Sample Petrographic Description
Sample Number | ALH 81012 |
Newsletter | 6,1 |
Location | Allan Hills |
Field Number | 1490 |
Dimensions (cm) | 5.0 x 2.0 x 3.0 |
Weight (g) | 36.65 |
Original Classification | Eucrite |
Updated Classification | Eucrite (Polymict) |
Pairing | ALH 76005; ALH 77302; ALH 78040; ALH 78132; ALH 78158; ALH 78165; ALH 79017; ALH 80102; ALH 81006; ALH 81007; ALH 81008; ALH 81009; ALH 81010; ALH 81012; |
Mineral Composition (%Fa & %Fs) | |
Ferrosilite (mol%): 33-62 | |
Weathering | |
A/B | |
Fracturing | |
A | |
Macroscopic Description - Roberta Score | |
Flow marks are present on the shiny black fusion crust which covers 75% of ALH 81012. Small clasts (<2 mm) are abundant in the light gray interior matrix. A few areas have oxidized to an orangish-brown color. | |
Thin Section Description - Brian Mason | |
The section consists largely of brown grains of pigeonite up to 0.9 mm and colorless grains of plagioclase up to 0.6 mm in a comminuted groundmass of these minerals. A few lithic clasts, up to 2.5 mm across, are present; most show ophitic textures. Fusion crust is present along one edge. Microprobe analyses show pyroxene compositions ranging fairly continuously from Wo3En35Fs62 to Wo35En32Fs33; En content shows a limited range (30-40) except for one grain Wo8En48Fs44. Plagioclase composition range is An84-94, mean An89. The meteorite is a eucrite, but it differs from previously described eucrites from the Allan Hills in the range and distribution of pyroxene compositions. It resembles ALHA81009 closely and is tentatively paired with that meteorite. | |
Reclassification Notes (AMN 13,1) | |
Re-classified as a polymict eucrite in AMN 13, no. 1. |
Antarctic Meteorite Images for Sample ALH 81012 | ||||
Lab Photo(s) : | ||||
Antarctic Meteorite Images for Sample ALH 81012 | ||||
Thin Section Photo(s) : | ||||
References for Sample ALH81012 | |
Righter, K., Holmwood, A.P., 2020, Mineralogy and petrology of dark clasts in the Allan Hills 76005 polymict eucrite pairing group. Meteoritics & Planetary Science, 55, 781-799, doi: 10.1111/maps.13465. | |
Benoit, P. H., Sears, D. W. G., Akridge, J. M. C., Bland, P. A., Berry, F. J., Pillinger, C. T., 2000, The non-trivial problem of meteorite pairing. Meteoritics & Planetary Science, 35, 393-417. | |
Marvin, U. B., MacPherson, G. J., 1989, Field and Laboratory Investigations of Meteorites from Victoria Land and the Thiel Mountains Region, Antarctica 1982-1983 and 1983-1984. Smithsonian Contributions to the Earth Sciences Number, 28, 146. | |
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. | |
Scott, E. R. D., 1984, Pairing of meteorites found in Victoria Land, Antarctica. Memoirs of National Institute of Polar Research., Special issue 35, 102-125, http://ci.nii.ac.jp/naid/110000009967/en/. | |
Delaney, J. S., Prinz, M., Takeda, H., 1984, The polymict eucrites. Journal of Geophysical Research: Solid Earth, 89, C251-C288, http://dx.doi.org/10.1029/JB089iS01p0C251. |