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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 anomalous iron, is a carbon-rich, polycrystalline octahedrite that chemically does not fit into the current 13 defined groups. It's composition is 6.78% Ni, 0.35% P, 0.5% C. The parent taenite grains, each 3 - 8 cm in diameter, are separated by poorly defined grain boundaries. During cooling, the unique Widmanstatten structure within each grain developed independently. Graphite, forming intriguing "cake-like" structures, 1 to 2 mm across, are scattered throughout and visible in prepared samples. These "cakes" are composed of a massive graphitic center surrounded by graphite and a fine rim of kamacite particles. Redfields has a complex rapid primary cooling history that prevented normal Widmanstatten development. It was a rapidly cooling, polycrystalline taenite aggregate that was exposed to shock and reheating (Buchwald, 1975). As it (again?) cooled through 550 °C - 500 °C, the macrostructure (seen now) was fully developed when another cosmic shock event occurred that formed the Neumann bands. The graphite "cakes" in the Redfields meteorite are considered secondary structures forming at the end of primary cooling (crystallization). |
| Structurally, it resembles Santa Rosa, another anomalous iron. |
Figure 2. Scale bar 200 µm. |
| Meteorite - Redfields. |
Figure 3. Scale bar 150 µm. |
| Meteorite - Redfields. |
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