Members of the nakhlite group are distinct from other Martian meteorites with respect to their crystallization age (~1.3 Ga Nyquist et al. The meteorites Allan Hills (ALH) 84001, NWA 7034 (paired with NWA 7533), and the SNC clan (shergotittes, nakhlites, and chassignites) are samples of the crust of Mars, and together provide unique insights into the planet's evolution (e.g., Treiman et al. This isolation could relate to the scarcity of olivine in NWA 5790 because dissolution of olivine in other nakhlites by Martian groundwaters enhanced their porosity and permeability, and provided solutes for secondary minerals. The meteorite has therefore sampled a region of the lava flow/sill with little or no exposure to the aqueous solutions that altered other nakhlites. As petrographic results are also not definitive, we conclude that secondary minerals produced by Martian groundwaters are at best very rare within NWA 5790. δD values of the clay minerals range from −212 ± 109‰ to −96 ± 132‰, and cannot be used to distinguish between a terrestrial or Martian origin. The clay minerals are finely crystalline and comprise ~0.003 vol% of the meteorite. The presence of microbial remains within the coating confirms that the dust and its carbonate cement are terrestrial in origin, consistent with the carbon and oxygen isotope composition of the calcite. The calcite forms a cement to coatings of dust on the outer surface of the find and extends into the interior of the meteorite within veins. NWA 5790 contains calcite and rare clay minerals that are evidence for its exposure to liquid water. Furthermore, zoning of augite phenocrysts, and other petrographic and chemical characteristics suggest that NWA 5790 samples the chilled margin of its parent lava flow/sill. Its mineralogy differs from the other nakhlites with a high abundance mesostasis (38.1 ± 3.6 vol%) and scarcity of olivine (4.0 ± 2.2 vol%). Northwest Africa (NWA) 5790 is the most recently discovered member of the nakhlite group.

Olivine meteorite