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Mineralogy of the Almahata Sitta UreiliteMineralogy & 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. 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. 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. 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.
Document ID
20090034154
Acquisition Source
Johnson Space Center
Document Type
Conference Paper
Authors
Zolensky, Michael E.
(NASA Johnson Space Center Houston, TX, United States)
Herrin, J.
(Jacobs Engineering Group, Inc. Houston, TX, United States)
Friedrich, J. M.
(Fordham Univ. Bronx, NY, United States)
Rumble, D.
(Carnegie Institution of Washington Washington, DC, United States)
Steele, A.
(Carnegie Institution of Washington Washington, DC, United States)
Jenniskens, P.
(Search for Extraterrestrial Intelligence Inst. Mountain View, CA, United States)
Shaddad, M. H.
(Khartoum Univ. Sudan)
Le, L.
(Jacobs Engineering Group, Inc. Houston, TX, United States)
Robinson, G. A.
(Jacobs Engineering Group, Inc. Houston, TX, United States)
Date Acquired
August 24, 2013
Publication Date
October 4, 2009
Subject Category
Geophysics
Report/Patent Number
JSC-CN-18802
Meeting Information
Meeting: 41st Annual Meeting of the Division for Planetary Sciences of the American Astronomical Society
Location: Fajardo
Country: Puerto Rico
Start Date: October 4, 2009
End Date: October 9, 2009
Sponsors: American Astronomical Society
Distribution Limits
Public
Copyright
Other

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