Plate 67 



1. ToMBiGBEE Ri\'ER (Desoto\'ille), Alabama; hexahedrite; Xi-Co 4.7S-5.01 percent. 

 Hydroxide invading the mass near the surface along twinning planes indicated by the 

 Neumann lines. The delicacy of the invasion indicates that it is hydroxide and not intru- 

 sive melted magnetic oxide. Picral; X 60. U. S. National Museum. 



2. Seneca Township, Michigan; finest octahedrite; Ni-Co 11.67 percent. H}droxide 

 invading octahedral structure. The irregular penetration contrasts with the rounded out- 

 lines of areas of intrusive magnetic oxide (pis. 69, 70). Taenite lamellae are not affected. 

 Light picral; X 60. 



3. CooKEAiLLE. Tennessee; coarsest octahedrite; Ni-Co 6.75 percent. The mass is pene- 

 trated by hydroxide, which tends to follow grain boundaries. Taenite lamellae are not 

 affected. Picral 40 seconds; X 60. 



4. Forsyth County, North Carolina; nickel-poor ataxite; Ni-Co 6.08 percent. Inter- 

 granular invasion of hydroxide near the surface. The grains, elsewhere faint, are made 

 conspicuous. Picral 45 seconds; X 45. 



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