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Northwest Africa 998
Basic information Name: Northwest Africa 998
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 998
Observed fall: No
Year found: 2001
Country: (Northwest Africa)
Mass:help 456 g
NHM Catalogue:  5th Edition  (2000)  Martian (shergottite)
Meteoritical Bulletin:  MB 87  (2003)  Martian (nakhlite)
MetBase:  v. 7.1  (2006)  Nakhlite
Recommended:  Martian (nakhlite)    [explanation]

This is 1 of 32 approved meteorites classified as Martian (nakhlite).   [show all]
Search for other: Martian meteorites
Writeup from MB 87:

Northwest Africa 998

Algeria or Morocco

Purchased 2001 September

Martian meteorite (nakhlite)

A. and G. Hupé (xHupé) purchased, from dealers at the Tucson Gem and Mineral Show in 2002 February, the main mass from a 456 g stone that had been acquired at an unspecified site in western Algeria or eastern Morocco in 2001 September. Dimensions before cutting: 72 mm by 65 mm by 48 mm. Classification and mineralogy (A. Irving and S. Kuehner, UWS): a friable, dark green rock with minor orange-brown alteration products that probably are of pre-terrestrial origin. It is composed mainly of subhedral, olive-green, complexly zoned subcalcic augite (Fs22Wo39) with subordinate yellow olivine (Fa64), orthopyroxene (Fs49Wo4), interstitial plagioclase (Ab61Or4 containing 0.1 wt% SrO, and exhibiting normal birefringence), titanomagnetite, chlorapatite and pyrrhotite. The overall texture is that of a hypabyssal, adcumulate igneous rock, and the apparent crystallization sequence is olivine, orthopyroxene, titanomagnetite, augite, apatite, plagioclase. There is a weak preferred orientation of prismatic pyroxene crystals, many of which have very distinctive zoning, with cores of augite surrounded by irregular, inverted pigeonite rims (now consisting of orthopyroxene with fine augite lamellae). Trains of tiny melt inclusions are present along healed fractures within pyroxene; microprobe study confirms that most of these are K-Na-Al-bearing silicate glass, but some are intergrowths of glass and Fe-bearing carbonate, which may represent quenched immiscible silicate-carbonate liquids. Symplectitic intergrowths of titanomagnetite and low-Ca pyroxene are present at grain boundaries between large, discrete olivine and titanomagnetite grains, but are not present around chromian titanomagnetite inclusions within olivine. These observations suggest that a pre-terrestrial oxidation process produced the symplectites, and involved high temperature, deuteric fluid infiltration along grain boundaries; such fluids also may have produced the irregular pigeonitic rims on augite crystals. Secondary (probably pre-terrestrial) ankeritic carbonate, K-feldspar (some Fe-bearing), serpentine (?), calcite and a Ca sulfate are present on grain boundaries and within cracks in augite. Oxygen isotope composition (D. Rumble, CIW): replicate analyses of acid-washed augite by laser fluorination gave δ18O = +3.9 ± 0.2‰; δ17O = +2.4 ± 0.1‰; ∆17O = +0.30 ± 0.02‰. Specimens: type specimens, 20 g, UWS, 20 g, FMNH, and two polished thin sections, UWS; main mass, xHupé.

Data from:
  Table 8
  Line 32:
Origin or pseudonym:Morocco/Algeria
Place of purchase:Tucson, Az
Date:Sep 2001
Mass (g):456
Classifier:A. Irving, UWS
Type spec mass (g):40
Main mass:ROM
Comments:see separate entry
Plots: O isotopes:  
   and collections
FMNH: NW Quadrant/Geology The Field Museum of Natural History 1400 South Lake Shore Drive Chicago, IL 60605-2496, USA, United States; Website (institutional address; updated 22 May 2024)
ROM: Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada (institutional address; updated 18 Oct 2011)
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)
xHupé: (old address—now see GHupé or AHupé) G. and A. Hupe, 2616 Lake Youngs Court SE, Renton, WA 98058., United States (private address)
References: Published in Meteoritical Bulletin, no. 87, MAPS 38, A189-A248 (2003)
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     This is 1 of 9829 approved meteorites from (Northwest Africa) (plus 1851 unapproved names)

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