What is a leucitite in geology ?

Leucitite : definition

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.
Streckeisen diagrams (or QAPF diagrams) - Classification of plutonic and volcanic rocks
Leucitite from Vesuvius, Italy © Sammlung Institut f. Geologische Wissenschaften, FU Berlin