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Northwest Africa 12957
Basic information Name: Northwest Africa 12957
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 12957
Observed fall: No
Year found: 2018
Country: (Northwest Africa)
Mass:help 43 g
Recommended:  C3.00-ung    [explanation]

This is 1 of 5 approved meteorites classified as C3.00-ung.   [show all]
Search for other: Carbonaceous chondrites, Carbonaceous chondrites (type 3), and Ungrouped chondrites
Comments: Approved 31 Jan 2020
Writeup from MB 109:

Northwest Africa 12957 (NWA 12957)

(Northwest Africa)

Purchased: 2018

Classification: Carbonaceous chondrite (C3.00, ungrouped)

History: Purchased in Morocco in 2018.

Physical characteristics: Black irregular fragments. Cut face reveals a dark interior with small light chondrules.

Petrography: (J. Gattacceca, CEREGE) Chondrules with average apparent diameter 300±200 µm (n=25) set in a abundant iron-rich fine-grained matrix. Most chondrules have fine-grained rims. Opaques are metal, sulfides and magnetite. No phyllosilicates were observed. Raman spectra of the fine-grained matrix reveal the presence of polyaromatic carbonaceous matter characterized by a structural order comparable to type 2 chondrites, thus reflecting a peak metamorphic temperature lower than in the least metamorphosed type 3 chondrites (e.g., Semarkona).

Geochemistry: Olivine Fa24.3±20.8, range Fa1.0-Fa58.7, Fa PMD 79% (n=21), Cr2O3 in ferroan olivine 0.32±0.10 (n=16). Low-Ca pyroxene Fs8.8±12.7Wo1.5±0.8 (n=10). Matrix microprobe over an area of 30 × 30 µm2: total 84.4%, FeO 36.1 wt% (n=2). Oxygen isotopic composition (J. Gattacceca, C. Sonzogni, CEREGE) from analysis of one acid-washed 1.5 mg aliquot of a powdered 148 mg bulk sample is δ17O=-3.82‰, δ18O=1.45‰, Δ17O=-4.59‰ (linearized, slope 0.5247, analytical uncertainties 0.08‰, 0.12‰, 0.03‰ respectively

Classification: Carbonaceous chondrite (C3.00-ungrouped). The type 3 derives from the unequilibrated nature, the absence of phyllosilicates and abundance of metal. The subtype 3.00 derives from Raman spectroscopy. The ungrouped designation derives from petrography. Possibly paired with Chwichiya 002 despite having distinct oxygen isotopic composition.

Specimens: Type specimen at CEREGE. Main mass with Isabelle Pothier.

Data from:
  Table 0
  Line 0:
Date:P 2018
Mass (g):43
Weathering grade:low
Fayalite (mol%):24.3±20.8 (n=21)
Ferrosilite (mol%):8.8±12.7 (n=10)
Wollastonite (mol%):1.5±0.8
Magnetic suscept.:4.44
Classifier:J. Gattacceca, CEREGE
Type spec mass (g):8.83
Type spec location:CEREGE
Main mass:Isabelle Pothier
Comments:work name CM28; submitted by Jérôme Gattacceca
Plots: O isotopes:  
   and collections
CEREGE: CEREGE BP 80 Avenue Philibert, Technopole de l'Arbois 13545 Aix-en-Provence Cedex 4 France, France (institutional address; updated 29 Oct 2018)
References: Published in Meteoritical Bulletin, no. 109, in preparation (2020)
Find references in NASA ADS:
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     This is 1 of 9116 approved meteorites from (Northwest Africa) (plus 1873 unapproved names)

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