Sample Petrographic Description
Sample Number | ALH 81013 |
Newsletter | 6,1 |
Location | Allan Hills |
Field Number | 1645 |
Dimensions (cm) | 16.0 x 16.0 x 11.0 |
Weight (g) | 17727.00 |
Original Classification | Iron |
Updated Classification | Iron-IIAB |
Pairing | ALH 78100; ALH 81013; |
Macroscopic Description - Roy S. Clarke, Jr. | |
The highly distinctive external appearance of this specimen suggests that it is a fragment that separated during atmospheric break up from a larger mass with cubic cleavage. Its shape is that of a cube that has been shortened along one axis by severe and irregular ablation-sculpturing of a face. This face is the only one that is deeply sculptured with thumb-slze regmaglypts, giving the impression that it was part of the exterior surface prior to fragmentation. Its opposite face is approximately square, with slightly rounded edges, and appears to have been the leading surface during late stage ablation. All of the surfaces are covered with a thin reddish brown coating of secondary oxides which are somewhat thicker within the deeper depressions of regmaglypts. Thin cracks several centimeters long are present on all surfaces and tend to parallel the cubic axes of the specimen. | |
Thin Section Description - Roy S. Clarke, Jr. | |
A median slice was removed perpendicular to the square section of the specimen and parallel to opposite sides. One side of the slice was polished and macro-etched, resulting in an area of approximately 140 cm available for examination at low magnification. The matrix appears to be single crystal kamacite that etches to a dull finish, atypical for hexahedrites. Several small troilite-daubreelite inclusions are present, as are a few small schreibersites. Slight variations in kamacite reflectively appear to be due to tiny schreibersites that are unresolvable at low magnification. The most prominent surface feature is the system of orthogonal cracks mentioned above. They penetrate into the interior of the specimen. Neumann bands are absent. This cursory examination suggests that the meteorite is a hexahedrite of somewhat unusual metallography. It probably represents a separate fall, distinct from the typical hexahedrite ALH 78100. | |
Reclassification Notes (AMN OUTSIDE) | |
ALH 81013 was re-classified to IIAB based on the work of Wasson, J. T., Huber, H., Malvin, D. J., 2007, Formation of IIAB iron meteorites. Geochimica et Cosmochimica Acta, 71, 760-781. |
Antarctic Meteorite Images for Sample ALH 81013 | ||||
Lab Photo(s) : | ||||
References for Sample ALH81013 | |
Rubin, A. E., 2018, Carbonaceous and noncarbonaceous iron meteorites: Differences in chemical, physical, and collective properties. Meteoritics & Planetary Science, 53, 2357–2371. | |
Gao, X., Thiemens, M. H., 1991, Systematic study of sulfur isotopic composition in iron meteorites and the occurrence of excess 33S and 36S. Geochimica et Cosmochimica Acta, 55 Issue 9, Sep-91, 2671-2679, ISSN 0016-7037, http://dx.doi.org/10.1016/0016-7037(91)90381-E. | |
Jarosewich, E., 1990, Chemical analyses of meteorites: A compilation of stony and iron meteorite analyses. Meteoritics, 25, 323-337. | |
Nishiizumi, K., Elmore, D., Kubik, P. W., 1989, Update on terrestrial ages of Antarctic meteorites. Earth and Planetary Science Letters, 93(3), 299-313. | |
Wasson, J. T, Ouyang, X., Wang, J., Eric, J., 1989, Chemical classification of iron meteorites: XI. Multi-element studies of 38 new irons and the high abundance of ungrouped irons from Antarctica. Geochimica et Cosmochimica Acta, 53 Issue 3, Mar-89, 735-744, ISSN 0016-7037, http://dx.doi.org/10.1016/0016-7037(89)90016-1. | |
Marvin, U. B., Mason, B., 1984, Field and laboratory investigations of meteorites from Victoria Land, Antarctica. Smithsonian Contributions to the Earth Sciences Number, 26, 134. |