What is a leucitite in geology ?

Leucitite : definition

Streckeisen diagrams (or QAPF diagrams) - Classification of plutonic and volcanic rocks
A leucitite is a volcanic rock undersaturated with silica formed by automorphic crystals of leucite (of the order of 30% of the rock), in a dark paste with dominant augite (20% on average), melilite, nepheline, rare bytownite, sometimes olivine, and containing varying amounts of accessory minerals. It is an extremely rare feldspathoidite associated with tephrites and leucite basanite. Its plutonic equivalent is missourite.
Leucitite du Vésuve, Italie © Sammlung Institut f. Geologische Wissenschaften, FU Berlin