Meteorite from Mars

Nakhlite - NWA 998

Purchased in September 2001 in Western Algeria  . TkW 456g.

Classification and mineralogy: (A. Irving, S. Kuehner,): a friable, dark green rock with minor orange-brown alteration products that probably are of pre-terrestrial origin. 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, pyrrhotite. The overall texture of this Martian meteorite 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 in this martian meteorite; 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.