Primary and Secondary Structures - Meteorites
New England Meteoritical Services
 

Social Circle - when you fly too close to the Sun
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Meteorite - Social Circle, IVA Iron.

Meteorite - Gibeon, IVA Iron.

All recrystallized structures in Social Circle are secondary.
 
Social Circle is a fully recrystallized IVA fine octahedrite, with its entire 100kg mass exhibiting a uniform granulated texture. All kamacite within it has undergone recrystallization, while the taenite and plessite fields have largely broken down into the early stages of spheroidization.

In his comprehensive 1975 analysis, Buchwald found no evidence of artificial reheating, affirming that the meteorite’s secondary structures are of cosmic origin. He also identified "rhythmic growth lines" spanning large sections, suggesting cyclic reheating—likely from solar radiation—caused by repeated close orbits near the Sun with small perihelion distances.

For comparison, Figure 2 depicts a section of the Gibeon meteorite, another IVA iron meteorite. While Gibeon also shows recrystallization, it is far less extensive than in Social Circle.

 
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Figure 1. Scale bar 600 µm.

Social Circle.
All kamacite is recrystallized, the taenite and plessite fields are mostly decomposed to the beginning stages of spheroidizing.

 
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Figure 2. Scale bar 600 µm.

Gibeon, IVA.
The fine octahedral Widmanstatten pattern shows kamacite and taenite recrystallizion to a lesser degree than is seen in Social Circle.

 
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