Abstract
The proportions by volume of kamacite, taenite, and nonmetallic phases have been determined by quantitative metallography in five octahedrite meteorites: Grant, Bristol, Toluca, Odessa, and Canyon Diablo. Using the ratio of the kamacite/taenite phases and the Fe-Ni phase diagram, the lowest temperature (T0) at which these phases existed in equilibrium has been estimated, and its value employed in a calculation of the possible time intervals necessary for the formation of the Widmanstätten pattern in asteroidal bodies 100–200 km in radius and consisting either of an Fe-Ni alloy or of olivine with an iron core. It is concluded that the time intervals available for the formation of the Widmanstätten pattern need not have exceeded 108 years but could be longer if segregation occurred under pressure. The estimated T0 temperatures fall into two groups with mean values of approximately 460° and 525°C. The difference between these two values may be due to the different origin of the meteorites or to the different content of the nonmetallic phases.
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