Plate 49 



1. Wood's Mountain, North Carolina; finest octahedrite; Ni-Co 8.61 percent. The 

 nickel content is very low for a finest octahedrite. Part of a large troilite inclusion showing 

 the microstructure of irregular polyhedral grains. The black spots are oxide (visible 

 unetched). A band of swathing kamacite at left side of inclusion. The large dark area is 

 oxide. Picral; X 60. 



2. Walker County, Alabama; hexahedrite; Ni-Co 5.94 percent. Rounded troilite 

 inclusion surrounded by schreibersite. The black spots are due to chipping. Picral; X 60. 



3. Unidentified. A medium octahedrite, locality unknown (see pi. 74). A body of 

 troilite is partly penetrated by an elongated schreibersite body. By the reheating of 

 this iron the troilite and part of the schreibersite were fused. The two being almost 

 insoluble with each other in the solid state, the schreibersite in cooling was rejected from 

 the solution in droplike particles. Picral 80 seconds; X 60. 



4. Cedartown, Georgia; hexahedrite; Ni-Co 5.70 percent. Troilite inclusion surrounded 

 by schreibersite, etched with sodium picrate only; X 150. The small proportion of phos- 

 phide remaining in solution with the troilite is enough to cause the latter to be darkened by 

 picrate. In this case, unlike the preceding, it seems probable that the included white spots 

 are kamacite rejected as the kamacite-sulphide solution cooled. In such cases it usually 

 is rejected to the borders of the inclusion as "swathing kamacite," but in this case that proc- 

 ess was inhibited by the presence of the surrounding phosphide which solidified while the 

 inclosed troilite still contained more kamacite than it could retain in solid solution at room 

 temperature. 



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