analysis of " ii~on shale " 



Fe^Os 74.63 



FeO 3. 91 



NiO 9. 79 



CoO . 49 



CuO 



CaO 1. 27 



AI2O3 . 05 



SiO^ 1. 09 



CO2 . 35 



P , r-- . 10 



O . 15 



CI .08 



H2O 8. 02 



99.93 



In the interpretation of the above results, Farrington assigns ail 

 of the nickel and cobalt oxides to form " magnetite " along with the 

 ferrous iron, arriving at the following composition : 



Limonite 52^ 99 



Magnetite 42. 39 



Schreibersite . 64 



Graphite . 15 



Lawrencite , . 14 



Aragonite . 80 



Andradite 21 45 



Quartz . 21 



99.77 



3 See George P. Merrill. The meteor crater of Canyon Diablo, Arlz.j its history, origin, 

 and associated meteoric irons, Smithsonian Misc. Coll., vol. 50, pp. 461—498, particularly 

 pp. 484-487, 1908. 



* O. C. Farrington. Analysis of " iron shale " from Coon Mountain, Ariz. Amer. 

 Journ. Sci., vol. 22, pp. 303-309, 1906. 



