An intrusive, basic, igneous, carbonatite rock, distinctive in possessing primary calcite, and consisting of melilite (⅓); biotite (⅓); and pyroxene, calcite, and olivine (⅓). Feldspar is not present in the rock, its place being taken by the mineral melilite which has the general formula: X₂YZ₂O₇; where X = Ca, Na; Y = Mg, Al; Z = Si, Al. The type location for this rock is Alnö island off the coast of Sweden.