4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I07 



EXPLANATION OF PLATES 

 Plate i 



Fig. I. Slice, macro etch, X fs- 



Fig. 2. Portions of two kamacite bands, one horizontal, two vertical with 

 plessite in a variety of forms. The fields at left and upper right 

 show a dense gamma-alpha aggregate surrounded by borders of 

 clear fully transformed taenite. The narrow field or lamella in the 

 center, separating the vertical bands, is mostly clear taenite. In its 

 upper portion the structure is in part lamellar ; three dark areas show 

 oriented needles (lamellae) of the gamma-alpha mixture. A rounded 

 area of kamacite is enclosed near the top, and lower an oval of 

 kamacite with Neumann lines. In the center of the right-hand kamacite 

 band is a lamella of taenite gray or black by reason of super- 

 saturation with respect to kamacite. Picral 30 seconds, X 60. 



Plate 2 



Fig. I. Core of imperfectly transformed gamma-alpha aggregate in the cen- 

 ter of a triangular taenite body. The acicular structure shows some 

 orientation. Picral 15 seconds, X 400. 



Fig. 2. Edge of a plessite field. The taenite along the interface shows no gray- 

 ness, but is perfectly transformed. The specks and particles in the 

 kamacite (above) are probably taenite, showing black because of the 

 strong attack of the etchant along their interface. Picral 15 seconds, 

 X400. 



Plate 3 



Fig. I. A taenite lamella, with core of dark, acicular gamma-alpha aggregate 

 oriented in conformity with the general octahedral pattern. Picral 

 15 seconds, X 400. 



Fig. 2. Part of a plessite field. At upper right, a confused structure of gray 

 supersaturated taenite in a dark gamma-alpha aggregate, and kamacite 

 in lamellae and irregular particles. At lower left, imperfectly sphe- 

 roidized taenite. Between the two areas there has been some in- 

 vasion of hydroxide. Picral 15 seconds, X 400. 



Plate 4 



Fig. I. Part of the upper right portion of plate 3, fig. 2. The nature of 

 the structure is more evident. Picral 15 seconds, X 400. 



Fig. 2. An area in a zone of alteration. From upper left to lower right ; dense 

 core of a plessite field ; clear taenite border of a plessite field ; kama- 

 cite ; edge of slice. The kamacite shows a secondary granulation 

 caused by superficial heating in flight through the air, which also 

 probably homogenized the gamma-alpha aggregate in the plessite 

 field. In the kamacite area three original schreibersite inclusions have 

 been altered into an Fe-FcsP eutectic. These eutectic areas show 

 clear borders of phosphide, the excess of dissolved iron (kamacite) 

 having been able to migrate to the surrounding mass instead of being 

 entrapped to form dendrites. Picral 15 seconds, X 400. 



