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alnöite An intrusive, basic, igneous, carbonatite rock, distinctive in possessing primary calcite, and consisting of melilite (1/3); biotite (1/3); and pyroxene, calcite, and olivine (1/3). 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.