What is a nakhlite?
A nakhlite is a Martian meteorite made mainly of augite crystals that formed in a lava flow or shallow intrusion about 1.3 to 1.4 billion years ago.
Nakhlites are a group of Martian meteorites named after Nakhla, which fell near Alexandria in Egypt on 28 June 1911. About 40 stones fell, totalling about 10 kilograms.
What they are made of. Nakhlites are made mostly of elongated crystals of augite, a calcium-rich pyroxene, with smaller amounts of olivine and a fine-grained mesostasis of feldspar and other minerals. The crystals are often aligned, suggesting they settled or flowed together in a body of magma.
Age. They crystallised about 1.3 to 1.4 billion years ago, much younger than most meteorites, and were ejected from Mars together about 11 million years ago. About 20 or more nakhlites are known, and many seem to come from different layers of the same lava flow or group of flows.
Water on Mars. Nakhlites contain veins of iddingsite, a mixture of clays, iron oxides, carbonates and salts formed by water acting on olivine. Some veins are cut by the fusion crust, proving they formed on Mars before the rock arrived on Earth. Dating suggests this alteration happened hundreds of millions of years ago or later, showing that liquid water existed at times on Mars long after its early, wetter period.
Link with chassignites. Chassignites, olivine-rich Martian meteorites, have similar ages and ejection ages, suggesting they came from the same region.
Folklore. There is a story that a Nakhla stone killed a dog when it fell. The story is uncertain and probably not true, but it is often repeated.