(named after Mount Limburg in the Kaiserstuhl massif, Federal Republic of Germany), an igneous rock, an effusive analogue of alkali rocks, rich in dark-colored minerals. Limburgite is a vitrophyric rock with olivine and augite phenocrysts. The groundmass consists of a vitreous base of alkaline composition which may contain nepheline and plagioclase and microlites of augite and occasionally amphibole, hauyne, and leucite.