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 wholly recrystallized IVA, fine octahedrite. It is homogeneously granulated throughout its entire 100kg mass.

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

Buchwald's detailed study (1975) found no signs of artificial reheating, concluding that the secondary structures are genuinely cosmic. Buchwald also noted "rhythmic growth lines" that developed over large areas, indicating cyclic reheating by (most likely) solar radiation, i.e., repeated close orbital passages of small perihelion distances near the Sun.  

Figure 2 shows a section of the Gibeon, IVA, iron meteorite for comparison. Gibeon has also undergone recrystallization but to a much lesser extent.

 
 
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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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