Shergottite
The most common kind of Martian meteorite: a basaltic or olivine-rich volcanic rock from Mars.
Shergottites make up the large majority of known Martian meteorites. They are igneous rocks: some are basaltic, rich in pyroxene and plagioclase; others are olivine-phyric, with large olivine crystals in a finer groundmass; and some, called poikilitic or lherzolitic, have olivine enclosed in big pyroxene crystals. Nearly all were heavily shocked when they were blasted off Mars, so their plagioclase has been turned into a glass called maskelynite.
Many shergottites crystallised surprisingly recently, only a few hundred million years ago, showing that Mars was volcanically active far later than once assumed, although their exact ages are still debated. Pockets of shock-melted glass in some, such as the Antarctic find EETA79001, trap Martian atmospheric gases. The group is named after Shergotty, which fell in India in 1865. Zagami, which fell in Nigeria in 1962, and Tissint, which fell in Morocco in 2011, are other well-known examples.
A fresh shergottite has a glossy black fusion crust and a grey-green interior, often flecked with dark glass veins. Olivine-phyric types show yellow-green crystals. Confirmation needs oxygen isotope and mineral analyses in a laboratory.
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