Chassignite
A very rare Martian meteorite made mostly of olivine, a cumulate rock known as a dunite.
Chassignites are olivine cumulates: rocks formed when olivine crystals accumulated in a Martian magma chamber. In terrestrial terms they are dunites, typically more than about 90 per cent olivine, with minor pyroxene, chromite, feldspar and tiny melt inclusions trapped inside olivine grains. Their olivine is iron-rich compared with Earth's mantle, consistent with a more iron-rich Martian interior.
Only a handful are known. Chassigny fell in France on 3 October 1815 and was the first; NWA 2737, found in Morocco in 2000, was the second recognised. Their crystallisation ages of roughly 1.3–1.4 billion years and cosmic-ray exposure ages of about 11 million years closely match the nakhlites, so the two groups probably came from the same igneous complex on Mars and were launched by the same impact. Chassigny is also important for noble gases: its xenon differs from that of the Martian atmosphere and is used as a signature of the Martian interior.
Chassigny itself is pale yellowish-green and friable, while NWA 2737 is unusually dark, because intense shock darkened its olivine with nanoscale iron particles. Identification demands petrography, mineral chemistry and oxygen isotopes.
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