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fenite A rock that was first described from the Fen carbonatite intrusion in southern Norway. It is sodium-rich, metasomatic, orthoclase—nepheline—arfvedsonite—aegirine-bearing, and developed around carbonatite intrusions. Alkali-rich fluids, migrating away from the crystallizing carbonatite magma, react with the surrounding rocks, converting them to an assemblage of alkali-bearing minerals. This process of alkali metasomatism is given the specific name of ‘fenitization’ and produces particularly striking results when the country rocks are granites.