ABT. 21 OXIDATION OF METEOKIC lEOKS SHANNON 5 



Assuming 42.39 per cent of iron, nickel, and cobalt ferrites, all 

 strongly magnetic, in fine distribution through the stone, Farrington 

 explains the magnetic character of the material as assignable to this 

 cause. 



Barringer and Tilghman ^ had previously described these shale 

 balls and had, without giving analyses, concluded that the central 

 cores of unoxidized metallic iron were surrounded by a crust of 

 magnetic iron oxide which they presumed to be magnetite, sur- 

 rounded by an outer scaly and peeling crust of hydrated oxide or 

 limonite. Many of the masses are described by these authors as 

 containing green nickel hydroxide scattered through their mass. 

 No such green nickel compound was observed in the material exam- 

 ined by Farrington. 



Barringer and Tilghman concluded that the magnetic oxide or 

 magnetite crust was formed while the meteorites were passing 

 through the atmosphere and that this magnetic oxide was later de- 

 composed to limonite by atmospheric weathering. Farrington dis- 

 sents from this opinion and assigns all of the oxides to long weather- 

 ing of the metal. The latter seems the more reasonable view in con- 

 sideration of the thinness of the crust visible on all meteorites Imown 

 to have fallen within historic times. 



Wirt Tassin^ analyzed and described examples of the iron shale, 

 his first analysis being from the crust of a shale ball having a metal 

 core, while the second is of a platy mass of iron oxide having a 

 structure thought to be due to schreibersite. These analyses gave the 

 following results : 



Analyses of shale ialls iy Tassin 



1. 2. 



Fe^Os 78. 82 81. 07 



FeO .65 .00 



NiO 8.85 4.66 



CoO .39 .00 



MgO .02 1.00 



SiO. .76 1.47 



S, .01 .00 



P .20 .09 



CI .03 



C .10 



H2O 10.00 12.81 



99. 83 100. 10 



These results differ from those of Farrington, above, and of the 

 writer, below, in the very low ferrous iron content of the one and the 



^ D. M. Barringer and B. C. Tilghman. Proc. Pliila. Acad. Nat. Sei., vol. 57, pp. 

 861-914, 1925. Amer. Jonru. Sci., June, 1906, p. 402. 



8 Wirt Tassin : See George P. Merrill and Wirt Tassin. Contributions to the study of 

 the Can3ron Diablo rDeteorites. Smith. Misc. Coll. (quarterly issue), vol. 50, pt. 2, pp. 

 213-214, 1907. 



