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Northwest Africa 4797
Basic information Name: Northwest Africa 4797
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 4797
Observed fall: No
Year found: 2001
Country: Morocco
Mass:help 15 g
Meteoritical Bulletin:  MB 93  (2008)  Martian (shergottite)
Recommended:  Martian (shergottite)    [explanation]

This is 1 of 284 approved meteorites (plus 2 unapproved names) classified as Martian (shergottite).   [show all]
Search for other: Martian meteorites
Comments: Approved 14 Jan 2008
Revised 4 Aug 2008: final writeup
Writeup from MB 93:

Northwest Africa 4797


Find: 2001

Achondrite (Martian, shergottite)

History: Found in 2001 near Missour, Morocco, and acquired by Morocco Import of Erfoud, Morocco.

Physical characteristics: A single, dense, broken stone (15.0 g) with fusion crust on one side and visible regions of pale gray; vesicular glass interstitial to coarse silicate grains (Fig. 1). Several thin, dark-colored shock veins crosscut the specimen.

Petrography: (A. Irving and S. Kuehner, UWS; T. Bunch and J. Wittke, NAU) This very fresh specimen is predominantly a peridotite composed mostly of olivine chadacrysts (up to 1.5 mm) and zoned clinopyroxene oikocrysts (subcalcic augite and pigeonite, up to 9 mm across) with interstitial regions (apparently originally intercumulus) now consisting of vesicular glass containing sparse, very small, birefringent plagioclase microlites. Accessory phases are Ti-chromite, Mg-ilmenite (some with associated tiny baddeleyite grains), merrillite, and pyrrhotite. A shock injection vein (~1 mm wide) contains reacted xenocrysts and polycrystalline fragments of the peridotite material enclosed in a vesicular aggregate of fine grained (5-10 microns) interlocking olivine, augite and glass, and both margins of the vein exhibit even finer grained (<2 microns) selvages against the peridotite wallrock. This entire specimen has experienced very high shock pressures.

Geochemistry: Peridotite lithology: olivine (Fa31.3-32.7, FeO/ MnO = 49.3-53.0), augite (Fs14.6-16.0Wo35.3-29.9, FeO/MnO = 23.8-26.2), interstitial pigeonite (Fs25.2-26.3Wo14.8-7.9, FeO/ MnO = 27.8-31.8), plagioclase microlites in interstitial glass (An56.8Or0.8). Shock vein: olivine (Fa23.7-28.7, FeO/ MnO = 39.5-48.0, P2O5 = 0.28-0.46 wt%), augite (Fs14.3-16.3Wo41.4-36.4, FeO/MnO = 24.7-26.7), glass (average of 6 analyses, in wt%: SiO2 = 58.7, TiO2 = 1.4, Al2O3 = 14.3, FeO = 6.5, MnO = 0.22, MgO = 2.1, CaO = 11.8, Na2O = 2.7, K2O = 0.12, P2O5 = 1.8, SO3 = 0.17, Cl = 0.05). Bulk composition: (R. Korotev, WUSL; INAA data) FeO = 19.6, Na2O = 0.40 (both wt%), Ni = 330, La = 0.69, Sm = 0.52, Eu = 0.18, Tb = 0.19, Yb = 0.57, Lu = 0.080, Hf = 0.5 (all ppm). The chondrite-normalized rare earth element pattern is subparallel to that for Zagami, but at about half the absolute abundances, and there is a small negative Eu anomaly.

Classification: Achondrite (Martian, shergottite); extensive shock.

Specimens: A total of 3.3 g of sample, one polished thin section and one polished mount are on deposit at UWS. Morocco Import holds the main mass.

Submitted by: A. Irving, UWS.

Data from:
  Table 2
  Line 116:
Place of purchase:Missour, Morocco
   and collections
NAU: Geology, Bldg 12 Knoles Dr 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)
WUSL: Washington Univ., One Brookings Drive, St. Louis, MO 63130, United States (institutional address; updated 17 Oct 2011)
References: Published in Meteoritical Bulletin, no. 93, MAPS 43, 571-632 (2008)
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     This is 1 of 1904 approved meteorites from Morocco (plus 27 unapproved names) (plus 1 impact crater)

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