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Northwest Africa 8157
Basic information Name: Northwest Africa 8157
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 8157
Observed fall: No
Year found: 2011
Country: (Northwest Africa)
Mass:help 82 g
Classification
  history:
Meteoritical Bulletin:  MB 102  (2013)  CM2
Recommended:  CM2    [explanation]

This is 1 of 540 approved meteorites classified as CM2.   [show all]
Search for other: Carbonaceous chondrites, Carbonaceous chondrites (type 2), CM chondrites, and CM-CO clan chondrites
Comments: Approved 10 Dec 2013
Writeuphelp
Writeup from MB 102:

Northwest Africa 8157 (NWA 8157)

(Northwest Africa)

Purchased: Sept 2011

Classification: Carbonaceous chondrite (CM2)

Physical characteristics: Single stone with a fresh-looking fusion crust.

Petrography: (R.H. Hewins, C. Göpel, O. Boudouma, B. Zanda, MNHNP) Microprobe and SEM examination of a polished mount shows a highly altered, brecciated rock with clasts of CM2 material and with very few recognizable chondrules. It consists of fine-grained phyllosilicate-rich matrix containing serpentine, cronstedtite and PCP aggregates. The matrix is clastic and patchy with localized clusters of PCP. There are Type IA, IAB and IB (magnesian PO, POP, PP) chondrules, with fairly fresh olivine and pyroxene but altered metal, and one Al-rich chondrule, with unaltered Al-diopside phenocrysts and groundmass replaced by cronstedtite blades. The chondrite matrix consists of highly varied patches containing serpentine, cronstedtite and PCP intergrowths. There are abundant magnesian olivine crystal clasts in the matrix. Type II chondrules (ferroan) are represented only by ferroan olivine crystal clasts in the matrix. Refractory inclusions were not recognized. Fe-Ni sulfide, chromite and calcite are seen in minor quantities in the matrix. Kamacite survives only as rare droplets encased in Type I olivine phenocrysts.

Geochemistry: (R.H. Hewins, C. Göpel, O. Boudouma, B. Zanda) Olivine is Fa1.2±0.6, n=13, with 0.35 wt% Cr2O3 0.26 wt% CaO, and Fa26.9±6.7 , n=6, with FeO/MnO=101±14 and 0.35±0.20wt% Cr2O3. Pyroxene is En97.6±0.4Fs1.3±0.31Wo 1.1±0.1 n=5 and En61.6±6.5Fs1.6±0.1Wo36.7±6.4 n=3. Kamacite contains about 6 wt% Ni and 0.3 wt% Co. Oxygen isotopes (N. Assayag and P. Cartigny, IPGP): two determinations gave, respectively, δ18O = 3.811±0.009, 5.811±0.016; δ17O = -2.446±0.040, -0.601±0.026; Δ17O= -4.441,-3.663 (all per mil). Chromium isotopes (C. Göpel, IPGP) The bulk rock is characterized by its 54Cr excess: the δ54Cr value (1.006 ± 0.180) falls within the range (0.87- 1.13) defined by CB-CM chondrites (Shukolyukov and Lugmair, 2006; Yamashita et al., 2010; Trinquier et al., 2007; Rotaru et al., 1992).

Classification: CM2 chondrite.

Bibliography:
  • Yamakawa A., Yamashita K., Makishima A., and Nakamura E. (2010) Chromium isotope systematics of achondrites: chronology and isotopic heterogeneity of the inner Solar System bodies. Astrophys. J. 720, 150–154 (link)
Data from:
  MB102
  Table 0
  Line 0:
Place of purchase:Erfound, Morocco
Date:P Sept 2011
Mass (g):82
Pieces:1
Class:CM2
Fayalite (mol%):1.2±0.6
Ferrosilite (mol%):1.3±0.31; 1.6±0.1
Wollastonite (mol%):1.1±0.1; 36.7±6.4
Classifier:R. Hewins, MNHNP
Type spec mass (g):16.4
Type spec location:MNHNP
Main mass:Luc Labenne
Comments:Submitted by R. Hewins, MNHNP
Plots: O isotopes:  
Institutions
   and collections
MNHNP: Museum National d'Histoire Naturelle, IMPMC-CP52, 57 rue Cuvier, 75005 Paris, France, France; Website (institutional address)
IPGP: Institute de Physique du Globe de Paris, 1 rue Jussieu, 75252 Paris, Cedex 05, France (institutional address; updated 3 Nov 2014)
Labenne: 23, rue de Esperance, 75013 Paris, France; Website (private address; updated 29 Aug 2012)
Catalogs:
References: Published in Meteoritical Bulletin, no. 102, MAPS 50, 1662, September 2015
Find references in NASA ADS:
Find references in Google Scholar:
Geography: 
Coordinates:Unknown.

Statistics:
     This is 1 of 7328 approved meteorites from (Northwest Africa) (plus 1973 unapproved names)

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