This microscopic view, 1 millimeter across, of another martian meteorite shows the real colors of the mineral grains in the meteorite. The clear and cracked areas are the minerals olivine and pyroxene, just as in the other martian meteorites. The reddish and black veinlets and patches are clay and rust where the pyroxene and olivine reacted with liquid water. These veinlets of clay and rust are truncated by the the meteorite's fusion crust, which formed when the meteorite came through the Earth's atmosphere. The veinlets therefore must have formed before the meteorite came to Earth; it is most likely that the veinlets formed from water on Mars.
Photograph by Allan Treiman, Lunar and Planetary Institute