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Graphite "cakes" |
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| Meteorite, Redfields, ungrouped iron. |
Figure 1. Scale bar 200 µm. |
| Meteorite - Redfields. |
| Classification - Iron, ungrouped, 6.91% Ni, 0.14% P |
| Graphite "cakes", Secondary structures. |
| The title, "Graphite
Cakes," is a bit dramatic. While the title may not pique one's interest,
the image usually does. Redfields, an unusual iron meteorite, is a carbon-rich, polycrystalline octahedrite that defies classification within the 13 established groups. Its chemical makeup includes 6.78% nickel, 0.35% phosphorus, and 0.5% carbon. Its parent taenite grains, ranging from 3 to 8 cm in diameter, are divided by indistinct boundaries. As the meteorite cooled, each grain independently formed a distinctive Widmanstätten pattern. Scattered throughout the material are the intriguing graphite "cakes", 1 to 2 mm wide structures visible in polished samples. These "cakes" feature a solid graphitic core encased by graphite and a thin rim of kamacite particles. Redfields underwent a rapid and complex primary cooling process that disrupted typical Widmanstätten formation. Initially a polycrystalline taenite aggregate, it experienced shock and reheating events (Buchwald, 1975). As it cooled again through 550 °C to 500 °C, its current macrostructure took shape, only to be altered by another cosmic shock that produced the Neumann bands. The graphite "cakes" are secondary features that emerge at the close of the primary cooling phase. Structurally, Redfields resembles Santa Rosa, another anomalous iron meteorite. |
Figure 2. Scale bar 200 µm. |
| Meteorite - Redfields. |
Figure 3. Scale bar 150 µm. |
| Meteorite - Redfields. |
Listing of Structures |