Plate 38 



1. Smith's Mountain, North Carolina; fine octahedrite; Ni-Co 8.52 percent. A coarse 

 plessite field at moderate magnification. With strong etching the dense plessite appears 

 black but is not wholh' so with lighter etching. The kamacite lamellae reflect the orienta- 

 tion of the general pattern. All kamacite shows an acicular gamma-alpha transformation 

 structure. Taenite borders are scanty. Picral 80 seconds; X 30. U. S. National Museum. 



2. Seel.'\sgen, Prussia; coarsest octahedrite; Ni-Co 5.84 percent. Plessite field filled 

 with coarse irregular taenite lamellae. Near the edges are taenite areas dark because of 

 supersaturation. The Ni-Co percentage of this iron, given in an old analysis (1848), is 

 almost certainly too low. Picral 60 seconds; X 60. 



3. Seelasgen. a field of dense plessite with octahedrally oriented needles (lamellae) 

 of kamacite. Small curved schreibersite inclusion at upper left. The dense plessite is 

 formed by the low temperature transformation of a nickel-rich area, resulting in a structure 

 of extremely fine kamacite particles embedded in the transforming taenite. Picral 60 

 seconds; X 60. 



158 



