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Rhabdites and Schreibersite |
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| Meteorite - Abai, IAB Iron |
| Figure 1. Scale bar 60 µm. |
| Meteorite - Abai, IAB - Mg. |
| Classification - Iron, IAB-Mg, 6.11% Ni,
0.14% P Rhabdites - Secondary. |
| Rhabdites and schreibersite are both iron-nickel phosphides. Chemically, they are the same. The difference is where they nucleated. The formation of phosphides, nucleation, and precipitation took place in the solid state following the initiation of the gamma-iron/alpha-iron transformation, a phase change that marks the beginning of the Widmänstatten structure. The most nickel-rich grains of schreibersite formed at the interfaces of kamacite/taenite. Rhabdites, on the other hand, are characterized by a homogeneous nucleation of the same chemistry (Fe,Ni)3P, but in kamacite that is supersaturated with phosphorus. Both forms of nucleation occur at similar low temperatures of 400 ºC to 500 ºC. Rhabdites and schreibersite are present in many iron meteorites, but not all of them. Schreibersite has not been reported in the low Ni end of IVA irons, e.g., Gibeon. When phosphorous is abundant, above 0.4% (bulk), they form as angular plate-like inclusions. Schreibersite can be primary or secondary while rhabdites are considered as secondary structures. Prismatic rhabdites will be seen later in this series. |
| Meteorite - Cosby's Creek |
| Figure 2. Scale bar 20 µm. |
| Meteorite - Cosby's Creek |
| Classification - Iron, IAB-Mg, 6.57 Ni, 0.41% P |
| Plate-shaped rhabdites. |
| Meteorite - Cosby's Creek |
| Figure 3. Scale bar 20 µm. |
| Meteorite - Cosby's Creek |
| Classification - Iron, IAB-Mg, 6.57 Ni, 0.41% P |
| Plate-shaped rhabdites, side lighting to accent Neumann bands (lines). |
| Meteorite - Walker County |
| Figure 4. Scale bar 30 µm. |
| Meteorite - Walker County |
| Classification - Iron, IAB-Mg, 5.46 Ni, 0.28% P |
| Plate-shaped rhabdites. |
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