larvikite (lar'-vik-ite). An alkalic syenite, grading to monzonite, composed of phenocrysts of two feldspars (esp. oligoclase and alkali feldspar), often intimately intergrown, which comprise up to 90% of the rock, with diopsidic augite and titanian augite as the chief mafic minerals, and accessory apatite (generally abundant), ilmenite, and titaniferous magnetite, and less commonly olivine, orthopyroxene, biotite, and quartz or feldspathoids (less than 10 percent by volume). Its name, given by Brögger in 1890, is derived from Larvik, Norway.