|
||
| |
Troilite droplets |
| Return to Contents |
| Back...Next |
| Meteorite, N'Goureyma, Iron, ungrouped |
| Figure 1. Scale bar 600 µm. |
| N'Goureyma, troilite droplets. |
| N'Goureyma is an ungrouped, polycrystalline
iron meteorite with a martensitic-plessitic matrix. The chemistry is 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.
Buchwald, 1975, described it as having the lowest concentration of gallium and germanium of any known iron meteorite. It is also unusual in that there is no superstructure as in any washed-out Widmanstatten pattern, no dendrites, not a single kamacite lamellae, no Neumann bands, and no schreibersite or rhabdites reported. But what it does have are some of the most unusual shaped troilite inclusions seen in any iron meteorite (so far as is known). Troilite "commas" and "droplets" are common in N'Goureyma but fluidal structures are rare in iron meteorites. The cooling profile indicates a temperature decrease that would be too rapid for Widmanstatten development but long enough for some secondary structure development. Between cooling and reheating episodes, including atmospheric entry and shock, the mass was likely softened to an internal temperature that allowed blebs of troilite to liquefy briefly and (locally) flow in the softened kamacite. In Buchwald's "Handbook of Iron Meteorites," 1975, he closes on N'Goureyma with: "N'Goureyma may be the result of aggregation plus sintering of fine-grained material, followed by a cooling that was rapid relatively to what normal octahedrites underwent." Author's note: Sintering is more of a metallurgical term than meteoritical. It involves compacting and fusing small material particles together, creating solid structures without fully melting the base material. |
| Figure 2. Scale bar 800 µm. |
| N'Goureyma, troilite droplets. |
| Return to Contents |