4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 98 



It is to be noted that the granular border or aureole which developed 

 around all inclusions after the formation of the Neumann lines follows 

 the irregularities of the taenite, but the grain boundaries give no 

 evidence of mechanical deformation. 



In the Tamarugal (El Inca) iron the fracture of a troilite nodule 

 and the displacement of the broken halves are described and illustrated 

 by Rinne and Boeke. 1 Fractures and displacements in schreibersite 

 inclusions have also been observed by Brezina in the Puquios iron, 

 and by Cohen in that of Chesterville. 



Schreibersite and taenite inclusions of similar form are often juxta- 

 posed, or alternate with one another along band boundaries, and the 

 two substances are so nearly identical in appearance that they are not 

 easily distinguished except by selective etching (pi. 4) or by a hard- 

 ness test. 



Numerous schreibersite inclusions, which with ordinary etching 

 appear clear and featureless, reveal a highly developed eutectic struc- 

 ture when etched lightly with sodium picrate (pi. 6). The etching 

 must stop at exactly the proper stage, for a few additional minutes 

 will cause the structure to disappear in a uniform black. 



The anomalous structure shown in plate 9 is apparently an area 

 of phosphorus enrichment in kamacite. Except for the peculiar 

 eutectoid appearance the kamacite is little changed, Neumann lines and 

 rhabdites appearing within the area. The rhabdites, it will be noted, 

 are surrounded by phosphorus-poor aureoles, both within and without 

 the area. 



Schreibersite in the form of rhabdite is abundantly disseminated 

 through the mass in squares, rectangles, and rhombs, diversely ori- 

 ented, as shown in plate 9 and plate 8, figure 2. In the latter figure 

 the rhabdites are surrounded by black borders — an optical effect due 

 to the fact that, because of their hardness, polishing left them slightly 

 in relief and thus the light is reflected away from the iron immediately 

 surrounding them. 



Two or three minute grains of chromite were observed, but no 

 troilite. 



Neumann lines are conspicuous, often running uninterruptedly 

 across several bands with no change, or slight change, of direction at 

 the boundaries. 



Superficial heating during flight apparently caused partial or incipi- 

 ent alteration of the kamacite almost throughout the mass by the for- 



1 El Inca, ein neues Meteoreisen. Neues Jahrb. Min., Geol., Pal., Festband 

 1907, pp. 227-255. 



