Modified from Image Source: nmp.jpl.nasa.gov

A rock composed primarily of orthopyroxene. Non-terrestrial orthopyoxenites include diogenites and a single martian meteorite, ALH 84001, that was found in the Allan Hills region of Antarctica in 1984. ALH 84001 is a cumulate rock consisting of 97% coarse-grained, Mg-rich orthopyroxene, with small amounts of plagioclase, chromite, and carbonate. It was initially classified as a diogenite, however, the presence of oxidized Fe in chromite led to its reclassification as a Martian meteorite. This was subsequently confirmed by determination of its oxygen isotope composition. With a crystallization age of ~4.4 Ga, it is by far the oldest meteorite from Mars yet discovered. It probably represents a sample of the early crust, providing evidence for the earliest geologic history of Mars.

Some or all content above used with permission from J. H. Wittke.