2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



HEXAHEDRITES AND THE NICKEI^IRON SYSTEM 



The three types of iron meteorites, hexahedrites, octahedrites, and 

 ataxites, are accounted for by the nickel-iron phase diagram, fig. 1 ; 

 however, there are no clearly defined separations between the dif- 



900 



800 - 



700 - 



o 







K 600 



5 



q: 



Q. 



LU 



500 I 



400 - 



300 - 



200 



30 40 

 % NICKEL 



Fig. 1. — Nickel-iron phase diagram. The hexahedrites and nickel-poor 

 ataxites fall into the same area, i.e., left of the line AB and usually within the 

 area defined by the two dotted lines. A hexahedrite should consist of one nickel- 

 iron alloy, kamacite or alpha iron. 



ferent types. The hexahedrite group is located to the left of the 

 line AB in figure 1. These should consist of a single phase, alpha 

 iron or kamacite. The octahedrites fall in the area between AB and 

 AC and consist of two phases of nickel-iron alloys, kamacite (alpha 

 iron) and taenite (gamma iron). The third group, ataxites, should 



