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Shocked Irons |
| Listing of Structures |
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Meteorite, Tamarugal, Iron IIIAB |
| Meteorite, Paloduro, IIIE |
| Meteorite, Deelfontein, IAB-mg |
| Secondary structures
observed in iron meteorites-such as Neumann lines (bands), recrystallization of
kamacite, taenite, cohenite, and troilite, as well as deformation features-are
predominantly linked to shock events that occurred before these meteorites
reached Earth. In the distant past, iron meteorites likely experienced violent collisions between asteroids and planetoids. The most extreme of these impacts could have disrupted their parent body entirely. In a differentiated body, such an event would have exposed and shattered the iron-nickel core, fragmenting it into pieces. Consequently, it's reasonable to conclude that all iron meteorites bear some evidence of shock-altering events in their original (primary) structures, which manifest as these secondary structures. The images below illustrate examples of shock-related secondary structures identified in iron meteorites. One of the most dependable indicators of shock is the hardness of the metallic phases within these meteorites. Following the initial cooling phase, kamacite and taenite likely had a hardness of approximately 155 HV (Vickers). However, post-shock hardening can increase these values significantly, with measurements reaching 325 HV and even peaking at 475 HV in deformed kamacite and taenite (Buchwald, 1975). This complex hardening process provides insight into the intensity of shock events 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. |
| Listing of Structures |