Plate ?>5 



1. Trenton, Wisconsin; medium octahedrite; Ni-Co 7.73 percent (1869). The heavy 

 widely spaced lines, as well as the finer and shorter ones, might be mistaken for Neumann 

 lines, but they are due to a transformation structure; see figure 2. With heavy etching the 

 dense plessite is black, but much of it is black and unresolved even with much lighter etching, 



, except at very high magnification. Picral 50 seconds; X 60. 



2. Trenton. A portion of the area shown in figure 1. The upper left corner of this 

 photograph is at about the center of the right side of the plessite field in figure 1. With 

 higher magnification the resemblence to Neumann lines disappears. The lighter etching 

 does not show the grain boundaries in figure 1. Very light picral etch; X 150. 



3. Thunda, Australia; medium octahedrite; Ni-Co 9.05 percent. The kamacite, both 

 in the band (upper left) and within the plessite field, shows a characteristic gamma-alpha 

 transformation structure. Picral 50 seconds; X 60. American Museum of Natural History. 



4. Canton, Georgia; coarsest octahedrite; Ni-Co 7.20 percent. This iron consists almost 

 wholly of kamacite, which throughout shows an extraordinary development of the gamma- 

 alpha transformation structure, the result of rapid cooling in the gamma-alpha range, re- 

 sembling the martensitic Fe-C structure in artificial irons though much coarser. Picral 30 

 seconds; X 150, 



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