Harzburgite, an ultramafic, igneous rock, is a variety of peridotite consisting mostly of the two minerals olivine and low-calcium (Ca) pyroxene (enstatite); it is named for occurrences in the Harz Mountains of Germany.

Harzburgite typically forms by the extraction of partial melts from the more pyroxene-rich peridotite called lherzolite.

If partial melting of the harzburgite continues, all of the pyroxene may be extracted from it to form magma, leaving behind the pyroxene-poor peridotite called dunite.

Harzburgite may also form by the accumulation of olivine and low-Ca pyroxene in large magma chambers of basalt deep in continental crust (layered intrusions).

The classic example of a Proterozoic layered intrusion with cumulate harzburgite is the Stillwater igneous complex of Montana, U.S.A.