34 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



grains. Howell (1908) reports that the 10.64-kg. Ainsworth iron was 

 found beside a creek in Brown County, Nebr., about 6 miles north- 

 west of Ainsworth. His analysis gave 6.49 percent Ni, which, although 

 high for a hexahedrite, may be essentially correct because meteorites 

 with these phosphide inclusions can give a wide range of nickel values 

 depending upon the area selected for study. 



PHYSICAL CHARACTERISTICS RELATIVE TO THE FALLS 

 OF HEXAHEDRITES 



CLEAVAGE IN HEXAHEDRITES 



The cubical cleavage in hexahedrites may have an important 

 bearing on their geographical distribution. Two pieces of the Bogus- 

 slavka, Siberia, iron were found about 1,700 feet apart, yet they 

 fitted together, Thus, this hexahedrite was split, near the end of its 

 high- velocity flight, comparatively close to the earth while falling 

 nearly vertically. 



Any large piece produced by fragmentation of a larger hexahedrite 

 mass will be covered with cleavage surfaces. Also, it will have large 

 open cleavages and numerous small ones extending inward from its 

 surface. While such an irregularly shaped body is in space, the 

 poorly bonded pieces remain attached, but upon entry into our 

 atmosphere, conditions change. When the mass meets appreciable 

 atmospheric resistance, chunks cleave off. Small pieces will decelerate 

 quickly and may fall unnoticed, while the large mass may blaze its 

 way across the sky for hundreds of miles before falling to earth. 

 Hence, many of the cleavages in a hexahedrite approaching the earth 

 will part, causing fragments to separate. Because of this, more pieces 

 may break off from a hexahedrite than from a stony meteorite or 

 from other types of irons. It is said that an iron meteorite is more 

 likely to survive its flight in the atmosphere than a stony meteorite, 

 and conversely, that a stony meteorite is more likely to break in 

 flight than an iron. Because of the cleavages in hexahedrites, there 

 is some doubt about the survival of hexahedrites in flight. Thus, 

 cleavages in this group of irons may account for their geographic 

 distribution. 



SIZE DISTRIBUTION OF HEXAHEDRITES 



Data on the masses of hexahedrites have been summarized in table 

 15. Most of the large hexahedrites were never weighed; therefore 

 the weight estimates reported may be inaccurate. Ten of these irons 

 are said to have exceeded 100 kgs., but none of the 10 is as large as 



