STRUCTURE AND NATURE OF TROOSTITE 



107 



Fig. 1 — Mag. 3230X. Fig. 1 is reproduced from the Journal of the Frank- 

 lin Institute and shows a typical troostitic nodule sectioned on a plane passing through 

 the center. The nodule has developed as a globular mass about a nucleus. Radial 

 grains have developed. These grains change from light to dark when the nodule is 

 revolved about the optical axis of the microscope. Therefoie it is clear that the 

 small fan-shaped grains are differently oriented. Where nodular troostite forms 

 regranulation must occur. Where changes in orientation take place, grain boundaries 

 must result. The structure of the troostite has not been fully resolved in this photo- 

 graph. Compare with others which follow. 



