Nepheline-syenite

A foid-syenite where nepheline is the most abundant foid. A plutonic rock composed essentially of alkali feldspar and nepheline. It may contain an alkali ferromagnesian mineral, such as an amphibole (riebeckite, arfvedsonite, barkevikite) or a pyroxene (aegirine or aegirine-augite); the intrusive equivalent of phonolite. Sodalite, cancrinite, hauyne, and nosean, in addition to apatite, sphene, and opaque oxides, are common accessories. Rare minerals are also frequent accessories. Synonyms: foyaite, eleolite syenite, midalkalite Ref: AGI