Official Meteoritical Bulletin entry for Northwest Africa 998:
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.
Scientific abstracts and news regarding NWA 998:
New meteorite clues to life on Mars
SkyMania.com April 30, 2010
Scientists believe they may have found fresh evidence of life on Mars in a meteorite that crashed to
Earth. Microscopic strands were revealed inside the space rock, labeled NWA 998 when it was examined
at the University of Toronto, Canada. http://www.skymania.com/wp/2010/04/new-meteorite-clues-to-life-on-mars.html/