Vlasovite is a late phase in nepheline syenite and syenitic pegmatites. At Ascension Island it is found in miarolitic cavities in ejected blocks of peralkaline granite (Peralkaline rocks are deficient in aluminium but have sodium and potassium in excess of the amount needed to form feldspar). At the Lovozero Massif in Russia it is formed in areas of rock rich in microcline and albite in the contact zone between pegmatites and fenites (metasomatic rocks composed of alkaline feldspar, sodic pyroxene and alkaline amphibole), by the replacement of eudialyte. Associated minerals include arfvedsonite, aegirine, apatite and fluorite, in addition to microcline, albite and eudialyte.