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Shocked Irons |
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Meteorite, Tamarugal, Iron IIIAB |
| Meteorite, Paloduro, IIIE |
| Meteorite, Deelfontein, IAB-mg |
| Pre-terrestrial
secondary structures seen in iron meteorites - Neumann lines (bands),
kamacite/taenite/cohenite/troilite recrystallization, deformation, and more -
are mostly shock-related. At some point in an iron meteorite's distant history, violent collisions between asteroids and planetoids would have occurred. Some, particularly violent, would eventually have disrupted the parent body. In a differentiated body, this would have exposed the iron/nickel core, shattering it into fragments. From this, it is reasonable to conclude that all iron meteorites would have, to varying degrees, indications of shock-altering events in their primary structures. These are referred to as secondary structures. The following are images of some shock-related secondary structures found in iron meteorites. One of the most reliable indicators of shock is the hardness of the metallic meteoritic metals. After the primary cooling period, kamacite and taenite are likely to have been around 155 HV (Vickers). However, after shock hardening, values of 325 and peaks of 475 have been observed in deformed kamacite and taenite (Buchwald, 1975). This intricate process allows us to infer the severity of shock in most cases. |
| Figure 1. Scale bar 700 µm |
| Meteorite, Tamarugal, iron, IIIAB |
| Vickers hardness 270 - 335 |
| Subboundaries in kamacite lamellae, basket weave plessite field (center). Neumann bands in multiple directions. |
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| Figure 2. Scale bar 1.6 mm |
| Meteorite, Paloduro |
| Classification, Iron, IIIE |
| Vickers hardness 340 |
| Strongly shocked, melted troilite, recrystallized kamacite. |
| Figure 3. Scale bar 900 µm |
| Meteorite, Deelfontein |
| Classification, Iron, IAB-MG |
| Vickers hardness 380 |
| Coss-hatched Neumann lines, deformed, shock-melted troilite, the graphite has a unidirectional texture, severly corroded cohenite. |
| Figure 1. Scale bar 600 µm |
| Meteorite, Deelfontein |
| Classification, Iron, IAB-MG |
| Vickers hardness 380 |
| Neumann lines, deformed, shock-melted troilite, severly corroded cohenite, rhabdites. |
| Figure 5. Scale bar 400 µm |
| Meteorite, Deelfontein |
| Classification, Iron, IAB-mg |
| Vickers hardness 380 |
| Elongated decomposed cohenite inclusion. |
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