What is nephelinite in geology ?

Nephelinite : definition

Streckeisen diagrams (or QAPF diagrams) - Classification of plutonic and volcanic rocks
Nephelinite is an exceptional volcanic rock, leucocratic to mesocratic, composed mainly of nepheline, with a little titaniferous augite and other feldspathoids (sodalite, leucite, noséane or hauyne), melilite, and very exceptionally olivine . It occurs in blocks in other lavas and in some volcanic vents.