METEORITES — HENDERSON AND PERRY 



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nickel-rich ataxites in which the nickel content is much higher than 

 that of any octahedrite (see tables 2 and 3). 



The same general compomids of iron, nickel, etc., that occur in the 

 other groups are present in ataxites. The taenite is more abundant 

 in ataxites, and there is reason to believe that the nickel content of 

 the taenite is higher than in that found in octahedrites. Following 

 the line AC on figure 1 from higher temperatures to lower, we note 

 that as the melt cools the position of the line is shifted toward an 

 increasing nickel content. Investigation may show that taenite in 

 the same meteorite varies in composition. 



Studies of ataxites have not as yet progressed to the point where 

 all the structures can be accounted for. The logical approach to an 

 understanding of ataxites is through more complete investigation of 

 the features of both hexahedrites and octahedrites. 



Only those ataxites rich in nickel were included in table 3. Nickel- 

 poor varieties, with a composition similar to that of hexahedrites or 

 coarse octahedrites, exist, but the majority of published analyses of 

 ataxites indicate that their cobalt and nickel content falls within the 

 higher limits of composition of the finest octahedrites and extends even 

 beyond this range. 



Table 3. — Composition of high-nickel ataxites 



Because most of the analyses on nickel-rich ataxites are very old 

 and the cobalt and nickel contents may not be very accurately deter- 

 mined, a more complete table of this class was not attempted. Three 

 of the eight meteorites listed in this group, namely, Nordheim, Tawal- 

 lah, and Freda, have a slightly developed octahedral structure. In 

 both the Tawallah and Freda descriptions, mention is made of a fine- 

 grained acicular ground m.ass through which occur inclusions of 

 kamacite. In each case kamacite is surrounded by areas which are 

 largely taenite and which appear bright in the published photomicro- 

 graphs because taenite is resistant to the etching reagents used. This 

 arrangement is explained by assuming tliat the kamacite separated 



