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Taenite ribbons - Arlington, Sokoto |
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| Meteorites - Arlington, IIE Iron, ungrouped, Sokoto, IIIAB, Iron. |
| Figure 1. Scale bar 800 µm. |
| Meteorite, Arlington, IIE Iron. |
| Taenite ribbons. |
| The terms “taenite
lamellae” and “taenite ribbons” both refer to structures found
in iron meteorites, but they describe slightly different features. Taenite lamellae are thin, plate-like structures of taenite that form within the meteorite. They form through an exsolution process as the meteorite cools. Kamacite (a lower nickel content phase) exsolves from the taenite (a higher nickel content phase), creating thin, plate-like structures of taenite within the kamacite matrix, contributing to the Widmanstätten pattern. Taenite ribbons are elongated, ribbon-like structures of taenite that form during the slow cooling of the meteorite. The thin taenite ribbons in the photographs form at the expense of thick kamacite. The process is part of the complex phase transformations that occur during slow cooling. Initially, taenite forms as thick bands or ribbons. Kamacite (a low-nickel phase) forms within the taenite at lower temperatures. Kamacite grows at the expense of taenite, meaning that as kamacite crystals grow, they consume the surrounding taenite. As kamacite continues to grow, the remaining taenite is squeezed into thinner ribbons or lamellae. This results in the characteristic interlaced pattern of thin taenite ribbons and thicker kamacite bands seen in photographs. The final structure is a balance between the two phases, with the amount and thickness of taenite and kamacite depending on the cooling rate and the initial composition of the meteorite. |
| Figure 2. Scale bar 400 µm. |
| Meteorite, Arlington, IIE iron. |
| Taenite ribbons. |
| Figure 3. Scale bar 400 µm. |
| Meteorite, Sokoto, IIIAB iron. |
| Taenite ribbons. |
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