Plate }} 



1. Saxta Catharina, Brazil; nickel-rich ataxite; Xi-Co 34.45 percent. The micro- 

 structure of this specimen is unique, a very regular pattern of strongly oriented mottled 

 bands of darker and lighter color. The latter show a phosphide content with picrate etching, 

 and disappear in the vicinity of schreibersite inclusions. The mottled bands at the left are 

 part of the prevalent structure of the entire mass. The dark area surrounding the large 

 schreibersite inclusion is structureless. Similar areas surround all schreibersite inclusions, 

 large and small. Picral 50 seconds; X 30. Harvard University. 



2. Santa Catharina. Area shown in figure 1 with additional etching with neutral sodium 

 picrate. The large schreibersite inclusion is blackened and the light component darkens, 

 indicating a phosphide content. 



3. Santa Catharina. Typical area of mottled bands. Same specimen as the preceding. 

 Picral 25 seconds; X 150. 



4. Santa Catharina. In this specimen the mottled banded structure is much less dis- 

 tinct, being largely replaced by the confused striated pattern here shown. It is to be noted, 

 however, that this pattern, like the mottled bands in the Harvard specimen, disappears 

 around the rhabdites. Picral 30 seconds; X 60. U. S. National Museum. 



Santa Catharina consists essentially of taenite and presumably is wholly in the gamma 

 phase. Although it has been thought by many to be of terrestrial origin, the presence of 

 troilite and schreibersite, neither of which is found in terrestrial rocks, seems conclusive as 

 to its nature. 



The analysis of Damour (1877) gives: Fe 63.69; Xi 33.97; Co 1.48; P 0.05; C 0.20; S 0.16; 

 Si 0.01. No other analysis is available. In view of the frequent occurrence of schreiber- 

 site, and the presence of phosphide in the structural pattern, the above percentage of phos- 

 phorus seems low. 



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