PROCEEDINGS OF THE UNITED STATES NATIONAL MUSEUM 



by the 



SMITHSONIAN INSTITUTION 



U. S. NATIONAL MUSEUM 

 Vol. 99 Washington : 1949 No. 3241 



THE PIMA COUNTY (AKIZONA) METEORITE 



By E. P. Henderson and Stuart H. Perry 



Tlie name Pima County is provisionally given to a small but most 

 unusual iron meteorite acquired by Stuart H. Perry in 1947 from Prof. 

 Eldred G. Wilson, of the University of Arizona at Tucson. Its history 

 is unknown except that it was brought to the university many years ago 

 by someone who is supposed to have found it in the vicinity of Tucson, 

 Pima County, Ariz. 



The specimen, which has been given to the United States National 

 Museum by Mr. Perry, weighed only 210 grams. It is pyramidal in 

 shape, the base, which apparently was the evenest of the four sides, 

 having been partly polished. Standing on that surface, the pyramid 

 is about 11/2 inches high and 1% by 1% inches in the other two direc- 

 tions. Though the polished surface did not seem to have been sawed, 

 but only partly rubbed down, this iron may have been part of a larger 

 mass. If so, the larger mass is unknown, and the authors know of no 

 other nickel-poor ataxite having the same microstructure. 



The most striking feature of this iron is the remarkable flow struc- 

 ture developed on three of its pyramidal sides, consisting of deep fur- 

 rows and ridges which cover the surface and curve around one of the 

 edges between them. The fourth side is not furrowed and ridged but 

 shows some minute droplets of melted metal. The fused metal in 

 these flight markings shows minute pores formed by bubbles during 

 the time the iron was molten. 



The microstructure of the Pima County meteorite is that of a nickel- 

 poor ataxite, consisting of kamacite with a profuse dispersion of min- 

 ute particles of schreibersite. Generally grain boundaries are not 



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