BRAZIL - CE
Iron Meteorite - IVA Fine Octahedrite.
Corrosion appears to have attacked the mass quite uniformly and, consequently, removed at least several millimeters from the surface. There is no definitive indication that the mass has been reheated artificially, as one may suspect the very unusual microstructure. An engraved section displays a regular Widmanstätten pattern with straight and long lamellaes (W ~ 40) 0.30 ± 0.05 mm wide. Plessite occupies about 50% of the area and is developed mainly as a fine comb, repeating the crude Widmanstätten pattern and as fine-grained a + 'Y duplex structures. Schreibersite does not occur, even when the minimum grain limits precipitate, and rabdites were not observed. The total phosphorus content must therefore be well below 0.1% and possibly similar to that of Charlotte or Gibeon. Troilite is not present in the specimen analyzed, but it does occur as some 1-2 mm bubbles in the London sample. The normal kamacite phase of the lamellae gave way to a duplex structure of fine grains. No trace of Neumann original lines. The hardness is 200 ± 15. The taenite edges of the plessite fields have scallops, blurred edges and the interior of the plessite fields exhibits the same duplex structure as the Widmanstätten lamellae. The taenite lamellae, 30-50 microns in width, have a hardness of 230 ± 8. One possible interpretation of the very unusual structure seems to be that, after an initial normal cooling, a cosmic reheating occurred at 600-700 ° C, at least which "isothermal" taenite could be nuclear. Before overgrowth could occur, the heat source disappeared, and rapid cooling prevented the original structure from reappearing. Similar structures were produced experimentally by Brentnall & Axon (1962) and Staub et al. (1969). Similar reheated structures are also present in some other meteorites, especially Karasburg. Source: Buchwald (1975).
7.72% Ni, 0.05% P, 2.19 ppm Ga, 0.11 ppm Ge, 2.3 ppm Ir. Source: Buchwald (1975).
Fine octahedrite, bandwidth 0.30 ± 0.05 mm. The Crátheus material in the US National Museum is, therefore, a Gibeon type meteorite (group IVA), with anomalous "isothermal" taenite from a late reheating event. The specimen, which Curvelo (1950b) described and analyzed as Crátheus, is very different and was treated separately as Crátheus (1950). For more information, access the source link http://evols.library.manoa.hawaii.edu/bitstream/handle/10524/35673/vol2-Coy-Day(LO).pdf#page=5. Source: Buchwald (1975).
Not reported by the Meteoritical Bulletin Database. According to Buchwald (1975), the meteorite was first listed by Oliveira (1931) and studied by Andrade (1931). Source: Buchwald (1975).
The name Crátheus was applied to two different iron meteorites, which were called Crátheus (1931) and Crátheus (1950), referring to the date when they were first described in the literature. Crátheus (1931) was mentioned briefly by Oliveira (1931) in his catalog of Brazilian meteorites. He noted that a mass of 27.5 kg had been purchased in 1914 by the Geological Survey of Rio de Janeiro and gave a photograph of a deeply engraved section, which serves to establish the meteorite's identity. The only other information is from Andrade (1931), who presented an analysis and stated that the mass came from Crátheus, in the state of Ceará. Source: Buchwald (1975).
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