Plate 29 



1. San Cristobal, Chile; nickel-rich ataxite; Ni-Co 26.60 percenr. The nickel content 

 of this iron is close to the saturation ratio for kamacite in taenite. It therefore consists 

 almost wholly of taenite, with vestiges of ataxite structure. A number of areas of a perfect 

 pearlitic pattern are the outstanding feature of this extraordinary meteorite. The photo- 

 graph shows the general structure of the mass — a ground of clear taenite, with areas of 

 an acicular structure enclosing minute kamacite bodies, and black areas of an ultramicro- 

 scopic gamma-alpha aggregate analogous in structure to sorbite and troostite in steel. 

 Below is part of a pearlitic area. The iron etches slowly. Picral 75 seconds; X 30. Ameri- 

 can Museum of Natural History. 



2. San Cristobal. Part of the general structure at higher magnification. The struc- 

 ture of the acicular areas is more apparent. Many of the kamacite particles contain 

 minute inclusions of iron-phosphide eutectic. The black sorbiticlike areas are unresolved. 

 Picral 75 seconds; X 60. 



3. San Cristobal. Part of an acicular area with very light etching, showing only the 

 kamacite bodies which ha^e some octahedral orientation. The structure of the ground- 

 mass does not appear. Picral 20 seconds; X 60. 



4. San Cristobal. Part of an area of gamma-alpha pearlitic paraeutectoid. A small 

 finely lamellar area is surrounded by a coarser structure. Picral 20 seconds; X 30. 



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