Mineralogy of the Almahata Sitta Ureilite

Details Mineralogy of the Almahata Sitta Ureilite Mineralogy of the Almahata Sitta Ureilite

Sep 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.0906z&link_type=abstract

American Astronomical Society, DPS meeting #41, #9.06

Astronomy and Astrophysics

Astronomy

Scientific paper

Mineralogy & Petrography: Almahata Sitta, deriving from the asteroid 2008 TC3, is a coarse-grained- to porous fine-grained, fragmental breccia with subrounded mineral fragments and olivine aggregates embedded in a cataclastic matrix of ureilitic material [1]. Mineral fragments include polycrystalline olivine, low-calcium, pigeonite, and augite. Abundant carbonaceous aggregates containing graphite, microdiamonds and aliphatics. Kamacite, Cr-rich troilite, silica and schreibersite are abundant. The compositional range of the silicates is characteristic of the ureilites as a group, but unusually broad for an individual ureilite [2&3]. The dense lithology is typical for ureilites, but the porous lithology is anomalous. In the porous lithology pore walls are largely coated by crystals of olivine.
Classification: Almahata Sitta is an anomalous, polymict eucrite [1]. Anomalous features include large compositional range of silicates, high abundance and large size of pores, crystalline pore wall linings, and fine-grained texture. Tomography reveals that the pores define thin, discontinuous "sheets” connected in three dimensions, suggesting that they outline grains that have been incompletely welded together. The crystals lining the pore walls are probably vapor phase deposits. Therefore Almahata Sitta may represent an agglomeration of coarse- to fine-grained, incompletely reduced pellets formed during impact, and subsequently welded together at high temperature [4].
References [1] Jenniskens et al. (2009) Nature 458, 485-488; [2] Goodrich (1992) Meteoritics 27, 327-352; [3] Mittlefehldt et al. (1998) RiM 36, ch. 4; [4] Herrin et al. (2009) MAPS in press.

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