Plate 25 



1. Shingle Springs, California; nickel-rich ataxite; Ni-Co 17.34 percent, P 0.34 percent. 

 General structure of the iron, a dense groundmass with copious irregular inclusions of kama- 

 cite, somewhat oriented, of which practically all have inclusions of iron-phosphide eutectic. 

 Strong etching (to bring out the structure of the inclusions) blackens the groundmass. 

 Picral 50 seconds; X 60. U. S. National Museum. 



2. Shingle Springs. One of the kamacite inclusions at high magnification. The clear 

 rounded areas are phosphide, surrounded by kamacite, which darkens with etching because 

 of gamma-alpha admixture. The kamacite inclusion has an irregular border of clear, 

 fully coalesced taeiiite which darkens as it merges with the taenite of the grotindmass. 

 The latter presents a dense and confused structure, indicative of imperfect transformation. 

 Sodium picrate darkens the phosphide, but has no appreciable effect on the groundmass, 

 though the phosphorus content of the iron is fairly high. Picral 20 seconds; X 600. 



3. Ternera (Sierra de la Ternera), Chile; nickel-rich ataxite; Ni-Co 17.85 percent. 

 General structure of the iron at moderate magnification. Picral 40 seconds; X 60. U. S. 

 National Museum. 



4. Ternera. The same structure shown in figure 3 at high magnification. The para- 

 eutectoid is strongly and ver\' uniformly developed, the taenite areas indicating by their 

 clearness complete transformation. They can be distinguished from the kamacite by their 

 minute rounded inclusions of kamacite. Picral 15 seconds; X 600. 



145 



