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larvikite A coarse-grained, intrusive igneous rock that consists of essential potash feldspar, oligoclase feldspar, titaniferous augite, and sodic amphibole, together with accessory biotite, quartz, or nepheline (depending on the silica saturation), magnetite, zircon, and apatite. The two feldspar types occur in equal proportions, making the rock a type of monzonite. Larvikite was first described by Brögger in 1890 from the Larvik district of southern Norway. Larvikite can be an impressive ornamental stone.