Plate 74 



1. Social Circle, Georgia; medium octahedrite; Ni-Co 5.40 percent (Everhart in 

 McCallie, 1927). A granular plessite field altered by reheating. Picral 40 seconds; X 60. 

 American Museum of Natural History. 



2. Social Circle. Part of the area shown in figure 1 at higher magnification. The 

 center of this photograph is near the center of the upper half of figure 1. The darker grains 

 probably represent grains of dense plessite in which, after heating, the kamacite segregated 

 in particles in a black unresolved gamma-alpha mi.xture. Picral 40 seconds; X 150. 



3. Unidentified. This specimen is from the .American Museum of Natural History, 

 whose records aflford no indication of its origin. It is a medium octahedrite much altered 

 by cosmic reheating into the gamma-alpha range. This resulted in great alteration of dense 

 plessite, in which the gamma phase began to coalesce; the partial spheroidization of taenite 

 lamellae; and the production of a large amount of black gamma-alpha mixture. The photo- 

 graph shows (lower left to upper right) an irregular lamella of originally dense plessite be- 

 tween two kamacite bands. The large dark, or mostly dark, kamacite grains constitute 

 the prevailing pattern throughout the mass, with occasional clear or partly clear grains as 

 here shown. In the clear grains the taenite has segregated in minute spheroids and particles ; 

 in the dark areas segregation did not take place. Picral 40 seconds; X 60. 



4. Unidentified. Part of the area shown in figure 3 at higher magnification. The ples- 

 site shows rounded particles of taenite and particles of the black gamma-alpha aggregate in 

 a ground of clear kamacite. In the lighter grains the taenite has segregated in spheroidal 

 form. The gamma-alpha aggregate in the dark grains is partly resolved. Picral 40 seconds; 

 X 150. 



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