Nakhla; Lafayette; Governador Valadares; Y000593; Y000749; Y000802; Northwest Africa 817 and 998; MIL03346

The first three nakhlites identified above are all non-Antarctic meteorites which are available through various natural history museums and university institutes. Nakhla is also openly bought and sold by dealers and collectors. All are of significant size, but Nakhla is by far the largest and most desirable because it is a relatively fresh fall.

The nakhlites are pyroxene cumulates consisting mostly of augite and minor olivine in a very fine-grained mesostasis. The mesostasis is made of plagioclase, alkali feldspar, pyroxene, Fe-Ti oxides, sulfides and phosphates. Initial melt compositions may be determined from melt inclusions in olivine. Oxide minerals contain oxidized iron, a consistent feature in martian meteorites. Hydrated minerals are seen as amphibole in melt inclusions and iddingsite products of secondary weathering. Carbonate and sulfate salts are found, but less common than in other martian meteorites. The nakhlites are somewhat less shocked than the shergottites.

The bulk compositions of nakhlites are consistent with their mineralogy in being rich in Fe and Mg and poor in Al compared to basaltic shergottites. They have higher concentrations of incompatible elements than other cumulates and have light rare earth-enriched REE patterns in contrast with both basaltic and lherzolitic shergottites.

The crystallization ages of nakhlites are 1.3-1.4 Ga, intermediate between those of the young shergottites and ancient ALH84001. Their cosmic ray exposure ages, which date their ejection from Mars, are also intermediate at 8-12 Ma. Nakhla has been on Earth for 85 years, but terrestrial ages have not been measured for the other two nakhlites. The nakhlites are thus easily separated from the shergottites by mineralogy, bulk composition, and chronology. There seems to be no simple relationship between these martian meteorite rock types.