X-Ray diffraction analysis of cohenite from iron meteorites

Details X-Ray diffraction analysis of cohenite from iron meteorites X-Ray diffraction analysis of cohenite from iron meteorites

Apr 1967

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1967gecoa..31..621l&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 31, Issue 4, pp.621-628

Physics

3

Scientific paper

It has recently been observed that cohenite grains from iron meteorites show evidence of shock-induced alterations in crystal character. This paper reports the results of an X-ray diffraction investigation of cohenite from 50 Canyon Diablo meteorites and 8 Odessa shock standards. The crystal character of cohenite appears rather sensitive to shock pressure over the range 0-> 1000 kb. The alterations observed apparently represent successive stages in the solid state recrystallization of cohenite. This recrystallization probably occurs during the high-pressure portion of the shock wave since, because of cohenite's thermodynamic instability, the rate of its graphitization during low-pressure annealing appears to be much more rapid than its rate of recrystallization. It has been found possible to establish a pressure scale based upon features observed in diffraction photographs of cohenite grains from shock standards. This pressure scale is qualitatively consistent with the metallographic shock criteria proposed previously. The pressure gradient deduced by microscopy in a particular specimen has been verified and was found to be 40 kb/cm. Estimates, from metallographic criteria, of the degree of shock suffered by Canyon Diablo meteorites is essentially paralleled by shock estimates based on cohenite alteration. The sensitivity of the X-ray technique also serves to identify shocked meteorites which have not been at a pressure high enough to induce metallographic changes.

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