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Northwest Africa 11992 | |||||||||||||||||||||||||||||||
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Basic information | Name: Northwest Africa 11992 This is an OFFICIAL meteorite name. Abbreviation: NWA 11992 Observed fall: No Year found: 2007 Country: (Northwest Africa) Mass: ![]() | ||||||||||||||||||||||||||||||
Classification history: |
This is 1 of 451 approved meteorites classified as LL3. [show all] Search for other: LL chondrites, LL chondrites (type 3), Ordinary chondrites, and Ordinary chondrites (type 3) | ||||||||||||||||||||||||||||||
Comments: | Approved 9 Oct 2018 | ||||||||||||||||||||||||||||||
Writeup![]() |
Writeup from MB 107:
Northwest Africa 11992 (NWA 11992) (Northwest Africa) Purchased: 2007, Sept Classification: Ordinary chondrite (LL3) History: Found in northwest Africa, donated to Cascadia July 2012. Physical characteristics: In cut slices, exterior is dark gray and shiny, interior is gray with well-defined chondrules and has less metal than typically observed in fresh ordinary chondrites. Minimal weathering staining. Petrography: (A. Ruzicka, S. Goudy, Cascadia) Thin section shows well-defined chondrules with cluster chondrite texture and little intervening matrix. Glassy chondrule mesostases present but not abundant. Roughly half of low-Ca pyroxene grains show twinning suggestive of clinoenstatite polytype. Shock stage is S4. Shock effects are heterogeneous with S1 and S4 olivine grains predominant. Some bleached chondrules. Minimal weathering effects. Geochemistry: (M. Hutson, Cascadia) Olivine (Fa30.0±4.0, N = 140; Cr2O3 0.05±0.02 wt%, N = 56), low-Ca pyroxene (Fs20.2±6.8Wo1.4±1.1, N = 143). Classification: LL3 chondrite, estimated subtype 3.7. Iron contents in olivine and low-Ca pyroxene unusually high for LL3. LL indicated by low metal content and low weathering grade and overlap with LL for olivine Fa and low-Ca pyroxene Fs. Type 3 indicated by texture, presence of chondrule glass, abundance of clinoenstatite, and variable olivine and pyroxene compositions. Subtype indicators can be best reconciled with subtype of 3.7 to 3.8: Fa contents suggest 3.7-3.9, Fs contents suggest 3.4-3.9, olivine chrome contents suggest 3.5. Specimens: A total of 22.7 g in one slice, a polished thin section, and potted butt are available at Cascadia. Mr. McKenzie holds the main mass. | ||||||||||||||||||||||||||||||
Data from: MB107 Table 0 Line 0: |
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Institutions and collections |
Cascadia: Cascadia Meteorite Laboratory, Portland State University, Department of Geology, Room 17 Cramer Hall, 1721 SW Broadway, Portland, OR 97201, United States; Website (institutional address; updated 28 Oct 2011) |
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Catalogs: |
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References: | Published in Meteoritical Bulletin, no. 107, MAPS 55, 460-462
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Geography: |
Statistics: This is 1 of 9092 approved meteorites from (Northwest Africa) (plus 1875 unapproved names) |