Primary and Secondary Structures - Meteorites
New England Meteoritical Services
 
 

Recrystallized Kamacite
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Meteorite - Seneca Falls, IAB Iron.
 
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Figure 1. Scale bar 200 µm.

Meteorite - Seneca Falls
Classification - Iron, IAB-Mg, 8.2% Ni, 0.3 P
Recrystallized kamacite - Secondary.

Seneca Falls is a medium octahedrite, IAB-Mg, with recrystallized primary structures. Originally, its kamacite formed as a primary phase, but was transformed into a secondary structure through recrystallization.

The meteorite underwent significant shock events, resulting in deformation and fracturing throughout its structure. Subsequent to these impacts, it experienced reheating. This thermal metamorphism drove the recrystallization of both kamacite and taenite.

In detail, the kamacite recrystallized into equiaxial grains ranging from 50 to 250 µm in diameter. Berwerth (1914) analyzed these polyhedral kamacite grains and suggested that Seneca Falls's unusual structure stemmed from artificial reheating. However, Buchwald (1975) later observed that the shock-melted troilite and taenite lamellae are fragmented into segments measuring 50 to 400 µm across, pointing to intense shock-reheating. Based on this evidence, Buchwald concluded that the recrystallization of Seneca Falls resulted from cosmic events rather than artificial processes.

Note the recrystallized taenite lamellae, bottom of image.
 
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Figure 2. Scale bar 100 µm.
Recrystallized kamacite lamellae, Seneca Falls.
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Figure 3. Scale bar 300 µm.
Recrystallized kamacite lamellae, Seneca Falls.
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Figure 4. Scale bar 300 µm.
Recrystallized kamacite lamellae, Seneca Falls.
 
 
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