Plate 13 



1. Grand Rapids, Michigan; fine octahedrite; Xi-Co 10.69 percent. Though containing 

 more nickel than Butler, the bands are not so fine. The general structure is similar to 

 that of Carlton (below), with large fields containing oriented taenite lamellae and dark 

 plessite. Taenite lamellae are less profuse than in Carlton because of the lower nickel 

 content. The area shown is typical, the dark plessite being indistinctly oriented. Picral 

 75 seconds; X 30. 



2. Grand Rapids. Part of the dark plessite shown in figure 1. Higher magnification 

 shows it to be composed of minute droplike taenite bodies. Picral 40 seconds; X 150. 



3. Carlton, Texas; finest octahedrite; Ni-Co 13.40 percent. A sample microetched; 

 X 1^0, ordinary light. The structure is seen to consist of very narrow kamacite bands 

 separated, for the most part widely, by plessite fields. The area of plessite largely pre- 

 dominates. With ordinary light the bands appear dark and the fields light. Compare 

 plate 3. 



4. Carlton. A kamacite band and part of a plessite field, the band containing a pro- 

 fusion of taenite lamellae. One lamella is an example of the so-called "spotted" taenite. 

 The plessite is more dense than in Grand Rapids, being unresolved at moderate magnifi- 

 cation. Below is an area of kamacite needles and spindles, such as appear in the interior 

 of dense plessite fields in other finest octahedrites. Compare Butler, Laurens County, 

 and Cowra, plates 12, 15, 17. Picral 75 seconds; X 30. 



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