Three-dimensional Analysis of Meteorite Mineral Textures:
Implications for Petrogenesis

James M. Britton
University of Massachusetts

The focus of this research is determining the phase relationships among the opaque minerals in iron meteorites and ordinary chondrites. These two classes of meteorites are the largest and most well-studied meteorite groups. They also represent near extremes of the meteorite spectrum, from iron to stony meteorites.

The major opaque phases in these meteorites are kamacite (an Fe-Ni alloy with up to 8 wt.% Fe), taenite (Fe-Ni with about 30% Ni), tetrataenite (Fe-Ni with approx. 50% Ni), and troilite (FeS). In the ordinary chondrites, these phases are accompanied by chromite (FeCr04), and other less abundant phases. In the iron meteorites, additional major phases can include cohenite (an iron carbide) and schreibersite (an iron phosphide).

The opaque phases are important to study because they provide insight into the thermal histories of meteorites. Compositional gradients within the taenite grains allow cooling rates to be calculated. This calculation is simpler in the iron meteorites where kamacite and taenite are in direct contact (one of the conditions for the calculation). In the ordinary chondrites, the relationship between the two phases is not obvious, and has never been studied in detail. It is assumed that all kamacite grains are connected to a taenite grain, or are connected via sulfides. If this fails to be true, then modification of the cooling rate equation for ordinary chondrites will be necessary.

The phase relations for the chondrites are being determined by doing a three-dimensional study. By imaging successive two-dimensional layers and inputting them into a three-dimensional modeling program, the spatial relations between grains can be evaluated. The phase relations for the iron meteorites are better understood, but this research focuses on the ways in which phases such as kamacite, taenite, and troilite behave differently between the two classes of meteorites.