Plate 69 



1. Seneca Township, Michigan, finest octahedrite; Ni-Co 11.67 percent. Intrusive 

 magnetic oxide filling a crack in the unaltered interior of the iron. Picral; X 120. 



2. Seneca Township. Photograph shows half the width of a crack filled with intrusive 

 oxide, similar to that shown in figure 1. The oxide in cooling de\-eloped in places an acicular 

 structure. Picral; X 150. 



3. Wood's Mountain, North Carolina; finest octahedrite; Ni-Co 8.61 percent. An area 

 changed wholly to limonite by weathering. The taenite is not oxidized, leaving a remnant 

 Widnianstiitten pattern of taenite lamellae and plessite fields. The black spots are surface 

 imperfections. Unetched; X 30. 



4. Smith's Mountain, North Carolina; fine octahedrite; Ni-Co 8.52 percent. Oxidized 

 area near the surface. The broad kamacite band has changed wholly to limonite. In the 

 coarse plessite fields on each side the same is true of the kamacite grains, and of the central 

 portions of the grains of dense plessite. These portions being composed of a fine aggregate of 

 kamacite and plessite, and relatively nickel-poor, were susceptible to oxidation. Their 

 high-nickel interfaces, however, resisted oxidation and thus remain as a remnant pattern. 

 Picral 60 seconds; X 60. U. S. National Museum. 



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