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Graphite nodules, Nantan, China

Graphite nodules (the egg-shaped inclusions pictured above) are referred to as "primary structures" in iron meteorites. They almost always have rims of taenite and schrebersite precipitated upon them during the cooling and crystallization phase.

Normally we only see a "sliced" view of these nodules after cutting into an iron meteorite but in this rare specimen sample we see complete nodules exposed through the effects of terrestrialization. Most of the meteorite has corroded away from the nodules leaving them exposed. The nodules resistance to terrestrial corrosion is is due to the taenite rims that surround the graphite nodules. Taenite (face centered cubic austenite, with more than 25% nickel) is highly resistant to terrestrial corrosion.

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