Orthopyroxenite is an ultramafic and ultrabasic rock that is almost exclusively made from the mineral orthopyroxene, the orthorhombic version of pyroxene and a type of pyroxenite. It can have up to a few percent of olivine and clinopyroxene.

Orthopyroxenites can also occur on other planets. ALH 84001 is a Martian meteorite that can be classified as an orthopyroxenite. It is the only meteorite found with that composition and the only member of the Martian orthopyroxenite group of meteorites.^[1]