Plate 58 



1. Rio Loa, Chile; hexahedrite; Ni-Co 5.70 percent. Typical area in zone of alteration, 

 with a profusion of rhabdites and part of a long schreibersite needle (lamella). Rhabdite 

 crystals have lost their form and become rounded by fusion. The needle, and many of the 

 rhabdites, show thornlike projections, caused by diffusion of the melted phosphide along 

 grain boundaries. Picral 200 seconds; X 60. 



2. Rio Loa. An area similar to figure 1 showing two parallel needles. Picrate etching 

 blackens the phosphide and makes more conspicuous its invasion of the surrounding nickel- 

 iron along grain boundaries. The faint incipient granulation, not visible in figure 1, is the 

 result of superficial heating during atmaspheric flight. The fact that it is brought out by 

 picrate etching suggests a trace of phosphide enrichment along the grain boundaries. Picral 

 200 seconds and 5 minutes neutral sodium picrate. 



3. Rio Loa. A group of schreibersite needles in the zone of alteration. The brief 

 heating fused the phosphide and obliterated the Neumann lines. The liquid phosphide of 

 the needles absorbed iron from the surrounding mass, and as it cooled the excess of 

 iron above the eutectic ratio was rejected. The eutectic core finally solidified, leaving 

 borders and rounded droplets of clear rejected iron. Picral 150 seconds; X 60. 



4. Rio LoA. Part of the area shown in figure 3 at higher magnification. The eutectic 

 structure of the core is apparent. Picral 150 seconds; X 300. 



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