The formation of clear taenite in ordinary chondrites

The metallic phases in six bronzite and six hypersthene chondrites were studied metallographically and by electron microprobe. All of the chondrites studied contain zoned taenite. In bronzite chondrites, only about 5 per cent of the zoned taenite abuts on kamacite (the rest being apparently isolated from it) whereas in hypersthene chondrites an average of over 20 per cent abuts on kamacite. The compositions of the centers of zoned taenite can be used to obtain cooling rates by Wood's method. Including Wood's results, 14 out of 18 ordinary chondrites have cooling rates between 1 and 10°C/m.y.