What is a chassignite?
A chassignite is a rare Martian meteorite made mostly of olivine, formed as crystals accumulated in a magma about 1.3 to 1.4 billion years ago.
Chassignites are a small group of Martian meteorites named after Chassigny, which fell in France on 3 October 1815. It was the first Martian meteorite to be recorded falling, although its Martian origin was not recognised until the 1980s.
What they are made of. Chassignites are dunites, rocks made mostly of olivine, about 90 per cent, with smaller amounts of pyroxene, feldspar, chromite and other minerals. The olivine is relatively iron-rich. Chassignites contain small pockets of trapped melt, called melt inclusions, which preserve information about the magma they formed from.
Formation. They are cumulates, formed when olivine crystals settled and accumulated at the bottom of a magma body.
Age and origin. Chassignites crystallised about 1.3 to 1.4 billion years ago, similar to the nakhlites. Both groups were ejected from Mars about 11 million years ago, suggesting they came from the same impact event and perhaps the same volcanic region.
Known examples. Only a few chassignites are known: Chassigny itself, NWA 2737, found in Morocco in 2000, and a few others. NWA 2737 is unusual because its olivine is dark brown to black, caused by shock.
Noble gases. Chassigny contains noble gases with a distinctive composition thought to represent the Martian interior, different from the Martian atmosphere. This makes it valuable for understanding how Mars's interior and atmosphere evolved.
Together with shergottites and nakhlites, chassignites were once grouped as SNC meteorites.