Plate 43 



1. Laurens County, South Carolina; finest octahedrite; Ni-Co 14.21 percent. Plessite 

 field showing a gamma-alpha aggregate, light in center, with a broad clear taenite border. 

 The variation in structure is apparently due to a concentration gradient, the nickel content 

 being less in the center. Such a gradient has been shown in other irons b\- quantitati\'e 

 nickel coloration. Picral 25 seconds; X 60. U. S. National Museum. 



2. Grant, New Mexico; medium octahedrite; Ni-Co 9.98 percent. Plessite field, the 

 right part of which is similar to figure 1. The lower left portion consists of lamellae of clear 

 taenite in a groundmass of kamacite, which in places merges with the kamacite of the sur- 

 rounding mass. Picral 3 to 5 seconds; X 60. 



3. Grant. Part of the darker untransformed structure shown in figure 2. Partly 

 resolved needles (lamellae) of dark gamma-alpha aggregate. Picral 3 to 5 seconds; X 600. 



4. Grant. Part of the lighter area of dense plessite shown in figure 2. Transformation 

 is more complete; elongated particles of taenite (slightl)' gray because of supersaturation) 

 in a ground of kamacite. Picral 3 to 5 seconds; X 600. 



163 



