|Northwest Africa 5717|
|Basic information||Name: Northwest Africa 5717|
This is an OFFICIAL meteorite name.
Abbreviation: NWA 5717
Observed fall: No
Year found: 2008
Country: (Northwest Africa)
Mass: 7.31 kg
This is 1 of 18 approved meteorites classified as Chondrite-ung. [show all]
Search for other: Ungrouped chondrites
Approved 22 Dec 2009|
Revised 11 Jan 2010: revised writeup
Writeup from MB 97:
Northwest Africa 5717
Chondrite (ungrouped, 3.05 subtype)
History and physical characteristics: In late 2006, just NW of Mahbas, Western Sahara, a single fresh stone was recovered that weighed 7.310 kg. Blanketed in fusion crust and showing only the slight spots of oxidation, there is one small fractured face where fusion crust is absent and the internal structure of a possible primitive sub-type is visible. The specimen was acquired in its entirely by a Moroccan meteorite and fossil dealer in Erfoud in late 2008, from whom it was purchased by Darryl Pitt in December of the same year.
Petrography: (T. Bunch and J. Wittke, NAU; A. Irving UWS): an assemblage of two unique chondrule lithologies: Lithology A, the apparent host, consists of dark, tightly packed chondrules that are surrounded by a sparse, cataclastic matrix composed of abraded chondrule rim material (matrix = 8 vol. %). Many of the chondrules have a thin rim of metal, sulfide, and fine-grained silicates. Chondrules are typically sub-round to sub-angular and range in size from 0.04 to 4.1 mm, mean = 0.455 mm. Matrix = 8 vol. % and metal, sulfides and metal oxides = 4 vol. %. Lithology B occurs as lumpy to swirling arrays of white to gray Mg-rich chondrules that range in size from 0.05 to 3.6 mm together with a prominent subset of microchondrules (5 vol. %) 0.012 to 0.050 mm in diameter. A few large (4 to 8.4 mm), irregular-shaped chondrule-like objects are present and consist mostly of enstatite. Strong compositional zoning is common in chondrule olivine and pyroxenes, which are set in a mesostasis of clear, optically isotropic glasses and quench crystals. Metal and sulfides occur as sub-rounded aggregates in the matrix (6 vol.%).
Geochemistry: Lithology A: Olivine cores, Fa9.7 – 20.8 (FeO/MnO mean = 40); rims, Fa16.2 – 35.6 (FeO/MnO mean = 36), ferroan olivine Cr2O3 = 0.23 - 0. 91 wt %, mean = 0.53. Lithology B: Olivine cores, Fa 0.03 – 3.4; Cr2O3 in olivine, 0.24 – 0.84 wt %, mean = 61. Olivine rims, Fa 17.2 – 27.5; Cr2O3 mean = 0.28 wt %. Ferroan olivine (Fa >8) Cr2O3 = 0.28– 0.78, mean = 0.47 wt %. Mg-rich cores in both lithologies show higher Cr2O3 contents relative to FeO rich rims. Chondrule enstatite is Fa 0.04 – 5.8Wo 0.7. Average composition of mesostasis glass is (in wt %, N = 6): Na2O = 4.65; MgO = 1.45; Al2O3 = 12.8; SiO2, 71.3; P2O5 = 0.45; K2O = 1.23; CaO = 1.38; TiO2 = 0.47; Cr2O3 = 0.04 and FeO = 5.7. Oxygen isotopes (D. Rumble, CIW): Analyses of two acid-washed whole rock samples by laser fluorination gave, respectively: lithology A, δ18O = 4.17 and 4.47; δ17O =2.73 and 2.90; Δ17O = 0.539 and +0.554 (all ‰); lithology B, δ18O = 3.15 and 3.68; δ17O = 1.72 and 2.01; Δ17O = +0.061 and +0.080.
Classification:.Chondrite (ungrouped, 3.05 subtype). Although the oxygen isotopic compositions for lithology A are similar to those of H chondrites, the very low metal content together with other characteristics are inconsistent with an H classification. Lithology B oxygen isotopic compositions are dissimilar from those of all other meteorites. The Δ17O values of lithology B are close to those of most enstatite-rich meteorites, but the mafic minerals are significantly more ferroan. Olivine Fa range and Cr2O3 contents of both litho
NAU: Geology, Bldg 12
Northern Arizona University, Flagstaff, AZ 86011, United States; Website (institutional address; updated 12 Apr 2012)
UWS: University of Washington, Department of Earth and Space Sciences, 70 Johnson Hall, Seattle, WA 98195, United States (institutional address; updated 15 Jan 2012)
CIW: Carnegie Insitution Washington, Geophysical Laboratory, 5251 Broad Branch Rd., NW, Washington DC 20015, United States (institutional address)
DPitt: Darryl Pitt, 225 West 83rd Street, New York, NY 10024, United States; Website (private address)
|References:||Published in Meteoritical Bulletin, no. 97, MAPS 45, 449-493 (2010)|
This is 1 of 5501 approved meteorites from (Northwest Africa) (plus 2104 unapproved names)
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