36 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



that survive the passage through the atmosphere would fall far short 

 of the main mass. The large body would go much farther into our 

 atmosphere before further breaking up or would fall to the ground 

 intact. The widely scattered geographic groups of hexahedrites must 

 be explained by some process that brings one large mass or a cluster 

 of separate similar irons along a trajectory that has a low angle of 

 approach to the earth. Chance recovery of hexahedrites does not 

 explain the distribution of these meteorites. 



INCLUSIONS 



As far as we know, hexahedrites have the same metallic inclusions 

 as octahedrites with the exception of cohenite, which is relatively 

 abundant in octahedrites but quite rare in hexahedrites. The reason 

 being that iron carbide is more soluble in gamma iron (taenite) than 

 in alpha iron (kamacite), the chief constituent of hexahedrites. 



The absence of any appreciable silicate inclusions also may be 

 significant. Although the Spanish meteorite Colomera was classified 

 as a hexahedrite with silicate inclusions, a restudy showed it to have 

 an octahedral pattern and a composition in the octahedrite range. 

 Since the included silicate is olivine, the Colomera iron may be a 

 pallasite, but the 151-gram sample in the U. S. National Museum is 

 too small to be useful in typing a meteorite weighing 134 kg. 



RADIATION AGES OF HEXAHEDRITES AND OCTAHEDRITES 

 AND TIME OF DAY OF FALLS 



Wanke (1960) noted that by plotting the log N^e against radius, 

 all meteorites with the same radiation age lie on a straight line. 

 Wanke's plot shows that nearly all the octahedrites lie in a narrow 

 band and thus may have the same radiation age, but that the hexa- 

 hedrites and ataxites lie definitely lower and thus may have a different 

 history. 



Wanke also observed that octahedrites fell between 12 and 24 

 hours of the day, whereas hexahedrites fell between 2 and 12 hours, 

 or during the morning. 



SUMMARY 



Seventy hexahedrites are considered in this study. Some of those 

 listed in the Prior-Hey (1952) catalog were omitted because they 

 were incorrectly classified in their original descriptions. When speci- 

 mens were unavailable for study, it was necessary to rely either upon 

 the author's notes made during visits to other collections, upon 



