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Troilite droplets |
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| Meteorite, N'Goureyma, Iron, ungrouped |
| Figure 1. Scale bar 600 µm. |
| N'Goureyma, troilite droplets. |
| N'Goureyma is a distinctive, ungrouped
polycrystalline iron meteorite characterized by a martensitic-plessitic matrix.
Its chemical composition includes 9.41% Ni, 0.56% Co, 0.05% P, 0.6% S, 0.07 ppm
Ga, 0.02 ppm Ge, and 0.6 ppm Ir. According to Buchwald (1975), it stands out
among iron meteorites for having the lowest recorded concentrations of gallium
and germanium. Structurally, it lacks several features typical of iron
meteorites: there is no evidence of a Widmanstätten pattern, dendrites,
kamacite lamellae, Neumann bands, or minerals like schreibersite or rhabdites.
What sets N'Goureyma apart is its extraordinary troilite inclusions, some of the most unusually shaped observed in any iron meteorite to date. These inclusions often appear as "commas" or "droplets," with fluidal structures that are rare in iron meteorites. The meteorite's cooling history suggests a rapid temperature drop-too fast to allow Widmanstätten pattern development but slow enough to permit some secondary structural formation. Episodes of cooling, reheating, shock, and atmospheric entry likely raised the internal temperature of the meteorite enough to soften the kamacite matrix. This softening may have briefly liquefied troilite blebs, allowing them to flow locally within the material. In his Handbook of Iron Meteorites (1975), Buchwald concludes: "N'Goureyma may represent the aggregation and sintering of fine-grained material, followed by a cooling process that was relatively rapid compared to that of typical octahedrites." Note: Sintering, a term more common in metallurgy than meteoritics, refers to the process of compacting and fusing small particles into a solid mass without fully melting the base material. |
| Figure 2. Scale bar 800 µm. |
| N'Goureyma, troilite droplets. |
| Listing of Structures |